Lahar Literature copy

Asymmetrical deltas below wave base: Insights from the Fraser River Delta, Canada

Sat, 26 Sep 2015 01:31:39 +0000

The Fraser River Delta exhibits distinct asymmetry in the sedimentological and neoichnological characteristics of the updrift (south) and downdrift (north) sides of the main distributary channel in water depths below storm-wave base. The asymmetry is the result of net northward tidal flow. Tides erode sediments across the updrift delta front, whereas the downdrift delta front is an area of net deposition. A submarine channel prevents sand eroded from the updrift delta front from reaching the downdrift delta. The updrift delta front and updrift upper prodelta are composed of sand or heterolithic sand and mud that show a low density of burrowing (Bioturbation Index 0 to 3) and are dominated by simple traces. The downdrift delta front and prodelta, and the updrift lower prodelta are composed of homogeneous muds with significantly higher bioturbation intensities (Bioturbation Index 3 to 6), and a more diverse suite of traces akin to Cruziana Ichnofacies. Using the Fraser River Delta as an archetype and comparing the Fraser to the Amazon River Delta, a preliminary model for deep-water (below storm wave base: ca 20 m) asymmetrical deltas is proposed. Firstly, deep-water asymmetrical deltas are recognized from sediments deposited below storm-wave base. At these depths, tidal and ocean currents are more likely to impact sediment transport, but wave processes are less effective as a sediment transport mechanism. Sediments deposited below storm-wave base in deep-water asymmetrical deltas will display the following: (i) the updrift delta front will be coarser-grained (for example, sand-dominated or heterolithic sand and mud), than the downdrift delta front (for example, mud-dominated); and (ii) the updrift delta front should show low diversity suites of simple burrows. Depending on sedimentation rates, the downdrift delta front and prodelta may show either high diversity suites of traces that are dominated by both complex and simple burrows (low sedimentation rates) or low density and diversity suites akin to the updrift delta front (high sedimentation rates). This article is protected by copyright. All rights reserved.

A contourite drift system on the Baffin Bay-West Greenland margin linking Pliocene Arctic warming to poleward ocean circulation

Mon, 14 Sep 2015 17:09:28 +0000

Terrestrial records from the Canadian Arctic Archipelago indicate that a temperate and moist climate prevailed during the Pliocene, i.e., before the intensification of Northern Hemisphere glaciations, but the controlling factors causing these conditions remains elusive. Here we present marine seismic reflection evidence of contiguous kilometer-scale sedimentary drifts, or contourites, buried below the West Greenland shelf, which relates high-latitude Pliocene warmth to intense geostrophic currents along the eastern Baffin Bay margin. Seismic to borehole correlation indicates that enhanced current-induced deposition began during the middle Miocene, ca. 17–15 Ma, and terminated during the late Pliocene onset of global cooling. The transition from along-slope sediment transport to trough-mouth fan progradation designates the onset of Greenland Ice Sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in Baffin Bay and the Nordic Seas from 3.3 to 2.7 Ma. Our results suggest that the Baffin Bay–West Greenland margin formed a late Neogene passageway for persistent ocean boundary currents, and we infer that the Pliocene high-latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the Arctic regions. Attenuation of the poleward heat flux conveyed by the paleo–current system may have been critical for allowing glacial buildup in the Canadian Arctic and northern Greenland during the late Pliocene. We further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation, which eventually caused the demise of meridional ocean circulation through Baffin Bay.

The extreme 2013/14 winter storms: hydrodynamic forcing and coastal response along the southwest coast of England

Mon, 07 Sep 2015 09:21:23 +0000

The southwest coast of England was subjected to an unusually energetic sequence of Atlantic storms during the 2013/2014 winter, with the 8-week period from mid-December to mid-February representing the most energetic period since at least 1953. A regional analysis of the hydrodynamic forcing and morphological response of these storms along the SW coast of England highlighted the importance of both storm- and site-specific conditions. The key factor that controls the Atlantic storm wave conditions along the south coast of southwest England is the storm track. Energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the English Channel relatively unimpeded. The timing of the storm in relation to the tidal stage is also important, and coastal impacts along the macro-tidal southwest coast of England are maximised when the peak storm waves coincide with spring high tide. The role of storm surge is limited and rarely exceeds 1 m. The geomorphic storm response along the southwest coast of England displayed considerable spatial variability; this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation. On west-facing beaches typical of the north coast, the westerly Atlantic storm waves approached the coastline shore-parallel, and the prevailing storm response was offshore sediment transport. Many of these north coast beaches experienced extensive beach and dune erosion, and some of the beaches were completely stripped of sediment, exposing a rocky shore platform. On the south coast, the westerly Atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast-facing beaches this results in large incident wave angles and strong eastward littoral drift. Many south coast beaches exhibited rotation, with the western part of the beaches eroding and the eastern part accreting. This article is protected by copyright. All rights reserved.

Significance of sediment transport processes during piedmont floods: the 2005 flood events in Switzerland

Mon, 07 Sep 2015 08:38:17 +0000

A long-lasting rainstorm event from 20 to 22 August 2005 affected a large part of the northern Alps and Prealps in Switzerland. It resulted in elevated discharges and flooding in many headwater catchments and mountain rivers. The associated geomorphic processes included shallow landslides, deep-seated slope instabilities, debris flows, and fluvial sediment transport. In many parts of the affected areas human activities are important, including many buildings, traffic lines and other infrastructure. In the steeper parts, geomorphic processes were mainly responsible for flow overtopping and sediment deposition both in and outside of the channel network. In the lower parts, lateral erosion and the exceedance of the channel discharge capacity were the main reasons for morphologic channel modification and flooding. Sediment-related processes contributed a lot to the overall damage. This article is protected by copyright. All rights reserved.

Preservation of meandering river channels in uniformly aggrading channel belts

Tue, 25 Aug 2015 03:28:34 +0000

Channel belt deposits from meandering river systems commonly display an internal architecture of stacked depositional features with scoured basal contacts due to channel and bedform migration across a range of scales. Recognition and correct interpretation of these bounding surfaces is essential to reconstruction of palaeochannel dimensions and to flow modelling for hydrocarbon exploration. It is therefore crucial to understand the suite of processes that form and transfer these surfaces into the fluvial sedimentary record. Here the numerical model ‘NAYS2D’ is used to simulate a highly sinuous meandering river with synthetic stratigraphic architectures that can be compared directly to the sedimentary record. Model results highlight the importance of spatial and temporal variations in channel depth and migration rate to the generation of channel and bar deposits. Addition of net uniform bed aggradation (due to excess sediment input) allows quantification of the preservation of meander morphology for a wide range of depositional conditions. The present authors found that the effect of vertical variation in scouring due to channel migration is generally orders of magnitude larger than the effect of bed aggradation. This explains the limited impact bed aggradation has on preservation of meander morphology. Moreover, lateral differences in stratigraphy within the meander belt are much larger than the stratigraphic imprint of bed aggradation. Repeatedly produced alternations of point bar growth followed by cut-off result in a vertical trend in channel and scour feature stacking. Importantly, this vertical stacking trend differs laterally within the meander belt. In the centre of the meander belt, the high reworking intensity results in many bounding surfaces and disturbed deposits. Closer to the margins, reworking is infrequent and thick deposits with a limited number of bounding surfaces are preserved. These marginal areas therefore have the highest preservation potential for complete channel deposits and are thus best suited for palaeochannel reconstruction. This article is protected by copyright. All rights reserved.

Diagnostic study of a high-precipitation event in the Western Mediterranean: adequacy of current operational networks

Tue, 25 Aug 2015 01:35:06 +0000

To investigate whether the spatial and temporal resolution of current operational observing systems in the Western Mediterranean (WMed) region suffice to adequately represent the atmospheric processes responsible for the initiation and intensification of convection, a diagnostic study of the HyMex Intensive Observation Period 8 (IOP8) is performed. During the IOP8, heavy rainfall with intense lightning and consequent devastating flash floods occurred in the WMed region. The synergy of operational networks in the northern WMed, including Global Positioning System (GPS) stations, rain gauges, weather stations, lightning sensors and radiosondes, was used to document in detail the evolution of the heavy precipitation event. In general, the resolution of the aforementioned networks adequately sampled the temporal and spatial variability of the atmospheric water vapour, as well as the position of mesoscale convergence zones which played a key role in the initiation and evolution of convective systems in this case. Nevertheless, high uncertainty was associated with the existence and location of moisture convergence zones and wind convergence lines over the sea, reflecting the need for model analysis and remote-sensing observations to complete the documentation of the event.

Variable and conflicting shear stress estimates inside a boundary layer with sediment transport

Tue, 18 Aug 2015 20:36:40 +0000

This paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions, using wind velocities measured synchronously at 13 heights over a 1.7 m vertical array using ultrasonic anemometry. The Reynolds decomposition technique determines at-a-point shear stresses at each measurement height, while the Law-of-the-Wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data. Analysis reveals significant inconsistencies between estimates derived from the two methods, on both a whole-event basis and as time-series. Despite a near-perfect fit of the Law-of-the-Wall, the point estimates of Reynolds shear stress vary greatly between heights, calling into question the assumed presence of a constant stress layer. A comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates. Results do show, however, that Reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate. The findings serve as a major cautionary message to the interpretation and application of single-height measurements of Reynolds shear stress and their equivalence to Law-of-the-Wall derived estimates, and these concerns apply widely to boundary layer flows in general. This article is protected by copyright. All rights reserved.

Prospects and challenges of simulating river channel response to future climate change

Fri, 07 Aug 2015 09:32:29 +0000

Due to the predicted impacts of future climate on hydrology, morphological changes to river channels are expected. Quantifying the magnitudes and rates of future channel change is important for sustainable river channel management. To date, reviews of simulation approaches for investigating river channels and the modelling of environmental change impacts on channel form and process have focused on contemporary process or palaeo perspectives. Hence, herein we review numerical modelling approaches available for reach-scale simulation of future river channels and the predicted in-channel hydro- and morphodynamic changes modelled. We found that despite their widespread availability, hydrodynamic, morphodynamic and cellular models have yet to be used routinely in future in-channel simulations, with cellular models in particular under-represented. Our review shows that predictions of within-channel changes vary greatly between hydro-climatic regions and under contrasting climate change scenarios, mainly due to varying input discharge scenarios; however, increased sediment transport and flood risk are usually predicted. Key challenges in simulating future channel change include representations of external forcing conditions, adequate temporal and spatial scales, transport equations, changing channel materials and lateral erosion; calibration and validation; simulation chains with multiple models; and identification of feedback systems and non-linearity. Nevertheless, despite these challenges, models with increasing complexity have recently been developed and so there is increasing potential in their application. One-dimensional hydro- and morphodynamic simulations, and cellular models, can be modified to reflect the requirements of future representations, such as grain size properties, whilst there is also now an increasing capability to include a greater quantity of external forcing conditions. Some studies, however, have demonstrated the need to develop two-dimensional models for application in centennial-scale studies. We recommend that a wider range of scenarios and the combined effects of multiple external forcing factors should be included, whilst studies are also needed from more hydrologically diverse reaches.

Abandoned channel fill sequences in the tidal estuary of a small mountainous, dry-summer river

Thu, 06 Aug 2015 08:08:42 +0000

This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub-centimetre resolution stratigraphic analyses to describe depositional processes and their resultant sedimentary deposits. Both abandonment sequences recorded quasi-annual scale fluvial/tidal deposition couplets. In both cases tidal deposits contained very little sand, were higher in organic and inorganic carbon content than the sandier, fluvially dominated deposits, and possessed millimetre-scale horizontal laminations. The two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. Aerial photographic analysis showed that the first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ13C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (one to five times mean discharge), while those of the second phase were consistent with suspended sediment from higher flows (seven to ten times mean discharge). When considered together, the results indicate that the early fill sequence recorded a reach experiencing regular fluvial deposition through flow conditions during the wet season, while the latter fill sequence records a reach more disconnected from the main stem in terms of flow and sediment. The major factor affecting the difference in sedimentation between the two fill periods appears to have been the morphology of the upstream river bend in relation to the position of the bifurcation node. During the first fill period the upstream entrance to Ropers Slough seems to have remained open in part due to the placement of its entrance on the outside of the mainstem river bend, and despite stronger tidal effects caused by a larger tidal prism and closer proximity to the tidal inlet. By the second fill sequence the upstream bend morphology had altered, placing the entrance to Ropers Slough on the inner bank of the mainstem bend, which resulted in more rapid plug bar formation. The role of tidal effects in the geomorphic trajectory of the two abandonment sequences is unclear, but appears to have been of lesser importance than local bifurcation geometry. This article is protected by copyright. All rights reserved.

Contrasting geomorphological storm response from two adjacent shorefaces

Fri, 17 Jul 2015 16:31:03 +0000

Shorefaces play a critical role in cross-shore sediment transport between the beach and inner shelf, particularly during storm conditions. A comparison and examination of storm-driven sedimentary changes on two adjacent shorefaces in Northern Ireland, located only five kilometres apart, revealed significantly different geomorphological responses. The steeper shoreface at West Strand responded with extensive sediment deposition across almost the entire shoreface, in contrast to the more dissipative and quasi-linear shoreface at Portstewart, which mostly showed nearshore bar changes. Results from the two sites, which have similar wave/wind characteristics and seabed sediments, suggest that: i) cross-shore morphology, ii) immediately previous (antecedent) shoreface morphodynamic behaviour and iii) the presence, or lack of, offshore sand appear to be the primary controls on storm-driven sedimentary changes attributed to the high-energy event. This article is protected by copyright. All rights reserved.

Assessing entrainment of bed material in a debris-flow event: a theoretical approach incorporating Monte Carlo method

Sun, 05 Jul 2015 22:21:01 +0000

Entrainment of underlying bed sediment by a debris flow can significantly increase the debris-flow magnitude. To study this phenomenon, a theoretical approach to assessing bed-sediment entrainment is presented. The approach is based on a static approximation that bed-sediment entrainment occurs when the shearing stress of the flow is sufficiently high to overcome the basal resistance of the bed sediment. In order to delineate erodible zones in a channel, we analyze the critical condition of this static equilibrium model, and subsequently propose a new concept of a critical line to detect the entrainment reaches in a channel. Considering the spatial and temporal uncertainties of the input parameter, the approach is further incorporated within a Monte Carlo method, and the distribution of entrainment zones and post-entrainment volumes can be analyzed. This approach is illustrated by back-analysis of the 2010 Yohutagawa debris-flow event, Japan. Results from 10 000 trials of Monte Carlo simulation are compared with the in situ surveys. It is shown that the present approach can be satisfactorily used to delineate erodible zones and estimate possible entrainment volume of the event. Discussion regarding the sensitivities and limitations of the approach concludes the paper. Copyright © 2015 John Wiley & Sons, Ltd.

Reconstruction of a destructive debris-flow event via numerical modeling: the role of valley geometry on flow dynamics

Tue, 23 Jun 2015 04:54:06 +0000

Debris-flows are widespread natural phenomena characterized by high mobility (high velocity and long runout distance) and impact forces, which frequently cause human casualties and significant damage to infrastructure. To better understand the dynamics of such events, analyzing in particular the effect induced by the valley geometry on flow velocity, runout and mobilized volumes, in this work we reconstruct a real debris-flow event through numerical modeling. Specifically, we used a modified version of the BING model, a fluid-dynamic depth-integrated numerical model for debris flows, which has been properly modified to account for width changes along the valley. The studied event, which occurred in Scaletta Zanclea (Messina, north-eastern Sicily, Italy) on October 1, 2009, is exceptionally well constrained by field and topographic information. In this respect the flow velocity, estimated from two specific locations on the basis of field evidence, the distribution of erosional and depositional areas along the Racinazzo valley, based on the comparison of pre- and post-event digital elevation models (DEMs), and the runout distance were used as constraints to calibrate the model. Furthermore, we report a detailed description of the main event characteristics based on hydrological records and witness reports. The numerical modeling results are consistent with witness reports and the severe damage recorded in the Scaletta Marina village, and highlight the effect of the valley geometry on both the debris flow velocity and the erosion/deposition processes. The effect of changing valley width has been also quantified, resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus. Copyright © 2015 John Wiley & Sons, Ltd.

A coupled hierarchical modeling approach to simulating the geomorphic response of river systems to anthropogenic climate change

Mon, 25 May 2015 00:00:06 +0000

Anthropogenic climate change is expected to change the discharge and sediment transport regime of river systems. Because rivers adjust their channels to accommodate their typical inputs of water and sediment, changes in these variables can potentially alter river morphology. In this study, a hierarchical modeling approach was developed and applied to examine potential changes in reach-averaged bedload transport and spatial patterns of erosion and deposition for three snowmelt-dominated gravel-bed rivers in the interior Pacific Northwest. The modeling hierarchy was based on discharge and suspended-sediment load from a basin-scale hydrologic model driven by a range of downscaled climate-change scenarios. In the field, channel morphology and sediment grain-size data for all three rivers were collected. Changes in reach-averaged bedload transport were estimated using the Bedload Assessment of Gravel-bedded Streams (BAGS) software, and the Cellular Automaton Evolutionary Slope and River (CAESAR) model was used to simulate the spatial pattern of erosion and deposition within each reach to infer potential changes in channel geometry and planform. The duration of critical discharge was found to control bedload transport. Changes in channel geometry were simulated for the two higher-energy river reaches, but no significant morphological changes were found for a lower-energy reach with steep, cohesive banks. Changes in sediment transport and river morphology resulting from climate change could affect the management of river systems for human and ecological uses. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental analysis on the impact force of viscous debris flow

Sun, 24 May 2015 23:57:13 +0000

A miniaturized flume experiment was carried out to measure impact forces of viscous debris flow. The flow depth (7.2–11.2 cm), velocity (2.4–5.2 m/s) and impact force were recorded during the experiment. The impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime. The three phases are the sudden strong impact of the debris flow head, continuous dynamic pressure of the body and slight static pressure of the tail. The variation of impact process is consistent with the change in the flow regime. The head has strong–rapid impact pressure, which is shown as a turbulent-type flow; the body approximates to steady laminar flow. Accordingly, the process of debris flows hitting structures was simplified to a triangle shape, ignoring the pressure of the tail. In order to study the distribution of the debris flow impact force at different depths and variation of the impact process over time, the impact signals of slurry and coarse particles were separated from the original signals using wavelet analysis. The slurry's dynamic pressure signal appears to be a smooth curve, and the peak pressure is 12–34 kPa when the debris flow head hits the sensors, which is about 1.54 ± 0.36 times the continuous dynamic pressure of the debris flow body. The limit of application of the empirical parameter α in the hydraulic formula was also noted. We introduced the power function relationship of α and the Froude number of debris flows, and proposed a universal model for calculating dynamic pressure. The impact pressure of large particles has the characteristic of randomness. The mean frequency of large particles impacting the sensor is 210 ± 50–287 ± 29 times per second, and it is 336 ± 114–490 ± 69 times per second for the debris flow head, which is greater than that in the debris flow body. Peak impact pressure of particles at different flow depths is 40–160 kPa, which is 3.2 ± 1.5 times the impact pressure of the slurry at the bottom of the flow, 3.1 ± 0.9 times the flow in the middle, and 3.3 ± 0.9 times the flow at the surface. The differences in impact frequency indicate that most of the large particles concentrate in the debris flow head, and the number of particles in the debris flow head increases with height. This research supports the study of solid–liquid two phase flow mechanisms, and helps engineering design and risk assessment in debris flow prone areas. Copyright © 2015 John Wiley & Sons, Ltd.

A comparison of the sedimentary records of the 1960 and 2010 great Chilean earthquakes in 17 lakes: Implications for quantitative lacustrine palaeoseismology

Mon, 04 May 2015 04:53:39 +0000

Seismically-induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent, well-documented, great megathrust earthquakes provide an ideal opportunity to calibrate seismically-induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 Mw 9·5 Valdivia and the 2010 Mw 8·8 Maule earthquakes in 17 lakes in South-Central Chile (i.e. lakes Negra, Lo Encañado, Aculeo, Vichuquén, Laja, Villarrica, Calafquén, Pullinque, Pellaifa, Panguipulli, Neltume, Riñihue, Ranco, Maihue, Puyehue, Rupanco and Llanquihue). A combination of image analysis, magnetic susceptibility and grain-size analysis allows identification of five types of seismically-induced event deposits: (i) mass-transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically-induced event deposits were compared to local seismic intensities of the causative earthquakes, eyewitness reports, post-earthquake observations, and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near-shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary, lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin, lacustrine turbidites type 1 are the most reliable type of seismically-induced event deposits in quantitative palaeoseismology, because they are almost exclusively triggered by earthquake shaking. Moreover, they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity, starting with no lacustrine turbidites type 1 at intensities between V½ and VI and reaching 100% when intensities are higher than VII½. Combining different types of seismically-induced event deposits allows the reconstruction of the complete impact of an earthquake.

Back-flow ripples in troughs downstream of unit bars: Formation, preservation and value for interpreting flow conditions

Mon, 27 Apr 2015 03:52:08 +0000

Back-flow ripples are bedforms created within the lee-side eddy of a larger bedform with migration directions opposed or oblique to that of the host bedform. In the flume experiments described in this article, back-flow ripples formed in the trough downstream of a unit bar and changed with mean flow velocity; varying from small incipient back-flow ripples at low velocities, to well-formed back-flow ripples with greater velocity, to rapidly migrating transient back-flow ripples formed at the greatest velocities tested. In these experiments back-flow ripples formed at much lower mean back-flow velocities than predicted from previously published descriptions. This lower threshold mean back-flow velocity is attributed to the pattern of velocity variation within the lee-side eddy of the host bedform. The back-flow velocity variations are attributed to vortex shedding from the separation zone, wake flapping and increases in the size of, and turbulent intensity within, the flow separation eddy controlled by the passage of superimposed bedforms approaching the crest of the bar. Short duration high velocity packets, whatever their cause, may form back-flow ripples if they exceed the minimum bed shear stress for ripple generation for long enough or, if much faster, may wash them out. Variation in back-flow ripple cross-lamination has been observed in the rock record and, by comparison with flume observations, the preserved back-flow ripple morphology may be useful for interpreting formative flow and sediment transport dynamics.

Climate change impacts on bedload transport in alpine drainage basins with hydropower exploitation

Fri, 24 Apr 2015 03:56:17 +0000

Sediment transport is known to have a significant impact on hydropower infrastructures and changes in sediment transport rates are important for sediment management measures and hydroelectricity production. In this study, we present how climate change may affect bedload transport in 66 high alpine catchments used by hydropower companies in the Valais, Switzerland. Future sediment yield is estimated with a runoff-based sediment transport model for the two future 30 year time periods 2021–2050 and 2070–2099. The analysis is integrated into a modelling chain in which error-corrected and downscaled climate scenarios generated in the framework of the ENSEMBLES project are coupled to the hydrological model PREVAH, glacier retreat and bedload transport. To calibrate the sediment transport model, we used the observed sediment volumes in water intakes and reservoirs if such data were available. The results obtained show on average a decrease of sediment yield due to the reduced runoff generation during summer, especially for the scenario period 2070–2099. A shift of the seasonal sediment transport regime with a current maximum during July and August to earlier months in the year is predicted. Projections of future sediment yield rely on the accuracy of the individual modeling chain elements. The different sources of uncertainty are discussed qualitatively. Copyright © 2015 John Wiley & Sons, Ltd.

Joint isotopic mass balance: a novel approach to quantifying channel bed to channel margins sediment transfer during storm events

Mon, 20 Apr 2015 03:56:50 +0000

The important role of floodplains and the broader riparian zone in providing temporary storage for a large fraction of the annual sediment load of rivers is well established, but this understanding is largely based on observations of the long-term average behavior of the catchment. Here we combine measurements of the fallout radionuclides 7Be and 210Pb and the stable isotopes of hydrogen in water to quantify fine sediment mobilization and storage in a stream and its channel margins during individual intermediate-sized storm events with recurrence intervals of a few months or less. We demonstrate this method using five storm events in a small (~15 km2), undeveloped, gravel-bedded tributary of the Connecticut River (USA). We estimate that in each storm, the mass of sediment deposited onto the margins accounts for almost 90% of the sediment mobilized from the bed, with the remainder of the mobilized bed sediment transported downstream as suspended load. The result that the bed is a net source of sediment to the stream and the margins a net sink is robust, but estimates of the mass of material eroded from the bed and deposited on the margins are less certain. The source of sediment to the bed remains unclear as, consistent with earlier studies, we observe only limited deposition of sediment to the bed during the storm events. The suspended sediment is organic-rich and thus its source may be associated with in-channel organic decay between storm events. Understanding the coupled interactions between discharge magnitude and frequency and sediment resupply at the event time scale has important implications for stream restoration efforts seeking to connect the channel and the broader riparian zone, and for the development of accurate sediment budgets and predictions of sediment flux from a watershed. Copyright © 2015 John Wiley & Sons, Ltd.

Reconstructing 4000 years of mass movement and tsunami history in a deep peri-Alpine lake (Lake Geneva, France-Switzerland)

Mon, 06 Apr 2015 00:34:22 +0000

The study of mass movements in lake sediments provides insights into past natural hazards at historic and prehistoric timescales. Sediments from the deep basin of Lake Geneva reveal a succession of six large-scale (volumes of 22 × 106 to 250 × 106 m3) mass-transport deposits, associated with five mass-movement events within 2600 years (4000 cal bp to 563 ad). The mass-transport deposits result from: (i) lateral slope failures (mass-transport deposit B at 3895 ± 225 cal bp and mass-transport deposits A and C at 3683 ± 128 cal bp); and (ii) Rhône delta collapses (mass-transport deposits D to G dated at 2650 ± 150 cal bp, 2185 ± 85 cal bp, 1920 ± 120 cal bp and 563 ad, respectively). Mass-transport deposits A and C were most probably triggered by an earthquake, whereas the Rhône delta collapses were likely to be due to sediment overload with a rockfall as the external trigger (mass-transport deposit G, the Tauredunum event in 563 ad known from historical records), an earthquake (mass-transport deposit E) or unknown external triggers (mass-transport deposits D and F). Independent of their origin and trigger mechanisms, numerical simulations show that all of these recorded mass-transport deposits are large enough to have generated at least metre-scale tsunamis during mass movement initiation. Since the Tauredunum event in 563 ad, two small-scale (volumes of 1 to 2 × 106 m3) mass-transport deposits (H and I) are present in the seismic record, both of which are associated with small lateral slope failures. Mass-transport deposits H and I might be related to earthquakes in Lausanne/Geneva (possibly) 1322 ad and Aigle 1584 ad, respectively. The sedimentary record of the deep basin of Lake Geneva, in combination with the historical record, show that during the past 3695 years, at least six tsunamis were generated by mass movements, indicating that the tsunami hazard in the Lake Geneva region should not be neglected, although such events are not frequent with a recurrence time of 0·0016 yr−1.

Downstream lightening and upward heavying: Experiments with sediments differing in density

Mon, 23 Mar 2015 01:01:21 +0000

Sorting and selective transport of particles by material density is important for understanding a wide range of processes, including the formation of mineral placers, deposition of mine tailings and routing of tracers and contaminants. This article describes an experimental study of the transport of mixtures of particles of differing density in a sediment-feed flume. During the runs, a downstream prograding wedge-shaped deposit was formed. Results show two sorting processes: (i) longitudinal sorting characterized by preferential deposition of heavy particles in the upstream part of the deposit – downstream lightening; and (ii) vertical sorting with less dense particles preferentially deposited in the lowermost portion of the migrating front – upward heavying. Downstream lightening is the analogue of the well-known downstream fining observed in the more studied case of mixtures of heterogeneous size with the same density. In both cases, the lighter particles are carried further downstream than the heavier particles. Upward heavying is unexpected when compared with deposits of heterogeneous size and same-density particles, where the heaviest (i.e. coarsest) particles are deposited in the lowermost part of the front. The physical mechanism underlying this upward heavying might be related to the physics of gravity-driven granular flows; the front of the deposit acts like a dense granular flow down an inclined plane. In this case, the denser particles settle away from the free surface and at the top of the heap, while the lighter particles flow to the bottom. As the front of the deposit advances, this progressively gives rise to an upward heavying pattern. The application of classical surface-based fractional bedload transport models suggests that equal mobility is not approached in the case of mixtures of particles with uniform size and different densities. This study hypothesizes that other mechanics related to the physics of the segregation processes in these systems contribute to these results.

A hydro-sedimentary modeling system for flash flood propagation

Tue, 18 Mar 2014 17:34:00 +0000

A hydro-sedimentary modeling system for flash flood propagation and hazard estimation under different agricultural practicesN. N. Kourgialas and G. P. KaratzasNat. Hazards Earth Syst. Sci., 14, 625-634, 2014 (PDF, 1289 KB)Special Issue

18 Mar 2014

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Overlapping sea level time series measured using different technologies: an example from the REDMAR Spanish networkB. Pérez, A. Payo, D. López, P. L. Woodworth, and E. Alvarez FanjulNat. Hazards Earth Syst. Sci., 14, 589-610, 2014 (PDF, 4437 KB)	13 Mar 2014
Which data for quantitative landslide susceptibility mapping at operational scale? Case study of the Pays d'Auge plateau hillslopes (Normandy, France)M. Fressard, Y. Thiery, and O. MaquaireNat. Hazards Earth Syst. Sci., 14, 569-588, 2014 (PDF, 6821 KB)	13 Mar 2014
Assessment methodology for the prediction of landslide dam hazardS. F. Dal Sasso, A. Sole, S. Pascale, F. Sdao, A. Bateman Pinzòn, and V. MedinaNat. Hazards Earth Syst. Sci., 14, 557-567, 2014 (PDF, 3034 KB)	12 Mar 2014
Landslide and slope stability evaluation in the historical town of Kruja, AlbaniaY. Muceku and O. KoriniNat. Hazards Earth Syst. Sci., 14, 545-556, 2014	10 Mar 2014
Results of the post flash-flood disaster investigations in the Transylvanian Depression (Romania) during the last decade (2001–2010)V. Arghiuş, A. Ozunu, I. Samara, and G. RoşianNat. Hazards Earth Syst. Sci., 14, 535-544, 2014 (PDF, 2743 KB)	04 Mar 2014
Application of GA–SVM method with parameter optimization for landslide development predictionX. Z. Li and J. M. KongNat. Hazards Earth Syst. Sci., 14, 525-533, 2014 (PDF, 1855 KB)	04 Mar 2014
Evaluation of wildland fire smoke plume dynamics and aerosol load using UV scanning lidar and fire–atmosphere modelling during the Mediterranean Letia 2010 experimentV. Leroy-Cancellieri, P. Augustin, J. B. Filippi, C. Mari, M. Fourmentin, F. Bosseur, F. Morandini, and H. DelbarreNat. Hazards Earth Syst. Sci., 14, 509-523, 2014 (PDF, 4963 KB)	04 Mar 2014
The anomalous low and high temperatures of 2012 over Greece – an explanation from a meteorological and climatological perspectiveK. Tolika, P. Maheras, I. Pytharoulis, and C. AnagnostopoulouNat. Hazards Earth Syst. Sci., 14, 501-507, 2014 (PDF, 495 KB)	04 Mar 2014
Investigating volcanic hazard in Cape Verde Islands through geophysical monitoring: network description and first resultsB. Faria and J. F. B. D. FonsecaNat. Hazards Earth Syst. Sci., 14, 485-499, 2014 (PDF, 5138 KB)	28 Feb 2014
Event-adjusted evaluation of weather and climate extremesM. Müller and M. KasparNat. Hazards Earth Syst. Sci., 14, 473-483, 2014 (PDF, 1645 KB)Discussion Paper (NHESSD)	28 Feb 2014
A model-based study of the wind regime over the Corinthian GulfI. Koletsis, V. Kotroni, and K. LagouvardosNat. Hazards Earth Syst. Sci., 14, 459-472, 2014 (PDF, 6452 KB) (82 KB)Discussion Paper (NHESSD)	28 Feb 2014
Karst show caves – how DTN technology as used in space assists automatic environmental monitoring and tourist protection – experiment in Postojna CaveF. Gabrovšek, B. Grašič, M. Z. Božnar, P. Mlakar, M. Udén, and E. DaviesNat. Hazards Earth Syst. Sci., 14, 443-457, 2014 (PDF, 4553 KB)Discussion Paper (NHESSD)	28 Feb 2014
The snow storm of 8 March 2010 in Catalonia (Spain): a paradigmatic wet-snow event with a high societal impactM. C. Llasat, M. Turco, P. Quintana-Seguí, and M. Llasat-BotijaNat. Hazards Earth Syst. Sci., 14, 427-441, 2014 (PDF, 9913 KB)	28 Feb 2014
GIS and remote sensing techniques for the assessment of land use change impact on flood hydrology: the case study of Yialias basin in CyprusD. D. Alexakis, M. G. Grillakis, A. G. Koutroulis, A. Agapiou, K. Themistocleous, I. K. Tsanis, S. Michaelides, S. Pashiardis, C. Demetriou, K. Aristeidou, A. Retalis, F. Tymvios, and D. G. HadjimitsisNat. Hazards Earth Syst. Sci., 14, 413-426, 2014 (PDF, 2677 KB)Discussion Paper (NHESSD)	26 Feb 2014
Numerical simulations of tsunamis generated by underwater volcanic explosions at Karymskoye lake (Kamchatka, Russia) and Kolumbo volcano (Aegean Sea, Greece)M. Ulvrová, R. Paris, K. Kelfoun, and P. NomikouNat. Hazards Earth Syst. Sci., 14, 401-412, 2014 (PDF, 2558 KB)Discussion Paper (NHESSD)	25 Feb 2014
The value of integrating information from multiple hazards for flood risk analysis and managementJ. T. Castillo-Rodríguez, I. Escuder-Bueno, L. Altarejos-García, and A. Serrano-LombilloNat. Hazards Earth Syst. Sci., 14, 379-400, 2014 (PDF, 1051 KB)Discussion Paper (NHESSD)	25 Feb 2014
Regional economic impacts of natural hazards – the case of the 2005 Alpine flood event in Tyrol (Austria)C. PfurtschellerNat. Hazards Earth Syst. Sci., 14, 359-378, 2014 (PDF, 1525 KB)Special Issue	25 Feb 2014
Development of an operational modeling system for urban heat islands: an application to Athens, GreeceT. M. Giannaros, D. Melas, I. A. Daglis, and I. KeramitsoglouNat. Hazards Earth Syst. Sci., 14, 347-358, 2014 (PDF, 3630 KB) Discussion Paper (NHESSD) Special Issue	21 Feb 2014
Efficient GIS-based model-driven method for flood risk management and its application in central ChinaY. Liu, J. Zhou, L. Song, Q. Zou, J. Guo, and Y. WangNat. Hazards Earth Syst. Sci., 14, 331-346, 2014 (PDF, 6328 KB) Discussion Paper (NHESSD)	21 Feb 2014
Rainfall thresholds for shallow landslide occurrence in Calabria, southern ItalyC. Vennari, S. L. Gariano, L. Antronico, M. T. Brunetti, G. Iovine, S. Peruccacci, O. Terranova, and F. GuzzettiNat. Hazards Earth Syst. Sci., 14, 317-330, 2014 (PDF, 3678 KB) Discussion Paper (NHESSD)	20 Feb 2014

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1 October 2013

Thu, 10 Oct 2013 08:53:00 +0000

1 October 2013

Abstract: PLINIVS Study Centre of University of Naples Federico II has developed a methodology that aims to estimate, in probabilistic terms, the direct and the indirect economic impacts of a Sub-Plinian I or Strombolian type eruption of Vesuvius. The economic model has been implemented as a complementary tool of the Volcanic Impact Simulation Model, a tool developed at PLINIVS Center available to the Italian Civil Protection Department (DPC) decision makers to quantify the potential losses consequent to a possible eruption of Vesuvius or Campi Flegrei. Along the expected time history of the eruptive event all the possible “direct costs” and the “factors” (indirect costs) impacting the economic growth in the event area have been identified. Each cost factor is built up through a specific algorithm that is fed by various providers, in order to run software that will estimate the global amount of economic damage from a volcanic event. The model does not include the economic evaluation of intangibles (e.g. human casualties), while the evaluation of damage to the local cultural heritage (historical buildings, archeological sites, monuments, etc.), is linked to the economic impact on tourism, estimated into indirect costs. The architecture of the model is based on a simulation logic, which allows an evaluation of different economic impact scenarios through input changes, allowing the model to be used as a tool to support the decision making process.

