Structural Geology

Thursday video: structural geology I

2012-05-31T19:43:00.000+01:00

Today's video introduces structural geology (part I). It is presented by Jonathan Bergmann and includes an interview with Dr. Randall Marrett. It is a good introduction to our little corner of the geological room, and it may be useful if you are deciding now what do you want to have as a profession later on. Be aware: structural geology is cool!!

If you are studying geology in school, or in college, this video is also useful for introducing the basic concepts of structural geology. If you have any questions... well, just ask, that is why there are comments in this blog!

Enjoy!

(yep, I know... I forgot to upload the video yesterday... ahem...)

Thursday video: Difference between crust and lithosphere

2012-05-24T22:26:00.001+01:00

Mechanical and chemical division of Earth.

Today's video deals with a topic of tectonics: the difference between crust and lithosphere. Many people mix these two things, and hopefully this video will help you to know when to talk about crust, and when to talk about lithosphere. It is very easy, but many people just don't pay enough atttention!

This video has been produced by Khan Academy, a non-profit organisation which aims "to provide a high education to anyone, anywhere". A really good initiative. Visit their site here, where you will find many resources of virtually anything!: www.khanacademy.org

Enjoy!

Source: http://www.youtube.com/watch?v=f2BWsPVN7c4

Thursday video: the Variscan orocline in Iberia

2012-05-17T05:30:00.000+01:00

An orocline is an orogenic belt where a change in horizontal direction occurs, characterising the mountain belt by a horizontal curvature or a sharp bend. We can find examples of oroclines in pretty much everywhere. A famous orocline are the Carpathians Mountains, formed by the subduction and continental collision between the European and the Apulian plates during the Alpine orogeny.

The Variscan orogen in Iberia also forms a remarkable orocline (but much older than the Carpathians!), and this video shows its evolution, with emphasis in the different timing of granitic bodies emplacement. Very interesting indeed!

This video is the companion of a paper published in Tectonics last year by a series of researchers From the ODRE group (University of Salamanca), Universidad Complutense de Madrid, Natural History Museum of London, University of Victoria and St. Francis Xavier University, both in Canada.

Gutiérrez-Alonso, G., J. Fernández-Suárez, T. E. Jeffries, S. T. Johnston, D. Pastor-Galán, J. B. Murphy, M. P. Franco, and J. C. Gonzalo (2011), Diachronous post-orogenic magmatism within a developing orocline in Iberia, European Variscides, Tectonics, 30, TC5008, doi:10.1029/2010TC002845.

U-Pb (zircon) crystallization ages of 52 late-Variscan granitoid intrusions from NW Iberia (19 from new data, 33 from previous studies) constrain the lithospheric evolution of this realm of the Variscan belt of Western Europe and allow assessment of the relationship between oroclinal development and magmatism in late-Carboniferous-early Permian times. The U-Pb ages, in conjunction with a range of geological observations, are consistent with the following sequence of events: (i) oroclinal bending starts at 310--305 Ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts; (ii) between 305 and 300 Ma, melting continues under the outer arc of the orocline (Central Iberian Zone of the Iberian Variscan belt) and mid-crustal melting is initiated. Coevally, the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure; (iii) between 300 and 292 Ma, foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle; (iv) cooling of the lithosphere between 292 and 286 Ma resulting in a drastic attenuation of lower crustal high-temperature melting. By 285 Ma, the thermal engine generated by orocline-driven lithospheric thinning/delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts. The model proposed explains the genesis of voluminous amounts of granitoid magmas in post-orogenic conditions and suggests that oroclines and similar post-orogenic granitoids, common constituents of numerous orogenic belts, may be similarly related elsewhere.

Thursday video: strike and dip

2012-05-10T00:30:00.000+01:00

If you don't have clear what is dip and strike, then take a look to this video. I am planning to post more advanced stuff, but this blog is open to everyone and of course, many different levels of knowledge.

BUT... have in mind that this video could be more precise when she talks about anticlines and synclines in the first slide, and about the direction of strike (which... I wrote some months ago about it). In any case, it is a good introduction for students and the general public.

Enjoy!

Thursday video: Debunking expanding Earth

2012-05-03T06:00:00.000+01:00

Where the mass comes from?

Have you ever heard about the "Expading Earth" hypothesis? Have you ever watched or even listened to the videos posted in YouTube by comic artist Neal Adams? Well, then you may be as amazed as I am by the imagination and persistence of this man.