1 September 2013

Abstract: Cobeñas et al. (2012) describe deposits from the 2-ka eruption of Misti volcano, southern Peru. They propose a tephra-fall deposit overlain by voluminous pyroclastic-flow and surge deposits, which are overlain by proportionally minor lahar deposits and a debris-avalanche deposit of limited distribution. Some of their data corroborate our earlier work (Harpel et al., 2011), but three of their primary interpretations differ dramatically from ours and have important hazard implications. Voluminous flowage deposits crop out, and we present evidence that the majority contain diagnostic features suggesting that they are lahar deposits rather than pyroclastic-flow deposits. Their pyroclastic-flow deposit volume is also unrealistically large and not consistent with the extant deposits. The purported debris-avalanche deposit is texturally identical to the lahar deposits and has none of the features typically associated with debris-avalanche deposits. Associating such a unit with collapse and formation of a notch in the south crater rim lacks supporting data and disregards the myriad other reasons such notches can form. They divide the tephra-fall deposit into three beds, suggest that it underlies the pyroclastic-flow deposits, and infer that the eruption ceased after pyroclastic flow formation. We delineate six beds and present evidence that the upper beds persistently crop out between the pyroclastic-flow and lahar deposits. We infer from our eruption sequence that the eruption continued vigorously after pyroclastic-flow formation.

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The history of human-induced soil erosion: Geomorphic legacies

Mon, 07 Oct 2013 08:40:00 +0000

The history of human-induced soil erosion: Geomorphic legacies, early descriptions and research, and the development of soil conservation—A global synopsis

1 November 2013Markus Dotterweich

Abstract: This paper presents a global synopsis about the geomorphic evidence of soil erosion in humid and semihumid areas since the beginning of agriculture. Historical documents, starting from ancient records to data from the mid-twentieth century and numerous literature reviews form an extensive assortment of examples that show how soil erosion has been perceived previously by scholars, land surveyors, farmers, land owners, researchers, and policy makers. Examples have been selected from ancient Greek and Roman Times and from central Europe, southern Africa, North America, the Chinese Loess Plateau, Australia, New Zealand, and Easter Island. Furthermore, a comprehensive collection on the development of soil erosion research and soil conservation has been provided, with a particular focus on Germany and the USA.Geomorphic evidence shows that most of the agriculturally used slopes in the Old and New Worlds had already been affected by soil erosion in earlier, prehistoric times. Early descriptions of soil erosion are often very vague. With regard to the Roman Times, geomorphic evidence shows seemingly opposing results, ranging from massive devastation to landscapes remaining stable for centuries. Unfortunately, historical documentation is lacking. In the following centuries, historical records become more frequent and more precise and observations on extreme soil erosion events are prominent. Sometimes they can be clearly linked to geomorphic evidence in the field. The advent of professional soil conservation took place in the late eighteenth century. The first extensive essay on soil conservation known to the Western world was published in Germany in 1815. The rise of professional soil conservation occurred in the late nineteenth and early twentieth centuries. Soil remediation and flood prevention programs were initiated, but the long-term success of these actions remains controversial. In recent years, increasing interest is to recover any traditional knowledge of soil management in order to incorporate it into modern soil conservation strategies. The study shows that local and regional variations in natural settings, cultural traditions, and socioeconomic conditions played a major role for the dynamics and the rates of soil erosion on a long-term perspective. Geomorphic evidence and historical sources can often complement each other, but there should be also an awareness of new pitfalls when using them together.

Fault — Dissolution front relations and the Dead Sea sinkhole problem

1 November 2013Michael Ezersky | Amos Frumkin

Abstract: There are two conflicting models of sinkhole development along the Dead Sea (DS). The first one considers structural control on sinkholes, constraining them to tectonic lineaments. This hypothesis is based on seismic reflection studies suggesting that sinkholes are the surface manifestations of active neotectonic faults that may serve as conduits for under-saturated groundwater, enabling its access across aquiclude layers. Another hypothesis, based on results of multidisciplinary geophysical studies, considers the salt edge dissolution front as the major site of sinkhole formation. This hypothesis associates sinkholes with karstification of the salt edge by deep and shallow undersaturated groundwater. Our recent seismic reflection and surface wave studies suggest that salt formed along the active neotectonic faults. Sinkholes form in a narrow strip (60–100m wide) along a paleo-shoreline constrained by faults and alluvial fans which determined the edge of the salt layer. This scenario reconciles the two major competing frameworks for sinkhole formation.

A comparison between Bayes discriminant analysis and logistic regression for prediction of debris flow in southwest Sichuan, China

Abstract: In this study, the high risk areas of Sichuan Province with debris flow, Panzhihua and Liangshan Yi Autonomous Prefecture, were taken as the studied areas. By using rainfall and environmental factors as the predictors and based on the different prior probability combinations of debris flows, the prediction of debris flows was compared in the areas with statistical methods: logistic regression (LR) and Bayes discriminant analysis (BDA). The results through the comprehensive analysis show that (a) with the mid-range scale prior probability, the overall predicting accuracy of BDA is higher than those of LR; (b) with equal and extreme prior probabilities, the overall predicting accuracy of LR is higher than those of BDA; (c) the regional predicting models of debris flows with rainfall factors only have worse performance than those introduced environmental factors, and the predicting accuracies of occurrence and nonoccurrence of debris flows have been changed in the opposite direction as the supplemented information.

Erosion of a granite inselberg, Gross Spitzkoppe, Namib Desert

1 November 2013A. Matmon | A. Mushkin | Y. Enzel | T. Grodek

Abstract: Namibia, with its passive margin setting, long-term tectonic stability, and long-lasting arid climate is a typical granitic landscape characterized by numerous dominating inselbergs. The Namib has been the focus of quantitative studies on the overall rates of bedrock exhumation, escarpment retreat, and sediment generation, transport, and deposition. Results from these studies indicate steady bedrock erosion rates ranging between 1 and 5mmkyr−1 over the last 105–106yr. This rate was determined from samples collected mostly from small inselbergs with low relief. How fast the large and “classic” inselbergs, which dominate the Namib Desert landscape, erode, generate sediment, and contribute to the overall sediment supply has yet to be systematically examined.We document erosion rates of the Gross Spitzkoppe (GS), one of the largest inselbergs in the Namib Desert, Namibia, based on measured concentrations of 10Be in samples collected from bedrock, boulders, and surface grus. The results suggest a slow lowering rate (1–2mmkyr−1), while the overall slope processes deliver sediment to the base of the cliff with 5–6×105atomsg−1 quartz. This concentration is equivalent to an average erosion rate of ~8mmkyr−1, 2–3 times faster than the bedrock lowering rate. Thus, the inselberg has been eroding by cliff retreat. The concentration of cosmogenic isotopes in slope sediment is controlled by exposure time on the slope, weathering of exposed bedrock, and weathering of subsurface bedrock.Sediment continues to accumulate cosmogenic isotopes while being transported on the flat pediments surrounding the inselberg. Within 1–2km from the base of the GS, the concentration doubles to ~10×105atomsg−1 quartz. The increase is achieved by dosing due to exposure and mixing with highly dosed sediment eroded from near subsurface bedrock. From this area, grus is transported through a network of low gradient channels to the Atlantic Ocean, ~100km away. Cosmogenic isotope concentration in sediment increases to ~30×105 atoms of 10Beg−1 quartz, which is 3–4 times higher than that measured in the grus close to the GS and is controlled by the erosion rate of stable bedrock throughout the entire drainage basin. Dosing due to exposure during transport obviously contributes to the overall measured concentration in the sediment as it approaches the ocean.

Flank instability of Stromboli volcano (Aeolian Islands, Southern Italy): Integration of GB-InSAR and geomorphological observations

Abstract: Stromboli is characterized by frequent explosions of variable energy and periodically interrupted by more energetic blasts emitting large volumes of material. The pressurization of a volatile-poor, high-porphyritic magma column that is gas-recharged by the deep-seated, volatile-rich, low-porphyritic magma precedes such events and produces deformations on the NW flank of the volcano, Sciara del Fuoco. By integrating geomorphological observations with long-term displacements from ground-based interferometric radar since December 2007, we identified two landslides whose movements are strongly related with volcanic activity. Movement patterns obtained through a novel long-term analysis of GB-InSAR data permitted us to hypothesize the type of movement and depth for both landslides. Furthermore their position allowed us to affirm that the effusive vent formed in 2007 at 400ma.s.l., was the result of the deflection of a feeder dike caused by landslide fractures, thus showing the important role of geomorphological discontinuities in volcanic environments.

Shallow and deep-seated regolith slides on deforested slopes in Çanakkale, NW Turkey

1 November 2013Yunus Levent Ekinci | Murat Türkeş | Alper Demirci | Ahmet Evren Erginal

Abstract: This study deals with the stripping of regolith on a steep slope by surface wash and shallow landslides and a deep-seated landslide at a lower slope that took place on 17 February 2003 at the village of Mazılık, east of Çanakkale, Turkey. Soil loss and shallow slides dominate on the deforested steep slopes in the study area and occur preferentially along slope-parallel sub-horizontal joint planes with clay coatings, particularly oxyhydroxides that are rich in Fe but poor in Mn as a result of weathering under well-drained conditions. Gully erosion also occurs where the regolith cover is relatively thick (up to ~4m). The area of the deep-seated landslide, however, is dominated by silty clay (46%). A geoelectrical resistivity survey revealed a clay-rich zone at depths of ~3–10m, corresponding to the slip surface of the slide, which was associated with excessive water content after the snowy day of 14 February 2003 with a daily precipitation of ~16.4mm. Based on Thornthwaite's water budget analysis, the study area has a slide-prone condition with excess soil-moisture content, heavy rainfall events, snow accumulation and snow melting in winter months, and low soil permeability also favouring slope instability.

Estimation of debris flood magnitudes based on dendrogeomorphic data and semi-empirical relationships

1 November 2013Klaus Schraml | Barbara Kogelnig | Christian Scheidl | Markus Stoffel | Roland Kaitna

Abstract: Magnitude estimations of hydrogeomorphic processes contain crucial information for hazard assessments and for the understanding of longer term landscape evolution. In this study, we reconstruct magnitudes of debris floods for a torrential catchment in Tyrol by combining dendrogeomorphic time series of events with semi-empirical equations used to predict event volumes. Reconstructed debris flood magnitudes cover eight decades (A.D. 1930–2008) and vary from 2900 to 45,900m3. We illustrate that magnitude estimates derived from tree-ring data and semi-empirical equations represent a valuable contribution to the documentation and understanding of hydrogeomorphic processes and that they can complement fragmentary time series in small watersheds for periods covering decades up to centuries. Limitations of the approach are mainly inherent to the age and spatial distribution of sampled trees and may thus influence reconstructed event magnitudes as one goes back in time.

Selection of a taxonomic level for soil mapping using diversity and map purity indices: A case study from an Iranian arid region

1 November 2013A. Jafari | S. Ayoubi | H. Khademi | P.A. Finke | N. Toomanian

Abstract: There is a growing demand for digital soil maps for environmental planning, modeling and management. If mapped soil classes are taken from a hierarchical taxonomic system, a question arises: which taxonomic level is most appropriate to be depicted on the map with a given sample size, available environmental covariates and the strength of predictive relations between covariates and the soil classes? Pedodiversity, the study and measurement of soil diversity, can be considered as a framework to analyze spatial patterns depicted on soil maps. This paper discusses the selection of the taxonomic level for soil mapping in an arid region in southeast Iran on the basis of (1) the purity of a digital soil class map derived from an artificial neural network (ANN) prediction method using environmental covariates and (2) pedodiversity indices of these soil maps. The prediction of soil classes and the calculation of diversity indices were carried out for taxonomic categories of order, suborder, great group, and subgroup. Using the feed forward back-propagation algorithm, three-layer ANNs with input, hidden and output layers were trained for soil class prediction at each category level. In most predictions, the combined use of terrain attributes and geomorphic surfaces provided the best results. When the taxonomic level changed from order to subgroup, the purity decreased, whereas the values of the diversity indices increased. The highest purity and lowest diversity are observed at the order level, indicating a good quality map in terms of its purity, but reflecting only little soil diversity, thus with a low usage potential. On the other hand, soil maps at the level of subgroup illustrate high diversity and low purity, so that the predicted map units are highly uncertain. This map is also inappropriate for users. We introduced an index combining the diversity and purity which indicated that the best taxonomic level for soil mapping in the study area is the great group, with both high diversity and purity.

Biogeomorphic interactions in the Turtmann glacier forefield, Switzerland

1 November 2013Jana Eichel | Michael Krautblatter | Sebastian Schmidtlein | Richard Dikau

Abstract: Glacier forefields are dynamic environments dominated by active paraglacial processes and simultaneous vegetation succession, triggered by glacier retreat since the Little Ice Age. While these dynamics are accelerating in the last decades owing to climate change, interactions between vegetation and geomorphic processes and components and the resulting patterns are only partly understood. Using a biomorphic approach based on preexisting geomorphic and glaciological data, geomorphic activity was classified and mapped in the Turtmann glacier forefield, Switzerland. Vegetation and environmental parameters were sampled. Vegetation analysis was subsequently carried out with vegetation classification and ordination for identifying relationships to environmental parameters. A paraglacial impact on vegetation succession could be shown and differentiated according to geomorphic activity on constant terrain age. Biogeomorphic concepts were then applied to explain these patterns. Three biogeomorphic succession phases were identified and related to degrees of activity, species composition, and strength of interactions. Integrating our results into the paraglacial concept, we show how the paraglacial adjustment of a glacier forefield is significantly affected by biogeomorphic interactions.

Bed coarsening, riffle shortening, and channel enlargement in urbanizing watersheds, northern Kentucky, USA

1 November 2013Robert J. Hawley | Katherine R. MacMannis | Matthew S. Wooten

Abstract: Stream systems naturally respond to watershed land use dynamics, particularly in urban developments with unmanaged impervious areas. Such urban-provoked alterations to channel morphology cause water quality impairments, have adverse effects on aquatic biota, and pose risks to adjacent public infrastructure. Over the past four years we have collected detailed hydrogeomorphic data at 40 unique stream locations throughout northern Kentucky, with at least two rounds of annually repeated surveys at 70% of the sites and three rounds of surveys at 50% of the sites. Analysis of this time-series data encompassed measured rates of instability across three distinct dimensions including (1) channel cross sections, (2) longitudinal profiles, and (3) bed material particle composition. Regression analyses between geomorphic change and 2011 watershed imperviousness indicated stream cross sections in urban/suburban watersheds tend to be getting larger—their overall shape is both deepening and widening. Additionally, stream riffle lengths are shrinking and their pools are becoming both longer and deeper; and finally, their bed material composition is coarsening, particularly in streams in the early stages of watershed development. By documenting fluvial geomorphologic dynamics in such detail, this study highlights the process by which unmitigated urbanization homogenizes stream habitat and degrades aquatic ecosystems. This improved, process-based understanding of the urban-induced channel response sequence has clear implications to both stormwater management and stream/ecosystem restoration, particularly in stream systems where headcut migration is a primary driver of channel instability.

Influence of deep-seated gravitational slope deformations on landslide distributions: A statistical approach

1 November 2013M. Capitani | A. Ribolini | P.R. Federici

Abstract: The influence of deep-seated gravitational slope deformations (DSGSDs) on the distribution of translational landslides was analyzed in the Milia basin, Tuscany, Italy. Detailed geomorphological mapping, combined with the analysis of aerial photography, enabled us to build two landslide inventories. One inventory including landslides before 1975 was used to create statistical models, whereas the other inventory including landslides after 1975 was used to validate the models. Geology, slope angle, slope aspect, distance to hydrographic elements, and distance to tectonic lineaments were considered as landslide-predisposing factors. To quantify the importance of DSGSDs as another landslide-predisposing factor, the DSGSD presence/absence map was introduced in the stepwise statistical analysis. The landslide inventory maps and factor maps were processed using a conditional analysis on all possible factor combinations to produce landslide susceptibility maps with five susceptibility classes. The results indicate that the DSGSDs significantly affect landslide distribution.

Bayesian framework for mapping and classifying shallow landslides exploiting remote sensing and topographic data

Abstract: We propose a semi-automatic approach to detect, map and classify rainfall-induced shallow landslides. The approach combines the classification of a post-event multispectral satellite image with information on the morphometric signature of landslides in a Bayesian framework. We apply the approach in two steps. First, we detect and map the rainfall-induced landslides separating the stable ground from the failed areas. Next, we classify internally the landslides separating the source from the run out areas. We obtain the prior probability from the Mahalanobis discriminant function used to classify the satellite image, and the likelihood from the frequency distribution of terrain slope and cross section convexity in the pre-existing shallow landslides. We tested the approach in southern Taiwan, in a catchment where Typhoon Morakot caused abundant landslides in August 2009. Using the semi-automatic approach, we obtained a detailed event landslide inventory map that we compared to an inventory obtained through the visual interpretation of post-event ortho-photographs taken a few days after the landslide triggering rainfall event. Quantitative comparison in a Geographical Information System revealed a degree of matching between the two event inventories exceeding 90%. The approach is general and flexible, and can be used with different satellite imagery and topographic data. Best suited in landscapes where shallow landslides leave distinct radiometric and topographic signatures, the approach is expected to facilitate the production of event landslide inventory maps with positive consequences for geomorphological investigations, landslide hazard and risk modeling, and for post event recovery efforts.

Human-induced stream channel abandonment/capture and filling of floodplain channels within the Atchafalaya River Basin, Louisiana

1 November 2013Daniel E. Kroes | Thomas F. Kraemer

Abstract: The Atchafalaya River Basin is a distributary system of the Mississippi River containing the largest riparian area in the lower Mississippi River Valley and the largest remaining forested bottomland in North America. Reductions in the area of open water in the Atchafalaya have been occurring over the last 100years, and many historical waterways are increasingly filled by sediment. This study examines two cases of swamp channels (

High-frequency monitoring of debris-flow propagation along the Réal Torrent, Southern French Prealps

Abstract: The Réal Torrent (2.3km2 drainage area) is a very active debris-flow torrent in the French Prealps. It was equipped with three high-frequency monitoring stations in late 2010 to investigate the triggering conditions and propagation of debris flows along the 2-km long torrent channel. The monitoring system combines different techniques including rain gauges and measurements of ground vibrations and flow elevations.In spring and summer of 2011, five rainfall-triggered debris-flow events occurred along the torrent. Most debris fronts deposited in the upstream part of the channel but one large front (1.9–2.0m high) propagated to the catchment outlet with a mean velocity of about 3ms−1. The volume of this main debris surge was 3900m3 near the hillslope sources and increased downstream: 5500m3 in the middle part and 8600m3 near the catchment outlet. The debris flow developed a more mature flow pattern as it progressed downstream. Multiple debris and hyperconcentrated surges were observed upstream, while a single debris surge occurred near the catchment outlet. The front-height remained relatively constant during its propagation, whereas its viscosity and velocity tended to decrease downstream as the channel slope decreases. The growth of this main debris surge could be explained by the entrainment of in-channel sediments and the coalescence of the multiple preliminary surges.For the 2011 events, rainfall burst duration and intensity were the main factors controlling the occurrence, volume and runout distance of debris flows. Antecedent channel conditions (sediment recharge, bed wetness and antecedent rainfall) are also important factors, but further investigations are necessary to better understand the role of these factors regarding the triggering and propagation of debris flows in the Réal Torrent.

Reactivation of supply-limited dune fields from blowouts: A conceptual framework for state characterization

1 November 2013Thomas E. Barchyn | Chris H. Hugenholtz

Abstract: Aeolian dune fields mantle the Earth in both vegetated (stable) and unvegetated (active) states. Changes in state are poorly understood; in particular, little is known about reactivation (devegetation) from a vegetated state. Available evidence indicates that dune reactivation can be driven by changes in aridity, increased wind speed, fire, biogenic disturbance, human disturbance, or a combination of the previous. How these controls fit together and define the reactivation potential of dune fields is presently unknown. Here we develop a framework to describe reactivation potential for a specific case: presently vegetated, supply-limited dune fields that develop blowouts under a unidirectional wind. We first define a conceptual model of blowout expansion, and then split the functions of vegetation in a stable dune field into: (i) maintenance of a protective skin, and (ii) blowout suppression. We model reactivation as disturbance breaking through the protective skin, which forms a blowout that is either (i) suppressed by colonizer species, or (ii) capable of advancing downwind and reactivating part of the dune field. The capacity for disturbance to break through the protective skin is a function of disturbance magnitude, area, and resistance of the skin. The blowout suppression capacity of a dune field is a function of sediment flux, blowout depth (related to geomorphology), and colonizer species vitality. By plotting a given dune field with two variables (protective skin breach rate and blowout suppression capacity) we define four states: (i) stable, (ii) blowout dominated, (iii) reactivating, or (iv) stable but disturbance susceptible. We reinforce the conceptual model with qualitative examples and discussion of experiments on grassland-stabilized dunes in Canada. Overall, our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields.

The geomorphic effectiveness of a large flood on the Rio Grande in the Big Bend region: Insights on geomorphic controls and post-flood geomorphic response

1 November 2013David J. Dean | John C. Schmidt

Abstract: Since the 1940s, the Rio Grande in the Big Bend region has undergone long periods of channel narrowing, which have been occasionally interrupted by rare, large floods that widen the channel (termed a channel reset). The most recent channel reset occurred in 2008 following a 17-year period of extremely low stream flow and rapid channel narrowing. Flooding was caused by precipitation associated with the remnants of tropical depression Lowell in the Rio Conchos watershed, the largest tributary to the Rio Grande. Floodwaters approached 1500m3/s (between a 13 and 15year recurrence interval) and breached levees, inundated communities, and flooded the alluvial valley of the Rio Grande; the wetted width exceeding 2.5km in some locations. The 2008 flood had the 7th largest magnitude of record, however, conveyed the largest volume of water than any other flood. Because of the narrow pre-flood channel conditions, record flood stages occurred.We used pre- and post-flood aerial photographs, channel and floodplain surveys, and 1-dimensional hydraulic models to quantify the magnitude of channel change, investigate the controls of flood-induced geomorphic changes, and measure the post-flood response of the widened channel. These analyses show that geomorphic changes included channel widening, meander migration, avulsions, extensive bar formation, and vertical floodplain accretion. Reach-averaged channel widening between 26 and 52% occurred, but in some localities exceeded 500%. The degree and style of channel response was related, but not limited to, three factors: 1) bed-load supply and transport, 2) pre-flood channel plan form, and 3) rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope. The post-flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine-grained benches inset within the widened channel margins. The most significant post-flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment.

Assessment of channel changes in a Mediterranean ephemeral stream since the early twentieth century. The Rambla de Cervera, eastern Spain

1 November 2013Francisca Segura-Beltrán | Carles Sanchis-Ibor

Abstract: An analysis of morphological changes during the last six decades is presented for a 16.5-km reach of the Rambla de Cervera, a Mediterranean ephemeral stream located in eastern Spain. Channel changes were analysed through a range of techniques, specifically the analysis of aerial photographs with geographical information systems (GIS) and comparison of topographic surveys. The gravel channel underwent a general decline over the study period, losing width (68.5%) and surface area (45.7%) caused by the development of established islands frequently attached to the floodplain. These morphological changes exhibit an interesting temporal variability, with a maximum decrease of the gravel channel in the period 1946–1956 and another narrowing stage between 1977 and 1991. Two periods (1956–1977 and 1991–2006) also had mixed performance. In addition, incision processes occurred along the entire study reach at an average depth of 3.5m. Natural and human-induced factors producing contradictory effects are considered responsible for changes in the Rambla de Cervera.

The processes and timing of sediment delivery from headwaters to the trunk stream of a Central European mountain gully catchment

1 November 2013Annegret Larsen | Hans-Rudolf Bork | Alexander Fuelling | Markus Fuchs | Joshua R. Larsen

Abstract: Gully systems determine downstream water quality and sediment loads since they are located where streams begin. They are often only considered as a sediment source, and the degree to which gully systems also store sediment, and the timescales of this storage, have received less attention. Gully sediment storage is important because many sedimentary archives, such as floodplains and lakes, have recorded increases in sedimentation rates particularly in Medieval times, which are interpreted as the result of increased slope erosion and gully activity. At present there is insufficient evidence directly linking such other sedimentary archives and gully systems. There is also a lack of long term records which may indicate how the major external controls, climatic or anthropogenic, might determine gully responses. To address this, we analysed sediment sources and sinks within a small (43ha) gully catchment in the Spessart Mountains, Germany. We found five main phases of erosion and deposition since ~13ka, which revealed catchment vegetation significantly controlled geomorphic responses. A loss of vegetation due to climate deterioration (e.g. Younger Dryas) or deforestation (e.g. Medieval period) caused widespread slope instability and the aggradation of the gully thalweg. In contrast, well forested conditions before the Medieval period, and again in recent years, re-stabilised the slopes, leading to gully incision with knickpoint retreat. This result differs from previous interpretations of gully activity in Central Europe that gully erosion mostly occurred in Medieval times. Our results also demonstrate that only the initial phase of knickpoint retreat is significant for supplying sediment to the gully fan and trunk stream. Then knickpoint retreat leads to a relative increase in the thalweg storage capacity downstream, which limits further sediment export. This has important implications for the interpretation of floodplain ages, since the initial supply of gully sediment to trunk streams may not coincide with human impact. Instead, there will be a lagged response between catchment reforestation and the onset of gully incision, which in this study is up to ~150years. Therefore, the assumption of a direct causal link between increases in floodplain sedimentation and slope erosion may not always be valid.

Human induced soil erosion and gully system development in the Late Holocene and future perspectives on landscape evolution: The Myjava Hill Land, Slovakia

1 November 2013Markus Dotterweich | Miloš Stankoviansky | Jozef Minár | Štefan Koco | Pavol Papčo

Abstract: In humid climate zones, like Central Europe, past soil erosion and gullying are strongly connected with agricultural expansion, and extreme soil erosion events often play an important role in land abandonment. This paper provides a case study to demonstrate the interaction between land use, soil erosion, floodplain development, and land use changes in a 0-order catchment in the Babikovce catchment, Myjava Hill Land, situated in western Slovakia. Sedimentological, pedological, geoarchaeological and historical data indicate two main periods of intensive hillslope erosion and gullying since the High Middle Ages. In particular, a few extreme precipitation events (or rapid snowmelts) caused intensive runoff events and gullying on cleared land. The formation of the gully system and fan deposits in the Babikovce catchment and other areas also forced the occurrence of intensive muddy floods and caused floodplain aggradation and meander changes along rivers in the Myjava Hill Land. As a result, the development of the dense network of permanent gullies in the Myjava Hill Land can be associated with the transformation of woodland into farmland and later land abandonment. Today, the area is highly truncated by soil erosion and very difficult to farm.

Shallow caves and blowholes on the Nullarbor Plain, Australia — Flank margin caves on a low gradient limestone platform

1 November 2013Shannon Burnett | John A. Webb | Susan White

Abstract: The Nullarbor Plain of southern Australia is a very extensive limestone platform with relatively few large caves for its size, but contains thousands of blowholes, sub-circular vertical shafts up to 1–2m in diameter, which often connect to similar-sized sub-horizontal passages. Recent detailed systematic surveys of large areas of the Nullarbor Plain have provided new distribution data showing that blowholes and associated shallow caves are concentrated in a 25–30km-wide band located >75km inland. The known density of these features (up to 43/25km2) underestimates the cave porosity because the strong draughts blowing from many of the blowholes indicate that they connect to extensive cave systems of small passages. These shallow caves are relict phreatic features; their entrances (blowholes) were opened as the land surface was lowered by denudation. The band of blowholes and caves is located along the Late Miocene (~6Ma) shoreline across the Nullarbor, when there was a eustatic stillstand. The caves formed in the zone of enhanced dissolution at the seaward margin of the freshwater lens along the carbonate coastline, and can therefore be regarded as flank margin caves on a low gradient limestone platform; a flank margin setting relatively unknown prior to this study. The width of the band of flank margin caves, which is substantially greater than previously documented for this cave type, reflects the very low gradient of both the ground surface and water table, together with the influence of tidal fluctuations and regression of the shoreline. Flank margin cave development stopped when the sea retreated rapidly in the Late Miocene–Early Pliocene due to a period of tilting and uplift. The band of flank margin caves has high permeability and substantial porosity, and would therefore form an excellent, largely overlooked, type of palaeokarst petroleum reservoir.

Quantifying long-term changes in gully networks and volumes in dryland environments: The case of Northern Ethiopia

1 November 2013Amaury Frankl | Jean Poesen | Mitiku Haile | Jozef Deckers | Jan Nyssen

Abstract: Understanding historical and present gully development is essential when addressing the causes and consequences of land degradation, especially in vulnerable dryland environments. For Northern Ethiopia, several studies exist on the severity of gully erosion, yet few have quantified gully development. In this study, gully network and volume development were quantified over the period 1963–2010 for an area of 123km2, representing the regional variability in environmental characteristics. Gully networks were mapped from small-scale aerial photographs and high-resolution satellite images. For the latter, visualizing Google Earth images in 3D proved to be very suitable to investigate gully erosion. From the changes in networks and volumes over the period 1963–2010, the occurrence of one cut-and-fill cycle is apparent. From a largely low-dynamic gully system in the 1960s, network expansion and increased erosion rates in the 1980s and 1990s caused the drainage density and volume to peak in 1994. The average gully density (Dtotal) was then 2.52kmkm−2 and the area-specific gully volume (Va) 60×103m3km−2. This coincides with soil losses by gully erosion (SLg) of 17.6tha−1y−1 over the period 1963–1994. By 2010, improved land management and the region-wide implementation of soil and water conservation measures caused 25% of the gully network to stabilize, resulting in a net infilling of the gully channels over the period 1994–2010. The study validates previous findings that land degradation by gullying was indeed severe in Northern Ethiopia in the second half of the 20th century, but also shows that when proper land management is applied, a gully can be transformed into a linear oasis, which increases the resistance of gullies to further erosion.

Dunes on planet Tatooine: Observation of barchan migration at the Star Wars film set in Tunisia

1 November 2013Ralph D. Lorenz | Nabil Gasmi | Jani Radebaugh | Jason W. Barnes | Gian G. Ori

Abstract: Sand dune migration is documented with a readily-available tool (Google Earth) near Chott El Gharsa, just north-west of Tozeur, Tunisia. As fiducial markers we employ a set of buildings used to portray the fictional city Mos Espa. This set of ~20 buildings over roughly a hectare was constructed in 1997 for the movie Star Wars Episode 1 — The Phantom Menace. The site now lies between the arms of a large “pudgy” barchan dune, which has been documented via satellite imaging in 2002, 2004, 2008 and 2009 to have moved from ~140m away to only ~10m away. Visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position: a smaller set nearby was substantially damaged by being overrun by dunes circa 2004. The migration rate of ~15m/yr decreases over the observation period, possibly as a result of increased local rainfall, and is consistent with barchan migration rates observed at other locations worldwide. The migration rate of this and two other barchans suggests sand transport of ~50m3/m/yr, somewhat higher than would be suggested by traditional wind rose calculations: we explore possible reasons for this discrepancy. Because of the link to popular science fiction, the site may be of pedagogical interest in teaching remote sensing and geomorphic change. We also note that nearby playa surfaces and agricultural areas have a time-variable appearance. The site's popularity as a destination for Star Wars enthusiasts results in many photographs being posted on the internet, providing a rich set of in-situ imagery for continued monitoring in the absence of dedicated field visits.

Basal shear stress of debris flow in the runout phase

1 November 2013V. D'Agostino | F. Bettella | M. Cesca

Abstract: A laboratory device is proposed to assess the basal shear stresses generated by debris-flow mixtures during their runout phase. The device consists of an inclinable box with a gate facing a deposition plane. The box is filled with a selected debris-flow mixture, and after sudden opening of the gate, the features of the dam-break deposit can be measured. Based on some simplified assumptions of the energy balance, a methodology is proposed to assess basal shear stresses. The device has been tested using sediment samples from debris-flow deposits generated by two catchments of the Dolomites (Cortina d'Ampezzo, Belluno, Italy) by carrying out runout tests for different sediment concentrations by volume. The results show how the static Coulomb friction law is valid in the runout phase, with friction angles on the order of the angle of repose of the same material in dry conditions. The data elaboration also yields an innovative constitutive equation for shear stresses. This relation merges the Coulomb mixture approach with the concept of a one-phase flow with a certain rheology. This integration offers a useful insight into the weaknesses of the rheological approach if it is not properly scaled up to the ambient pressure of interest.

Analysis of the deep-seated gravitational slope deformations over Mt. Frascare (Central Italy) with geomorphological assessment and DInSAR approaches

Abstract: A quantitative and innovative DGSD (deep gravitational slope deformation) assessment method that used integrated remote sensing was tested in the central Apennine mountain range (Italy). The movement rate was calculated for selected test areas using the differential SAR interferometry small baseline subset (SBAS) technique. The selected test areas were previously identified by interpreting both aerial photos and using 32 ERS radar images taken between 1993 and 2000. More than 15cm of cumulative surface displacement occurred across the Podalla DGSD along the satellite line of sight (LoS). Moreover, the displacement time series showed non-linear deformation rates, which included periods of accelerated movement correlated with strong rainfall. The high estimated Podalla DGSD activity indicates that this type of study should be conducted to monitor the evolution of this phenomenon. In addition, the DInSAR movement rate can be used to improve mapping and identify DGSDs in specific landscapes.

Morphotectonic analysis of the Lunigiana and Garfagnana grabens (northern Apennines, Italy): Implications for active normal faulting

1 November 2013Deborah Di Naccio | Paolo Boncio | Francesco Brozzetti | Frank J. Pazzaglia | Giusy Lavecchia

Abstract: This work integrates existing structural geology data with new detailed geomorphic analyses of the fluvial network to characterize active and potentially seismogenic faults bordering the Lunigiana and Garfagnana basins in the northern Apennines of Italy. These two basins are NW–SE-oriented asymmetric grabens, bordered by several normal faults with a poorly known, but probable recent slip history. Several strong earthquakes (M 5.0–6.5) have occurred in the area in the last millennium, demonstrating that this is one of the most seismically active areas of the northern Apennines. However, the lack of reliable instrumental data for strong earthquakes, generally low deformation rates, and poor exposures of faulted Quaternary sediments render the characterization of active, seismogenic faults problematic.Here, we quantify the relationships between faults and watershed-scale geomorphology using 10-m digital topography to extract channel and basin metrics, such as steepness, concavity, and stream length-gradient indices of modeled river longitudinal profiles. In particular, convex segments of longitudinal profiles (knickpoints) are investigated in the spatial context of suspected active faults. Several knickpoints arise locally from juxtaposed rock types of different erodibility; however, many others mapped along major normal faults have a clear tectonic origin. In fact, the height of the footwall knickpoints (the closest to the fault trace) varies along-strike the fault, increasing toward the fault center and tapering off toward the fault tips, mimicking the expected displacement profile of a fault. In these cases, we consider the knickpoint height as a proxy of the fault throw accumulated by the youngest fault activity, probably during the late Quaternary. The along-strike distribution of knickpoint heights helps in defining the likely segmentation pattern of the fault system. The identified active normal fault segments have lengths ranging from 9.5 to 28.5km. The inferred late Quaternary throw rate ranges from 0.3 to 0.8mm/a; however, the absence of any offset datable material limits our ability to assign precise numeric ages and rates of offset to the faulting.

Assessment of river bank erosion in Southern Minnesota rivers post European settlement

1 November 2013Andrew C. Kessler | Satish C. Gupta | Melinda K. Brown

Abstract: River bank erosion is one of the major sources of sediment for many rivers around the world. With the current emphasis on developing total maximum daily loads (TMDLs) for impaired waters in the United States, there is heightened interest in quantifying background sediment levels in rivers. In this study, we assessed variations in river bank erosion over time using a combination of 1855 Public Land Survey System plats, aerial photographs from 1938 to 2009, and light detection and ranging (lidar) data from 2005 to 2009 for sediment impaired rivers in Southern Minnesota. Results showed that bank erosion was episodic, making comparisons of erosion rates from dissimilar time intervals unreliable. For comparable time intervals, average river bank retreat rates (0.51myr−1 from 1855 to 1938 vs. 0.37myr−1 from 1938 to 2009) were statistically similar (t=2.13, p=0.14) suggesting that bank erosion rates have remained stable since European settlement. Comparisons over shorter time intervals of 1938–1971 and 1971–2009 also showed similar statistical trends (t=0.76, p=0.45) with average river bank retreat rates of 0.57 and 0.50myr−1, respectively. However, additional 145 observations of bank retreat were found in the period 1971–2009 relative to 1938–1971, indicating that the number of actively eroding river banks may have increased over time. Contrary to assumptions made in the literature, bank erosion measurements using lidar data showed a poor relationship (r2=0.01 to 0.36) with river bank physical features (face area, inclined surface area, length, slope, height, and aspect), thus suggesting that extrapolating a limited number of bank erosion observations to the whole length of a river will lead to erroneous predictions. This lack of relationship was expected considering that most of these bank physical features do not fully represent bank erosion processes such as seepage, freeze–thaw, river migration, under cutting and sapping. We conclude that, in assessing conservation measures or developing TMDLs to manage river sediment loads, (1) background levels of suspended sediments from river bank erosion should be established using comparable time intervals, and (2) up scaling of discrete volume loss measurements to an entire reach should be avoided.

Evaluating short-term morphological changes in a gravel-bed braided river using terrestrial laser scanner

Abstract: Braided rivers are dynamic and complex environments shaped by the balance of the flow and sediment regimes and by the influence of the riparian vegetation and disturbances such as floods. In particular, the balance between sediment supply and transport capacity can determine the morphological evolution of a river. For instance, aggrading and widening trends are distinctive of reaches where sediment supply is higher than transport capacity. In contrast, incising and narrowing tendencies are dominant. The aim of the present study is to analyze the short-term morphological dynamics and the processes of erosion and sediment deposition along a small reach of a relatively unimpacted gravel-bed braided river (Tagliamento River, northeast Italy) using a terrestrial laser scanner (TLS). The study area is around 23ha and has been surveyed before after two periods with relevant flood events, two of which were higher than the bankfull level and occurred between September 2010 and September 2011. The very high point clouds density allowed us to derive three high resolution digital elevation models (DEMs) with 0.125×0.125m pixel size. Scan data cloud merging was achieved with an overall high degree of accuracy and resolution (subcentimeter). Topographic data were more accurate for exposed surfaces than those collected in wet areas. A detailed net of dGPS control points allowed us to verify the high quality of the DEMs derived from the surveys (RMSE of about 5cm). Two DEMs of difference (DoD) were computed, revealing different and consistent episodes of erosion and deposition within the analyzed area, and changes in morphology of channel and bars could also be detected, such as bar edge accretion and bank erosion demonstrating a strong dynamicity of the Tagliamento River. Moreover, a very detailed estimation of the surface roughness in the study area has been carried out, permitting a large-scale analysis of the roughness values distribution. The results of the analysis on the TLS collected data show that along a river with a high natural character (i.e., Tagliamento River), the dynamic processes are also common during low magnitude events.

Two-dimensional geomorphological characterization of a filled abandoned meander using geophysical methods and soil sampling

Abstract: Using geophysical methods for the geomorphological characterization of subsurface features has numerous advantages over traditional exploration methods, because of their noninvasive and rapid nature. In this study, we compared the results of four geophysical methods with each other. We also discuss their possibilities and limitations in a geomorphological investigation. Electrical resistivity tomography (ERT), refraction seismic (RS), ground penetrating radar (GPR), and multichannel analysis of surface waves (MASW) methods were applied at an abandoned meander in northern Saxony to map a predefined structure. By combining these methods, we were able to characterize and delineate subsurface features of the abandoned meander, including a point bar, a channel, and a cutbank. Core samples obtained from sonic drilling were used to validate the findings of both seismic methods. However, we found that electrical resistivity tomography and ground penetrating radar lacked penetration depth and could only be used to resolve shallower subsurface layers. The ERT, GPR, RS, and MASW can be used to gather images of subsurface structures. The MASW in particular provides supplementary information about the channel's internal structure (with respect to lateral and vertical resolution). Besides fluvial–morphological features, we also detected inverse velocity structures within the channel. This allowed us to characterize the abandoned meander using information about its layer distribution and material composition. However, we were only able to characterize and delineate the subsurface features of the abandoned meander by combining all of the aforementioned methods.

Distribution and inferred age of exfoliation joints in the Aar Granite of the central Swiss Alps and relationship to Quaternary landscape evolution

1 November 2013Martin Ziegler | Simon Loew | Jeffrey R. Moore

Abstract: Exfoliation joints are well-known natural fractures limited to near the ground surface. Relatively few details, however, are known about their distribution and age in the Swiss Alps. Exfoliation joints follow the landscape surface at the time of their formation; the age of the associated landscape feature then provides a maximum age of exfoliation joints. While landscape forms can change through time, exfoliation joints preserve elements of former landscape morphologies by their undisturbed orientations. The Grimsel region of the Central Alps is well-suited for analyzing the impact of erosional episodes, and accompanying stress changes, on exfoliation joint formation in granitic rocks. Mapping above and below ground revealed that exfoliation joints are widespread and occur between valley bottoms and mountain crests within glacial (inner and hanging U-shaped trough valleys, glacial cirques, and steep mountain crests) and predominantly fluvial landforms (gently inclined linear slopes above the inner trough valleys, narrow inner-valley gorges, and steep V-shaped side gullies). Based primarily on their geometric properties at the ground surface, three exfoliation joint types were distinguished in our study area: (1) closely spaced (

Evolution of thermokarst in East Siberian ice-rich permafrost: A case study

Abstract: Thermokarst lakes and basins are major components of ice-rich permafrost landscapes in East Siberian coastal lowlands and are regarded as indicators of regional climatic changes. We investigate the temporal and spatial dynamics of a 7.5km2, partly drained thermokarst basin (alas) using field investigations, remote sensing, Geographic Information Systems (GIS), and sediment analyses. The evolution of the thermokarst basin proceeded in two phases. The first phase started at the Pleistocene/Holocene transition (13 to 12ka BP) with the initiation of a primary thermokarst lake on the Ice Complex surface. The lake expanded and persisted throughout the early Holocene before it drained abruptly about 5.7ka BP, thereby creating a >20m deep alas with residual lakes. The second phase (5.7ka BP to present) is characterized by alternating stages of lower and higher thermokarst intensity within the alas that were mainly controlled by local hydrological and relief conditions and accompanied by permafrost aggradation and degradation. It included diverse concurrent processes like lake expansion and stepwise drainage, polygonal ice-wedge growth, and the formation of drainage channels and a pingo, which occurred in different parts of the alas. This more dynamic thermokarst evolution resulted in a complex modern thermokarst landscape. However, on the regional scale, the changes during the second evolutionary phase after drainage of the initial thermokarst lakes were less intense than the early Holocene extensive thermokarst development in East Siberian coastal lowlands as a result of a significant regional change to warmer and wetter climate conditions.

Historical evolution of a micro-tidal lagoon simulated by a 2-D schematic model

1 November 2013D. Bonaldo | G. Di Silvio

Abstract: Coastal transitional environments such as estuaries, coastal inlets and tidal lagoons are the result of the interaction of several exogenous forcing factors (e.g. tidal regime, local wind and wave climate, sea-level rise, sediment supply) many of which are, in principle, variable in time over historical and geological timescales. Besides the natural variability of the external constraints, human interventions in some components of the system can either directly or indirectly affect long-term sediment dynamics in the whole system.In this paper the evolution of a schematic tidal basin, with non-uniform sediments and subject to geological and anthropogenic processes, is reproduced by means of a two dimensional morphodynamic model and qualitatively compared to the events which historically took place in the Venice Lagoon during the last four centuries; the trend for the next 200years is also investigated. In particular, the effect on both morphology and bottom composition of river diversion, jetty construction, human-induced subsidence and channel dredging are presented and discussed.

Identifying palaeo-ice-stream tributaries on hard beds: Mapping glacial bedforms and erosion zones in NW Scotland

1 November 2013Tom Bradwell

Abstract: Ice streams are fed by tributaries that can extend deep into the heart of ice sheets. These tributaries are born at onset zones — the abrupt transitions from slow sheet flow to fast streaming flow that often occur at significant topographic steps on hard beds (bedrock-dominated beds). For this reason, tributary onset zones leave only a subtle erosional geomorphic signature in the landscape record that is rarely studied. This paper examines, in detail, the geomorphic signature of ice-sheet flow on a hard bed at the head of a palaeo-ice stream. We use field survey techniques to map glacial bedforms within an ~200-km2 area of hard crystalline bedrock in a landscape of ‘areal scour’ around Loch Laxford in NW Scotland. The bedrock bedforms range from plastically moulded (p-forms) and wholly abraded forms, to stoss–lee forms and plucked surfaces all on an outcrop scale (1–100m). We devise a five-zone classification system to map (in a GIS) the presence, absence, and abundance of glacial erosional forms within 619 (500-m square) grid cells. We go on to use these erosional bedform zones, along with known glaciological relationships to interpret the spatial and altitudinal pattern of palaeo-ice sheet processes and glacier dynamics in this part of NW Scotland. Our interpretation highlights the strong vertical thermal zonation on mountains, and the spatial variations in ice rheology (softness), ice temperature and, by inference, ice velocity in troughs — intimately associated with the onset of ice streaming in tributaries. Consequently, we define the Laxfjord palaeo-ice-stream tributary — a feeder to the Minch palaeo-ice stream in NW Scotland. Finally, we suggest that this new mapping approach could be performed in other deglaciated hard-bed terrain to examine, more widely, the subtle erosional signatures preserved in areas traditionally thought to represent ice sheet ‘areal scour’.

Kinematics and geological constraints of the slow-moving Pisciotta rock slide (southern Italy)

1 November 2013P. De Vita | M.T. Carratù | G. La Barbera | S. Santoro

Abstract: The Pisciotta landslide is a slow-moving deep-seated rock slide in the Campania region of southern Italy, which has damaged a provincial road several times in the last decades and currently poses a hazard to the national railway that intersects the toe of the landslide. The landslide involves an Oligocene turbidite series, which is composed of intercalated calcarenites, marls and mudrocks.The principal objectives of this study were to investigate the morphological evolution of the unstable slope, quantitatively analyse ground deformations and construct an engineering-geological model that is consistent with the spatial features of the landslide. The long-term evolution of the unstable slope was assessed through the examination of available aerial photos from 1943 to 2006. Kinematic analyses of the ground deformations were conducted based on observed progressive displacement of the road, as evident from the topographic maps and orthophotos (1955–2006), and the bi-weekly displacement survey of 50 targets distributed across the landslide area (September 2006–March 2009). The engineering-geological model of the landslide was reconstructed from the stratigraphic data obtained from the study of borehole data and monitoring of inclinometers as well as from geological, structural and geophysical surveys. The analysis of the aerial photographs revealed an early stage of deformation in 1943, which has been gradually widening since then. In addition to the main scarp and the landslide flanks, other significant landslide structures such as the longitudinal and transverse cracks as well as the positive or negative morphologies were monitored and mapped in the subsequent years. These studies indicated a progressive erosion of the upper part of the slope and a bulging of the foot. Long-term kinematic analysis based on the progressive displacements of the road allowed the measurement of the ground deformations from 1955 to 2009, which revealed a cumulative horizontal displacement of up to 53m and an average velocity of 0.98myear−1, which has increased in the recent decades. In addition, the recent monitoring of the ground deformations demonstrated a continuous activity with an approximately constant rate of displacement and a composite kinematic history of the landslide body through differential displacements and associated velocities. The engineering-geological model of the landslide was found to be controlled by specific stratigraphic and structural constraints. The landslide involves a stratigraphic interval of the Saraceno Formation (Nord-Calabrese tectonic unit) with a largely marly–argillaceous composition whose structural setting displays complex folding (at the mesoscale) and faulting with an approximately monocline attitude of bedding and a downslope dip direction at the macroscale. The left flank of the landslide rests on a normal fault.

Fluvial response to Holocene volcanic damming and breaching in the Gediz and Geren rivers, western Turkey

Abstract: This study discusses the complex late Holocene evolution of the Gediz River north of Kula, western Turkey, when a basaltic lava flow dammed and filled this river valley. Age control was obtained using established and novel feldspar luminescence techniques on fluvial sands below and on top of the flow. This dating constrained the age of the lava flow to 3.0–2.6ka. Two damming locations caused by the lava flow have been investigated. The upstream dam caused lake formation and siltation of the upstream Gediz. The downstream dam blocked both the Gediz and a tributary river, the Geren. The associated lake was not silted up because the upstream dam already trapped all the Gediz sediments. Backfillings of the downstream lake are found 1.5km upstream into the Geren valley. The downstream dam breached first, after which the upstream dam breached creating an outburst flood that imbricated boulders of 10m3 size and created an epigenetic gorge. The Gediz has lowered its floodplain level at least 15m since the time of damming, triggering landslides, some of which are active until present. The lower reach of the Geren has experienced fast base level lowering and changed regime from meandering to a straight channel. Complex response to base level change is still ongoing in the Geren and Gediz catchments. These findings are summarized in a diagram conceptualizing lava damming and breaching events. This study demonstrates that one lava flow filling a valley floor can block a river at several locations, leading to different but interrelated fluvial responses of the same river system to the same lava flow.

Arctic and Antarctic submarine gullies—A comparison of high latitude continental margins

Abstract: Submarine gullies are common features of high latitude continental slopes and, over the last decade, have been shown to play a key role in continental margin evolution, submarine erosion, downslope sediment transport, slope deposits, and the architecture of petroleum reservoirs. However, the processes that form these gullies, the timescales over which they develop, and the environmental controls influencing their morphology remain poorly constrained. We present the first systematic and comparative analysis between Arctic and Antarctic gullies with the aim of identifying differences in slope character, from which we infer differences in processes operating in these environments.Quantitative analysis of multibeam echosounder data along 2441km of the continental shelf and upper slope and morphometric signatures of over 1450 gullies show that six geomorphically distinct gully types exist on high latitude continental margins. We identify distinct differences between Arctic and Antarctic gully morphologies. In the Arctic data sets, deep relief (>30m gully incision depth at 50m below the shelf edge) and shelf-incising gullies are lacking. These differences have implications for the timescales over which the gullies were formed and for the magnitude of the flows that formed them. We consider two hypotheses for these differences: (1) some Antarctic gullies developed through several glacial cycles; and (2) larger Antarctic gullies were formed since the Last Glacial Maximum as a result of erosive flows (i.e., sediment-laden subglacial meltwater) being more abundant on parts of the Antarctic margin over longer timescales.A second difference is that unique gully signatures are observed on Arctic and on Antarctic margins. Environmental controls, such as the oceanographic regime and geotechnical differences, may lead to particular styles of gully erosion observed on Arctic and Antarctic margins.

Open Access

Quaternary sea-level change and slope instability in coastal areas: Insights from the Vasto Landslide (Adriatic coast, central Italy)

1 November 2013Marta Della Seta | Salvatore Martino | Gabriele Scarascia Mugnozza

Abstract: This paper focuses on the possible role of sea-level change in triggering and controlling large coastal slope instabilities, and focuses on the representative case study of the Vasto Landslide. The town of Vasto is 143ma.s.l. and sits atop an uplifted Quaternary regressive sequence widely outcropping along the Adriatic coast of central Italy. The coastal slope is affected by large slope instabilities (e.g. “Vasto Landslide”) including evidence of present activity. Well-documented historical disruptive events affected the town and the coastal slope in 1816, 1942 and 1956. Field evidence suggests that sea cliff retreat must have removed considerable volumes of rock before the activation of the large slope failures. Thus, a geological-evolutionary model of the landslide is proposed here that considers the landforms, geological evidence and borehole stratigraphy, as well as the combined effect of Quaternary uplift and eustatic oscillations on the coastal slope. Significant evolutionary steps were identified, and a slope stability analysis was performed using a stress–strain numerical modeling solved by a Finite Difference Method (FDM) to analyze the following: 1) the landslide mechanism, 2) the type of activity, and 3) the cumulative deformations that occurred during the morpho-evolutionary steps. Numerical modeling was calibrated by considering the present landforms as well as the effects recorded during historical events. The results confirm that the Vasto Landslide was activated in the Middle Pleistocene (215ka BP) as a consequence of wave-cut erosion and progressive uplift of the coastal slope. Moreover, the landslide evolved as a retrogressive, single-styled landslide comprising two major blocks. Using this framework, the historical events are interpreted as local re-activations, due to meteorological factors, of the ancient rupture surfaces affecting the entire slope.

Topographic precursors and geological structures of deep-seated catastrophic landslides caused by Typhoon Talas

1 November 2013Masahiro Chigira | Ching-Ying Tsou | Yuki Matsushi | Narumi Hiraishi | Makoto Matsuzawa

Abstract: Typhoon Talas crossed the Japanese Islands between 2 and 5 September 2011, causing more than 70 deep-seated catastrophic landslides in a Jurassic to Paleogene–lower Miocene accretion complex. Detailed examination of the topographic features of 10 large landslides before the event, recorded on 1-m DEMs based on airborne laser scanner surveys, showed that all landslides had small scarps near their future crowns prior to the slide, and one landslide had linear depressions along its future crown as precursor topographic features. These scarps and linear depressions were caused by gravitational slope deformation that preceded the catastrophic failure. Although the scarps may have been enlarged by degradation, their sizes relative to the whole slopes suggest that minimal slope deformation had occurred in the period immediately before the catastrophic failure. The scarp ratio, defined as the ratio of length of a scarp to that of the whole slope both measured along the slope line, ranged from 5% to 21%. Careful examination of aerial photographs from another four large landslides, for which no high-resolution DEMs were available, suggested that they also developed scarps at their heads beforehand. Twelve of the 14 landslides we surveyed in the field had sliding surfaces with wedge-shaped discontinuities that consisted of faults and bedding, suggesting that the buildup of pore pressure occurs readily on wedge-shaped discontinuities in a gravitationally deformed rock body. Most of the faults were undulatory and were probably thrust faults that formed during accretion. Other types of gravitational deformation were also active; e.g., flexural toppling and buckling were observed to have preceded one landslide.

Holocene river dynamics in Northland, New Zealand: The influence of valley floor confinement on floodplain development

1 November 2013J.M. Richardson | I.C. Fuller | K.A. Holt | N.J. Litchfield | M.G. Macklin

Abstract: Valley floor mapping, sedimentology, and 14C-dating have been used to reconstruct the fluvial history at eight floodplain sites spread throughout Northland, a region removed from the main areas of tectonic and volcanic activity in New Zealand. We present a probability-based record of Holocene river behaviour for Northland using 14C-dated Holocene fluvial deposits and compare this with independent palaeoclimate proxy records from the North Island. Holocene floodplain evolution and fluvial behaviour have been conditioned by the degree of valley-floor confinement. In the most and least confined valley settings, Holocene floodplain evolution has involved the development of a single floodplain surface. At partly confined sites, the river terrace and floodplain geomorphology are more complex. Region-wide progressive floodplain alluviation through the mid to late Holocene and a period of increased river activity between 3500 and 2800cal.YBP in response to climatically driven increases in sediment supply was followed by a period of valley floor incision and terrace formation beginning after 1900cal.YBP. In partly confined valley settings, this was followed by the aggradation of a lower Holocene floodplain surface, with rapid rates of vertical accretion in response to post-settlement catchment disturbance. The results of this study indicate that valley floor confinement has played a major role in controlling Northland Holocene river floodplain development, producing a continuum of floodplain and river terrace landforms in response to climatically and anthropogenically driven variations in sediment flux.

Discussion of ‘Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland’ by Douglas Howard, Sheryl Luzzadder-Beach and Timothy Beach, 2012

Abstract: This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘jökulhlaup’, for part of the Jökulsá á Fjöllum in north-central Iceland. They propose that this flood was the largest on Earth. We consider that the magnitude of the jökulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to jökulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of jökulhlaups along the Jökulsá á Fjöllum. We argue herein that whilst a range of landforms and sediments that are attributable to jökulhlaups can be observed along the Jökulsá á Fjöllum, these are not necessarily diagnostic of jökulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.

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Depositional features of co-genetic turbidite–debrite beds and

Mon, 07 Oct 2013 07:48:00 +0000

Depositional features of co-genetic turbidite–debrite beds and possible mechanisms for their formation in distal lobated bodies beyond the base-of-slope, Ulleung Basin, East Sea (Japan Sea)

1 December 2013

Abstract: A detailed analysis of the MR1 (11–12kHz) sonar images, chirp (2–7kHz) profiles, core sediments and 14C ages from the latest Quaternary lobated bodies (LB) on the deep (>2100m water depth) basin plain of the western Ulleung Basin reveals depositional features and context of co-genetic turbidite–debrite beds in the LB on the distal setting and a plausible mechanism for generating these beds. Eight LB are present in the basin plain, ca. 30–60km beyond the base-of-slope, and were generally deposited retrogressively. Older and more distal LB 1–4 have large dimensions (>27km long, 15–25km wide). In contrast, younger and less distal LB 5–8 are small (8.8–31.5km long, 1.2–12km). The muddier, larger LB 1 and 2 were most likely originated from the relatively large-scale sediment failures on the muddy upper slopes (>350–400m water depth) between 18.5 and 20.0cal. ka B.P. On other hand, the sandier, smaller LB 6 and 7 were deposited between 17.0 and 17.5cal. ka B.P., probably by the relatively small-scale sediment failures on the sandy uppermost slope, shallower than 350–400m water depth. In LB 1, a lower sandy-mud turbidite is transitional upward into an upper mud-matrix debrite having small, rounded mud clasts. In contrast, LB 6 exhibits a gradual upward change from a lower clay-poor, sandy turbidite to an upper clay-rich, sand-matrix debrite with large, interlocking mud clasts. Each mixed bed in LB 1 and 6 can represent a co-genetic (or linked) turbidite–debrite bed formed by the down-dip flow transformation from turbidity current to debris flow at a point during the same event. The abundant large-scale (up to 20–25m deep, 3–5km long) erosions of fine-grained substrates near the base-of-slope area suggest that the down-dip transformation was driven by incorporation of mud via erosional bulking by turbidity currents reaching the base-of-slope area. The different clay/sand content and size/shape of mud clasts in the co-genetic turbidite–debrite beds between LB 1 and 6 imply that the composition (sandy or muddy) and dimension of initial turbidity current approaching the base-of-slope, the volume of eroded masses from the fine-grained substrates, and the transport distance of sediment gravity flows from the erosional areas of muddy substrates can be all important factors controlling the depositional styles of co-genetic turbidite–debrite beds.

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Pyroclastic density currents (PDC) of the 16–17 August 2006 eruptions of Tungurahua

Mon, 07 Oct 2013 07:43:00 +0000

Pyroclastic density currents (PDC) of the 16–17 August 2006 eruptions of Tungurahua volcano, Ecuador: Geophysical registry and characteristics

1 September 2013

Abstract: Tungurahua, located in the Eastern Cordillera of the Ecuadorian Andes, is a 5023m-high active volcano, notable for its extreme relief (3200m), steep sides, and frequent eruptive cycles. From 1999 until 2006 Tungurahua experienced short periods of low to moderate strombolian activity, characterized by fire fountaining, explosions, frequent ash falls and debris flows, and no PDC events. Without warning, Tungurahua initiated PDC activity on 15–16 July 2006, which became more intense on the night of 16–17 August 2006, which is the focus of this study.Continuous monitoring of Tungurahua has employed seismic (both short period and broadband (BB) instruments), SO2 gas emission (COSPEC and DOAS), and geodetic methods (EDM, tilt meters, and GPS), in addition to thermal imagery (airborne and ground-based). Acoustic flow monitors (AFM) installed to monitor lahar activity were important for detecting PDC events. Acoustic signals were monitored at Riobamba, 40km to the SW, as well as by infrasound sensors at Tungurahua's BB seismic stations.Based on geophysical parameters, visual observations, and PDC deposit characteristics, four phases of distinct eruptive activity are recognized during the 16–17 August episode. Phase I (08H37 to 21H13 of 16 Aug.) (local time) experienced low to moderate strombolian activity with occasional high energy impulsive bursts and small PDC. Phase II (21H13-16 Aug. to 00H12-17 Aug.) was characterized by a number of discrete events with high amplitude seismo-acoustic signals, followed by the generation of larger PDC that overran monitoring stations and had velocities of 30–33m/s. After midnight, Phase III (00H12 to 01H14) saw an intense period of unrelenting eruptive activity corresponding to the episode's greatest energy release. It was characterized by subplinian activity accompanied by a series of high energy outbursts and constant low frequency jetting that together formed a continuous plume. It was during this phase that the largest PDC were produced, reaching the surrounding river valleys. Phase IV (after 01H14) followed the cessation of the paroxysmal eruption, but witnessed many granular PDC generated by degassed lava spill outs from the crater that developed lobe and channel morphology on the cone's lower flanks. Hours later a blocky lava flow issued from the crater.During these episodes, more than 30 PDC events were detected, the majority being small flows that remained high on the cone. The two largest PDC occurred after midnight, probably generated by fountain collapse. Their descent down the cone's upper steep flanks (~28°) and 2.4km in length favored air entrainment, resulting in PDC with greater fluidity. These flows had volumes of 9 to 17×106m3 and produced widespread, but relatively thin (1–2m thick) normally-graded deposits at their distal ends. The character and evolution of the PDC activity apparently reflect decreasing volatile contents of the magma and a diminishing magma supply.

Relationship between Kamen Volcano and the Klyuchevskaya group of volcanoes (Kamchatka)

1 August 2013Tatiana G. Churikova | Boris N. Gordeychik | Boris V. Ivanov | Gerhard Wörner

Abstract: Data on the geology, petrography, mineralogy, and geochemistry of rocks from Kamen Volcano (Central Kamchatka Depression) are presented and compared with rocks from the neighbouring active volcanoes. The rocks from Kamen and Ploskie Sopky volcanoes differ systematically in major elemental and mineral compositions and could not have been produced from the same primary melts. The compositional trends of Kamen stratovolcano lavas and dikes are clearly distinct from those of Klyuchevskoy lavas in all major and trace element diagrams as well as in mineral composition. However, lavas of the monogenetic cones on the southwestern slope of Kamen Volcano are similar to the moderately high-Mg basalts from Klyuchevskoy and may have been derived from the same primary melts. This means that the monogenetic cones of Kamen Volcano represent the feeding magma for Klyuchevskoy Volcano. Rocks from Kamen stratovolcano and Bezymianny form a common trend on all major element diagrams, indicating their genetic proximity. This suggests that Bezymianny Volcano inherited the feeding magma system of extinct Kamen Volcano. The observed geochemical diversity of rocks from the Klyuchevskaya group of volcanoes can be explained as the result of both gradual depletion over time of the mantle N-MORB-type source due to the intense previous magmatic events in this area, and the addition of distinct fluids to this mantle source.

Magma system response to edifice collapse

1 August 2013Pavel Izbekov | Evgenii Gordeev | John Eichelberger | Michael West

Chronology of Bezymianny Volcano activity, 1956–2010

1 August 2013Olga A. Girina

Abstract: Bezymianny Volcano is one of the most active volcanoes in the world. In 1955, for the first time in history, Bezymianny started to erupt and after six months produced a catastrophic eruption with a total volume of eruptive products of more than 3km3. Following explosive eruption, a lava dome began to grow in the resulting caldera. Lava dome growth continued intermittently for the next 57years and continues today. During this extended period of lava dome growth, 44 Vulcanian-type strong explosive eruptions occurred between 1965 and 2012. This paper presents a summary of activity at Bezymianny Volcano from 1956 to 2010 with a focus on descriptive details for each event.

Recent eruptions at Bezymianny volcano—A seismological comparison

1 August 2013Michael E. West

Abstract: For the past few decades, Bezymianny volcano has erupted once to twice per year. Here, I examine eight eruptive events between 2006 and 2010. This is the first time period for which proximal or broadband seismic data have been recorded at Bezymianny. Several recurring patterns are demonstrated in advance of eruptions. Eruptions are generally preceded by 12–36h of tremor energy elevated by 2 to 3 orders of magnitude. Locatable earthquake activity is quite erratic in the days before eruptions. For eruptions of juvenile magma, however, the cumulative moment magnitude increases with the repose time since the previous eruption. Though tenuous, this relationship is statistically significant and could improve forecasts of Bezymianny eruptions. The most energetic eruptions demonstrate increasing multiplet activity in the run-up, followed by a rapid cessation at the time of eruption. When present, this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting. Very long period seismicity (>20s periods) accompanies some eruptions. These tend to be the same short-lived high-energy eruptions that exhibit multiplet precursors. Four eruptions are examined in detail to illustrate the variety in eruption mechanisms. Lava dome collapses, sustained eruptions, singular paroxysmal explosions and post-explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating Bezymianny. Compared to Bezymianny's fifty-year modern history, recent eruptions have been shorter-lived and separated by longer repose times. Some evidence suggests that these eruptions may be increasingly explosive—a speculation that carries significant hazard implications. If true, however, this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors, suggesting an ability to improve the already excellent eruption forecasts available for Bezymianny.

Surface deformation of Bezymianny Volcano, Kamchatka, recorded by GPS: The eruptions from 2005 to 2010 and long-term, long-wavelength subsidence

1 August 2013Ronni Grapenthin | Jeffrey T. Freymueller | Sergey S. Serovetnikov

Abstract: Since Bezymianny Volcano resumed its activity in 1956, eruptions have been frequent; recently with up to 1–2 explosive events per year. To investigate deformation related to this activity we installed a GPS network of 8 continuous and 6 campaign stations around Bezymianny. The two striking observations for 2005–2010 are (1) rapid and continuous network-wide subsidence between 8 and 12mm/yr, which appears to affect KAMNET stations more than 40km away where we observe 4–5mm/yr of subsidence, and (2) only the summit station BZ09 shows slight deviations from the average motion in the north component at times of eruptions.The network-wide subsidence cannot be explained by tectonic deformation related to the build-up of interseismic strain due to subduction of the Pacific plate. A first order model of surface loading by eruptive products of the Kluchevskoy Group of Volcanoes also explains only a fraction of the subsidence. However, a deep sill at about 30km under Kluchevskoy that constantly discharges material fits our observations well. The sill is constrained by deep seismicity which suggests 9.5km width, 12.7km length, and a 13° dip-angle to the south-east. We infer a closing rate of 0.22m/yr, which implies a volume loss of 0.027km3/yr (0.16m/yr and 0.019km3/yr considering surface loading). Additional stations in the near and far field are required to uniquely resolve the spatial extent and likely partitioning of this source.We explain the eruption related deformation at BZ09 with a very shallow reservoir, likely within Bezymianny's edifice at a depth between 0.25km and 1.5km with a volume change of 1–4×10−4km3. Much of the material erupted at Bezymianny may be sourced from deeper mid-crustal reservoirs with co-eruptive volume changes at or below the detection limit of the GPS network. Installation of more sensitive instruments such as tiltmeters would allow resolving of subtle co-eruptive motion.

Rapid changes in magma storage beneath the Klyuchevskoy group of volcanoes inferred from time-dependent seismic tomography

Abstract: We present the results of time-dependent local earthquake tomography for the Kluchevskoy group of volcanoes in Kamchatka, Russia. We consider the time period from 1999 to 2009, which covers several stages of activity of Kluchevskoy and Bezymianny volcanoes. The results are supported by synthetic tests that recover a common 3D model based on data corresponding to different time windows. Throughout the period, we observe a robust feature below 25km depth with anomalously high Vp/Vs values (up to 2.2). We interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust. This mantle channel directly or indirectly determines the activity of all volcanoes of the Kluchevskoy group. In the crust, we model complex structure that varies over time. During the pre-eruptive period, we detected two levels of potential magma storage: one in the middle crust at 10–12km depth and one close to the surface just below Kluchevskoy volcano. In 2005, a year of powerful eruptions of Kluchevskoy and Besymiyanny volcanoes, we observe a general increase in Vp/Vs throughout the crust. In the relaxation period following the eruption, the Vp/Vs values are generally low, and no strong anomalous zones in the crust are observed. We propose that very rapid variations in Vp/Vs are most likely due to abrupt changes in the stress and deformation states, which cause fracturing and the active transport of fluids. These fluids drive more fracturing in a positive feedback system that ultimately leads to eruption. We envision the magma reservoirs beneath the Kluchevskoy group as sponge-structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system.

Open Access

Constraints on magma processes, subsurface conditions, and total volatile flux at Bezymianny Volcano in 2007–2010 from direct and remote volcanic gas measurements

Abstract: Direct and remote measurements of volcanic gas composition, SO2 flux, and eruptive SO2 mass from Bezymianny Volcano were acquired between July 2007 and July 2010. Chemical composition of fumarolic gases, plume SO2 flux from ground and air-based ultraviolet remote sensing (FLYSPEC), and eruptive SO2 mass from Ozone Monitoring Instrument (OMI) satellite observations were used along with eruption timing to elucidate magma processes and subsurface conditions, and to constrain total volatile flux. Bezymianny Volcano had five explosive magmatic eruptions between May 2007 and June 2010. The most complete volcanic gas datasets were acquired for the October 2007, December 2009, and May 2010 eruptions. Gas measurements collected prior to the October 2007 eruption have a relatively high ratio of H2O/CO2 (81.2), a moderate ratio of CO2/S (5.47), and a low ratio of S/HCl (0.338), along with moderate SO2 and CO2 fluxes of 280 and 980t/d, respectively, and high H2O and HCl fluxes of ~45,000 and ~440t/d, respectively. These results suggest degassing of shallow magma (consistent with observations of lava extrusion) along with potential minor degassing of a deeper magma source. Gas measurements collected prior to the December 2009 eruption are characterized by relatively low H2O/CO2 (4.13), moderate CO2/S (6.84), and high S/HCl (18.7) ratios, along with moderate SO2 and CO2 fluxes of ~220 and ~1000t/d, respectively, and low H2O and HCl fluxes of ~1700 and ~7t/d, respectively. These trends are consistent with degassing of a deeper magma source. Fumarole samples collected ~1.5months following the May 2010 eruption are characterized by high H2O/CO2 (63.0), low CO2/S (0.986), and moderate S/HCl (6.09) ratios. These data are consistent with degassing of a shallow, volatile-rich magma source, likely related to the May eruption. Passive and eruptive SO2 measurements are used to calculate a total annual SO2 mass of 109kt emitted in 2007, with passive emissions comprising ~87–95% of the total. Total annual volatile masses for the study period are estimated to range from 1.1×106 to 18×106t/year. Annual CO2 masses are ~8 to 40 times larger than can be explained by degassing of dissolved CO2 within eruptive magma, suggesting that the eruptive magma contained a significant quantity of exsolved volatiles sourced either from the eruptive melt or unerupted magma at depth. Variable total volatile fluxes ranging from ~3000t/d in 2009 to ~49,000t/d in 2007 are attributed to variations in the depth of gas exsolution and separation from the melt under open-system degassing conditions. We propose that exsolved volatiles are quickly transported to the surface from ascending magma via permeable flow through a bubble and/or fracture network within the conduit and thus retain their equilibrium composition at the time of segregation from melt. The composition of surface CO2 and H2O emissions from 2007 to 2009 are compared with modeled exsolved fluid compositions for a magma body ascending from entrapment depths to estimate depth of fluid exsolution and separation from the melt. We find that at the time of sample collection magma had already begun ascent from the mid-crustal storage region and was located at maximum depths of ~3.7km in August 2007, approximately 2months prior to the next magmatic eruption, and ~4.6km in July of 2009 approximately five months prior to the next magmatic eruption. These findings suggest that the exsolved gas composition at Bezymianny Volcano may be used to detect magma ascent prior to eruption.

The magma plumbing system of Bezymianny Volcano: Insights from a 54year time series of trace element whole-rock geochemistry and amphibole compositions

1 August 2013Stephen J. Turner | Pavel Izbekov | Charles Langmuir

Abstract: Samples from 33 individual eruptions of Bezymianny volcano between 1956 and 2010 provide an opportunity to study in detail the temporal evolution of an arc volcano. Major element and ICP-MS trace element analyses show that the eruptive products shifted progressively from relatively silicic magma in 1956 (~60.4% SiO2) to more mafic compositions (e.g. 56.8% SiO2 in 2010). Amphibole compositions changed concurrently from low-Al2O3 to high-Al2O3. Whole rock element-element variation diagrams show tight compositional arrays, some with a distinct kink in the late 1970s, which cannot be reproduced by fractionation of a single magma along a liquid line of descent. Amphibole thermobarometry indicates amphibole crystallization in two separate reservoirs, one between 200 and 300MPa, and another between 500 and 750MPa. Liquid compositions calculated from the amphibole analyses show that liquids stored in each reservoir become increasingly mafic from 1956 to 2010, suggesting that each reservoir received magma inputs from more mafic sources throughout the eruptive cycle.End member mixing analysis of the dataset allows calculation of three end member compositions that can be combined in varying proportions to reproduce major and trace element whole rock compositions. The end-member mixing proportions vary systematically between 1956 and 2010, with maxima for end-members A, B and C during 1956, 1977, and 2010, respectively. Major element compositions of phenocrysts, combined with published trace element partition coefficients, show that each end member may have evolved from a common parental magma by fractionation of three different mineral assemblages, possibly due to different pressures of crystallization and volatile contents. The petrologic data are consistent with three magma reservoirs at different depths. Magmas from the shallowest reservoir erupted first, with increasing proportions of deeper reservoirs over time. Past studies have demonstrated similarities in eruptive style between Bezymianny and both Mount St. Helens and Soufrière Hills volcanoes. Contrasting time series data show that the magma plumbing systems of Mount St. Helens and Bezymianny have little in common, while Soufrière Hills may be a better analog. Similar eruptive styles at the surface do not necessarily reflect similar systems of magma supply and evolution at depth.

Along-arc variations in lithospheric mantle compositions in Kamchatka, Russia: First trace element data on mantle xenoliths from the Klyuchevskoy Group volcanoes

1 August 2013D.A. Ionov | A. Bénard | P.Yu. Plechov | V.D. Shcherbakov

Abstract: We provide results of a detailed study of the first peridotite xenoliths of proven mantle origin reported from Bezymyanny volcano in the Klyuchevskoy Group, northern Kamchatka arc. The xenoliths are coarse spinel harzburgites made up mainly of Mg-rich olivine as well as subhedral orthopyroxene (opx) and Cr-rich spinel, and also contain fine-grained interstitial pyroxenes, amphibole and feldspar. The samples are unique in preserving the evidence for both initial arc mantle substrate produced by high-degree melt extraction and subsequent enrichment events. We show that the textures, modal and major oxide compositions of the Bezymyanny xenoliths are generally similar to those of spinel harzburgite xenoliths from Avacha volcano in southern Kamchatka. However, coarse opx from the Bezymyanny harzburgites has higher abundances of light and medium rare earth elements and other highly incompatible elements than coarse opx from the Avacha harzburgites. We infer that (1) the sub-arc lithospheric mantle beneath both Avacha and Bezymyanny (and possibly between these volcanoes) consists predominantly of harzburgitic melting residues, which experienced metasomatism by slab-related fluids or low-fraction, fluid-rich melts and (2) the degrees of metasomatism are higher beneath Bezymyanny. By contrast, xenolith suites from Shiveluch and Kharchinsky volcanoes 50–100km north of the Klyuchevskoy Group include abundant cumulates and products of reaction of mantle rocks with silicate melts at high melt/rock ratios. The high melt flux through the lithospheric mantle beneath Shiveluch and Kharchinsky may be related to the asthenospheric flow around the northern edge of the sinking Pacific plate; lateral propagation of fluids in the mantle wedge south of the plate edge may contribute to metasomatism in the mantle lithosphere beneath the Klyuchevskoy Group volcanoes.

Phase equilibria constraints on pre-eruptive magma storage conditions for the 1956 eruption of Bezymianny Volcano, Kamchatka, Russia

1 August 2013Vasily D. Shcherbakov | Owen K. Neill | Pavel E. Izbekov | Pavel Yu. Plechov

Abstract: Phase equilibria experiments were performed on andesites from the catastrophic 1956 eruption of Bezymianny Volcano, Kamchatka, Russia, to determine pre-eruptive magma storage conditions. Fifteen experiments were conducted under water-saturated conditions, with oxygen fugacity equal to the Ni–NiO oxygen buffer, at temperatures between 775 and 1100°C and pressures between 50 and 200MPa. Simultaneous amphibole and plagioclase crystallization is reproduced at ≤850°C and ≥200MPa. The simultaneous crystallization temperature range of the plagioclase–clinopyroxene–orthopyroxene–Fe–Ti oxide assemblage increases with decreasing pressure, from 840 to 940°C at 150MPa to 940–1020°C at 50MPa. Melt inclusion compositions in plagioclase phenocrysts and matrix glass match experimental melt compositions reproduced at 50–100MPa and ≤50MPa, respectively. Presence of the silica phase in groundmass and mature amphibole breakdown rims suggests that magma has been stored at ca. 3km depth prior to the final ascent for at least 40days. Syn-eruptive ascent led to decompression-driven crystallization, which caused a temperature increase from 850–900°C to 950–1000°C.

Decoding crystal fractionation in calc-alkaline magmas from the Bezymianny Volcano (Kamchatka, Russia) using mineral and bulk rock compositions

1 August 2013Renat R. Almeev | Jun-Ichi Kimura | Alexei A. Ariskin | Alexey Yu. Ozerov

Abstract: We present a new dataset for whole-rock major, trace, isotopic, and phenocryst compositions indicating a genetic link between andesites of the Holocene eruptions of the Bezymianny stratovolcano (the Bezymianny stage), the andesitic to dacitic Late Pleistocene lava dome complex (the pre-Bezymianny stage), and the magnesian to high-alumina basalts of the adjacent Kliuchevskoi Volcano. We demonstrate that volcanic products from the Bezymianny stage of volcano evolution are most likely the products of magma mixing between silicic products of the earliest stages of magma fractionation and the less evolved basaltic andesite parental melts periodically injected into the magma reservoir. In contrast, the intermediate and silicic magmas of the pre-Bezymianny stage together with basalts from Kliuchevskoi much more closely resemble the liquid line of descent and may represent a unique prolonged and continuous calc-alkaline trend of magma evolution from high-magnesian basalt to dacite. As a result of the geothermobarometry, we recognize variable conditions of magma fractionation and magma storage beneath Bezymianny for different magma types during its evolution since the Late Pleistocene: (1) 1100–1150°C, 500–640MPa, 1–2.5wt.% H2O for parental basaltic andesite; (2) 1130–1050°C, 700–600MPa, 2.5–5wt.% H2O for two-pyroxene andesites; (3) 1040–990°C, 560–470MPa, 5–6.5wt.% H2O for orthopyroxene-bearing andesites; (4) 950–1000°C, 450–150MPa, 3.5–5.5wt.% H2O for hornblende-bearing andesites; and (5) 950–900°C, 410–250MPa, 6–7wt.% H2O for dacites. Repeated basalt injections and magma fractionation combined with internal mixing in the magma chamber are the main processes responsible for both the complex petrography and the geochemical trends observed in the lavas of Bezymianny Volcano.

Numerical simulation of plagioclase rim growth during magma ascent at Bezymianny Volcano, Kamchatka

1 August 2013N.V. Gorokhova | O.E. Melnik | P.Yu. Plechov | V.D. Shcherbakov

Abstract: Slow CaAl-NaSi interdiffusion in plagioclase crystals preserves chemical zoning of plagioclase in detail, which, along with strong dependence of anorthite content in plagioclase on melt composition, pressure, and temperature, make this mineral an important source of information on magma processes. A numerical model of zoned crystal growth is developed in the paper. The model is based on equations of multicomponent diffusion with diagonal cross-component diffusion terms and accounts for mass conservation on the melt–crystal interface and growth rate controlled by undercooling. The model is applied to the data of plagioclase rim zoning from several recent Bezymianny Volcano (Kamchatka) eruptions. We show that an equilibrium growth model cannot explain crystallization of naturally observed plagioclase during magma ascent. The developed non-equilibrium model reproduced natural plagioclase zoning and allowed magma ascent rates to be constrained. Matching of natural and simulated zoning suggests ascent from 100 to 50MPa during 15–20days. Magma ascent rate from 50MPa to the surface varies from eruption to eruption: plagioclase zoning from the December 2006 eruption suggests ascent to the surface in less than 1day, whereas plagioclase zoning from March 2000 and May 2007 eruptions are better explained by magma ascent over periods of more than 30days). Based on comparison of diffusion coefficients for individual elements a mechanism of atomic diffusion during plagioclase crystallization is proposed.

The role of polybaric crystallization in genesis of andesitic magmas: Phase equilibria simulations of the Bezymianny volcanic subseries

1 August 2013Renat R. Almeev | Alexei A. Ariskin | Jun-Ichi Kimura | Galina S. Barmina

Abstract: Using the updated COMAGMAT model, the crystallization sequences of a Bezymianny Volcano basaltic andesite (Kamchatka, Russia) are simulated in a wide range of thermodynamic conditions (P–T–fO2) as a function of H2O concentration. Comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1.5–2wt.% H2O stored under 490–520MPa pressure in the magma plumbing system beneath Bezymianny Volcano. The initial magma originates as a result of the polybaric evolution of mantle-derived high-Mg basaltic magmas of the adjacent Kliuchevskoi Volcano. The subsequent evolution of derivative hydrous and alumina-rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of ~12MPa per 1% of crystallization. In the course of polybaric crystallization, compositions of pyroxene-bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent. However, hornblende-bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene-bearing andesite formation. They require high water contents and high pressures of crystallization. In this case, liquid composition should deviate from the chemical trend defined by the whole rock compositions.

Spatial patterns of geomorphic surface features and fault morphology based on diffusion equation modeling of the Kumroch Fault Kamchatka Peninsula, Russia

1 August 2013Sarah N. Cervera Heinlein

Abstract: Remote sensing data sets are widely used for evaluation of surface manifestations in active tectonic areas. This study utilizes ASTER GDEM and Landsat ETM+data sets with Google Earth images draped over terrain models. This study evaluates the surrounding surface geomorphology of the study area with these data sets and the morphology of the Kumroch Fault using diffusion modeling to estimate diffusion constants (κ), as well as to estimate slip-rates by means of real ground data measured across fault scarps by Kozhurin et al. (2006). The study area is located southeast of the Bezymianny Volcano within the Central Kamchatka Depression. It is part of the Kumroch Fault Zone. The area contains numerous geomorphic features indicative of active deformation, such as fault scarps, ponds, offset streams, and glacier moraines.The ASTER GDEM and Landsat ETM+data together with Google Earth imagery were used to create accurate geomorphic maps of specific sites within the study area along the western flank of the East Kamchatka Range. Previous studies have estimated the time elapsed since slip initiation of the faulted surface on the Kumroch Fault and the slip-rate by dividing the offset of moraines by the age of the ruptured surface. Slip-rates along the Kumroch Fault vary from 2.0mm/yr–2.5mm/yr, determined from previous 14C studies with time frames of 11.5ka to 14ka. Other slip-rates for the Kumroch Fault were determined from previous studies through tephra and stratigraphic chronology. These produced rates of 0.6mm/yr, with time frames of 3.2ka–10.5ka. Models of the evolution of fault scarp morphology provide the amount of time elapsed since slip initiated on a faults surface. They may therefore provide more accurate estimates of slip-rate than those calculated by dividing scarp offset by the age of the ruptured surface. Profile modeling of scarps collected by Kozhurin et al. (2006) show that the scarps were formed by several events distributed over time. They were evaluated using a constant slip-rate (CSR) solution which yields a value A/κ (1/2 slip rate/diffusivity). Time elapsed since slip initiated on the fault is determined by establishing a value for κ and measuring total scarp offset. For this study, CSR nonlinear modeling assisted in estimates of κ which along the Kumroch Fault range from 8m2/ka to 14m2/ka. Slip-rates have been estimated to range from 0.6mm/yr to 1.0mm/yr since 3.4ka–3.7ka. This method provides a quick and inexpensive way to gather data for a regional tectonic study and establish estimated rates of tectonic activity.

Volcanic structure and composition of Old Shiveluch volcano, Kamchatka

1 August 2013Natalia Gorbach | Maxim Portnyagin | Igor Tembrel

Abstract: This paper reports results of a new comprehensive geological mapping of the Late Pleistocene Old Shiveluch volcano. The mapping results and geochemical data on major and trace element composition of the volcanic rocks are used to characterize spatial distribution, eruptive sequence and volumetric relationships between different rock types of the volcano. Old Shiveluch volcano had been constructed during two main stages: initial explosive and subsequent effusive ones. Pyroclastic deposits of the initial stage are represented by agglomerate and psephytic tuffs with very few lava flows and form at least 60% of volume of the Old Shiveluch edifice. The deposits of the second stage are dominantly lava flows erupted from four vents: Central, Western, Baidarny and Southern, reconstructed from the field relationships of their lava flows. About 75% of the Old Shiveluch edifice, both pyroclastic deposits and lava, are composed of magnesian andesites (SiO2=57.3–63.8 wt.%, Mg#=0.53–0.57). The most abundant andesitic lavas were coevally erupted from the Central and Western vents in the central part of the edifice. Less voluminous high-Al basaltic andesites (SiO2=53.5–55.7wt.%, Mg#=0.52–0.56) were produced by the Western, Baidarny and Southern vents situated in the south-western sector. Small volume high-Mg basaltic andesites (SiO2=53.9–55.0wt.%, Mg#=0.59–0.64) occur in the upper part of the pyroclastic deposits.Andesites of Old and Young Shiveluch Volcanoes have similar compositions, whereas Old Shiveluch basaltic andesites are compositionally distinctive from those of the Young Shiveluch by having lower Mg#, SiO2, Cr and Ni, and higher Al2O3, FeOT, CaO, TiO2, and V contents at given MgO. Geochemical modeling suggests that the compositions of the intermediate Old Shiveluch magmas can be reasonably explained by simple fractional crystallization of olivine, clinopyroxene, plagioclase and magnetite (±hornblende) from water-bearing (~3wt.% H2O) high-Mg# basaltic parental magma at intermediate to shallow crustal depths (60wt.%, Mg#0.65) played a relatively minor role in creating the compositional diversity of the Old Shiveluch magmas compared to the Young Shiveluch ones. The pronounced change in the Shiveluch magma compositions could have been related to adjustments of the magma plumbing system beneath Old Shiveluch following the large scale sector collapse in the Late Pleistocene that enabled a common mixing of evolved and primitive magmas on the later, Holocene stage of the volcano evolution.

Role of large flank-collapse events on magma evolution of volcanoes. Insights from the Lesser Antilles Arc

1 August 2013Georges Boudon | Benoît Villemant | Anne Le Friant | Martine Paterne | Elsa Cortijo

Abstract: Flank-collapse events are now recognized as common processes of destruction of volcanoes. They may occur several times on a volcanic edifice pulling out varying volumes of material from km3 to thousands of km3. In the Lesser Antilles Arc, a large number of flank-collapse events were identified. Here, we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles.On Montagne Pelée (Martinique), magma production rate has been sustained during several thousand years following a 32ka old flank-collapse event. Basic and dense magmas were emitted through open-vent eruptions that generated abundant scoria flows while significantly more acidic magmas were produced before the flank collapse. The rapid building of a new cone increased the load on magma bodies at depth and the density threshold. Magma production rate decreased and composition of the erupted products changed to more acidic compared to the preceding period of activity. These low density magma generated plinian and dome-forming eruptions up to the Present. In contrast at Soufrière Volcanic Centre of St. Lucia and at Pitons du Carbet in Martinique, the flank-collapses have an opposite effect: in both cases, the acidic magmas erupted immediately after the flank-collapses. These magmas are highly porphyritic (up to 60% phenocrysts) and much more viscous than the magmas erupted before the flank-collapses. They have been generally emplaced as voluminous and uptight lava domes (called “the Pitons”). Such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice loading before the flank-collapse.

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Strain localization in homogeneous granite near the brittle–ductile

Fri, 04 Oct 2013 08:09:00 +0000

Strain localization in homogeneous granite near the brittle–ductile transition: A case study of the Kellyland fault zone, Maine, USA

November 2013

Abstract: We present a detailed case study of a strike-slip shear zone that cut homogeneous granite near the brittle–ductile transition. This zone contains three distinct strain facies: (1) a 2–3-km-wide belt of foliated granite, (2) a 100–300-m-wide belt of small localized shear zones, and (3) a 200–400-m-wide belt of ultramylonite that includes both homogeneous and local pinstripe ultramylonites. The foliated granite formed via dislocation creep of quartz and minor dissolution–precipitation creep and dislocation creep of feldspar under amphibolite-facies conditions shortly after granite crystallization. The localized shear zones and homogeneous ultramylonites formed directly from pseudotachylyte and cataclasite, and they deformed by granular flow—grain-boundary sliding coupled with dissolution–precipitation creep. These deformation features reveal a three-phase rheologic evolution in granite near the brittle–ductile transition. Phase 1 is recorded by the foliated granite, and the rheology was governed by dislocation creep of quartz. Phase 2 was a transient period of brittle deformation and represents a temporal strength maxima in the fault zone. Phase 3 was a long-lived period of ductile deformation, and the rheology was governed by the granular flow mechanism. Strain weakening in this zone was a direct result of grain size reduction and phase mixing during transient brittle deformation.

Strain distribution within a km-scale, mid-crustal shear zone: The Kuckaus Mylonite Zone, Namibia

November 2013

Abstract: The subvertical Kuckaus Mylonite Zone (KMZ) is a km-wide, crustal-scale, Proterozoic, dextral strike-slip shear zone in the Aus granulite terrain, SW Namibia. The KMZ was active under retrograde, amphibolite to greenschist facies conditions, and deformed felsic (and minor mafic) gneisses which had previously experienced granulite facies metamorphism during the Namaqua Orogeny. Lenses of pre- to syn-tectonic leucogranite bodies are also deformed in the shear zone. Pre-KMZ deformation (D1) is preserved as moderately dipping gneissic foliations and tightly folded migmatitic layering. Shear strain within the KMZ is heterogeneous, and the shear zone comprises anastomosing high strain ultramylonite zones wrapping around less deformed to nearly undeformed lozenges. Strain is localized along the edge of leucogranites and between gneissic lozenges preserving D1 migmatitic foliations. Strain localization appears controlled by pre-existing foliations, grain size, and compositional anisotropy between leucogranite and granulite. The local presence of retrograde minerals indicate that fluid infiltration occurred in places, but most ultramylonite in the KMZ is free of retrograde minerals. In particular, rock composition and D1 fabric heterogeneity are highlighted as major contributors to the strain distribution in time and space, with deformation localization along planes of rheological contrast and along pre-existing foliations. Therefore, the spatial distribution of strain in crustal-scale ductile shear zones may be highly dependent on lithology and the orientation of pre-existing fabric elements. In addition, foliation development and grain size reduction in high strain zones further localizes strain during progressive shear, maintaining the anastomosing shear zone network established by the pre-existing heterogeneity.

Late magmatic healed fractures in granitoids and their influence on subsequent solid-state deformation

Available online 1 October 2013Neil S. Mancktelow | Giorgio Pennacchioni

Abstract: Late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and/or leucocratic veins but have not been previously described. Such biotite-rich trails, with lengths of a few centimetres to several tens of centimetres, widths of a few millimetres, and a variable orientation, are ubiquitous in meta-granitoids of the Neves area (Tauern Window, Eastern Alps, Italy). These pre-Alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the Alpine orogeny, allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid-state ductile shear zones to be directly assessed. Numerical models considering power-law viscous materials predict that planar arrays of a weaker mineral (e.g. biotite) oriented at around 45° to the shortening direction should nucleate and localize viscous deformation. However, no discernible localization on the natural small-scale biotite trails is observed, even when they delineate planes that were well-oriented for shear reactivation. In contrast, heterogeneous shear zones nucleated on larger scale (> 1-10 m long) planar compositional or structural boundaries such as joints, dykes, quartz veins, alteration layers surrounding veins, and zones of magma mingling outlined by densely packed clusters of basic enclaves, irrespective of their orientation relative to the imposed shortening direction. Clearly some crucial aspect is missing from purely viscous numerical models. We propose that this missing aspect is the observed interplay between fracture and flow, with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre-existing healed magmatic fractures. Natural granitoids have a truly elasto-plasto-viscous rheology even at low differential stress (as in the Neves example) and for high grade metamorphic conditions considered as typical of wet “ductile” middle crust.

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Introduction to the special issue: The field tradition in geomorphology

Fri, 04 Oct 2013 07:04:00 +0000

Introduction to the special issue: The field tradition in geomorphology

15 October 2013Carl J. Legleiter | Richard A. Marston

Abstract: In recognition of the critical role of field observations in the ongoing development of our discipline, the 43rd annual Binghamton Geomorphology Symposium (BGS) celebrated The Field Tradition in Geomorphology. By organizing a conference devoted to this theme, we sought to honor the contributions of pioneering, field-based geomorphologists and to encourage our community to contemplate how field work might continue to provide unique insight into a new, more technologically-driven era. For example, given recent advances in remote sensing methods such as LiDAR, what kind of added value can field work provide? Similarly, how can field-based studies contribute to societally relevant, large-scale questions related to climate change and sustainable management of the Earth system? Motivated by such questions, the 2012 BGS was convened in Jackson Hole, WY, a new, Western location that enabled participation by Rocky Mountain and west coast research groups underrepresented at previous Binghamton symposia. Also, in keeping with the field tradition theme, the 2012 BGS emphasized field trips, including a rafting excursion down the Snake River and an overview of the tectonic and glacial history of Jackson Hole. The on-site portion of the symposium consisted of invited oral and poster presentations and contributed posters, including many by graduate students. Topics ranged from an historical overview of the development of geomorphic thinking to long-term sediment tracer studies to a commentary on the synergy between LiDAR and field mapping. This special issue of Geomorphology consists of papers by invited authors from the 2012 BGS, and this overview provides some context for these contributions. Looking forward, we hope that the 43rd annual BGS will stimulate further discussion of the role of field work as the discipline of geomorphology continues to evolve, carrying on the field tradition into the future.

Faith in floods: Field and theory in landscape evolution before geomorphology

15 October 2013David R. Montgomery

Abstract: Opinions about the origin of topography have long marked the frontier between science and religion. The creation of the world we know is central to religious and secular world views; and until recently the power to shape landscapes lay beyond the reach of mortals, inviting speculation as to a role for divine intervention. For centuries, Christians framed rational inquiry into the origin of topography around theories for how Noah's Flood shaped mountains and carved valleys. Only as geologists learned how to decipher Earth history and read the signature of Earth surface processes did naturalists come to understand the forces that shaped the world. In this sense, the historical roots of geomorphology lie in the tension between faith in theories and the compelling power of field observations—issues that remain relevant to the practice of geomorphology today.

Geomorphology: Perspectives on observation, history, and the field tradition

15 October 2013John D. Vitek

Abstract: Other than a common interest in form and process, current geomorphologists have little in common with those who established the foundations of this science. Educated people who had an interest in Earth processes during the nineteenth century cannot be compared to the scholars who study geomorphology in the twenty-first century. Whereas Earth has undergone natural change from the beginning of time, the human record of observing and recording processes and changes in the surface Is but a recent phenomena. Observation is the only thread, however, that connects all practitioners of geomorphology through time. As people acquired knowledge related to all aspects of life, technological revolutions, such as the Iron Age, Bronze Age, agricultural revolution, the atomic age, and the digital age, shaped human existence and thought. Technology has greatly changed the power of human observation, including inward to the atomic scale and outward into the realm of space.Books and articles describe how to collect and analyze data but few references document the field experience. Each of us, however, has experienced unique circumstances during field work and we learned from various mentors how to observe. The surface of Earth on which we practice the vocation of geomorphology may not be much different from a hundred years ago but many things about how we collect data, analyze it and disseminate the results have changed. How we function in the field, including what we wear, what we eat, how we get there, and where we choose to collect data, clearly reflects the complexity of the human system on Earth and the processes and forms that arouse our interest. Computers, miniaturization of electronics, satellite communications and observation platforms in space provide access to data to aid in our quest to understand Earth surface processes. Once, people lived closer to nature in primitive shelters in contrast with life in urban environments. But as urban life continues to expand and people need to know how Earth operates, geomorphologists, therefore, serve humanity today as the primary observers and reporters in the realm of Earth surface processes.

Geomorphology in context: Dispatches from the field

15 October 2013Carol P. Harden

Abstract: Field research enables a researcher to view geomorphic systems in broader contexts than those envisioned while at a desk and can yield unanticipated insights that change the course of an investigation or affect the interpretation of results. Geomorphological field research often produces ‘aha!’ moments, epiphanies that enhance understanding and lead toward more complete explanation of the processes and landforms under study. This paper uses examples from ‘aha!’ moments in the field to demonstrate the importance of field observation as a way of gaining information about the broader contexts of research sites, especially in process geomorphology. Spatial contexts include the scales of processes and features, linkages between a study site and its surroundings, and information observed in the field about other processes, anthropogenic activities, or unexpected factors that might affect a study. Temporal contexts, not as evident in the field, place a research site in a longer term history of changes and adjustments. Finally, exploring an abstract set of mental contexts reveals reasons that expectations differ from the realities encountered in the field—constraints and biases that a researcher may not have noted—and the possibility that the unexpected can potentially advance geomorphic research. Time spent in the field complements scientific reductionism and provides opportunities to appreciate the richness and complexity of Earth surface systems.

The field tradition in mountain geomorphology

15 October 2013David R. Butler

Abstract: Fieldwork has a long and honored tradition in mountain geomorphology, and justifiably so. Many features and processes present in mountains occur at fine to very fine spatial scales that simply do not lend themselves well to analyses via remote methods. The nature of the sampling of data in mountain environments also constrains the use of computational techniques, such as GIS, in favor of on-site data collection. In addition, when one is present in the field in mountains, the dynamic nature of the landscape often provides unexpected rewards that could not be planned for in a campaign of remote analysis. These aspects of scale, sampling, and serendipity make on-site fieldwork still the preferred method for geomorphological research in mountain environments. Several examples of features occurring at fine spatial scale that could only be effectively examined in the field are presented in this paper, as well as examples of data sampling occurring at fine scale. I also illustrate several instances where being on-site, at a specific unexpected moment, in the dynamic mountain environment provided scientific insight that could only be obtained through the serendipity of being there. Why continue to conduct geomorphological fieldwork in mountains? “Because the mountains are there”!

The complexity of the real world in the context of the field tradition in geomorphology

15 October 2013Ellen Wohl

Abstract: Among the dominant twentieth century conceptual models of geomorphology that rely on insights resulting from field-based research are Stanley A. Schumm's formulations of complex response, intrinsic thresholds, river metamorphosis, and spatial zonation of drainage basins. Schumm's research focused primarily on finer grained alluvial channels in lower relief environments. As a result of his work, most investigators now approach river process and form within a framework based on three fundamental assumptions. First, channel changes are abrupt and driven by crossing external and internal thresholds. Second, channel change is likely to be asynchronous, resulting in different portions of a river or a river network behaving in very different manners at a given point in time. Third, different portions of a river network are dominated by distinct disturbance regimes and resulting suites of geomorphic processes and forms. More recent research on resistant-boundary mountain channels illustrates how field evidence demonstrates that river process and form are inherently nonlinear, with spatial and temporal thresholds. Multithread channels can form within unconfined valley segments in mountainous river networks of the Colorado Front Range, but only in the presence of biotic drivers in the form of (i) old-growth forest that facilitates the formation of closely spaced, channel-spanning logjams or (ii) beavers that build dams. Thresholds of channel and valley geometry govern the occurrence and persistence of jams and dams, and these channel obstructions initiate specific nonlinear responses in valley and channel form. When the biotic drivers are removed, river metamorphosis occurs. Alluvial channels, which are typically regarded as being relatively responsive to changes in water and sediment yield and substrate composition, and channels with more resistant boundaries that typically respond to external changes over longer timespans exhibit nonlinear complex behavior. In both cases, the nonlinear behavior of rivers with numerous interdependent variables, multiple internal and external thresholds, and complex responses would be difficult to conceptualize and quantify in the absence of extensive field data. One of the management implications of complex, nonlinear behavior is that a one-size-fits-all approach to managing rivers is inadequate. Field research, initially focused on understanding specific examples of river process and form, revealed underlying patterns that give rise to conceptual models broadly applicable within fluvial geomorphology.

The role of fieldwork in rock decay research: Case studies from the fringe

Abstract: Researchers exploring rock decay hail from chemistry, engineering, geography, geology, paleoclimatology, soil science, and other disciplines and use laboratory, microscopic, theoretical, and field-based strategies. We illustrate here how the tradition of fieldwork forms the core knowledge of rock decay and continues to build on the classic research of Blackwelder, Bryan, Gilbert, Jutson, King, Linton, Twidale, and von Humboldt. While development of nonfield-based investigation has contributed substantially to our understanding of processes, the wide range of environments, stone types, and climatic variability encountered raises issues of temporal and spatial scales too complex to fit into attempts at universal modeling. Although nonfield methods are immensely useful for understanding overarching processes, they can miss subtle differences in factors that ultimately shape rock surfaces. We, therefore, illustrate here how the tradition of fieldwork continues today alongside laboratory and computer-based investigations and contributes to our understanding of rock decay processes. This includes the contribution of fieldwork to the learning process of undergraduates, the calculation of activation energies of plagioclase and olivine dissolution, the high Arctic, the discovery of a new global carbon sink, the influence of plant roots, an analysis of the need for protocols, tafoni development, stone monuments, and rock coatings. These compiled vignettes argue that, despite revolutionary advances in instrumentation, rock decay research must remain firmly footed in the field.

The impact of local geochemical variability on quantifying hillslope soil production and chemical weathering

15 October 2013Arjun M. Heimsath | Benjamin C. Burke

Abstract: Soil-mantled upland landscapes are widespread across the habitable world, support extensive life, and are the interface between the atmosphere, hydrosphere, and lithosphere but typically are not cultivated. Soil found across such landscapes fits the conceptual framework of a physically mobile layer derived from the underlying parent material along with some locally derived organic content. The extent and persistence of these upland soils depend on the long-term balance between soil production and erosion. Here we briefly review methods used to quantify the physical and chemical processes of soil production and erosion and revisit three granitic study areas in southeastern Australia and northern California that enabled early quantification of the soil production function and topographic controls on chemical weathering. We then present new major and trace element data from 2-m by 2-m pits dug at each field site to quantify local variability of Zr concentrations and the chemical index of alteration (CIA), weathering indices used to determine chemical weathering rates and extents in soils and saprolites. Using both new and previously published data, we compare differences between local variability and regional, as well as intersite variability of these important indices. For each of the 2-m pits, we collected 25 samples and found that the simple mean and the 2σ standard deviation best describe the local variation in the data. We also find that the variability in the 2-m pit data lies within variability observed in the same data from samples collected in individual soil pits across each of the field sites and that the differences between sites are consistent with previously published results. These observations highlight the importance of quantifying local scale variability in studies that use similar, multifaceted measurements to quantify hillslope soil production and erosion processes.

Interplay between field observations and numerical modeling to understand temporal pulsing of tree root throw processes, Canadian Rockies, Canada

15 October 2013Y.E. Martin | E.A. Johnson | O. Chaikina

Abstract: During the cycle of forest disturbance, regeneration, and maturity, tree mortality leading to topple is a regular occurrence. When tree topple occurs relatively soon after mortality and if the tree has attained some threshold diameter at breast height (dbh) at the time of death, then notable amounts of soil may be upheaved along with the root wad. This upheaval may result in sediment transfers and soil production. A combination of field evidence and numerical modeling is used herein to gain insights regarding the temporal dynamics of tree topple, associated root throw processes, and pit-mound microtopography. Results from our model of tree population dynamics demonstrate temporal patterns in root throw processes in subalpine forests of the Canadian Rockies, a region in which forests are affected largely by wildfire disturbance. As the forest regenerates after disturbance, the new cohort of trees has to reach a critical dbh before significant root plate upheaval can occur; in the subalpine forests of the Canadian Rockies, this may take up to ~102years. Once trees begin to reach this critical dbh for root plate upheaval, a period of sporadic root throw arises that is caused by mortality of trees during competition. In due course, another wildfire will occur on the landscape and a period of much increased root throw activity then takes place for the next several decades; tree sizes and, therefore, the amount of sediment disturbance will be greater the longer the time period since the previous fire. Results of previous root throw studies covering a number of regional settings are used to guide an exercise in diffusion modeling with the aim of defining a range of reasonable diffusion coefficients for pit-mound degradation; the most appropriate values to fit the field data ranged from 0.01m2y−1 to 0.1m2y−1. A similar exercise is then undertaken that is guided by our field observations in subalpine forests of the Canadian Rockies. For these forests, the most appropriate range of diffusion coefficients is in the range 0.001m2y−1 to 0.01m2y−1. Finally, the model of tree population dynamics is combined with the model of pit-mound degradation to demonstrate the integration of these combined processes on the appearance of pit-mound microtopography and soil bioturbation in subalpine forests of the Canadian Rockies. We conclude that the appearance of notable pit-mound microtopography is limited to very specific time periods and is not visible for much of the time. Most of the hillslope plot is affected by root throw during the 1000-year model run time.

Mass movements and tree rings: A guide to dendrogeomorphic field sampling and dating

15 October 2013Markus Stoffel | David R. Butler | Christophe Corona

Abstract: Trees affected by mass movements record the evidence of geomorphic disturbance in the growth-ring series, and thereby provide a precise geochronological tool for the reconstruction of past activity of mass movement. The identification of past activity of processes was typically based on the presence of growth anomalies in affected trees and focused on the presence of scars, tilted or buried trunks, as well as on apex decapitation. For the analyses and interpretation of disturbances in tree-ring records, in contrast, clear guidelines have not been established, with largely differing or no thresholds used to distinguish signal from noise. At the same time, processes with a large spatial footprint (e.g., snow avalanches, landslides, or floods) will likely leave growth anomalies in a large number of trees, whereas a falling rock would only cause scars in one or a few trees along its trajectory.Based on the above considerations, we examine issues relating to the interpretation and dendrogeomorphic dating of mass movements. Particular attention is drawn to sampling in terms of sample distribution across a study site, the actual selection of trees as well as to sample size (i.e., number of trees sampled). Based on case studies from snow avalanche, debris flow, and landslide sites, we demonstrate that thresholds can indeed improve dating quality and, at the same time, minimize noise in time series. We also conclude that different thresholds need to be used for different processes and different periods of the reconstruction, especially for the early stages of the reconstruction when the number of potentially responding trees will be much smaller. This paper seeks to set standards for dendrogeomorphic fieldwork, analysis, and interpretation for different processes of mass movements.

Tracing river gravels: Insights into dispersion from a long-term field experiment

15 October 2013J.K. Haschenburger

Abstract: Sediment dispersion is a fundamental component of the sediment transfer process in gravel-bed rivers. Modeling this process requires an understanding of the collective movement of mixed-size clasts. This study explores the temporal evolution of gravel dispersion to underscore the importance of field observation in informing modeling efforts. Magnetically tagged gravels deployed in Carnation Creek have been monitored repeatedly over 17years. Four metrics used to describe the extent of dispersion document that the overall shape in the spatial distribution of grain location changes over time. The general trends mask the complexity of the dispersion process, expressed by channel sections where tracers are concentrated regardless of grain size. The distribution of total grain displacement responsible for dispersion evolves as tracers become well mixed. Results demonstrate that observations from the field are crucial to the understanding and modeling of sediment dispersion because they provide key insights into the dispersion process that must be known a priori for mathematical modeling and similar observations cannot be collected using laboratory flumes.

Spatial and temporal patterns in channel change on the Snake River downstream from Jackson Lake dam, Wyoming

15 October 2013Nicholas C. Nelson | Susannah O. Erwin | John C. Schmidt

Abstract: Operations of Jackson Lake dam (JLD) have altered the hydrology and sediment transport capacity of the Snake River in Grand Teton National Park. Prior research has provided conflicting assessments of whether the downstream river was perturbed into sediment surplus or sediment deficit. In this paper, we present the results of an aerial photo analysis designed to evaluate whether the history of channel change indicates either significant deficit or surplus of sediment that could be expressed as narrowing or expansion of the channel over time. We analyze changes in braid index, channel width, channel activity, and net channel change of the Snake River based on four series of aerial photographs. Between 1945 and 1969, a period of relatively small main-stem floods, widespread deposition, and up to 31% reduction in channel width occurred throughout the Snake River. Between 1969 and 2002, a period of large main-stem floods, the style of channel change reversed with a decrease in braid index and an increase in channel width of up to 31%. These substantial changes in the channel downstream from the dam primarily occurred in multithread reaches, regardless of proximity to tributaries, and no temporal progression of channel narrowing or widening was observed. We demonstrate that channel change downstream from JLD is more temporally and longitudinally complex than previously described.

Geomorphology within the interdisciplinary science of environmental flows

15 October 2013Kimberly M. Meitzen | Martin W. Doyle | Martin C. Thoms | Catherine E. Burns

Abstract: The field tradition in geomorphology informs beyond studying landforms by also providing a stage for understanding how geomorphic elements influence the ecology of biota. The intersection between fluvial geomorphology and riverine ecology represents an ideal confluence to examine the contribution of the geomorphic field tradition to environmental flows, and show this area of riverine management as a research frontier for applied geomorphology. Environmental flows have consisted of a set of ecological-based stream flow guidelines designed to inform sustainable water resource management that supports healthy riverine habitats and provides sufficient water supply for society. Geomorphological understanding is central to environmental flows because it is the interaction between flow, form, and substrate that influences habitat type, condition, availability and biotic use across space and time. This relationship varies longitudinally, laterally, vertically, overtime, and across macro- to mesoscale morphologies within the riverine environment. The geomorphic template is, therefore, as integral as the flow. We reviewed studies where field evidence indicated that geomorphology impacts the effectiveness of environmental flow strategies and we make the case for the need to increase geomorphic considerations in environmental flows. Although flow is commonly referred to as the master variable in environmental flows, geomorphology mediates the effects of flow regime on ecological processes. Concepts and applications from this perspective on the role of geomorphology in riverine ecosystem research will inform the practice, policy, and implementation of environmental flows.

Multi-scale factors controlling the pattern of floodplain width at a network scale: The case of the Rhône basin, France

15 October 2013Bastiaan Notebaert | Hervé Piégay

Abstract: In this study the floodplain width (FW) was assessed for the entire Rhône catchment river network (32,160km long) to highlight controlling factors. The FW data, which is measured every kilometre on a digital elevation model (DTM), is aggregated into spatial homogenous segments using a Pettitt break detection test, resulting in aggregated geographical objects (AGO). Based on these AGOs, an analysis of the variability of the floodplain width was performed. The general pattern for the Rhône network shows a downstream increase in FW related to the concept of river continuum. This general pattern explains ca. 30% of the variation in FW. Deviations from this general trend are, however, large. Values for floodplain widths are normalized for catchment scale to study deviations that do not depend on scale effects. Based on a conceptual model, the main environmental parameters influencing FW were identified. These parameters include lithology and different parameters that influence the river profile, such as base level changes and tectonics, sediment load and discharge. An analysis of catchment-wide patterns shows that the main variations on the scaling effect are caused by lithology. Superposed on this general scaling pattern, disturbed by lithological variations, are the variations in floodplain width caused by disturbances in the geomorphic system, which influence floodplain slope, sediment, and water discharge and which include inherited landscapes. Although large data sets become increasingly available and the applied methodology reduces data noise, data availability and quality still hampers studies at a larger scale. Nevertheless, such information sources are becoming crucial because they are more and more accessible and diverse, and the analysis is now easier with the increasing capacities of GIS technologies. As a result, they are becoming very complementary to field studies to understand geomorphic processes at wider spatial and longer temporal scales. In a sense, the tradition of geomorphology may evolve in the next years, with image data providing additional evidence of Earth evolution.

‘You are HERE’: Connecting the dots with airborne lidar for geomorphic fieldwork

Abstract: The emergence of airborne lidar data for studying landscape evolution and natural hazards has revolutionized our ability to document the topographic signature of active and ancient surface processes. Notable lidar-facilitated discoveries, however, would not have been possible without the coupling of fieldwork and lidar analysis, which contradicts the ill-considered notion that high resolution remote sensing technologies will replace geomorphic field investigations. Here, we attempt to identify the primary means by which lidar has and will continue to transform how geomorphologists study landscape form and evolution: (1) lidar serves as a detailed base map for field mapping and sample collection, (2) lidar allows for rapid and accurate description of morphologic trends and patterns across broad areas, which facilitates model testing through increased accuracy and vastly increased sample sizes, and (3) lidar enables the identification of unanticipated landforms, including those with unknown origin. Finally, because the adoption of new technologies can influence cognition and perception, we also explore the notion that the ongoing use of lidar enables geomorphologists to more effectively conceptualize landforms in the field.

Refocusing geomorphology: Field work in four acts

15 October 2013Michael Church

Abstract: Geomorphology grew out of natural history. Natural history is conducted in the field. Accordingly, the early history of geomorphology was dominated by investigations in the field in the attempt to decipher the history of specific landscapes. The constraints of transport and accessibility dictated that field excursions be long and often arduous. These circumstances changed after the mid-twentieth century with the advent of modern transport, the introduction of remote sensing instruments and methods, and the increasing emphasis on mechanistic analysis of generic landscape-forming processes. The latter brought to geomorphology an increasingly reductionist perspective. Field work has become increasingly a matter of relatively short excursions to acquire specific measurements defined by model or theoretical criteria.But geomorphology is a system science, seeking to understand the compounded effects of many interacting processes. These effects include phenomena that emerge from the intersection of simpler physical and biological processes. While simple processes might be isolated and successfully analyzed by reductionist means, it is not clear that we can reverse the process and understand emergent phenomena by conflating our understanding of individual processes. Emergence is better understood initially by direct observation and induction. This was intuitively understood by early field scientists whose long seasons provided ample opportunity to observe such phenomena. Recent technological developments have enhanced our ability to comprehend the landscape system, but the effort will surely require comprehensive field experience if we are to regain the whole landscape view of the early field workers.

20th century sediment budget trends on the Western Gulf of Lions shoreface (France): An application of an integrated method for the study of sediment coastal reservoirs

Abstract: This paper presents a shoreface sediment budget established for the 20th century (1895-1984–2009) along the microtidal wave-dominated coast of the western Gulf of Lions (Languedoc-Roussillon, Mediterranean Sea, SE France). The implementation of a diachronic bathymetric approach, coupled with the definition of sand reservoirs (upper sand unit - USU) by very high-resolution seismic surveys and the results of LiDAR investigations, offers a new means of defining precisely the magnitude and change trends of the sediment budget. The aim of this study is to link the Large Scale Coastal Behaviour (LSCB) of the littoral prism (expressed in terms of shoreface sediment budget, shoreface sediment volume and spatial distribution pattern of cells) to climatic change, river sediment input to the coast, longshore sediment transport distribution, impact of hard coastal defence structures and artificial beach nourishment. The results show a significant reduction of the volume of the western Gulf of Lions littoral prism over 114yr (−26.1±4.6×106m3). From 1895 to 1984, the overall budget is slightly positive, with a volume estimated at 4.1±3.5×106m3. For 1984–2009, however, the estimated sediment budgets clearly indicate that erosion is dominant over the last 25years, with a volume loss of −30.2±4.2×106m3. In relation to the long-term sediment budget and longshore drift pattern, the long-term trend of the USU volume distribution displays strong spatio-temporal contrasts linked to longshore sediment drift, spatial distribution of fluvial sediment inputs and hard engineering structures. Locally, the sedimentary reservoir is significantly eroded within a century (−80% of USU), since the initial amount present was low and not sustainable. The emphasis is on the importance of considering the volume changes of available sediment reservoirs rather than their losses and gains. Erosion of the Languedoc-Roussillon shoreface is likely to continue in the future due to the "natural" decrease of river sediment input and the sand removal for human purposes. Consequently the littoral sand prism results in sedimentary reservoirs that are gradually being used up.

‘Looping caves’ versus ‘water table caves’: The role of base-level changes and recharge variations in cave development

Available online 30 September 2013Franci Gabrovšek | Philipp Häuselmann | Philippe Audra

Abstract: The vertical organization of karst conduit networks has been the focus of speleogenetic studies for more than a century. The four state model of Ford and Ewers (1978), which still is considered as the most general, relates the geometry of caves to the frequency of permeable fissures. The model suggests that the ‘water table caves’ are common in areas with high fissure frequency, which is often the case in natural settings. However, in Alpine karst systems, water table caves are more the exception than the rule. Alpine speleogenesis is influenced by high uplift, valley incision rates and irregular recharge. To study the potential role of these processes for speleogenesis in the dimensions of length and depth, we apply a simple mathematical model based on coupling of flow, dissolution and transport. We assume a master conduit draining the water to the spring at a base level. Incision of the valley triggers evolution of deeper flow pathways, which are initially in a proto-conduit state. The master conduit evolves into a canyon following the valley incision, while the deep pathways evolve towards maturity and tend to capture the water from the master conduits. Two outcomes are possible: a) deep pathways evolve fast enough to capture all the recharge, leaving the master conduit dry; or b) the canyon reaches the level of deep pathways before these evolve to maturity. We introduce the Loop-to-Canyon ratio (LCR), which predicts which of the two outcomes is more likely to occur in certain settings. Our model is extended to account for transient flow conditions. In the case of an undulating master conduit, floodwater is stored in troughs after the flood retreat. This water seeps through sub-vertical fractures (‘soutirages’) connecting the master conduit with the deep pathways. Therefore, the loops evolve also during the dry season, and the LCR is considerably increased. Although the model is based on several approximations, it leads to some important conclusions for vertical organization of karst conduit networks and stresses the importance of base-level changes and transient recharge conditions. It therefore gives an explanation of speleogenesis that relies much more on the dynamic nature of water flow than on the static fracture density.

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1 September 2013

Fri, 04 Oct 2013 06:12:00 +0000

1 September 2013

Abstract: In this paper, we illustrate laboratory experiments whose purpose is to study the vertical segregations that are commonly observed in deposits of dense geophysical flows (such as pyroclastic flows and rock avalanches). In these experiments, we use rock cuboids with 5mm long edges as matrix and rock cuboids with 2cm long edges as segregating clasts. A rotating disk is used to apply frictional stresses at the base of the granular masses. In our experiments, segregating cuboids with density smaller than or equal to that of the matrix particles rise whereas segregating cuboids with density larger than that of the matrix particles sink. The granular flows are imaged through the glass container of the experimental apparatus by a high-speed video camera at 2000fps. By means of particle image velocimetry analysis of the movies, we study the vertical gradient of particle agitation that exists within the granular flows where agitation increases downward because of the interaction with the subsurface asperities. The high-speed movies show that it is the particle agitation within the flows that exerts an upward force and that, when this force is larger than the weight of the segregating clast, the clast rises whereas, when it is smaller, the clast sinks. The most important result in our set of experiments is that the threshold which separates the values of density of the segregating clasts that segregate upward and the values of density of the segregating clasts that segregate downward is larger than the density of the matrix particles. This explains the upward segregation of dense lithics that is frequently observed in deposits of geophysical flows. This upward segregation is due to the fact that the resultant of the collisions exerted by the matrix particles is a force strong enough to push upward also dense and heavy fragments.

1 September 2013

Abstract: New multibeam bathymetry data are presented for the South Sandwich intra-oceanic arc which occupies the small Sandwich plate in the South Atlantic, and is widely considered to be a simple end-member in the range of intra-oceanic arc types. The images show for the first time the distribution of submarine volcanic, tectonic and erosional–depositional features along the whole length of the 540km long volcanic arc, allowing systematic investigation of along-arc variations. The data confirm that the volcanic arc has a simple structure composed of large volcanoes which form a well-defined volcanic front, but with three parallel cross-cutting seamount chains extending 38–60km from near the volcanic front into the rear-arc. There is no evidence for intra-arc rifting or extinct volcanic lines. Topographic evidence for faulting is generally absent, except near the northern and southern plate boundaries. Most of the volcanic arc appears to be built on ocean crust formed at the associated back-arc spreading centre, as previously proposed from magnetic data, but the southern part of the arc appears to be underlain by older arc or continental crust whose west-facing rifted margin facing the back-arc basin is defined by the new bathymetry. The new survey shows nine main volcanic edifices along the volcanic front and ca. 20 main seamounts. The main volcanoes form largely glaciated islands with summits 3.0–3.5km above base levels which are 2500–3000m deep in the north and shallower at 2000–2500m deep in the south. Some of the component seamounts are interpreted to have been active since the last glacial maximum, and so are approximately contemporaneous with the volcanic front volcanism. Seven calderas, all either submarine or ice-filled, have been identified: Adventure volcano, a newly discovered submarine volcanic front caldera volcano is described for the first time. All but one of the calderas are situated on summits of large volcanoes in the southern part of the arc, and most are associated with current or historic volcanic or hydrothermal activity. Shallow shelves around the islands are generally 1–10km wide. Submerged banks up to 1100m deep are interpreted as subsided erosional surfaces. Seamounts and emergent volcanoes experienced a range of mass wasting processes including by landsliding and smaller mass flows.

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Recent Engineering Geology Articles

Mon, 30 Sep 2013 08:39:00 +0000

Recent Engineering Geology Articles

Recently published articles from Engineering Geology.

Natural stone reinforcement of discontinuities with resin for industrial processing

8 November 2013
A.M. López-Buendía | C. Guillem | J.M. Cuevas | F. Mateos | M. Montoto

Abstract: Natural stone is used as a construction material thanks to its aesthetic, mechanical, and durable properties. Frequently, some pieces of stone show weakness planes that are critical from the mechanical point of view because they can restrict their processing in the Stone Industry. Treatment with epoxy resin has become widely used due to good performance and good finishing properties.Crema Marfil (also known as Ivory Cream) has been chosen for this study as a widely used Spanish commercial marble. It corresponds to a well-cemented biosparry limestone that includes 5 main families of discontinuity planes: A: open stylolites; B: partially open stylolite; C: well-cemented stylolite with iron oxides and clay minerals; D: well-cemented stylolite with calcite; and E: calcitic veins.Reinforcement by consolidation under vacuum conditions with epoxy resin was applied in samples and slab of Crema Marfil. Epoxy resin in water emulsion and epoxy resin in solvent were specifically formulated and adapted to the characteristics of the migration properties of weakness planes.The evaluation of the weakness planes strength of untreated and impregnated marble was made by using the Brazilian test. Following a strict criterion of sampling, it was possible to obtain very local and precise information about the strength of those weakness planes and their consolidation improvement.Detailed fractographic study was made based in the selected blocks from the front of the quarry and extracting slabs and core samples for consolidation and testing.Results showed significant improvement in the tensile strength of the weakness planes at laboratory scale that can be applied to the Stone Industry. The methodology will provide a very good tool to evaluate the improvement for any other treatment for mechanical modification, mainly in weakness planes. The consolidation efficiency depends on the nature of the pathway properties (connected porosity, wettability with the resin, permeability, tortuosity) and the strength and adhesion of the resin.

Influence of salt solutions on the swelling pressure and hydraulic conductivity of compacted GMZ01 bentonite

8 November 2013
Chun-Ming Zhu | Wei-Min Ye | Yong-Gui Chen | Bao Chen | Yu-Jun Cui

Abstract: During the long-term operation of a deep geological repository, infiltration of groundwater with different chemical compositions can affect the buffer/backfill properties of compacted bentonite. Using a newly developed apparatus, swelling pressure and permeability tests were carried out on densely compacted GMZ01 bentonite samples, which has an initial dry density of 1.70Mg/m3, with de-ionized water as well as NaCl and CaCl2 solutions at different concentrations. Salinity effects of infiltrating solutions on swelling pressure and hydraulic conductivity of tested samples were investigated. Results obtained show that the swelling pressure of GMZ01 bentonite decreases with increasing concentration of infiltrating solutions, while the degree of the impact decreases with the increase of concentrations. Moreover, swelling pressure reaches stability more rapidly in case of high concentrations. The hydraulic conductivity of GMZ01 bentonite increases with the increase of solution concentrations. Comparison shows that the impact of NaCl solutions on the swelling pressure and hydraulic conductivity is higher than that of CaCl2 solutions at same concentrations. This may be explained by the impact of cation types on the microstructure of bentonite.

Effects of pore water chemical composition on the hydro-mechanical behavior of natural stiff clays

Abstract: Boom Clay and Ypresian Clays have been considered as potential geological host formations for radioactive waste disposal in Belgium. Considering the significant differences in pore water chemical composition between several sites involving these two formations as well as the possible evolution of the chemical composition during the large lifespan of a radioactive waste disposal, it appeared important to investigate the effects of pore water chemical composition on the hydro-mechanical behaviors of these two potential host formations. In this study, these effects were investigated by carrying out specific œdometer tests. Different compositions were considered for this purpose: distilled water, synthetic site water, and Sodium Chloride solutions at concentrations of 15 and 30g/L. Clear effects of pore water chemical composition on the hydro-mechanical behavior were observed: increasing pore water salt concentration gave rise to (i) increase of œdometric modulus Eœd, permeability K and consolidation coefficient Cv; and (ii) decrease of compression slope c′c, swelling slope c′s and secondary compression coefficient Cαe, which is in agreement with the diffuse double layer theory and the clay particle aggregation as identified by microstructural analyses. Furthermore, the pore water chemical composition effects were found to be mineralogy, stress state and salt concentration dependent: (i) Ypresian Clays with higher smectite content showed clearer chemical effect on the coefficient of consolidation Cv; (ii) the chemical effects on compressibility and swelling capacity parameters were found to be attenuated with increasing vertical stress; and (iii) the increase of chemical effect with increasing pore water salinity was limited to a certain salt concentration. The competition between the physico-chemical and mechanical effects was identified: the pore water chemical composition effect is clear only in the low-stress range where the hydro-mechanical behavior is dominated by the physico-chemical effect.

Combining scanning electron microscopy and compressibility measurement to understand subsurface processes leading to subsidence at Tauhara Geothermal Field, New Zealand

8 November 2013
Bridget Y. Lynne | Michael Pender | Trystan Glynn-Morris | Fabian Sepulveda

Abstract: The Tauhara geothermal field is located within the Taupo Volcanic Zone, New Zealand and has undergone subsidence in three localized areas referred to as the Crown, Rakaunui and Spa Sights bowls, with measured subsidences of 0.9, 2.4 and 2.9m, respectively. These subsidence bowls are situated close to Taupo township and are of concern to the public and for geothermal developers. Therefore, an intensive subsidence study at the Tauhara field was undertaken to better understand and mitigate further subsidence. Tauhara and Wairakei are often referred to as one system as a shallow, low resistivity anomaly extends continuously across both fields. However, they are two individual fields with separate up-flows. Tauhara is located in the south of the system, while Wairakei is located in the northern area. The Wairakei field also has subsidence bowls that reach up to 15m in localized areas. Extraction of fluids from the Wairakei field began in 1958 (currently 171MWe) but did not begin at Tauhara until 2010 (currently 23MWe). At Wairakei, initial fluid withdrawal was from the Waiora Formation which extends under both the Wairakei and Tauhara fields. Since 1958, fluid pressure in the Waiora Formation has dropped and this pressure decline extends under both the Wairakei and Tauhara fields. A pressure drop has also been detected in the Mid Huka Falls Formation which is a permeable stratigraphic unit present at shallower depth (relative to the Waiora Formation) in both fields. The Tauhara subsidence investigation included drilling, with continuous core recovery, at selected sites located inside (THM 16), outside (THM 13, THM 14) and on the periphery (THM 12) of known subsidence bowls. Cored samples representative of the seven formations encountered were analyzed to establish their stiffness by determining their constrained modulus (CM) value. On the same samples, the effect of hydrothermal alteration was established using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), petrography and X-ray diffraction (XRD). Key findings include the following: (1) CM values ranged from 20 to 1800MPa; (2) THM 16 revealed the lowest CM values of the study (

New weathering classifications for granitic rocks based on geomechanical parameters

8 November 2013
M. Heidari | A.A. Momeni | F. Naseri

Abstract: Here we investigate the classification of weathering grade for granitic rocks from the Malayer granitoid, western Iran, using physico-mechanical parameters. The physical and mechanical properties of rock samples were measured across five weathering grades ranging from fresh rock to completely weathered. Statistical analyses, including simple regression and multiple linear regression, were applied to identify those physico-mechanical parameters that are most influenced by the progression of weathering. The parameters with significant correlations with weathering grade include strength retention index, p-wave velocity, porosity, Brazilian tensile strength, and point load index. On the basis of the statistical results, new classifications are developed. These classifications can be used to predict the engineering properties of the Malayer granitic rocks (Hamedan, NW Iran) and should have more general application to the quantitative classification of granitic rocks in Iran.

Slaking behavior of clay-bearing rocks during a one-year exposure to natural climatic conditions

8 November 2013
Tej P. Gautam | Abdul Shakoor

Abstract: Slaking of clay-bearing rocks, upon exposure to natural climatic conditions, is a common problem at many engineering projects. Depending upon the regional climate, clay-bearing rocks slake in response to heating and cooling, wetting and drying, and freezing and thawing cycles. However, laboratory methods used for assessing the slaking behavior of clay-bearing rocks, including the standardized methods by the American Society for Testing and Materials (ASTM) and the International Society for Rock Mechanics (ISRM), involve only wetting and drying treatments. In this study, we investigated the slaking behavior of clay-bearing rocks by exposing them to natural climatic conditions for a period of one year.Twenty clay-bearing rocks, consisting of 5 claystones, 5 mudstones, 5 siltstones, and 5 shales, were selected for the study. Twelve replicate samples of each rock type were prepared so that each sample consisted of 10 pieces, each piece weighing 40–60g, with a total weight of 450 to 550g. The samples were placed in separate metallic pans and exposed to natural climatic conditions from September 2009 to September 2010. Each month, one replicate sample of each rock type was removed from natural exposure and its grain size distribution was determined. Disintegration ratio (DR), defined as the ratio of the area under the grain size distribution curve of the slaked material for a given sample to the total area encompassing all grain size distributions, was used to evaluate the extent of disintegration upon slaking. DR can range from 0 to 1, with 0 indicating 100% slaking and 1 indicating no slaking. After 3months of exposure to natural climatic conditions, claystones, mudstones, siltstones, and shales exhibited DR values of 0.223, 0.302, 0.698, and 0.494, respectively. These results suggest that, over a given period of time, claystones slake the most and siltstones the least. Relating DR to clay content of the rocks studied reveals that rocks with higher clay contents slake more rapidly and extensively under natural climatic conditions than those with lower clay contents.

Geotechnical properties of gas oil-contaminated kaolinite

8 November 2013
Elahe Khosravi | Hasan Ghasemzadeh | Mohammad Reza Sabour | Hessam Yazdani

Abstract: The leakage of petroleum products contaminates the soil and changes its physical and mechanical properties. This paper is a part of an extensive laboratory program aimed at promoting greater understanding of the influence of petroleum-derived contaminants on the geotechnical properties of soils. The laboratory tests included basic properties, Atterberg limits, consolidation, direct shear, and unconfined compression tests, all of which were carried out on clean and contaminated kaolinite specimens at the same relative compactions. Contaminated specimens were prepared by mixing kaolinite with different gas oil contents. Results indicate an increase in the cohesion and a decrease in both the friction angle and compressibility of kaolinitic soils with increasing the gas oil content. Results are intended to provide an alternative to the treatment methods currently used in practice for petroleum-contaminated sites and help bridge/narrow the gap between research and practice in environmental protection of the sites.

Variability of geotechnical properties of a fresh landslide soil deposit

8 November 2013
H.F. Zhao | L.M. Zhang | Y. Xu | D.S. Chang

Abstract: Natural soils exhibit large variations in their engineering properties. It is essential to characterize the variability of common design soil properties within a large representative soil element and to investigate the effect of sample size on the variability of these soil properties. In this study, field tests on two 1.0m cubes were conducted at a recent landslide site. Each cube was divided into 64 unit cubes of 0.25m size, and adjacent unit cubes were combined into samples of 0.5m and 0.75m sizes. The variability of dry density, mean particle size (D50) and coefficient of uniformity (Cu) is quantified at different size scales. Random field theory is adopted to characterize the spatial soil variability within these two 1.0m cubes. Both the point coefficient of variation (COVp) and the coefficient of variation of the spatial average (COVa) of each of the three soil parameters decrease rapidly as the sample size increases. However the mean values of these soil parameters are insensitive to the sample size. The COVp of dry density is smaller than those of D50 and Cu. The scale of fluctuation for dry density is much larger than those for D50 and Cu.

Generalized unconfined seepage flow model using displacement based formulation

Available online 29 September 2013
Pedro Navas | Susana López-Querol

Abstract: Modelling seepage along with the mechanical response of deformable earth dams under transient conditions, is a very complicated task, since it involves coupling between different phases, computation of free surfaces variable in time, and thus it requires algorithms for integration in time. These aspects represent a combination of several problems, which are usually undertaken in a separate way, uncoupling mechanical response and flow through the porous media. When such computations are carried out, most of the times rigid solid skeleton is considered, without a comprehensive analysis of the degree of accuracy achieved with such assumptions. Moreover, it is rather difficult to find in the literature coupled formulations under transient conditions. In this paper, a numerical finite element, coupled, transient model for analysing unconfined seepage through earth dams, is presented. This model is based on Biot’s equations, in terms of displacements (so called u – w formulation). The iterative procedure to obtain free surfaces by changing impermeability boundary conditions is implemented in this model. This generalized model is validated against several cases found in the literature. After that, several relevant aspects of the particular problem of fast emptying of a reservoir, and the calculation of the limiting drawdown speed for not compromising the earth dam safety, are explored. Thus, the influences of different drawdown speeds, soil permeability values, stiffness and geometries in a theoretical rectangular earth dam, have been analysed in terms of effective vertical stress changes at relevant points inside the dam. In summary, all these studied cases show the suitability of the presented methodology for evaluating such situations in real earth dams, and give hints on the more significant aspects to be considered in the earth dams design.

Measuring the in situ deformation of retaining walls by the digital image correlation method

Available online 21 September 2013
Shih-Heng Tung | Meng-Chia Weng | Ming-Hsiang Shih

Abstract: In this study, the digital image correlation (DIC) method was used to monitor the full-field deformation of a retaining wall. Two retaining walls located in mountainous areas of Taiwan were investigated. The first, Fushan slope, was characterized by substantial long-term deformation, and the second, Bulao slope, was located beneath an expressway and was severely damaged by Typhoon Morakot. This paper first describes the preparation procedures for in situ applications of the DIC method. Various environmental factors such as fog, rain, light direction, and spot mark clarity affected measurement precision, and consequently produced monitoring images that were unsuitable for further analysis. The DIC analysis results clearly indicate the deformation pattern of the retaining walls. The proposed method is accurate and effective for performing long-term monitoring of retaining walls, and the results can be used to accurately predict the tendency, location, and quantity of retaining wall displacement. Therefore, the proposed DIC method can be implemented to prevent disasters caused by landslide.

Strength and deformation properties of Dunkirk marine sediments solidified with cement, lime and fly ash

Available online 20 September 2013
Dongxing Wang | Nor Edine Abriak | Rachid Zentar

Abstract: Most of previous studies concerning solidification of dredged sediments focus mainly on the strength and environmental properties, but the deformation properties have not been fully appreciated. The present study emphasizes the deformation characteristics of marine sediments by using deformation parameters. A series of unconfined compression tests were performed on about 150 standard samples of 13 designed mixes. After analyzing the stress–strain curves of different mixes at 14, 28, 60 and 90days, the effect of binder content (as cement, lime and fly ash) on peak strength and failure strain is discussed. It can be found addition of fly ash improves the mechanical performance of lime-treated sediments, but damages the strength of cement-treated sediments. The lime-fly ash binder can substitute lime and cement-fly ash binder to solidify sediments owing to lower cost, waste recycling and good ability to gain strength. The concept of strength ratio is introduced to evaluate the development of unconfined compressive strength with curing time and binder content. By comparison, the relationship between failure strain and unconfined compressive strength is calculated as σ=(20~130) εf and the failure strain ranges mainly between 1% and 2%. The deformation modulus defined at 50% of peak strength is explored for designed materials at different binder contents and different curing times. The development of deformation modulus is in accordance with unconfined compressive strength. A quantitative correlation E50=119.91 UCS is therefore determined according to large quantities of test results. Finally, the microstructure of solidified sediments is observed by using scanning electron microscopy.

Sedimentary and hydraulic characterization of a heterogeneous glaciofluvial deposit: Application to the modeling of unsaturated flow

Available online 19 September 2013
D. Goutaland | T. Winiarski | L. Lassabatere | J.S. Dubé | R. Angulo-Jaramillo

Abstract: Flows in the unsaturated zones of alluvial deposits are often poorly understood at the scale of structures such as stormwater infiltration basins. The heterogeneous nature of the sediment inherent to this type of formation can lead to preferential flows. The difficulty of quantifying them lies in obtaining hydrodynamic parameters representative of the soil structure in-situ,when the latter is inaccessible. This study proposes a method of estimating the hydrodynamic parameters of the lithofacies composing a glaciofluvial deposit (east Lyon, France) and their integration in a 2D flow model to model flow in theunsaturated zone. The approach developed comprises a sedimentological study based on the Miall code, carried out to determine the analogy between the lithofacies of the study site and those of two glaciofluvial reference sites currently in the process of formation (Chamonix, France; Breidamerkurjökull, Iceland), thereby permitting easy access to all the lithofacies identified on the study site. The water retention and hydraulic conductivity curves were obtained on the reference sites by using Beerkan type infiltration tests for finely textured materials, completed by the Arya and Paris model and data from the literature for coarser materials. Thus hydrofacies corresponding to all the lithofacies were characterized. These hydrofacies were used to model a drainage phase on the study site at the scale of a trench (13.50 m long x 2.50 m deep). The model highlighted the importance of the role played by the spatial distribution of hydrofacies on flows, with a pronounced capillary barrier effect of the very coarse lithofacies and a sand lens leading to funneled flows. By assuming that there is a direct link between the sedimentary lithological heterogeneity and the unsaturated hydrodynamic properties of the materials composing its different structures, it was possible to perform a detailed hydrodynamic characterization of the unsaturated zone that could then be used to model flows, and in particular highlight preferential flows.

Coupled thermo-hydro-mechanical–chemical behaviour of cemented paste backfill in column experiments. Part I: Physical, hydraulic and thermal processes and characteristics

17 September 2013
Alireza Ghirian | Mamadou Fall

Abstract: Cemented paste backfill (CPB) technology has been widely used to fill underground mine voids for underground mine support and/or tailings disposal. Once placed, the CPB structure is subjected to strong coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes. In this paper, an experiment with insulated-undrained high columns has been carried out to understand these THMC processes. A CPB mixture is loaded into two columns and instrumented with various sensors to monitor the evolution of temperature, pore water pressure and suction for a period of 150days. In addition, four other CPB columns are cured at 7, 28, 90 and 150days, and then extensive laboratory testing is carried out on the CPB samples with regards to their thermal conductivity, saturated hydraulic conductivity, water retention properties, and mechanical and physical properties. Also, the rate of evaporation is monitored in a cylindrical CPB sample for the entire period of study. The results obtained show that a higher temperature can result in faster microstructural refinement and hence lower fluid transport ability. Reduction in the degree of saturation decreases thermal conductivity. The hydraulic properties are strongly coupled to chemical and mechanical factors. Mechanical deterioration following surface shrinkage and cracks can increase the saturated hydraulic conductivity. Also, changes in pore fluid chemistry affect microstructural evolution and can influence physical properties, such as void ratio and degree of saturation. Moreover, the obtained results support that the THMC properties of CPB are strongly coupled due to several internal mechanisms, such as heat of hydration, self-desiccation, suction development and cement hydration. The findings can contribute to a better understanding on the behaviour of CPB and thus towards the designing of more cost-effective and durable CPB structures. The results of the evolution of the mechanical, chemical and microstructural processes are discussed in a companion paper (see Part II, this issue).

Gas permeability in the excavation damaged zone at KURT

17 September 2013
Won-Jin Cho | Jin-Sub Kim | Changsoo Lee | Huei-Joo Choi

Abstract: An in-situ experiment to measure the gas permeability using nitrogen gas has been carried out at KURT (KAERI Underground Research Tunnel) to investigate the change of permeability in the EDZ (excavation damaged zone). The results showed that the permeability decreases with an increasing distance to a location about 2m deep from the tunnel wall, and then maintains a somewhat constant value. The size of the EDZ can be estimated to be about 2m from the viewpoint of permeability, and in the EDZ, the permeabilities seem to be increased up to 2 orders of magnitude compared with those in the intact rock. The EDZ was estimated to be 1.2m from the tunnel wall on the basis of the deformation modulus measured through a Goodman jack test. The EDZ size estimated based on the permeability is larger than that from the Goodman jack test. The fractures have a more significant influence on the hydrological properties compared with the mechanical ones because a fluid flow occurs principally through fractures in the crystalline rock.

Damage to sewerage systems during the 2004 Earthquake in Niigata-ken Chuetsu, Japan

17 September 2013
Gi-Chun Kang | Tetsuo Tobita | Susumu Iai

Abstract: The 2004 earthquake in Niigata-ken Chuetsu, Japan, caused widespread damage to sewer pipelines due to uplift behaviors caused by ground settlement after liquefaction. Sewer pipelines, which are important lifelines, suffer damage when sewerage systems cease to operate over a long period of time. Manholes ejected from the ground's surface can disrupt traffic. To study the failure mechanism after the earthquake, the Nagaoka city government conducted an open-cut survey of the damaged sewerage systems. The main features of the collected data included the locations of damaged sections and the inclination of the sewer pipes before and after the earthquake. In the present study, the cause of damage to the sewerage systems was investigated using the datasets and the standard penetration test (SPT) borehole logs. The relationship between the sewer pipeline damage and the geological settings in the affected area reveals that the groundwater depth and the geotechnical properties of the original subsoils acted as the key parameters influencing the manhole uplift behavior. Also, the uplift mechanism was investigated through centrifuge modeling tests, and these findings agree well with the test results obtained in this study.

Land subsidence and ground failure associated to groundwater exploitation in the Aguascalientes Valley, México

Abstract: Ground failure associated with land subsidence due to groundwater withdrawal is the main geotechnical hazard in the Aguascalientes Valley, causing enormous economic loss by damage to public and private properties, including urban infrastructures. The Aguascalientes Valley forms a tectonic graben flanked by north-to-south trending normal faults, where the hydrologic, hydrogeologic and anthropogenic conditions are favorable for ground deformation. The intensive withdrawal of groundwater has produced a critical decline in potentiometric levels, particularly beneath the Aguascalientes City, where most of the ground failures have occurred. Most of the ground failures observed in this valley are directly linked to irregularities of the bedrock and buried paleo-channels. Currently, the damage caused by ground failures is variable and considerable, even though local government is aware of this problem and has undertaken actions in order to mitigate the ground failure-related damages, for instance: mapping the location of ground failures in the entire valley, carrying out resistivity surveys aimed at detecting incipient ground failures and buried cracks, and carrying out gravimetric surveys for detecting zones in the subsoil with the geologic conditions for the potential development of ground failures.

Effects of high temperature processes on physical properties of silica sand

17 September 2013
S.G. Zihms | C. Switzer | J. Irvine | M. Karstunen

Abstract: High temperature processes may alter soil properties, creating potential risks of subsidence, erosion and other hazards. Soils may be exposed to high temperatures during some aggressive contaminant remediation processes as well as natural events such as fires. Characterising the effects of high temperatures on soil properties is essential to understanding the potential hazards that may arise after exposure. Thermal treatment and smouldering remediation were carried out on silica sand used here as a simple soil. Changes observed in physical properties were associated with the treatment type and exposure temperature. Particle, minimum and maximum densities were independent of heat treatment type and temperature. In contrast, particle size distribution, mineralogy, capillary rise, and hydraulic conductivity were linked to treatment type and exposure temperature with the most substantial changes associated with smouldering remediation. Changes in colour and mass loss with increasing temperature suggest changes within the crystal structure of the silica sand beyond loss of moisture content within the pore space and dehydration of iron deposits from goethite to hematite. Based on these observations, exposure to high temperature processes and the complex geo-chemical reactions during smouldering remediation can have significant effects on soil properties. Monitoring after exposure is advisable to determine the severity of exposure and any mitigation measures that may be necessary.

Swell and shrinkage characterizations of unsaturated expansive clays from Texas

17 September 2013
Anand J. Puppala | Thammanoon Manosuthikij | Bhaskar C.S. Chittoori

Abstract: Expansive soils have long been recognized as problematic because they cause failure to civil structures constructed above them. The main problem of these soils can be attributed to poor understanding of the volume changes caused by moisture fluctuations. Current swell and shrinkage characterization models are limited by both the lack of standardized tests and tests that employ volume changes in uniaxial direction. In the present research, a comprehensive laboratory investigation was undertaken to study the volume change related swell–shrinkage behaviors of five different types of expansive clayey soils sampled from various regions in Texas, USA. Extensive experimental programs consisting of basic, chemical and mineralogical soil properties were first determined. Three-dimensional free swell and shrinkage tests were performed on all soils at various compaction moisture content conditions. Soil–water characteristic curves (SWCCs) of all test soils were determined by studying the suction potentials of these soils over a wide range of moisture contents. Volume change measurements of soils showed a good correlation with soil properties, including plasticity and soil compaction properties. SWCC results also showed a clear variation in SWCC profiles of soils with respect to soil plasticity. Overall, a large database of soil properties was developed and is presented here. It includes physical and mineralogical properties, as well as engineering swell, shrinkage and SWCC test results.

Mechanical behavior of groundwater seepage in karst collapse pillars

17 September 2013
Haibo Bai | Dan Ma | Zhanqing Chen

Abstract: Groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars (KCPs), which are widely distributed in North China. In order to study the mechanism of groundwater inrush from coal seam floor, the variable mass dynamics and nonlinear dynamics were introduced. A mechanical model–plug model is established to describe the behavior of water seepage flow in coal-seam-floor containing KCP. The study shows that: (1) If the mass of the KCP keeps steady, the water seepage velocity in the KCP and the surrounding rocks will reach a constant value soon; (2) if the mass of the KCP and the surrounding rocks increases by grouting, etc, the seepage velocity in the KCP and the surrounding rocks will reach its minimum value gradually, and (3) if the mass of the KCP and the surrounding rocks decreases by scouring, the flow velocity in the KCP and the surrounding rocks shows a monotone increase, the water flow may change into pipe flow, especially when a large number of the mass of the KCP and the surrounding rocks enters into goaf road, which may lead to instable flow and cause groundwater inrush.

Analysis of electron microscope images of soil pore structure for the study of land subsidence in centrifuge model tests of high-rise building groups

17 September 2013
Zhen-Dong Cui | Ya-Jie Jia

Abstract: The scanning electron microscopy (SEM) images of soil pore structures were quantitatively analyzed for the study of land subsidence in the centrifuge model tests of high-rise building groups in this paper. The changes of the macrostructure and microstructure characteristics of the soils before and after centrifuge model test were studied, including the void ratio, the equivalent diameter, the circularity, the shape factor, the distribution of the orientation angle and the morphological fractal dimension of pores. The results demonstrated that the real filling rate can be estimated by 115% of the filling rate calculated by the Otsu method or be estimated by the normalized threshold of the SEM images between [0.34, 0.36]. Variations of the calculated filling rate with the adopted threshold showed the Gaussian function relationship. After the consolidation, 28.0% and 29.6% of the total pore area of the silty clay of layer No. 4 and the clayey soil of layer No. 8 were reduced, respectively, which illustrated the great compressibility and showed good agreement with the large macroscopic subsidence. The pores with radii more than 1μm occupied the vast majority of the total pore area. The fractal dimension of the pore shapes decreased after the consolidation. Considering the changes of the average eccentricity and the average shape factor, during the soil consolidation, the pores were not simply flattened but parts of the boundaries of pores were compressed to be closed, which made the shape of pores more regular.

Seismic hazard assessment for greater North China from historical intensity observations

17 September 2013
Jingwei Liu | Zhenming Wang | Furen Xie | Yuejun Lv

Abstract: Seismic hazards in greater North China were estimated from 500years of intensity observations. Historical intensity observations were collected, the completeness of the earthquake catalog was tested, and aftershocks were deleted. The intensity data were digitized and placed in a geographic information system (GIS). Finally, the digitized intensity data were analyzed to determine the frequency–intensity relationship (i.e., seismic hazard curve). Seismic risks were also estimated, assuming a Poisson distribution for earthquake occurrence in time. The results show that greater North China faces significant seismic hazards and risks. The results also show that the current design peak ground acceleration (PGA) for greater North China might not be adequate, particularly for the Beijing, Tianjin, and Tangshan areas.

Thermal conductivity of soils and rocks from the Melbourne (Australia) region

17 September 2013
D. Barry-Macaulay | A. Bouazza | R.M. Singh | B. Wang | P.G. Ranjith

Abstract: The thermal conductivity of soils and rocks is an important property for the design of thermally active ground structures such as geothermal energy foundations and borehole heat exchange systems. This paper presents the results of a laboratory study of the thermal conductivity of soils and rocks from around Melbourne, Australia. The thermal conductivity of six soils and three rock types was experimentally measured using both a thermal needle probe and a divided bar apparatus. Soil samples were tested at a wide range of moisture contents and densities. The results demonstrated that the thermal conductivity varied with soil moisture content, density, mineralogical composition and particle size. Coarse grained soils were observed to have a larger thermal conductivity than fine grained soils. In addition, the thermal conductivity of soils increased with an increase in dry density and moisture content. Siltstone, sandstone and basalt rock samples were tested dry and water saturated. They demonstrated an increase in thermal conductivity with an increase in density when dry. However, when water saturated, siltstone and sandstone showed no significant correlation between density and thermal conductivity; whereas a linear increase in thermal conductivity with density was observed for the saturated basalt samples. These differences were attributed to both variations in mineralogy and anisotropy of each sample. The thermal conductivity data obtained from this study provides an initial database for soils and rocks from the Melbourne (Australia) region which can serve for the design of thermo-active structures installed locally and in locations with similar ground conditions.

Empirical and mathematical formulation of the shear behavior of rock joints

17 September 2013
Arash Usefzadeh | Hamed Yousefzadeh | Hossein Salari-Rad | Mostafa Sharifzadeh

Abstract: In this paper, an empirical model based on an earlier model by Goodman and laboratory investigations of the shear behavior of limestone rock joints are presented. For developing such a model, a series of laboratory experiments were carried out on joint specimens under constant normal load (CNL). The model of shear behavior consists of two non-linear parts; the initial section includes the onset of shearing to the peak shear strength and the post-peak covering the behavior to the end of the shear test. Input data to the model include the peak and residual strength at the corresponding shear displacements. The proposed model shows very good agreement with the laboratory results and is capable of predicting the shear behavior of rock joints. Following the development of the empirical model, the investigations focused on the model by Saeb and Amadei (1992) and a mathematical model was proposed to consider both the shear and normal stiffness behavior of rock joints under constant normal stress and conditions. In this study, the proposed mathematical model was based on the aforesaid empirical model instead of the Goodman model. The capability of the proposed mathematical model to predict the behavior of rock joints under constant normal stiffness conditions was assessed using the laboratory results reported by Seidel and Haberfield (2002a,b). The model showed good correlation with the experimental data.

Hydraulic conductivity and microstructure changes of compacted bentonite/sand mixture during hydration

Abstract: Compacted bentonite-based materials are often considered as sealing/backfill materials in deep geological repository for high level radioactive waste. A good understanding of their hydration process is essential as this process is directly related to over-pack corrosion and nuclide migration. In this study, the unsaturated hydraulic properties of MX80 bentonite/sand mixture were characterized by carrying out a series of experiments including water retention test, infiltration test as well as microstructure observation. It was found that with suction decrease under constant volume condition, the hydraulic conductivity decreased followed by an increase after a suction threshold. At suctions higher than 12.6MPa, hydration led to progressive large-pore clogging by exfoliation of clay particles. On the contrary, when saturation was approached (suction lower than 4.2MPa), the large-pore quantity increased due to the creation of two-dimensional pores. It was also observed that the soil hydraulic conductivity changed following the same tendency as the large-pore quantity during hydration. In other words, water transfer was primarily governed by the network of large-pores.

Characterisation and engineering properties of Tiller clay

17 September 2013
A. Gylland | M. Long | A. Emdal | R. Sandven

Abstract: A detailed characterisation of the quick clay underlying the NTNU research site at Tiller, Trondheim is presented. The objective of the work is to provide guidance on quick clay parameters to engineers and researchers working with similar clays in Scandinavia and North America especially on landslide hazard assessment. The material is lightly overconsolidated and is characterised by its high degree of structure and very high sensitivity (quick clay). Clay and water contents are both about 40%. The plasticity index is low (5%). This relates to the low active minerals of the clay and silt fractions (illite/chlorite and quartz/feldspars respectively). Undrained shear strength is of the order of 30kPa to 50kPa (medium stiff) and increases with depth. The deposit is consistent across the site and its properties are similar to other Norwegian quick clays. Significant efforts have been made into examining sample disturbance effects on the material. It was found that thin walled steel fixed piston samples can yield results similar to those of block samples provided the work is carried out with extreme care and storage time is minimised. The piezocone (CPTU) test proved very useful in characterising the material.

Coal seam surface modeling and updating with multi-source data integration using Bayesian Geostatistics

17 September 2013
Xiaojun Li | Peinan Li | Hehua Zhu

Abstract: A reliable coal seam surface model needs to reconcile all available geological data such as boreholes, cross-sections, and coal seam floor contour maps. In addition, the model should be updated when local geological information such as coal seam observations is available. This paper develops a Bayesian Geostatistical approach for coal seam surface modeling using multi-source geological data in different stages and at different scales. The proposed approach contains two major components: Bayesian maximum entropy (BME) nonlinear estimation method to incorporate boreholes, cross-sections, and coal seam floor contour maps obtained in geological survey stage, and Bayesian inference (BI) method to assimilate coal seam point observations and geological sketches of tunnels obtained in mining stage. Coal seam surface elevations and its uncertainties are first estimated using BME method. The regional estimates are then used in BI method as prior knowledge, and updated when coal seam observations at a local scale are available. This provides a systematic and rigorous framework to incorporate multi-source geological data, and an effective way to improve the accuracy of coal seam surface models. The proposed approach is illustrated through a case study of a 3D subsurface modeling of the Wang-feng-gang Coal Mine, China. The coal seam surface estimates are compared with those of Ordinary kriging and Bayesian kriging methods, and compared with observed values along two tunnels in mining process.

Compressional behaviour of various size/shape sand–clay mixtures with different pore fluids

17 September 2013
A.F. Cabalar | R.A. Hasan

Abstract: Sand–clay mixtures can be considered as a composite matrix of coarser and finer particles. Nature of the interaction between coarser (sand) and finer (clay) particles can be demonstrated using intergranular void ratio (es), and transition fines content (FCt). The common aspect of the intergranular void ratio equations is based on the determination of an empirical relationship between es and effective stresses (σ′), fines content (FC), and void ratio (e). However, there is a lack of theoretical basis for determining consistent es and FCt values. This paper presents an investigation carried out to relate the various sizes (0.3mm–0.6mm; 1.0mm–2.0mm) and shapes (R=0.43, S=0.67; R=0.16, S=0.55) of sands with clay in different viscosity pore fluids (0.94mm2/s; 10.65mm2/s) to compressional behaviour by determining es and FCt values. Oedometer tests performed during this investigation indicate that the higher viscosity pore fluid in a specimen could cause a lower compressibility, and the sand with lower roundness (R) and sphericity (S) values exhibit higher FCt and Cc–s values.

Automated rockmass discontinuity mapping from 3-dimensional surface data

17 September 2013
Malte Vöge | Matthew J. Lato | Mark S. Diederichs

Abstract: Remote sensing technologies, specifically terrestrial-based static LiDAR and photogrammetry, are transforming from state-of-the-art to state-of-practice tools for engineering geologists. The complexity of available software packages to perform standard geomechanical analyses is slowing the widespread adoption of these technologies within the geotechnical community. The development of automated processing tools for feature extraction and data interpretation is aimed at eliminating the need for complex software and manual analysis. This paper presents the development of the algorithms used in the software program PlaneDetect for the automated identification and mapping of planar discontinuities within a 3-dimensional surface model of a jointed rockmass. The software employs a five stage procedure of: surface smoothing, edge detection and masking, blast damaged detection and masking, discontinuity identification, and discontinuity set clustering. The software outputs a stereonet of discontinuity orientations colored by joint set family, an image of the 3-dimensional model with each mapped discontinuity colored by the set family, and a text file of discontinuity orientations. The results of the geomechanical analyses computed by PlaneDetect in comparison to the manual mapping results are more statistically reliable based on less user bias. The time saving realized through using PlaneDetect for mapping discontinuities is approximately ten times compared to the manual mapping approaches.

Resistance of caprock to hydraulic fracturing due to CO2 injection into sand lens reservoirs

Abstract: The geomechanical stability of caprock is critical to the long-term safety of geologic storage of CO2 in depleted oil reservoirs. Based on the theory of rock fracture mechanics in deep formations, we propose a quantitative assessment framework for the resistance of caprock to hydraulic fracturing due to CO2 injection and storage in a sand lens reservoir. By simplifying the sand lens reservoir as a lenticular crack model, we developed a formula for the Mode-I stress intensity factor at the crack tip (pinch-out tip of the sand lens reservoir) and the in situ fracture toughness of the surrounding caprock. We then established a preliminary threshold for assessing the resistance of caprock to hydraulic fracturing. Based on this threshold, the critical hydraulic fracturing pressure at the pinch-out tip of a sand lens reservoir and the allowable injection pressure at the bottom hole of an injection well can be estimated. This quantitative assessment framework has been verified for use in sand lens reservoirs with a case study of the Daqingzijing CO2 storage site in the Jilin oil field, China. These results provide important implications for assessing the resistance to hydraulic fracturing in similar reservoirs with stratigraphic pinch-outs in impermeable formations, preventing caprock fracturing and water or gas channeling during CO2 injection.

Using inverse analysis to estimate hydraulic properties of unsaturated sand from one-dimensional outflow experiments

17 September 2013
Nam To-Viet | Tuk-Ki Min | Hosung Shin

Abstract: A one-dimensional (1-D) vertical draining test for Jumunjin sand was carried out in one-step and multi-step outflow conditions. An inverse analysis method was conducted to determine the hydraulic properties of unsaturated soil. A non-linear optimization method combining a finite element code and inversion analysis was used to minimize the objective function, defined by the difference between observed and predicted data. Unsaturated hydraulic parameters in van Genuchten model were estimated using soil suction measurements in 10cm intervals and an outflow rate at the bottom of a sand column. The predicted hydraulic properties and the experimental results were in close agreement when the measurements were compared from the one-step and multi-step outflow experiments. The results also showed that the multi-step outflow experiment was more appropriate in determining the unsaturated hydraulic properties than the one-step outflow experiment. The comparison between predicted and measured results concluded that the inverse analysis based on the 1-D outflow experiment was reliable and useful to determine the hydraulic properties of unsaturated soils.

Quantitative hydraulic analysis of pre-drillings and inflows to the Gotthard Base Tunnel (Sedrun Lot, Switzerland)

17 September 2013
Olivier Masset | Simon Loew

Abstract: A systematic pre-drilling campaign was undertaken during the excavation of the Sedrun South lot of the Gotthard Base Tunnel. This tunnel section is located 897 to 2026m below a high alpine topography and located in fractured crystalline basement rocks of the Gotthard massif. The section covered by the systematic drilling campaign extends over 5km in the Nalps hydropower lake region and aimed to support decisions and counter measures related to tunnel drainage induced surface deformations. The pre-drillings conducted in both tunnel tubes included 30 cored and 94 destructive drillings with a length ranging from 17.5 to 358.5m.This paper presents in detail the results from pre-drilling and tunnel inflow monitoring. A new methodology is presented and discussed that allows for quantitative analysis of fracture transmissivity and equivalent continuum hydraulic conductivity from basic pre-drilling inflow and pressure observations, using a simplified form of the Jacob and Lohman solution for transient inflow rate to a well of constant drawdown in a confined aquifer. Uncertainties with respect to the derived hydraulic conductivity values are estimated through Monte Carlo simulation and compared with results from digitally controlled borehole outflow and pressure build-up tests.The spatial distribution of fracture transmissivity and equivalent continuum hydraulic conductivity is presented and compared with tectonic and lithological properties. It is suggested that both steeply dipping, regional brittle faults and lithologic contacts with significant stiffness contrasts impact the distribution of preferential groundwater pathways at depth. Along fault strike strong small scale variations in brittle fault architecture lead to low hydraulic conductivity correlations between the two tunnel tubes separated by 40m. Normal to fault strike larger groundwater inflows cluster within domains of several hundred meters in length.The hydraulic conductivities from pre-drilling analysis are used for inflow prediction for the excavated tunnel. Compared to the small-scale (50m) variations of hydraulic conductivity as derived from pre-drilling analysis the sampled volumes of long term tunnel inflows are at least one order of magnitude larger (>500m). This leads to very uniform steady state inflow rates of 500–1000m long monitoring sections for cumulative tunnel inflows. These inflows range between 3 and 5l/s·km and compare very well with the predicted tunnel inflows from geometric mean hydraulic conductivity as derived from pre-drilling analysis.

Field and laboratory resistivity monitoring of sediment consolidation in China's Yellow River estuary

17 September 2013
Xiaolei Liu | Yonggang Jia | Jiewen Zheng | Hongxian Shan | Honglei Li

Abstract: Traditional methods for in situ monitoring of the dynamic physical process within marine sediments are not efficient and effective enough, and determination of the consolidation state of marine sediments in the Yellow River estuary remains a challenging problem. However, the recent development of in situ testing technology for resistivity methodology creates new possibilities. Our combined analysis of laboratory and field experimental results demonstrates the consolidation process and the contemporaneous physical, mechanical and electrical properties of marine sediments in the Yellow River estuary, and we discuss the feasibility of and that influence in situ monitoring of the sediment consolidation process using a multi-electrode probe. These results demonstrate that resistivity is a good indirect predictor of porosity, which is the primary factor affecting resistivity behavior during the consolidation process. Values for empirical constants a and m for Yellow River estuary sediment can be obtained based on Archie's formula. The relationship between resistivity and the geotechnical strength of silty sediments in the Yellow River estuary shows that the penetration resistance (determined by a light penetration test) and undrained shear strength (determined by a vane shear test) are closely correlated to resistivity with a power function during the consolidation process of a uniform-originated seabed. This study confirms that resistivity monitoring using a multi-electrode probe is a relevant method to estimate the degree and state of sediment consolidation in real time and in situ. More work is needed to investigate the implications of this for the prediction and prevention of geological disasters in estuarine areas.

Karst flash-flood forecasting in the city of Nîmes (southern France)

17 September 2013
P. Fleury | J.C. Maréchal | B. Ladouche

Abstract: In southern France, karst flash-floods may be the result of two, potentially cumulative, phenomena:−Floods from highly localized events that mostly occur during autumn and are locally known as Cevenol rain events;−Floods exacerbated by recent rainfall events that contributed to saturation of the aquifer before the storm event, thereby increasing runoff.In any case, flash floods occurring in a karst landscape are directly linked to the structure and hydraulic properties of the karst aquifer.A methodology was developed for the city of Nîmes for forecasting these dangerous events, based on the study and modelling of karst-aquifer response to rain events. This work was composed of: (i) Definition of how the Nîmes system functions, leading to a conceptual model; (ii) Modelling of this conceptual model; (iii) Definition of a tool for hazard management, presented as an abacus and tested on particular strong rainfall event.

Evaluation on strength and deformation behavior of red sandstone under simple and complex loading paths

17 September 2013
Sheng-Qi Yang | Hong-Wen Jing

Abstract: Triaxial compression experiments were carried out for red sandstone to investigate its strength and deformation failure behavior under simple and complex loading paths. In this research, tested confining pressure is in the range from 5 to 35MPa. Under simple loading path, the peak strength, residual strength and critical damage threshold of red sandstone all increase with the confining pressure, which are in good agreement with the linear Mohr–Coulomb criterion. To investigate the re-fractured mechanical behavior of pre-cracked red sandstone with different post-peak stress drops, two complex loading paths with only one specimen are put forward to obtain the strength and deformation parameters of red sandstone. The differences of strength and deformation parameters of red sandstone between simple and complex loading paths are evaluated detailed. The elastic moduli of red sandstone under simple and complex loading paths all increase nonlinearly with the confining pressure. It is suggested and recommended to predict the peak strength of rock under simple loading path by adopting complex loading path A (increasing gradually the confining pressure) not complex loading path B (reducing gradually the confining pressure). On the basis of the linear Mohr–Coulomb criterion, a kind of new method is put forward to revise the peak strength of red sandstone under complex loading path A, which is testified to be right and reasonable. The investigated conclusions are very significant for ensuring the stability and safety of deep underground rock engineering.

Headcut migration prediction of the cohesive embankment breach

17 September 2013
Gensheng Zhao | Paul J. Visser | Patrik Peeters | Johannes K. Vrijling

Abstract: Headcut erosion occurs in the development of a cohesive embankment breach and plays an important role in the breaching process. The headcut development is a mixed process of sediment erosion and mass failure. Based on momentum equilibrium, the critical incipient velocity is derived from the forces of particle weight under water, cohesive force among particles around the clay particle, uplift force, and drag force. Via the turbulent boundary layer flow theory, the critical stress can be connected with these forces. The formulae for the incipient stress and the critical velocity have been calibrated and validated with the results of undisturbed clay tests. A moment equilibrium-based method is proposed to simulate the headcut development and migration in a cohesive embankment breach due to overtopping flow. The hypothesis is given that the particle and mass are removed in the minimum moment on the breach slope. It is found that the tested results give good predictions of the headcut erosion development on the breach slope by validating laboratory data. The proposed method can be important and valuable to predict the breaching process in cohesive embankments.

Expected Ground Motion at the Historical Site of Poggio Picenze, Central Italy, with reference to current Italian Building Code

Abstract: The amplification of the ground motion at the surface is greatly influenced by the geotechnical characteristics of the soil formations below the ground surface. Traditionally, analyses of the ground response are deterministic, which means no consideration of the aleatory nature of geotechnical parameters of soil layers like density, shear wave velocity, etc. A fully stochastic procedure for estimating the site amplification of ground motion allows taking into account the record-to-record variability in an input ground motion and the uncertainty in dynamic soil properties and in the definition of the soil model. In particular, their effect on response spectra at the ground surface can be evaluated. With this procedure, it is pretended to reduce the aleatory variability into the soil model.In this work, the soil profile below the San Felice Martire church, at Poggio Picenze (L’Aquila area, Abruzzo, Central Italy), has been studied basically on field geologic observations and drilling and geophysical tests retrieved from previous investigation campaigns. The dynamic soil properties were obtained by literature and by the test results. Amplification effects at the site under investigation have been estimated using fully 1D stochastic site response analyses and for the object motion 7 real records compatible to the Italian code-based spectrum referred to 475-year return period. The Italian building code defines the reference seismic action in terms of elastic acceleration response spectra derived from the results of a probabilistic seismic hazard study.The results in terms of accelerograms and acceleration response spectrum (with the associated dispersion) indicated a clear amplification of the input motion at the basement of San Felice Martire church due to the lithostratigraphic characteristics of the soil deposits at the site under investigation.

Determination of mechanical properties of flysch using laboratory methods

Available online 7 September 2013
G.P. Tziallas | H. Saroglou | G. Tsiambaos

Abstract: The paper deals with the determination of the mechanical properties of heterogeneous rocks in the laboratory and proposes a methodology for predicting the rock mass strength of flysch formations consisting of siltstone – sandstone alternations in different proportions. In order to simulate such formations, composite specimens comprising superimposed disks of intact sandstone and siltstone material with different thickness ratios were prepared. Wave velocity (P and S), uniaxial and triaxial compressive strength and Young’s modulus of the composite samples were determined in the laboratory. According to the laboratory results, the uniaxial compressive strength and Young’s modulus decrease with the increase of the siltstone percentage in the specimens, and yields the strength of siltstone when the siltstone percentage in the rock is equal to 37 %. Additionally, the triaxial compression tests on composite samples revealed a significant decrease of the mi parameter for a siltstone percentage of only 17%. A comparison is made between the results of the present study with similar laboratory and empirical references from literature. Finally, it was possible to suggest how the relation between uniaxial compressive strength, σci, and siltstone percentage, sl, may differ according to the ratio of the compressive strength of the two main rocks, weak and strong, which comprise the heterogeneous rock.

Sliding displacements due to subduction-zone earthquakes

Available online 30 August 2013
Alfredo Urzúa | John T. Christian

Abstract: Empirical studies of earthquake ground motions have developed relations between sliding displacement and acceleration ratio and other parameters such as Arias intensity. Computations using strong motion records from the Maule 2010 Chile M=8.8 earthquake indicate that the published relations do not conform well to the computed displacements, and some tend to be unconservative. Extensions to the empirical equations incorporating Arias intensity are, if anything, less accurate. These results suggest that these empirical relations may not apply to subduction zone events and indicate that further study using records from other recent subduction zone events is appropriate. Examining the analytical solutions for sliding displacements induced by sinusoidal shaking and the definition of Arias intensity leads to an improved normalization for sliding displacements. When this improved normalization is applied to the records from three different earthquakes in different parts of Chile, the results are nearly identical, and the results for the Chi Chi and Northridge earthquakes are very close to those from the Chilean events. Suggestions for practical use of the new normalization relations are provided.

Effects of near-fault seismic loadings on run-out of large-scale landslide: A case study

Available online 26 August 2013
Yingbin Zhang | Guangqi Chen | Lu Zheng | Yange Li | Jian Wu

Abstract: This study presents the run-out analysis of the Daguangbao landslides subjected to near-fault multi-direction earthquake forces using discontinuous deformation analysis (DDA). The Daguangbao landslide is the largest landslide induced by the 2008 Wenchuan earthquake. In order to investigate the effects of near-fault seismic force on landslide run-out, kinematic behavior of sliding mass is simulated by a dynamic discrete numerical analysis method called DDA. In this simulation, based on the shape of failure surface and the feature of slope geology, the whole slope is divided into three parts: base block, upper sliding mass, and lower sliding mass. Then two sliding masses are divided into the smaller discrete deformable blocks based on pre-existing discontinuities. Size effect of the huge landslide is also considered. Baseline corrected real horizontal and vertical ground motions are taken as volume force acting to the base block. The results show that seismic force has a significant influence on the landslide progression, sliding distance, and shape of post-failure. Results of the horizontal-and-vertical situation are in good agreement with those obtained from post-earthquake field investigation, remote sensing image and description from the survivors.

Assessing the coefficient of the earth pressure at rest from shear wave velocity and electrical resistivity measurements

19 August 2013
Liyuan Tong | Lian Liu | Guojun Cai | Guangyin Du

Abstract: Determination of earth pressure coefficient K0 in natural soil deposits is a significantly important issue in geotechnical engineering. This paper evaluates the feasibility of predicting K0 values from measurements of vertical and horizontal shear wave velocities [Vs(VH), Vs(HH), and Vs(HV)], and vertical and horizontal electrical resistivities (SV, SH). A series of seismic piezocone tests (SCPTU), improved crosshole (CH) tests, and soil resistivity tests using a modified laboratory apparatus were carried out at two research sites in Jiangsu Province of China and results were used to develop two existing K0-shear wave velocity correlations for prediction of K0. The seismic and electrical resistivity test results showed that both the shear wave velocity ratios, Vs(HH)/Vs(HV) or Vs(HV)/Vs(VH), and the horizontal to vertical electrical resistivity ratio, SH/SV, may provide a good indicator of the inherent soil anisotropy at these sites. The existing Vs–K0 prediction framework largely requires determining Cs(HV)/Cs(HH) ratio and a simple procedure for evaluating this ratio based on the measured horizontal and vertical electrical resistivities. The K0 values predicted by shear wave velocity at both sites are also compared with values determined by Jaky's formula and Mayne & Kulhwy's formula. In normally consolidated (NC) soils, the K0 values predicted from these methods showed good agreement. However, for over-consolidated (OC) soils at shallow depths, certain variations between different methods are noted. Further investigations of the effects of overconsolidation ratio on K0 predictions will lead to the correction factors for better prediction of K0 for OC soils. This paper has confirmed that reasonable predictions of K0 for natural soil deposits can be made using the proposed methodology.

Open Access

Quantification of uncertainties in soil–water characteristic curve associated with fitting parameters

19 August 2013
Qian Zhai | Harianto Rahardjo

Abstract: Soil–water characteristic curve (SWCC) is commonly expressed using best fit equations with several fitting parameters. These fitting parameters are determined by best fitting experimental data with the best fit equations. Residual errors always exist after the regression procedure for the determination of these fitting parameters. Statistical theory suggests that uncertainties of the determined SWCC can be estimated from the variance of these fitting parameters and the residual errors. In this paper, equations for the confidence limits of the best fitted SWCC are developed to quantify the uncertainties in the determined SWCC associated with the fitting parameters. Applications of the confidence limits in evaluating the performance of best fit equations and suggestion for experimental measurements are presented in this paper.

The use of discrete fracture network simulations in the design of horizontal hillslope drainage networks in fractured rock

Abstract: Characteristics of fracture networks are explored in a discrete fracture network framework to provide design guidelines for horizontal drainage networks in fractured rock. Central to the study is defining how fracture attributes relate to fracture network structure and network-scale fluid flow, and in turn, how flow characteristics of fracture networks influence horizontal drain length and orientation. Multiple realizations of stochastic fracture networks, generated from both synthetic and field-specific data sets, serve as a basis for understanding physical fracture network structure and resultant global flow and for performing intersection analyses of hillslope drains with flowing fractures. Study results indicate that the logarithm of the standard deviation of fracture transmissivity, log(σT), is the single most important attribute for drainage network design, as higher values of log(σT) describe heterogeneous flow patterns where only a small portion of the network conducts a significant quantity of fluid. Thus recommended drain lengths for intersecting significantly conductive fractures increase with increases in log(σT). Fracture trace length, orientation, and density also play a role, albeit secondary to the distribution of transmissivity, in defining drain length as a function of drain orientation relative to the mean fracture set orientation. The spatially discontinuous nature of fracture networks and the wide range in transmissivity values found in natural fracture networks tend to produce high degrees of variability in computed intersection distances between drains and fractures conducting significant quantities of fluid. To account for this variability, a conservative approach is recommended where horizontal drain lengths along a pre-defined orientation are scaled by discrete fracture network computed intersection distances equal to the upper 95th confidence interval.

THM coupling sensitivity analysis in geological nuclear waste storage

19 August 2013
Fabrice Dupray | Chao Li | Lyesse Laloui

Abstract: A deep geological repository involving a multi-barrier system constitutes one of the most promising options to isolate high-level radioactive waste from the human environment. In order to certify the efficiency of waste isolation, it is essential to understand the behaviour of the confining geomaterials under a variety of environmental conditions. The efficiency of an Engineered Barrier System (EBS) is largely based on thecomplex behaviour of bentonite. To contribute to a better understanding of the processes involved in the EBS, a case study for sensitivity analysis has been defined and is studied using a thermo-hydro-mechanical (THM) finite element approach including a consistent thermo-plastic constitutive model for unsaturated soils. The model also features a coupled THM approach of the water retention curve. Various couplings were studied separately and in combination in order to determine the significance of each. The same principle is applied to physical phenomena such as vapour diffusion. This study clearly highlights the effects that need to be taken into consideration for a correct assessment of EBS behaviour.

Improvement of dynamic soil properties induced by preloading verified by a field test

Abstract: Presented here are the results of an elaborate field preloading study on a liquefaction-susceptible site. Preloading was applied by a temporary embankment 9m high. Prior and after preloading, borings with standard penetration tests, cone penetration tests and geophysical studies were performed. During the process of embankment construction and demolition, settlements, excess pore pressures and vertical and horizontal stresses were recorded versus time at different locations. A partial embankment failure occurred during the preloading process. Methods are proposed and verified which predict (i) risk of failure during the construction of the preload embankment and (ii) stresses and displacements and (iii) the change in the shear wave velocity and cyclic liquefaction strength induced by the preload embankment.

Alumina filler waste as clay replacement material for unfired brick production

Abstract: This paper presents the results of an investigation for the application of alumina filler wastes and coal ash waste for unfired brick production. Mechanical test and durability assessment were carried out on unfired brick test specimens made using marl clay soil and alumina filler waste as a target material, and 70% mix of coal ash waste were used as commercials additive (Portland cement and Lime) replacement. The laboratory results demonstrate that the compressive strength resistance of the unfired bricks reduced as the clay replacement level increased. The unfired brick test specimens made with the blended mixtures containing coal ash waste and lime tended to achieve higher strength values when compared with the coal ash waste and Portland cement blends. The unfired brick test specimens were able to withstand the repeated 48-hour freezing/thawing cycles. The results obtained suggest that there is potential to manufacture unfired bricks from alumina filler waste and coal ash waste.

Microstructural observations of shear zones in sensitive clay

19 August 2013
Anders Samstad Gylland | Håkon Rueslåtten | Hans Petter Jostad | Steinar Nordal

Abstract: The present work assesses the structure and evolution of shear zones in sensitive ‘quick’ clays from the initiation to the well-established state. This assessment is done by utilizing laboratory and small scale field experiments combined with the analysis of thin sections in light microscopy and SEM. High resolution X-ray tomography (‘micro-CT’) is also applied. In combination, detailed 2D and 3D visualization of the shear zones is achieved. Shear zones are suggested to be formed in mm-thick continuous fields of displacement. With increasing shear displacement, sets of micron-sized minor shears develop within the main shear zone. These initiate, terminate and merge both in the plane and out-of-the-plane directions. The minor shears are characterized by distinct particle reorientation where the flaky clay particles and mica grains are aligned parallel to the direction of shear. A porosity reduction is observed in the minor shears. This is a direct observation of material contractancy and implies migration of water from the shear zone into the undisturbed matrix. The width of the main shear zone is considered to be related to the applied rate of shear while the minor shears have a width determined by the micro-texture of the sediment. The observed multi-scale structure of the shear zones, which is governed by complex inner mechanics, is challenging the ‘smooth shear zone’ concept that is commonly applied in numerical simulations. This is motivating a further improvement of such tools and the testing of other types of clay sediments.

Site frequency response characterisation of the Maltese islands based on ambient noise H/V ratios

19 August 2013
Alexander Vella | Pauline Galea | Sebastiano D'Amico

Abstract: The Maltese islands in the Central Mediterranean are composed of a simple 4-layer sedimentary sequence of Oligocene–Miocene limestones and clays, highly disturbed by synsedimentary to recent tectonic activity, so that the surface outcrops present a variety of lithologies, as well as complex geomorphology. The seismic history of the islands includes a number of damaging earthquakes, the largest intensity since 1500 being EMS-98 VII–VIII in 1693. In this study a first seismic site response survey was undertaken over the whole archipelago, by recording ambient noise and applying the H/V (Horizontal-to-Vertical Spectral Ratio) technique. The results show a clear correlation between site response and outcrop geology. In general, where the two oldest layers, the Lower Coralline Limestone and the Globigerina Limestone outcrop, the H/V is flat above 0.5Hz. A thick layer of clays and marls (Blue Clay) deposited originally on top of the Globigerina Limestone is preserved in the western half of the archipelago, and this strongly influences the site response. Where the clay outcrops at the surface, it produces the highest amplitudes, and peak frequencies ranging between 2 and 5Hz, whereas all sites on the hard Upper Coralline Limestone, which overlies the clay in many regions, still exhibit H/V peaks at a consistent frequency between 1 and 2Hz, which we attribute to the presence of the underlying clay. Results were validated by a second measurement survey and numerical modelling. The site effect induced by the clay layer has implications for the assessment of seismic risk, as well as for the validity of using VS30 as a proxy for site class and site amplification.

Shear wave velocity as function of cone penetration test measurements in sand and silt mixtures

19 August 2013
Laura Tonni | Paolo Simonini

Abstract: A database of research-quality piezocone test (CPTU) results and shear wave velocity Vs measurements, assembled in the context of an ambitious research project carried out at the Treporti test site (Venice, Italy), has been interpreted in order to study the seismic response of the predominantly silty sediments forming the Venetian lagoon basin as well as to explore potential correlations for such intermediate soils. The experience gained so far with the Treporti database and other field data collected in the lagoon area has shown that the mechanical behavior of Venetian soils cannot be easily interpreted using the existing and well-established CPTU-based approaches, hence the interest in examining whether or not the seismic response of these sediments, expressed in terms of shear wave velocity, follows the framework published for other soils. The applicability to the available data of a number of existing correlations, originally developed either for sands or fine sediments, has been first investigated and updated relationships have been then suggested. Furthermore, the small-strain stiffness calculated from Vs measurements has been compared with the field stiffness derived from the observed performance of a full-scale test embankment built in the Treporti site, so as to verify common design assumptions. The verification and calibration of existing approaches are likely to constitute a useful contribution to the practice of geotechnics not only in the Venetian lagoon area, but also in the silty deposits usually present in the surrounding alluvial plain and other similar depositional environments, allowing rapid estimates of seismic soil classification as well as small-strain stiffness properties for preliminary design or at sites where only cone penetration data are available.

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Assessment of sample frequency bias and precision in fluvial flux

Mon, 30 Sep 2013 08:18:00 +0000

Assessment of sample frequency bias and precision in fluvial flux calculations – An improved low bias estimation method

30 October 2013F. Worrall | N.J.K. Howden | T.P. Burt

Summary: Despite the importance of calculating the flux of solutes and particulates through the global fluvial network the number of studies that have considered the bias and precision of any method is limited. Furthermore, no study has, on the basis of the bias of the method, proposed new methods with a lower bias nor considered the implications of the bias estimation for existing published studies. Using 3years of high frequency data (hourly) for dissolved organic carbon (DOC) this study systematically degraded the data and recalculated the flux for varying sample frequencies and considered a range of interpolation, ratio and extrapolation methods. The results show that:(i)Interpolation and ratio methods showed a consistent, small bias for sampling frequencies up to every 14days, but bias rapidly increased for lower sample frequencies with the flux estimates being between 40% and 45% of the “true” flux at 31day (monthly) sampling.(ii)The best ratio method was based upon correction against an unrealistic assumption that river flow was normally distributed.(iii)Extrapolation methods based on fixed sampling period monitoring proved to be erratic but no better than interpolation methods.Based upon the nature of the sources of variation within the flow and solute datasets we propose the following method for calculating the fluvial flux (F) of a solute: F=KE(Ci)Qtotalwhere: Qtotal=the total flow in a year (m3/yr); E(Ci)=the expected value of the sampled concentrations (mg/l); and K=a conversion factor. This new method preserved all the available flow information and had a bias of as low as 8% for monthly sampling. When the method was applied to DOC flux from Great Britain bias correction meant a 97% increase in the national flux over previous estimates.

Simulation of lake–aquifer interaction at Lake Naivasha, Kenya using a three-dimensional flow model with the high conductivity technique and a DEM with bathymetry

30 October 2013Yohannes Yihdego | Robert Becht

Summary: Aquifers near Lake Naivasha, Kenya are important water resources and are used extensively for irrigation and for municipal and domestic water supplies. Head data for a 79-year period (1932–2010) were analyzed to develop a conceptual model of aquifer–lake interaction and used to develop a three-dimensional numerical model. A three-dimensional groundwater flow model with four layers was used to simulate ground-water flow in the aquifers and lake–aquifer interaction. The lake is simulated by specifying a high hydraulic conductivity for lake-volume grid cells. The 90m Digital Elevation Model (DEM) that includes the bathymetry improved the 3-D representation of the lake in the groundwater system and helped to define the deformed layer that honors the stratigraphy. The calibration process was carried out using PEST in conjunction with pilot points and regularization. The finite difference groundwater model results were comparable with measured head data and isotopic and hydro-chemical data. The sensitivity of the computed lake level was tested using the “high-K” method to the choice of K2/K1, where K2 and K1 are the hydraulic conductivity of the lake node and the aquifer (respectively). Higher values of K2/K1 should be used with higher regional gradients on the order of 0.002 to ensure mainly accurate calculations of seepage rates to and from the lake.

Hydrograph and chloride pollutograph analysis of Hobbs Brook reservoir subbasin in eastern Massachusetts

30 October 2013David W. Ostendorf

Summary: Hyetographs, hydrographs, pollutographs, and deicing agent applications are analyzed with linear reservoir theory to explain the fate and transport of water and chloride in a small (1km2) urban watershed subbasin. The subbasin delivers highway runoff to a public supply reservoir in eastern Massachusetts. Aquifer, vadose zone, and highway drainage systems deliver hydrographs with physically plausible exponential decay constants and seasonally varying discharge fractions. Continuous data from November 2005 to August 2012 suggest that baseflow contributes 48% of the water volume past a USGS gaging station at the subbasin outlet, while interflow and runoff calibration of 162 hydrographs yield respective water volume estimates of 21% and 31%. Specific conductivity, also measured continuously at the gage, is a surrogate for dissolved chloride concentration. The average chloride concentration for the 82month period of record is 0.334kgCl−/m3 at the gage, which exceeds the USEPA secondary drinking water standard of 0.250kgCl−/m3 for dissolved chloride. Model calibration of 162 pollutographs suggests that baseflow contributes 61% of the chloride mass past the gage over the period of record, while the interflow and runoff chloride mass fractions are 17% and 22%. Most (85%) of the chloride flux past the gage is attributable to state application of chloride based deicing agents on major highways, with the remaining 15% due to municipal applications on local streets in the subbasin. A perennial stream with a small, urban watershed in a cold climate is likely to discharge an appreciable flux of subsurface chloride all year long.

Addressing ten questions about conceptual rainfall–runoff models with global sensitivity analyses in R

30 October 2013Mun-Ju Shin | Joseph H.A. Guillaume | Barry F.W. Croke | Anthony J. Jakeman

Summary: Sensitivity analysis (SA) is generally recognized as a worthwhile step to diagnose and remedy difficulties in identifying model parameters, and indeed in discriminating between model structures. An analysis of papers in three journals indicates that SA is a standard omission in hydrological modeling exercises. We provide some answers to ten reasonably generic questions using the Morris and Sobol SA methods, including to what extent sensitivities are dependent on parameter ranges selected, length of data period, catchment response type, model structures assumed and climatic forcing. Results presented demonstrate the sensitivity of four target functions to parameter variations of four rainfall–runoff models of varying complexity (4–13 parameters). Daily rainfall, streamflow and pan evaporation data are used from four 10-year data sets and from five catchments in the Australian Capital Territory (ACT) region. Similar results are obtained using the Morris and Sobol methods. It is shown how modelers can easily identify parameters that are insensitive, and how they might improve identifiability. Using a more complex objective function, however, may not result in all parameters becoming sensitive. Crucially, the results of the SA can be influenced by the parameter ranges selected. The length of data period required to characterize the sensitivities assuredly is a minimum of five years. The results confirm that only the simpler models have well-identified parameters, but parameter sensitivities vary between catchments. Answering these ten questions in other case studies is relatively easy using freely available software with the Hydromad and Sensitivity packages in R.

Measuring and modeling maize evapotranspiration under plastic film-mulching condition

Summary: Plastic film-mulching techniques have been widely used over a variety of agricultural crops for saving water and improving yield. Accurate estimation of crop evapotranspiration (ET) under the film-mulching condition is critical for optimizing crop water management. After taking the mulching effect on soil evaporation (Es) into account, our study adjusted the original Shuttleworth–Wallace model (MSW) in estimating maize ET and Es under the film-mulching condition. Maize ET and Es respectively measured by eddy covariance and micro-lysimeter methods during 2007 and 2008 were used to validate the performance of the Penman–Monteith (PM), the original Shuttleworth–Wallace (SW) and the MSW models in arid northwest China. Results indicate that all three models significantly overestimated ET during the initial crop stage in the both years, which may be due to the underestimation of canopy resistance induced by the Jarvis model for the drought stress in the stage. For the entire experimental period, the SW model overestimated half-hourly maize ET by 17% compared with the eddy covariance method (ETEC) and overestimated daily Es by 241% compared with the micro-lysimeter measurements (EL), while the PM model only underestimated daily maize ET by 6%, and the MSW model only underestimated half-hourly maize ET by 2% and Es by 7% during the whole period. Thus the PM and MSW models significantly improved the accuracy against the original SW model and can be used to estimate ET and Es under the film-mulching condition.

Storage-based Approaches to Build Floodplain Inundation Modelling Capability in River System Models for Water Resources Planning and Accounting

Abstract: Two conceptual storage-based approaches have been developed for incorporating floodplain inundation modelling capability in two water resources planning models. Approach one is a simple method suitable for data limited environment, in which, flow in a river reach within a floodplain is partitioned into two components, in-stream and overbank flow, based on the in-stream capacity. A flood volume-area relationship derived from the flood inundation time series, which is generated by analysing daily MODIS imagery, is used to estimate flooded area for the overbank flow. The losses due to evaporation and groundwater seepage from floodplain are calculated using the estimated flooded area. This approach was implemented in the floodplain area of the Murray-Darling Basin in Australia. The simulated flow was compared with gauged data in 216 stations. The model has produced daily time series of floodplain stores and fluxes. The mass-balance analysis shows that the long term mass balance error was negligible for all floodplain reaches.Approach two is more comprehensive and suitable for areas with high resolution topography data. LiDAR data is used to divide a floodplain into multiple storages based on pre-defined threshold of floodplain inundation heights. The storage characteristics including disconnected storage volume (or, dead storage) and hydraulic connectivity between floodplain storages and a river reach are derived from the LiDAR data using a spatial data processing technique. This information is used to estimate floodplain inundation area for overbank flow. Approach 2 successfully simulated inundation depths, duration and extents in two reaches of Murrumbidgee floodplain. The performance of Approach 2 is highly satisfactory in terms of flood extent, depth and duration at a very high spatial resolution.The key limitations of Approach one are that this approach is unable to produce the spatial variability of floodplain inundation depth and extent and it does not incorporate dead storage. These limitations can be overcome by integrating it with Approach two. A key advantage of Approach two is the quick run time compared to a two dimensional hydrodynamic model. This makes the approach highly suitable to be incorporated in river system models for various scenario analyses for planning and management, which requires the model to run for over 100 years at a daily time step. The limitations of this approach are the requirement of very high resolution topographic data and the inability to produce flood velocity

CO2 partial pressure and CO2 emission in the Lower Mekong River

Available online 29 September 2013Siyue Li | X. X. Lu | Richard T. Bush

Abstract: CO2 evasion from freshwaters is recently included in assessing global carbon budgets, while large uncertainty of global estimates results from incomplete spatial coverage of aquatic carbon emission. Here we examined the dissolved inorganic carbon (DIC) and carbon dioxide partial pressure (pCO2) in riverine water from historical records at 46 stations for the period 1972-1998 in the Lower Mekong River (LMR). The river system presented an exceptional temporal and spatial variability of dissolved inorganic carbon (DIC) species. The alkalinity concentration of the LMR varied from 687-3189 μeq/l with an average of 1524 μeq/l (median value: 1586 μeq/l), 1.2 times the global median value. Spatial patterns showed diminishing alkalinity downstream at the main-channel stations along the LMR. Similar to many other Himalayan rivers, alkalinity varied seasonally and inversely related to river runoff with a variation factor of 1.2-1.6, despite a water dilution of sevenfold to thirteen-fold in the summer flood season. The pCO2 levels ranged from 224-5970 μatm with a total average of 1090 μatm and obvious monthly and spatial variations. Under-saturated pCO2 samples (

Hydrogeochemical characteristics of streams with and without acid mine drainage impacts: A paired catchment study in karst geology, SW China

Available online 29 September 2013Jing Sun | Changyuan Tang | Pan Wu | William H.J. Strosnider | Zhiwei Han

Abstract: A paired catchment study was used to assess hydrochemical characteristics of streams in AMD (acid mine drainage)-impacted and non-AMD-impacted catchments in a karstic region, SW China. The catchments shared similar geology, slope, aspect, area and climate, but different land use since one encompassed mining activities. As a result, hydrogeochemical characteristics of the AMD-impacted water were dominantly controlled by oxidation of pyrite, while that of non-AMD-impacted were influenced by water-rock reactions. It is also coincident with the source of δ34SSO4 in both waters. Upstream, unit ion fluxes of the AMD-impacted catchment for Ca, Mg, H, Fe and SO4 were 17 g/(m2·yr), 2 g/(m2·yr), 0.0002 g/(m2·yr), 17 g/(m2·yr) and 136 g/(m2·yr), respectively, while unit ion fluxes of the non-AMD-impacted catchment were much lower than that of the AMD-impacted catchment. Along the flow, fluxes of H, Ca, Mg, Fe and SO4 decreased in the AMD-impacted water, but increased in the non-AMD-impacted water. The observation was coincident with variations of ion concentrations in both waters along the flow, supported by PHREEQC modeling of minerals such as goethite, jarosite(ss), melanterite, scorodite, calcite, and dolomite. It suggests that the transport of constituents of interest (except for Ca and Mg) is dramatically different in these catchments. Results provide important information on karst system response to AMD, together with the baseline data to understand the degree and type of impairment.

Afforestation and changes in forest composition affect runoff in large river basins with pluvial regime and Mediterranean climate, Chile

Available online 29 September 2013Andres Iroume | Hardin Palacios

Summary: Chile has developed an important economy based on some 2.6 million hectares of planted forests which have been questioned because of their impact on water resources. This report analyses the water response associated with forest plantation expansion and changes in tree species composition in six large river basins (from 94 to 1545 km2) of pluvial regime located between 37°30’ and 39°S in central-southern Chile, an area characterized by a Mediterranean climate. Long term discharge and precipitation records were obtained from national data bases and land uses for different time periods were generated using satellite images and digital maps. Annual water reductions were detected in three river basins where net increases in forested area affected more than the 16% of total catchment area. In the same basins and between the same periods reductions of summer runoff were also noticed although these decreases should be carefully considered as summer runoff also decreases in basins where no significant land use changes occurred. The analysis of the daily flow duration curves indicates that the highest effects occur for Q50% (daily discharge exceeded 50% of time) while Q80%, Q85%and Q90% are much less affected. Although forest plantation expansion and changes in tree species composition have the potential to reduce streamflow, since Q80% and Q90% are used to define permanent and continuous Water Rights according to the Chilean Water Code, it is possible that already existing permanent and continuous water rights could be only marginally affected by the increase of the planted area. The results presented in this document can be used to support discussions related to the development of water allocation regulations among competing economic water users.

Effect of Canopy Interception on Spatial Variability and Isotopic Composition of Throughfall in Japanese Cypress Plantations

Abstract: We conducted a field monitoring experiment examining throughfall in Japanese cypress plantations located in Tochigi Prefecture, eastern Japan. A set of 20 tipping-bucket rain gauges and throughfall collectors were placed in a lattice-like distribution throughout a 10 × 10-m experimental plot to investigate the effect of the forest canopy on the spatial variability of throughfall. The isotopic composition of throughfall and open rainfall were analyzed and compared for each rainfall event. A clear relationship between throughfall rate and the radial distance to the nearest tree trunk was observed when the influence of wind was negligible; however, such a systematic pattern of throughfall was not observed during rainfall events that occurred during windy conditions. The δ18O and δD values in throughfall varied considerably, reflecting different rainwater flow paths in the saturated canopy. The analysis of stable isotope ratios in the throughfall and its comparison with isotopic composition of rainwater hitting the canopy can help elucidate the interception processes in the forest canopy.

Application of natural attenuation for the control of petroleum hydrocarbon plume: mechanisms and effectiveness evaluation

Available online 29 September 2013H.Y. Chiu | A. Hong | S.L. Lin | R.Y. Surampalli | C.M. Kao

Abstract: The objective of this study was to evaluate the effectiveness and mechanisms of natural attenuation (NA) on the remediation of petroleum-hydrocarbon contaminated groundwater caused by gasoline and diesel fuel leakage. During the effectiveness investigation, site groundwater samples were collected and analyzed for the variations in geochemical indicators, microbial diversity, dominant bacteria, biodegradation rates, biodegradation capacity, and the trend of contaminant degradation. Results show that the total BTEX (benzene, toluene, ethylbenzene, and xylenes) concentrations dropped from 9.5 mg/L at the source zone to 0.06 mg/L at a 120-m downgradient line. The calculated BTEX biodegradation capacity (20 mg/L) was much higher than the BTEX concentrations (9.5 mg/L) within the most contaminated area. This indicates that the spilled BTEX could be completely biodegraded through different intrinsic microbial processes using available electron acceptors. Results from polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), and nucleotide sequence analyses reveal that the petroleum-hydrocarbon plume caused the bacterial variation in microbial communities, and more than 27 different petroleum-hydrocarbon degrading bacteria were observed in site groundwater indicating that BTEX could be biodegraded by the intrinsic bacterial consortium. Results also imply that the occurrence of intrinsic biodegradation was the major cause of the limited spreading of the BETX plume and reduction of contaminant concentrations. Results from Mann-Kendall test reveal that BTEX concentrations were decreasing in all monitor wells, and the BTEX first-order NA rate was 5.4×10-4 1/d along the transport path. The observed NA processes within the plume included the following: (1) depletion of electron acceptors (e.g., dissolved oxygen, nitrate, sulfate), (2) production of the degradation products (e.g., ferrous iron, sulfide, methane, CO2), (3) decreased BTEX concentrations along the groundwater flow direction, (4) a decreased trend of BTEX concentrations in monitor wells, (5) increased alkalinity, (6) increased microbial populations, (7) deceased pH in the spill source area, and (8) preferential removal of certain BTEX components along the transport path. Results indicate that NA can effectively contain the plume, and intrinsic biodegradation mechanisms were the major causes for contaminant removal. Results will be useful in applying NA as an alternative option for the management of petroleum-hydrocarbon contaminated sites.

Spatial prediction of flood susceptible areas using rule based decision tree (DT) and a novel ensemble bivariate and multivariate statistical models in GIS

Available online 29 September 2013Mahyat Shafapour Tehrany | Biswajeet Pradhan | Mustafa Neamah Jebur

Abstract: Flood is one of the natural hazards which occur all over the world and it is critical to be controlled through proper management. Severe flood events in Kelantan, Malaysia cause damage to both life and property every year, and therefore the development of flood model to recognize the susceptible areas in watersheds is important for decision makers. Remote sensing (RS) and geographic information system (GIS) techniques could be useful in hydrological studies while they are able to fulfill all the requirements for comprehensive, rapid and accurate analysis. The aim of the current research is to compare the prediction performances of two different approaches such as rule-based decision tree (DT) and combination of frequency ratio (FR) and logistic regression (LR) statistical methods for flood susceptibility mapping at Kelantan, Malaysia. DT is based on the rules which are created precisely and strongly by considering all the characteristics of the variables which can enhance the performance of the flood susceptibility mapping. On the other hand, LR as multivariate statistical analysis (MSA) has some weak points. For that reason, FR was used to analyze the impact of classes of each variable on flood occurrence and overcome the weakness of LR. At first, flood inventory map with a total of 155 flood locations was extracted from various sources over the part of the Kelantan. Then the flood inventory data was randomly divided into a testing dataset 70% (115 flood locations) for training the models and the remaining 30% (40 flood locations) was used for validation purpose. The spatial database includes digital elevation model (DEM), curvature, geology, river, stream power index (SPI), rainfall, land use/cover (LULC), soil type, topographic wetness index (TWI) and slope. For validation both success and prediction rate curves were performed. The validation results showed that, area under the curve for the results of DT and integrated method of FR and LR was 87% and 90% for success rate and 82% and 83% for prediction rate respectively.

Characterization and Quantification of Groundwater Sulfate Sources at a Mining Site in an Arid Climate: The Monument Valley Site in Arizona, U.S.A

Available online 29 September 2013Ziheng Miao | Kenneth C. Carroll | Mark L. Brusseau

Abstract: The Monument Valley site, a former uranium mining site located in the state of Arizona in the Southwest U.S.A, has high concentrations of sulfate in groundwater. Stable isotope analysis of S and O for sulfate, in combination with geochemical and hydrogeological data, was used to characterize the sources and fate of sulfate. The results indicate the existence of two discrete sources of sulfate (in excess of baseline levels): sulfuric acid released during ore processing and sulfate generated via sulfide-mineral oxidation. The contributions of the sources are related to spatial distributions of sulfate in the plume through analysis of groundwater travel times. Quantification of the sources using two isotope-analysis methods yielded similar results. The results indicate that sulfuric acid served as the primary source (mean = 427 mg/L, 69%), with sulfide-mineral oxidation providing a smaller contribution (mean = 147 mg/L, 31%). It appears that the major contribution to the sulfide-mineral oxidation component originates from oxidation of sulfide minerals in exposed bedrock residing in the primary recharge zone of the local aquifer, which provides an elevated sulfate background for groundwater. Conversely, the oxidation of sulfide minerals associated with the mine tailings appears to provide a relatively minor contribution (∼10% of the overall total). Interestingly, it appears that sulfuric acid served as a sustained source of sulfate for approximately 40 years. This may be related to the accumulation of sulfate salts (formed after neutralization and disposal of the sulfuric acid) in the source zone due to the arid climate of the site. Contrary to the typical assumption applied at many mining sites that sulfide-mineral oxidation is the primary source of sulfate, these sulfate salts are hypothesized to be the primary source for this site.

Recent trends in selected extreme precipitation indices in Senegal-A changepoint approach

Available online 29 September 2013Mamadou Adama Sarr | Malicki Zoromé | Ousmane Seidou | Christopher Robin Bryant | Philippe Gachon

Abstract: Precipitation regime is the number one factor in food productivity in the Sahel region. Recurrent droughts have caused several food crises in the region during the three last decades. The situation may not improve as a recent special IPCC report states that West Africa will likely experience longer and more intense droughts (IPCC, 2012) in the near future. As drought adversely affects food security, Sahelian decision-makers need to understand past and current trends in Sahelian precipitation to have some insight in what can be expected for the next five years. In this paper, time series of selected precipitation indices were calculated using 1950-2007 daily precipitation data from 31 stations across Senegal and analyzed for changes in temporal trends using a Bayesian multiple change point detection procedure. The selected indices are the mean (M) and the standard deviation (SD) of precipitation, the frequency of wet days (precipitation using threshold of ⩾ 1mm, Prcpl), the maximum number of consecutive dry days (precipitation

Surface water connectivity dynamics of a large scale extreme flood

Available online 29 September 2013Mark A Trigg | Katerina Michaelides | Jeffrey C Neal | Paul D Bates

Abstract: During flood inundation, river water passes from the main channel into the floodplain through floodplain channels and diffusive overbank flow. This flood water is then distributed within the floodplain depending upon internal connections, barriers and storage, and finally returns back to the river through drainage connections. This surface water connectivity can be complex and is important to many aspects of floodplain functioning, including ecology, sediment movement and flood risk. However, there is currently no accepted way of quantifying this connectivity objectively. We quantify surface water connectivity geostatistically as an objectively measurable characteristic of an observed flood event using a time series of MODIS (Moderate Resolution Imaging Spectroradiometer) surface water product for an extreme large scale flood event (11,000 km2 flooded area and 6 month duration) during 2011 in Bangkok, Thailand. We develop and apply a new gap filling method that better preserves the dynamic information of the event than simple aggregation methods. Comparison of MODIS results with the higher resolution Earth Observer 1 shows fundamental differences in the resolved connectivity with scale despite similar flooded area. The effect of the passage of the flood wave is directly observable in the river reach, as out-of-bank flooding progresses and increases connectivity along the river during rising water. Around peak flow, there is an increase in connectivity of the floodplain adjacent to the river as low lying areas fill. A step increase in connectivity is correlated with a major levee breach. During recession there is a rapid reduction in along river connectivity in the first week after the peak. This rapid reduction contrasted with a slow decrease in the floodplain connectivity as flooded depressions gradually drained reducing depth, while flood extent remained static for long periods. The connectivity analysis of the threshold in floodplain draining indicates that although spatial flood extent changes are small at this time, there is a reorganisation of the internal surface water connectivity within the flooded area. Thus through this measure of connectivity, we can see a clear structure to the event progression with new insights into flood dynamics that were not anticipated a priori.

An assembled extreme value statistical model of karst spring discharge

Abstract: Karst spring discharge processes are complicated and nonstationary, and can be expressed as long-term trends with periodic variation and random fluctuation. Based on the conceptual model, we propose an assembled extreme value statistical model (AEVSM) for obtaining the extreme distribution of spring discharge depletion under effects of extreme climate variability and intense groundwater development. We eliminated the trend and periodicity of spring discharge to acquire the residuals. Using the quantile plot and Kolmogorov-Smirnov methods, it can be demonstrated that the residuals are stationary. The m period return level of the residuals of spring discharge is obtained by using a generalized Pareto distribution (GPD). We thus acquired the spring discharge distribution of extreme values by combining the trend, periodicity and the return level of residuals. We applied an AEVSM to the monthly spring discharge records for Niangziguan Springs in China, from Jan. 1959 to Dec. 2009, and subsequently acquired the spring discharge distribution of extreme values. Results indicate that after Nov. 2014, the depletion rate of Niangziguan Springs discharge will accelerate, and the spring discharge has the risk of flow cessation with probability of 0.01 from Dec. 2021 to Oct. 2023. A 1% probability is admittedly small, but the probability will increase with time. The AEVSM is a robust method for analyzing the distribution of extreme karst spring discharge.

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A muddy megaturbidite in the deep central South China Sea deposited

Mon, 30 Sep 2013 08:17:00 +0000

A muddy megaturbidite in the deep central South China Sea deposited ~350yrsBP

1 December 2013

Abstract: In the central South China Sea basin below 4200m water depth in an area of about 90,000km2 a mud turbidite was observed that is a few centimeters to several tens of centimeters thick and hence, represents a fairly large volume of 15 to 20km3 classifying the deposit as megaturbidite. The host sediment accumulated below CCD and the mud turbidite itself does not contain any carbonate. Nonetheless, emplacement time could be dated by the AMS C-14 method at ~350yrsBP while burrowing organisms that colonized the mud turbidite shortly after deposition stored shells of planktic foraminifera in their burrows. The origin of the mud mass is unknown, but it can be inferred from the grain size at the base of the turbidite that decreases from SE to W and NW. Furthermore, towards its SE tip, the turbidite occurs in a somewhat shallower water depth. These observations and topographical considerations imply the NW margin of Borneo as a possible source area wherein mass movements are known to occur frequently. The mud turbidite is throughout fine-grained and rich in organic matter (~0.8% Corg). The thickness of the cover sediment reflects local variations of sedimentation rate within the central South China Sea basin.

1 December 2013

Abstract: Inshore turbid zone reefs on the Great Barrier Reef (GBR) occur within 20km of the mainland coast under marine environmental conditions (with respect to sedimentation rates, turbidity and water quality) that are generally considered marginal for reef growth. Despite this, data from various benthic habitat assessments report high (>30%) coral cover in these environments and reef core records show them to be characterised by relatively rapid rates of vertical accretion (2–8mm/year), a long-term trend indicative of high net carbonate productivity and in-situ carbonate framework accumulation. However, the lack of quantitative data on terrigenous sediment input and flux rates, and on carbonate production rates has inhibited understanding of both ecological timescale rates of carbonate production and the aggregated long-term net impacts of sediments on reef growth. To address this knowledge gap a modern carbonate budget and terrigenous sediment model, that quantified allochthonous sediment inputs onto, within and off reef, was developed at two inshore reefs: Middle Reef and Paluma Shoals. Both are located within the central region of the GBR and are subjected to high terrigenous sediment load (>11,000tonnes/year) and fluctuating turbidity (5 to >100mg/L) regimes. Based on sediment dynamic modelling, over 81% of sediments delivered were transported off reef, with net sediment accumulation limited to sheltered reef habitats. Net carbonate production was high (>6.9kg/m2/year) due to high coral cover (>30%), high coral calcification rates (Acropora average 6.3g/cm2/year), and low bioerosion rates (0.3 to 5kg/m2/year), but varied spatially with highest net carbonate production (>10kg/m2/year) within deep (>−2m at LAT) windward reef zones. High carbonate framework production has enabled Middle Reef and Paluma Shoals to vertically accrete rapidly: Middle Reef establishing at depths of ~4m, Paluma Shoals at ~3m depth and both reaching sea level in

Frequency and Timing of Landslide-Triggered Turbidity Currents within the Agadir Basin, offshore NW Africa: are there associations with climate change, sea level change and slope sedimentation rates?

Available online 27 September 2013James E. Hunt | Russell B. Wynn | P.J. Talling | D.G. Masson

Abstract: Older sequence stratigraphic models suggested that submarine landslide and turbidite activity is greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level transgressions and highstands. The Moroccan Turbidite System comprises three depocentres, of which Agadir Basin is closest to the Moroccan slope and Canary archipelago. The very large volumes of sediment transported by individual sediment flows in this system suggest that they are triggered by landslides. Extensive core coverage and dating control for the Agadir Basin deposits has provided an excellent opportunity to derive accurate records of turbidite (and associated landslide) frequency for the last 600ka. Previous studies in the more distal Madeira Abyssal Plain depocentre have indicated that large volume (>50km3) turbidites occurred at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that two major turbidites (beds A5 and A12) occurred during glacial-interglacial transitions associated with OIS4 and OIS6. However, this association is based on just two examples, and two other large-volume turbidites (beds A7 and A11), did not occur at a stage boundary. The main conclusion of this study is that 90% of turbidites and landslides occurred during rising and high sea level, which represent 40% of the total time during the last 600ka. Only 10% of the turbidites and landslides occurred during glacials (40% of the time), with a paucity of turbidites and landslides at peak glacial lowstands. A comparison to sediment accumulation rates in the source area of the turbidite, suggests that landslides did not occur preferentially during periods of more rapid sedimentation rate, although sedimentation rates in this area only varied from 4-6 gcm-2ka-1.

Discrimination of sediment provenance using rare earth elements in the Ulleung Basin, East/Japan Sea

Available online 27 September 2013In kwon Um | Man Sik Choi | Jang Jun Bahk | Yun Ho Song

Abstract: In order to discriminate the origins of Ulleung Basin (East/Japan Sea) sediments using rare earth elements (REEs), sediments from 15 box cores and one piston core collected in the shelf, slope, and basin were analyzed for major elements (Al, Fe, Ca, and Mn) and REEs. The major sedimentary components in this basin were presumed to be detrital materials from land, even in the basin sediments, based on Al and organic contents (carbon and opal). Post-depositional recycling processes involving Fe and Mn were identified in the basin sediments. Thus, the Ce anomaly and the fractionation factors of light REEs (LREEs) and middle REEs (MREEs) relative to heavy REEs (HREEs) could not be used as provenance indicators in the deep basin sediments (>2,000m of water depth) based on a feasibility check using their covariation with Fe and Mn. For the shelf, slope, and basin B (sites near islands; water depths of 1,200~1,800m) regions, the Eu anomaly, LREEN/HREEN, and MREEN/HREEN could be successfully used to discriminate possible provenances, including Nakdong River sediments (NRS), Chinese River sediments (CRS), Ulleungdo volcanic rocks (UVR), and Dokdo volcanic rocks (DVR).From the provenance indicators, slope as well as the shelf sediments (called the Korea Strait shelf mud; KSSM) in the Ulleung Basin can be regarded as mixtures of NRS and CRS with decreasing portions of NRS in the KSSM with distance from the Nakdong River. Basin B sediments were mixtures of UVR or DVR and CRS. These findings can be explained if sediments discharged from the Nakdong River were transported and deposited (KSSM) northward within the strong coastal front in normal periods and if sediment flumes from summer floods flowed out across the coastal front, were carried with the Tsushima Warm Current, and then deposited in the slope area. This study indicated that CRS were very important detrital sediments and that REE compositions can be successfully used as a provenance indicator in even hemipelagic sediments close to land.

A quantitative analysis of Recent arid coastal sedimentary facies from the Arabian Gulf Coastline of Abu Dhabi, United Arab Emirates

Available online 27 September 2013Stephen W. Lokier | Alice Knaf | Sean Kimiagar

Abstract: This study presents the results of the first quantitative analysis of surface sediments along multiple transects of the Arabian Gulf shoreline of Abu Dhabi, United Arab Emirates. The natural coastline of this low-angle carbonate ramp depositional system is being anthropogenically modified at an unprecedented rate. As this system is much-employed as a Recent analogue for many ancient depositional sequences, it is imperative that sedimentological characteristics of natural facies occurrences are accurately recorded for employment in future applications. We establish distinct relationships between the geomorphic setting and sediment characteristics. Siliciclastic grains admixed to this system are naturally-sourced from the Pliocene Ghayathi Formation and from aeolian sediment influx during dust storms. This natural source of siliciclastic detritus in being increasingly superseded by siliciclastic material derived from anthropogenic activities. Evaporite minerals are similarly being contributed from anthropogenic sources. The occurrence of mud to silt-grade sediments is primarily controlled by the presence of a sediment-binding microbial mat that prevents the removal of fine material during high energy events. Similarly, the presence of a halite crust in the upper tidal flats and supratidal zone prevents aeolian deflation. This study did not establish any clear relationship between coastal geomorphic setting and the bioclastic components present in the sediments. This finding has major implications for the application of bioclasts in fine-tuning palaeoenvironmental interpretation of ancient carbonate ramp coastal systems.

Abstract: This paper reports a reanalysis of calcification rates of 328 Porites cores from the Great Barrier Reef from which previous workers have concluded that a 14% reduction in calcification rates has occurred between 1990 and 2005. In this reanalysis it is shown that the apparent reduction in the Porites spp. calcification rate in the last two decades is at least partly due to a combination of (a) ontogenetic effects (disregarded in the previous analysis), combined with a highly variable age distribution of the coral growth bands with time, and (b) a systematic data bias clearly evident in the last growth band of each core. When the outermost growth band in addition to bands which have record age less than 20years was excluded from the analysis, the dramatic fall in calcification after 1990 was no longer evident.

Abstract: The nearshore Middle Ordovician (early Darriwilian) deposits of the Baltoscandian Basin, formed on the flank of tectonically stable Fennoscandian Shield, comprise numerous soft-sediment deformation structures. The areal extent of the deformed interval extends up to 9000km2 from NW Estonia to SE Sweden. The deformation structures occur within a meter-scale sandstone horizon that includes load casts, flame structures, ball-and-pillow morphologies, up to 2m wide sedimentary dykes, autoclastic breccias, sand volcanoes, and other related soft-sediment deformation structures. Evidently, these deformation structures formed during a single seismic event that caused liquefaction and fluidization of the water-saturated unconsolidated shallow marine sediments within almost the entire sandstone unit (Pakri Formation). Probably a unique catastrophic earthquake of magnitude 7 or higher occurred in this region penecontemporaneously with the deposition of these sediments. The ultimate cause of seismic event of such magnitude in the tectonically stable Baltoscandian Basin is unclear. However, deposition and deformation of the Pakri Formation fall within the Middle Ordovician meteoritic bombardment period which resulted from the disruption of a large parent body in the asteroid belt approximately 470Ma ago. This in turn suggests a potential impact-origin for the single catastrophic earthquake in the tectonically stable study region. Although impact crater of suitable age is currently not known from the region, then previous studies have documented some impact metamorphic shock lamellae (i.e. PDFs) and abundant extraterrestrial chromite grains from the deformed sediments.

Integration of bed characteristics, geochemical tracers, current measurements, and numerical modeling for assessing the provenance of beach sand in the San Francisco Bay Coastal System

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Erosive effects of the storm Helena (1963) on Basse Terre Island (Guadeloupe

Mon, 30 Sep 2013 03:54:00 +0000

Erosive effects of the storm Helena (1963) on Basse Terre Island (Guadeloupe - Lesser Antilles Arc)

Available online 29 September 2013Pascal Allemand | Christophe Delacourt | Eric Lajeunesse | Olivier Devauchelle | François Beauducel

Abstract: Erosive effects of the tropical storm Helena that hit the volcanic island of Basse Terre (Guadeloupe – Lesser Antilles Arc) on 24 October 1963 has been measured using 80 aerial images acquired by the French geographic institute (IGN-Institut Géographique National) at the approximate scale of 1/8000 less than three months after the storm Helena. On these images, 253 landslides triggered during the storm were identified and mapped. These landslides were located in the central region of the island where catchments exhibit the highest relief. Even though the average thickness of the landslides was only 1m, i.e., less than the thickness of the weathered layer, the total volume of displaced sediments corresponded to an average denudation of 2800 Tons km-2, i.e., 1.4mm, on the watersheds affected by landsliding. To assess the erosional significance of this single climatic event, we compare the volume of sediment mobilized by the storm Helena to the long-term denudation rate. The latter, estimated from a calculation of the total volume of material eroded since the emplacement of lavas using a digital elevation model, is found to be 0.14mm/y. Assuming that Helena is representative of the storms that hit Basse-Terre Island during the Quaternary, we find that a return period of about 10 to 15years is enough to account for the long term denudation rate recorded for this Island. Such a period is comparable with the actual return period of the tropical cyclones of the order of 4 to 5years, suggesting that the erosion of Basse-Terre Island is entirely controlled by tropical hurricanes.

Natural and human influence on loess gully catchment evolution: A case study from Lublin Upland, E Poland

Available online 29 September 2013Józef Superson | Jan Rodzik | Jan Reder

Abstract: This paper presents the functioning of a gully system catchment in the loess area of the Lublin Upland (eastern Poland) based on investigations of soil and sediment sequences filling the valley floors and correlative sediments on the alluvial fan at the valley outlet. Stages of the catchment’s evolution are proposed, from the Meso-Holocene (8400–5100 BP) followed by prehistorical and historical stages of human activity to modern times (gully erosion). Varying erosional processes have been identified over a period of about 2800years BP: washing and sediment deposition on the alluvial fan at early stages followed by multi branched gully system development. Later on, land use change of deforestation and agriculture led to dissection of gully edges by a system of badlands. This study demonstrates the roll of the human factor as a shifting agent between dominant geomorphic processes in the same catchment area over a long period of time.

Ecologically relevant geomorphic attributes of streams are impaired by even low levels of watershed effective imperviousness

Abstract: Urbanization almost inevitably results in changes to stream morphology. Understanding the mechanisms for such impacts is a prerequisite to minimizing stream degradation and achieving restoration goals. However, investigations of urban-induced changes to stream morphology typically use indicators of watershed urbanization that may not adequately represent degrading mechanisms and that commonly focus on geomorphic attributes such as channel dimensions that may be of little significance to the ecological goals for restoration. We address these shortcomings by testing if a measure characterizing urban stormwater drainage system connections to streams (effective imperviousness, EI) is a better predictor of change to ecologically relevant geomorphic attributes than a more general measure of urban density (total imperviousness, TI). We test this for 17 sites in independent watersheds across a gradient of urbanization. We found that EI was a better predictor of all geomorphic variables tested than was TI. Bank instability was positively correlated with EI, while width/depth (a measure of channel incision), bedload sediment depth, and frequency of bars, benches, and large wood were negatively correlated. Large changes in all geomorphic variables were detected at very low levels of EI (

The influence of surface and tectonic processes on landscape evolution of the Iberian Chain (Spain): Quantitative geomorphological analysis and geochronology

Available online 29 September 2013V.N. Scotti | P. Molin | C. Faccenna | M. Soligo | A. Casas-Sainz

Abstract: In tectonically active areas, the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes. We investigated the recent landscape evolution of the Iberian Chain (NE Spain), an intraplate thrust-belt formed in Cenozoic times and characterized by a dome-shaped topography. In its central sector the landscape is dominated by low relief surfaces, Late Neogene(?) in age, presently standing at an average altitude of 1300m. A recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape. In this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters, focusing on topography (map of local relief, swath profiles) and hydrography (basin hypsometric curve and integral, basin asymmetry factor, river longitudinal profiles and relative indices), and using SRTM DEM. The results of morphometric analysis have been coupled with radiometric uranium-series dating of calcareous tufas lying on fluvial strath terraces. The obtained ages allow the estimation of incision rate along the High Tajo and Martin rivers. Our results indicate that uplift and rock-type erodibility are the main factors influencing landscape evolution of the study area. The incision rates are very similar throughout the central sector of the range, indicating that, despite subtle local variation, the rivers are responding to a main tectonic input: the regional uplift. In conclusion, the Iberian Chain landscape is in a transient state in response to a recent dome-like uplift. Indeed, the fluvial processes that weakly incised this landscape at a rate of ~0.6mm/yr are approaching a radial pattern. On the basis of geological and geomorphic constraints, we hypothesize the uplift started around or after 3Ma.

Geomorphic and land cover identification of dust sources in the eastern Great Basin of Utah, U.S.A.

Available online 29 September 2013Maura Hahnenberger | Kathleen Nicoll

Abstract: This study identifies anthropogenically disturbed areas and barren playa surfaces as the two primary dust source types that repeatedly contribute to dust storm events in the eastern Great Basin of western Utah, USA. This semi-arid desert region is an important contributor to dust production in North America, with this study being the first to specifically identify and characterize regional dust sources. From 2004–2010, a total of 51 dust event days (DEDs) affected the air quality in Salt Lake City, UT. MODIS satellite imagery during 16 of these DEDs was analyzed to identify dust plumes, and assess the characteristics of dust source areas. A total of 168 plumes were identified, and showed mobilization of dust from Quaternary deposits located within the Bonneville Basin. This analysis identifies 4 major and 5 secondary source areas for dust in this region, which produce dust primarily during the spring and fall months and during moderate or greater drought conditions, with a Palmer Drought Index (PDI) of −2 or less. The largest number of observed dust plumes (~60% of all plumes) originated from playas (ephemeral lakes) and are classified as barren land cover with a silty clay soil sediment surface. Playa surfaces in this region undergo numerous recurrent anthropogenic disturbances, including military operations and anthropogenic water withdrawal. Anthropogenic disturbance is necessary to produce dust from the vegetated landscape in the eastern Great Basin, as evidenced by the new dust source active from 2008–2010 in the area burned by the 2007 Milford Flat Fire; this fire was the largest in Utah’s history due to extensive cover of invasive cheatgrass (Bromus tectorum) along with drought conditions. However, dust mobilization from the Milford Flat Burned Area was limited to regions that had been significantly disturbed by post-fire land management techniques that consisted of seeding, followed by chaining or tilling of the soil. Dust storms in the eastern Great Basin negatively impact air quality and transportation in the populated regions of Utah; this study details an improved forecasting protocol for dust storm events that will benefit transportation planning and improve public health.

Morphotectonic and neotectonic control on river pattern in the Sierra de la Cantera piedmont, central Precordillera, province of San Juan, Argentina

Available online 28 September 2013Laura P. Perucca | Martín Rothis | Horacio N. Vargas

Abstract: The drainage pattern on the western piedmont of the Sierra de La Cantera is divergent, typical of alluvial fans and showing anomalies that are directly related to the trace of La Cantera thrust. In previous studies, two types of anomalies were identified: upstream of the fault scarp, rivers have a broom-shaped pattern, while downstream -in the hanging block- streams become denser, more sinuous and incised. In this contribution, these morphotectonic aspects were analyzed in detail, making direct and indirect analysis to quantify the relationship between these anomalies and the faults affecting alluvial fans. In addition, the influence of neotectonic activity on smaller water course patterns in the alluvial fan areas was investigated in order to find indicators of on-going vertical movements, since the spatial arrangements of these piedmont channels are determined by slope and structure, where active faults cause diversions or anomalies. Topographic profiles in two selected channels cutting across the trace of the fault were performed using a differential GPS in order to establish the relationship between the sinuosity and slope of these rivers. The results obtained allow us to state that the most sinuous channels have lower slopes and are located in the hanging wall of the fault. Morphometric analysis of scarps stated that active tectonics have played an essential role in controlling the drainage pattern in the piedmont, leading the rivers to adjust to these slope variations.Finally, based on the geomorphologic, stratigraphic, structural and seismological characteristics and parameters analyzed, La Cantera Thrust is considered a seismogenic source of significance to the nearby towns (>700,000 inhabitants) and also to the large-scale dams built downstream along the San Juan River.

A LIDAR, GIS and basic spatial statistic application for the study of ravine and palaeo-ravine evolution in the upper Vipava valley, NW Slovenia

Available online 27 September 2013Tomislav Popit | Boštjan Rožič | Andrej Šmuc | Žiga Kokalj | Timotej Verbovšek

Abstract: The analysis of high resolution airborne lidar topography represents an essential tool for the geomorphological investigation of surface features. Here we present a detailed lidar-based geomorphological analysis of the ravines cut into the slopes of the upper Vipava valley, NW Slovenia. The NE slopes are defined by an Oligocene thrust-front of Mesozoic carbonates overthrusted on Tertiary flysch and covered by numerous fan-shaped Quaternary gravity flows, deposited in palaeo-ravines cut into the flysch base rock. In contrast, the opposite SW slopes are composed solely of flysch. The large dextral-slip Vipava fault extending in the NW-SE direction is present in the central part of the valley. Our research revealed that although the ravines on both slopes of the Vipava valley are lithologically and tectonically controlled, significant statistical differences in their directions exist. Thus, ravines on opposite slopes are not solely related to the Vipava fault system deformation, but instead reflect a more complex tectonic setting. We believe that the ravines are controlled by second-order faults and fault zones that connect the Vipava fault with adjacent faults. On the SW slopes, these include connecting faults between the Vipava and the southwestern Raša fault, with the ravines on the NE slopes formed in fault zones connecting the Vipava and northeastern Predjama faults.

Producing a landslide inventory map using pixel-based and object-oriented approaches optimized by Taguchi method

Available online 26 September 2013
Vahid Moosavi | Ali Talebi | Bagher Shirmohammadi

Abstract: Landslides are considered one of the most important natural hazards. Mapping landslides and producing landslide inventory maps have received special attention from a wide range of specialists. The main objective of this study was to produce landslide inventory maps using advanced pixel-based (ANN and SVM) and object-oriented approaches. The most important challenge in this case is to determine the optimum structure of classification methods. The Taguchi method was to perform optimization of the structure of ANN and SVM and segmentation process in the object-oriented classification method. Results showed that the Taguchi method can be effectively used to cope with this problem. It significantly reduces the number of classification tests. We also showed that there were no significant differences existed between ANN and SVM approaches (χ2 value of 3.33). However, we demonstrated that object-oriented approaches significantly outperformed the pixel-based classification methods (Z value of 5.70) in producing a landslide inventory map. The accurate map produced using an object-oriented approach (overall accuracy of 0.90) effectively determines the shape of landslides and also efficiently shows the intensifying effects of land use changes in the occurrence of landslides.

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3-D Mohr circle construction using vein orientation data from Gadag

Thu, 26 Sep 2013 09:06:00 +0000

3-D Mohr circle construction using vein orientation data from Gadag (southern India) – Implications to recognize fluid pressure fluctuation

November 2013

Abstract: In this paper orientations of quartz veins from the Archaean age lode-gold bearing region of Gadag (southern India) are used to determine the relative stress and fluid pressure (Pf) conditions by constructing 3-D Mohr circle. Anisotropy of magnetic susceptibility (AMS) analysis of the host massive metabasalt reveals that the magnetic foliation is NW–SE striking, which is related to early NE–SW compression (D1/D2 deformation) that affected the region. The quartz veins have a wide range of orientations, with NW–SE striking veins (steep northeasterly dips) being the most prominent. Vein emplacement is inferred to have taken place under NW–SE compression that is known to have caused late deformation (D3) in the region. It is argued that the NW–SE fabric defined the pre-existing anisotropy and channelized fluid flow during D3. The permeability was initially low, which resulted in high Pf (>σ2). 3-D Mohr circle analysis indicates that the driving pressure ratio (R′) was 0.94, a condition that favoured fracturing and reactivation of fabric elements (foliations and fractures) having a wide range of orientations. This led to an increase in permeability and fluid flowed (burped) into the fractures. Resulting vein emplacement and sealing of fractures led to a reduction of Pf (σ2). Thus, it is concluded that the quartz veins in the Gadag region are a consequence of an interplay between conditions that fluctuated from Pf > σ2 to Pf

October 2013

Abstract: The segmented growth of the Markgrafneusiedl normal fault in the late Miocene clastic sediments of the central Vienna Basin (Austria) was investigated by construction of a detailed three-dimensional (3D) structural model. Using high resolution 3D seismic data, the fault surface and marker horizons in the hanging wall and the footwall of the Markgrafneusiedl Fault were mapped and orientation, displacement and morphology of the fault surface were quantified. Individual, fault segments were identified by direct mapping of the deflection of the marker horizons close to the fault surface. Correlating the size of the identified segments with the magnitude of fault drag and displacement distribution showed that fault evolution progressed in several stages. The proposed method allows the detection of segments that are not recorded by the magnitude of displacement or fault morphology. Most importantly, detailed mapping of marker deflections in the hanging wall could help to constrain equivalent structures in the footwall, which may represent potential hydrocarbon traps.

Strain localization in homogeneous granite near the brittle-ductile transition: A case study of the Kellyland fault zone, Maine, USA

Available online 24 September 2013W.A. Sullivan | A.S. Boyd | M.E. Monz

Abstract: We present a detailed case study of a strike-slip shear zone that cut homogeneous granite near the brittle-ductile transition. This zone contains three distinct strain facies: (1) a 2–3-km-wide belt of foliated granite, (2) a 100–300-m-wide belt of small localized shear zones, and (3) a 200–400-m-wide belt of ultramylonite that includes both homogeneous and local pinstripe ultramylonites. The foliated granite formed via dislocation creep of quartz and minor dissolution-precipitation creep and dislocation creep of feldspar under amphibolite-facies conditions shortly after granite crystallization. The localized shear zones and homogeneous ultramylonites formed directly from pseudotachylyte and cataclasite, and they deformed by granular flow—grain-boundary sliding coupled with dissolution-precipitation creep. These deformation features reveal a three-phase rheologic evolution in granite near the brittle-ductile transition. Phase 1 is recorded by the foliated granite, and the rheology was governed by dislocation creep of quartz. Phase 2 was a transient period of brittle deformation and represents a temporal strength maxima in the fault zone. Phase 3 was a long-lived period of ductile deformation, and the rheology was governed by the granular flow mechanism. Strain weakening in this zone was a direct result of grain size reduction and phase mixing during transient brittle deformation.

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15 October 2013

Mon, 23 Sep 2013 05:24:00 +0000

15 October 2013

Abstract: The preserved sedimentary expression of fluvial successions accumulated in salt-walled mini-basins records the complex history of basin subsidence, the style of sediment supply, and the pattern of sediment distribution in response to a range of fluvial processes throughout the evolution of such basins. Temporal and spatial variations in the rate of basin subsidence govern the generation of accommodation space, whereas the rate and style of sediment supply govern how available accommodation is filled; together these parameters act as principal controls that dictate the gross-scale pattern of fluvial sedimentation. Additional factors that influence fluvial stratigraphic architecture in salt-walled mini-basins are: (i) the trend and form of inherited basement lineations and faults that control the geometry, orientation and spacing of salt walls that develop in response to halokinesis; (ii) salt thickness and composition that dictate both the maximum potential basin-fill thickness within a developing mini-basin and the rate of evacuation (migration) of salt from beneath evolving mini-basins, leading to the growth of confining salt walls, uplift of which may generate surface topographic expression that influences fluvial drainage patterns; (iii) climate that dictates fluvial style and the processes by which sediment is distributed; and (iv) the inherited direction of drainage relative to the trend of elongate salt walls and locus of sediment supply that dictates how sediments are distributed both within a single mini-basin and between adjacent basins.Examples of fluvial sedimentary architectures preserved in salt-walled mini-basins from a number of geographic regions are used to illustrate and document the primary controls that influence patterns of fluvial sediment accumulation. The distribution of fluvial architectural elements preserved within mini-basins follows a predictable pattern, both within individual basin depocentres and between adjoining basins: drainage pathways preferentially migrate to topographic lows within basins, such as developing rim-synclines, and away from topographic highs, such as uplifting salt walls or developing turtle-back structures.This paper demonstrates a range of fluvial–halokinetic interactions through consideration of a series of case studies, which demonstrate the current understanding of fluvial response to salt-walled mini-basin evolution and which highlight gaps in the current understanding.

Stratigraphic architecture of alluvial–aeolian systems developed on active karst terrains: An Early Pleistocene example from the Ebro Basin (NE Spain)

15 October 2013

Abstract: During the Early Pleistocene, fluvial, alluvial and aeolian depositional systems interacted in the central Ebro Basin, Spain, constructing wide alluvial plains over a Neogene evaporite substratum. Fluvial sediments, mainly longitudinal gravel bars and channels, are interdigitated with gravel mass flow and distal mudflat deposits. Aeolian sedimentation is registered as aeolian dunes and sand sheets. Episodes of fluvial deposition alternated with periods of alluvial fan progradation and aeolian deposition. These changes are related to climate-driven water availability. Stratigraphic units and deformation structures show synsedimentary karstification of the evaporite substratum that, although karst was not restricted to any particular climate scenario, was probably favoured during periods of high water availability. Karstification conditioned the development of local sedimentary depocentres which, in turn, influenced the distribution of sedimentary subenvironments as well as the accumulation and preservation of aeolian dunes and lacustrine–palustrine deposits. Stratigraphic architecture shows that thickening of the series due to karst subsidence did not occur homogeneously, but was controlled by diachronous subsidence resulting in numerous angular unconformities. In subsiding karst areas transport capacity was reduced and sediment preservation increased.

Alluvial fans and megafans along the southern side of the Alps

Available online 20 September 2013Alessandro Fontana | Paolo Mozzi | Mauro Marchetti

Abstract: The foreland basin of the southern European Alps is characterized by large fan-shaped alluvial systems fed by the main montane valleys and these depositional systems present an extent of 300–3000 km2, with a length of 30–70 km. Most of them are megafans, characterized by evident longitudinal differentiation in which steep piedmont sector consists of amalgamated gravels, while the distal portion has a gradient

Open Access

Drowning events, development and demise of carbonate platforms, and controlling factors: The Late Barremian-Early Aptian record of Southeast France

Available online 20 September 2013Jean-Pierre Masse | Mukerrem Fenerci-Masse

Abstract: In Provence and Languedoc, SE France, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age; their timing, referred to ammonite zones or subzones, is as follows:(1)Late Barremian (D1), at the G.erhardtia sartousiana -Imerites giraudi boundary(2)Middle Bedoulian (D2), at the Deshayesites weissi-Deshayesites deshayesi boundary,(3)Mid late Bedoulian (D3) in correspondence with the “Roloboceras hambrovi subzone”,(4)Late Bedoulian (D4) at the Deshayesites grandis-Dufrenoya furcata transition.Notwithstanding their relatively wide regional, lateral continuity, the depositional hiatus, linkage with exposure, palaeobathymetric range and offset, and geographical extent of drowning discontinuities are not uniform.The late Barremian drowning (D1) is marked either by the development of a permanent intra-shelf basin with ammonites associated with the re-organisation of platform-basin relationships, or by the wide extent of Palorbitolina-Heteraster facies, which develops to the detriment of the antecedent rudist facies. The drowning event is followed by platform recovery during the early Bedoulian, but the corresponding development of shallow water carbonates is subsequently interrupted by the emergence of an uplifted bulge trending sub-parallel to the Provence-Languedoc margin. The Middle Bedoulian drowning (D2) is concurrent with the sealing of the antecedent palaeotopography and the wide development of Palorbitolina facies, then bioclastic and coral facies tend to recover. The Mid late Bedoulian drowning (D3) is characterized by an overall deepening phase, with ammonite-bearing marly facies or cherty limestones, shallow bioclastics being locally present. The late Bedoulian drowning (D4) records the deposition of deep water marls.Evidence is lacking that global sea level changes or transgressive-regressive cycles had a significant impact on drowning events, and some evidence that changes in temperature and productivity of the ocean may have contributed to these phenomena in conjunction with other factors.Through distension fault activity is regarded as a major controlling factor for the origin of the late Barremian deepening event, its associated palaeogeographic re-organisation, ensuing emergence of the Provence-Languedoc marginal bulge and its subsequent detumescence coeval with the Middle Bedoulian drowning. Associated changes in facies types, from rudist to Palorbitolina, reflect sea-water deepening coupled with trophic modifications.As agents of differential subsidence, tectonic phenomena are also testified by the contrasting regional patterns of palaeobathymetric offsets combined with drowning events. They are a clue for understanding thickness changes and coeval modifications in the overall orientation of the progradational polarity of the platform system, towards the adjacent basinal areas.Environmental changes, essentially the two main OAE1a subevents, are regarded as significant agents of the Mid late and late Bedoulian drownings, whereas tectonic processes are also involved in the corresponding deepening. However, the effects of the OAE events on the functioning of the shallow carbonate factory are poorly understood and are still needs to be investigated.The rise in atmospheric carbon dioxide pressure and, as a consequence, the reduction of the calcification potential of benthic organisms, both reported in the literature, are not clearly reflected in the composition of the biota: aragonite-dominated organisms such as caprinid rudists thrive throughout the Bedoulian. The role of acidification in platform demise is therefore questionable.

Demise of Late Triassic carbonate platforms triggered the onset of a tide-dominated depositional system in the Dolomites, Northern Italy

Available online 19 September 2013G. Gattolin | A. Breda | N. Preto

Abstract: Facies analysis of the mixed carbonate-siliciclastic Upper Triassic Heiligkreuz Formation in the Cortina-Tofane area (Dolomites, Northern Italy) shows a tide-dominated sedimentary succession developed in a marine strait environment connecting two small sub-basin on the western margin of Tethys Ocean. Both ebb and flood paleocurrents are preserved and their directions are in agreement with the strait orientation, as inferred from the geographic position of high-relief carbonate platforms in the substrate. Facies and sedimentary structures including planar cross stratification, herringbone cross stratification, flaser to wavy to lenticular bedding and cyclical alternations of mainly oolitic-siliciclastic vs. mainly bioclastic-muddy laminae related to variations of the hydraulic regime have been described and compared with other tide-dominated systems developed in confined marine conditions, and in particular with the Plio-Pleistocene deposits of the central Mediterranean Sea. However, in contrast with all other known cases, this tidal system did not develop in tectonically confined submarine grabens or canyons, but rather in a narrow marine passage between two relict high-relief carbonate platforms.

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A GIS-based volcanic hazard and risk assessment of eruptions sourced

Mon, 23 Sep 2013 04:08:00 +0000

A GIS-based volcanic hazard and risk assessment of eruptions sourced within Valles caldera, New Mexico

Available online 22 September 2013Rebecca Alcorn | Kurt S. Panter | Pece V. Gorsevski

Abstract: The objective of this study is to evaluate the spatial extent of a possible future eruption using a GIS-based volcanic hazards tool designed to simulate pyroclastic fallout and density currents (PDCs) as well as lava flows and to assess the social and economic vulnerability of the area at risk. Simulated pyroclastic fall deposits originating from the El Cajete crater within the Valles Caldera, Jemez Volcanic field, New Mexico, are calibrated to isopach and lithic isopleth maps of the Lower and Upper El Cajete as constructed by Wolff et al. (2011). The change in the axial orientation of fall deposits between the Lower and Upper El Cajete is best matched using seasonal variations in wind speed and direction based on modern atmospheric records. The calibration of PDCs is based on the distribution and run-out of the Battleship Rock Ignimbrite. Once calibrated, hazards are simulated at two other vent locations determined from probability distributions of structural features. The resulting hazard simulation maps show the potential distribution of pyroclastic fall, PDCs and lava flows, indicating areas to the S/SE of Valles Caldera to be at greatest risk.To assess hazard preparedness, social vulnerability is evaluated for all census-designated places (CDP) within the study site. Based on methods by the Hazards and Vulnerability Research Institute, twenty-four variables were selected as proxies of social vulnerability and a principal component analysis is used to generate eight components, which accounts for 64% of the total variance. The eight component scores are summed into a final score for each CDP, and the standard deviations from the mean of the scores is mapped with the CDPs, allowing for an easy visualization of areas considered more socially vulnerable.Economic vulnerability is evaluated through a multi-criteria evaluation of population, infrastructure, road types and land use. Each variable is categorized and assigned a value representing relative vulnerability based on cost and importance. The variables are assigned weights relative to one another through a pairwise comparison and summed together into a final map showing the distribution of economic vulnerability, which is useful when used with the hazard simulation maps for targeting areas for mitigation to reduce economic loss.In order to evaluate the overall risk, the hazard simulation maps and vulnerability assessments are aggregated through weighted linear combination and pairwise comparison matrices, creating a total of three risk maps. Although the actual maps provide greater detail, overall, based on the criteria chosen, the risk maps show that ash fall has the greatest impact, effecting areas up to 50kmS/SE of the Valles Caldera, including highly vulnerable cities, such as Los Alamos and White Rock. The PDCs and lava flow hazards, however, impact significantly smaller areas, primarily disturbing forested land. The methodology presented in this paper allows for a robust analysis of the risks posed by eruptions sourced from the Valles Caldera and is especially useful in focusing mitigation strategies to reduce the loss from such hazardous events.

A model for calculating eruptive volumes for monogenetic volcanoes – Implication for the Quaternary Auckland Volcanic Field, New Zealand

Abstract: Distributed or monogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency. Investigating this in detail is hindered by the difficulty in evaluating ages of volcanic events as well as volumes erupted in each volcano. Eruptive volumes are an important input parameter for volcanic hazard assessment and may control eruptive scenarios, especially transitions between explosive and effusive behaviour and the length of eruptions. Erosion, superposition and lack of exposure limit the accuracy of volume determination, even for very young volcanoes. In this study, a systematic volume estimation model is developed and applied to the Auckland Volcanic Field in New Zealand. In this model, a basaltic monogenetic volcano is categorised in six parts. Subsurface portions of volcanoes, such as diatremes beneath phreatomagmatic volcanoes, or crater infills, are approximated by geometrical considerations, based on exposed analogue volcanoes. Positive volcanic landforms, such as scoria/spatter cones, tephras rings and lava flow, were defined by using a Light Detection and Ranging (LiDAR) survey-based Digital Surface Model (DSM). Finally, the distal tephra associated with explosive eruptions was approximated using published relationships that relate original crater size to ejecta volumes. Considering only those parts with high reliability, the overall magma output (converted to Dense Rock Equivalent) for the post-250 ka active Auckland Volcanic Field in New Zealand is a minimum of 1.704 km3. This is made up of 1.329 km3 in lava flows, 0.067 km3 in phreatomagmatic crater lava infills, 0.090 km3 within tephra/tuff rings, 0.112 km3 inside crater lava infills, and 0.104 km3 within scoria cones. Using the minimum eruptive volumes, the spatial and temporal magma fluxes are estimated at 0.005 km3/km2 and 0.007 km3/ka. The temporal-volumetric evolution of Auckland is characterised by an increasing magma flux in the last 40 ky, which is inferred to be triggered by plate tectonics processes (e.g. increased asthenospheric shearing and backarc spreading of underneath the Auckland region).

Economic impact of explosive volcanic eruptions: A simulation-based assessment model applied to Campania region volcanoes

Available online 21 September 2013Giulio Zuccaro | Mattia Federico Leone | Davide Del Cogliano | Angelo Sgroi

Abstract: PLINIVS Study Centre of University of Naples Federico II has developed a methodology that aims to estimate, in probabilistic terms, the direct and the indirect economic impact of a Sub-Plinian I or Strombolian type eruption of Vesuvius. The economic model has been implemented as a complementary tool of the Volcanic Impact Simulation Model, a tool developed at PLINIVS Center available to the Italian Civil Protection Department (DPC) decision makers to quantify the potential losses consequent to a possible eruption of Vesuvius or Campi Flegrei. Along the expected time history of the eruptive event all the possible “direct costs” and the “factors” (indirect costs) impacting the economic growth in the event area have been identified. Each cost factor is built up through a specific algorithm that is fed by various providers, in order to run a software that will estimate the global amount of economic damage from a volcanic event. The model does not include the economic evaluation of intangibles (e.g. human casualties), while the evaluation of damage to the local cultural heritage (historical buildings, archaeological sites, monuments, etc.), is linked to the economic impact on tourism, estimated into indirect costs. The architecture of the model is based on a simulation logic, which allows an evaluation of different economic impact scenarios through inputs changes, allowing the model to be used as a tool to support the decision making process.

Late glacial explosive activity on Mount Etna: Implications for proximal–distal tephra correlations and the synchronisation of Mediterranean archives

Abstract: Plinian and Ignimbrite deposits represent explosive activity (ca. 17–19calka) within the predominantly effusive and mildly explosive (Strombolian) volcanic history of Mount Etna (Italy). Proximal glasses from the Biancavilla Ignimbrites and Unit D Plinian fall deposits are characterised. Fall deposits recorded at Acireale (D1b and D2b) and Giarre (D1a and D2a) are geochemically distinct confirming they relate to different eruptions. The Acireale Plinian fall (D1b and D2b) deposits compositionally overlap with the Biancavilla Ignimbrite deposits. These explosive eruptions from Etna are considered responsible for widespread ash dispersals throughout the central Mediterranean region, producing the marker tephra layers (Y-1/Et-1) recorded in marine and lacustrine sedimentary archives. Stratigraphically these distal tephras occur at or close to the onset of the last deglaciation (Termination 1) within their respective palaeoenvironmental records, therefore making them potentially crucial tephrostratigraphic markers. This study investigates distal tephra deposits thought to be from Etna recorded in the Ionian Sea (Y-1), Lago Grande di Monticchio (LGdM, Italy; tephras TM-11 and TM-12-1), Lago di Mezzano (Italy) and the Haua Fteah cave (Libya). The glass chemistry of Y-1 tephras recorded in the Ionian Sea and at Haua Fteah is consistent with the Biancavilla Ignimbrites (16,965–17,670calyrs BP) and the upper Acireale Plinian fall (D2b). The LGdM record indicates that explosive activity on Etna associated with Unit D spans a minimum of 1540±80 varve years. TM-12-1 (19,200–19,804calyrs BP) in LGdM appears to represent the oldest distal counterpart of Etna Unit D explosive activity and is associated with the lower Acireale (D1b) Plinian eruption. The proximally undefined TM-11 (17,640–18,324calyrs BP) and distal correlatives are geochemically distinct from the Ionian Sea Y-1 tephra. Such significant compositional differences seen between distal tephra layers are not observed within individual proximal units and are likely to indicate that the distal tephras relate to separate eruptive phases. Until proximal relationships can be established, the TM-11 type Y-1 equivalents should be termed TM-11. Great care should be exercised when using these distal ash layers to synchronise sedimentary records during a crucial period of environmental change.

15 August 2013

Abstract: Effusion rate is a key parameter to model lava flow advance and associated risks. Estimation of effusion rate from thermal remote-sensing using satellite data has matured to the point where it can be an operational monitoring tool, notably for volcanoes without a ground observatory. However, robust physical models, as required for quantitative interpretations, have not yet been adequately developed. The current and widely used method relates the satellite-measured radiated power to the flow effusion rate through the lava area, with an empirical fit that assumes a low surface cooling efficiency. Here we use novel fluid dynamic laboratory experiments and viscous flow theory to show that assuming low convective cooling at the surface of the flow leads to a systematic underestimation of the effusion rate. This result, obtained for the case of a hot isoviscous gravity current which cools as it flows, relies only on the respective efficiency of convection and radiation at the flow surface, and is independent of the details of the internal flow model. Applying this model to lava flows cooling under classical wind conditions, we find that the model compares well to data acquired on basaltic eruptions within the error bars corresponding to the uncertainties on natural wind conditions. Hence the thermal proxy deduced from the isoviscous model does not seem to require an additional fitting parameter accounting for internal flow processes such as crystallization. The predictions of the model are not correct however for thick lava flows such as highly viscous domes, because a thermal steady state is probably not reached for these flows. Furthermore, in the case of very large basaltic flows, extra cooling is expected due to self-induced convection currents. The increased efficiency of surface cooling for these large eruptions must be taken into account to avoid a gross – and dangerously misleading – underestimate of the effusion rate.

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15 August 2013

Thu, 19 Sep 2013 09:38:00 +0000

15 August 2013

Abstract: Our study is aimed to develop a 3D physical model of the Campi Flegrei geothermal system, in order to achieve a more accurate and comprehensive representation of the hydrothermal processes occurring in the caldera. The new model, developed by using the TOUGH2 code simulator, accounts for the caldera rocks' physical properties, bathymetry and water table topography. In particular, the computational domain is constrained by density values obtained by tomographic inversion of gravity data collected during several surveys at CF both onshore and offshore the caldera. Empirical relations between density and porosity and between porosity and permeability, derived by published data on samples cored in deep wells or collected in outcrops, allowed us to characterize the main rocks physical parameters controlling the dynamic of the CF geothermal system. We have performed and compared several simulations investigating the effects of the injection at depth, underneath Solfatara crater, of a hot gaseous mixture rich in CO2. We show that, with respect to the available literature on 2D axisymmetric models, the effects of the water table topography together with the bathymetry and the heterogeneous distribution of the rocks' physical properties, lead to important differences in the hydrothermal circulation of fluids at CF. These constraints allow the activation of convective cells with different behaviors, which produce variable patterns of temperature inside the hydrothermal system. As a consequence, the predominant effect is again represented by a central plume below the Solfatara crater, but with a non-axisymmetric structure and a wider extension. Additionally, high temperature zones are present near the coastline and in the middle part of the submerged area of the caldera with a SE–NW alignment.Moreover, our results indicate that, the submerged part of the CF caldera would deserve a more accurate study and survey, being affected by phenomenon of heating and degassing. This information could be very useful in terms of hazard assessment and volcanic risk mitigation in such an active and densely inhabited volcanic and geothermal area.

15 August 2013

Abstract: El Barronal complex consists of a succession of andesite lavas and andesite volcaniclastic facies interbedded with carbonate and siliciclastic sedimentary rocks. Carbonate and siliciclastic rocks were deposited in a shallow-marine environment during periods of volcanic quiescence. Lavas consist of an inner coherent core grading outward into hyaloclastite breccia made of dense clasts that in turn grade into hyaloclastite breccia made of vesicular clasts, in massive to layered zones. Volcaniclastic facies contain clasts produced during explosive eruptions and reworked clasts from sources above wave base. Volcaniclastic facies were deposited from cold granular flows with different grain size populations. Stratigraphy and facies architecture at El Barronal suggest that a succession of several discrete eruptive events occurred with a similar cyclic pattern made of an initial explosive phase followed by effusive emplacement of lavas, in turn followed by a period of quiescence of volcanic activity. Hyaloclastic fragmentation of magma took place in the final stages of lava emplacement, allowing only for local disorganization of the jigsaw-fit texture.

15 August 2013

Abstract: Understanding the underlying structure of data from volcano monitoring is essential to identify precursors to changes in eruptive activity and to comprehend volcanic processes. However, effective analysis of longer-term trends in these signals is challenging as volcanic data are not necessarily statistically stationary or linear, particularly those from lava dome-forming volcanoes, which are commonly characterised by pulsatory eruptive activity. Here, we use detrended fluctuation analysis (DFA), a statistical technique previously applied to nonstationary data, to identify long-range (slowly decaying, e.g. power-law) correlations in a number of time-series of volcano seismicity recorded during the recent dome-forming eruptions of Volcán de Colima, Mexico, and Soufrière Hills Volcano, Montserrat. For all the time-series analysed, correlation strength varies through time and/or on different timescales; in some cases, this variation is periodic, seasonal, and/or related to activity. These results may provide new insights into eruptive processes and possibly further constrain the generation mechanisms of a number of the volcano-seismic event classes analysed. Furthermore, the correlation properties of real-time seismic measurements are shown (retrospectively) to contain information valuable to real-time volcano monitoring that is not identifiable by conventional analysis techniques. This study therefore demonstrates that long-range correlation analysis may be useful for extracting additional information from monitoring data at dome-forming or similar volcanoes.

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