Neil defends the idea, and even calls it "theory" (sorry Neil, but yours is not a theory... check out in some dictionary what is the scientific meaning of theory), that our planet Earth is in constant expansion, and there is a conspirancy and cover up of these "facts". Well... this is funny up to some point. The truth is that this is quite sad, because YouTube is a website that many kids use and it end up spreading this unscientific positions. But, how a 12 year old kid may know that?

If you have ever had to answer to some friend why the Earth doesn't grow, if you have ever found a person who thinks that Neil* is right and the rest of the world is wrong... Well, watch this video, produced by "potholer54", an Australian journalist with many interesting videos. Send it to your friends, to the ones who think science is about covering facts!

Have fun... and I will try to post something more serious next Thursday. Or perhaps we will discuss why Earth is not flat :0)

*Well, he and a few more: http://en.wikipedia.org/wiki/Expanding_Earth

How to calculate an apparent dip from a real dip (and viceversa) using orthographic projection and trigonometry

2012-05-01T20:14:00.000+01:00

Any student of geology in any university in the world learn during its degree the relationship between the real dip and the infinite apparent dips that a plane contains. Most of students learn how to calculate a real dip from a couple of apparent dips or, inversely, how to work out an apparent dip given the real dip and another direction using the stereonet.

Stereographic projection provides an awesome graphic method for these calculation, which is very useful if one has to do a bunch of calculation, but it is not very useful if we have to deal with a large collection of data, or if we need to have a high degree of precision. Then, it is time for orthographic projections and the always useful trigonometry.

Let's imagine that we have a known plane, and we need to calculate an apparent dip. We know the dip angle and the dip direction or strike, and obviously we know the direction along we want to know the apparent dip. In this context,

δ = real dip. Note that the real dip is always measured along the maximum slope direction for a plane. No apparent dip can be larger than the real dip.

α = apparent dip. This is the dip measure along a line which is not the maximum slope direction.

β = angle between the strike direction of the plane and the apparent dip direction.

You could think that it is difficult, but it is actually quite easy. The "trick" lies on relating the three triangles involved in the diagram (one containing a and b, another containing c and b, and another containing a and c). (Note that c is the hypotenuse of the horizontal triangle)

The following trigonometric relations are quite straight and don't need much explanation:

(1) sin β = a/c; a = c ∙ sin β

(2) tan δ = b/a; b = a ∙ tan δ

(3) tan α = b/c; b = c ∙ tan α

(4) b = a ∙ tan δ

(5) b = c ∙ tan α

(6) a = c ∙ sin β

Clear so far? Now, if you equal (4) and (5), and substitute a by (6),

(7) a ∙ tan δ = c ∙ tan α

(8) c ∙ sin β ∙ tan δ = c ∙ tan α

(9) sin β ∙ tan δ = tan α

what you obtain is a direct relation between α and δ. If you want to know the real dip from an apparent dip, use (11). If you want to calculate the apparent dip from the real dip, then use (10)

(10) α = arctan (sin β ∙ tan δ)

(11) δ = arctan (tan α / sin β)

Easy, isn't it?

Why you would need to use that? Well, for example, I need it sometimes; I work interpreting satellite images, focusing on structural geology. When I measure fracture lengths on a plane, I cannot really measure their length: What I measure is an "apparent length". That means, I measure the projection of a line on a horizontal plane. For example, a 100 m fracture on a plane dipping 80 degrees will look very short if the direction of that fracture is the dip direction of the plane, but it will look as 100 m if the fracture is oriented along the strike. Any direction in between, will be variable. If it is variable, how can we correct it? knowing the apparent dip in that direction.

This method provides a way of correcting this distorsion, simply using any spreadsheet. You know the length of every single fracture, and the length you have measured. You also know the real dip of the plane (well, I can measure it on the DEM!), the strike, and that is all you need to know. But this will be another explanation, coming soon :-)

Feel free to make any comments, or perhaps any correction of suggestion. Hopefully this has been useful for you.

Geo-vandalism in Bartlett Wash, Utah

2012-04-27T09:51:00.000+01:00

Dr. Bruce Trudgill (assistant professor at Colorado School of Mines) has reported in the Geotectonics email list an act of geo-vandalism in the Bartlett Wash outcrop, in southeast Utah (USA).

Quoting Bruce,

Many of you may have visited this spectacular location on university or industry field trips, or for your own research purposes. The location of the exposure is on a splay off the main Moab Fault, and it illustrates many aspects of brittle deformation and fluid flow, as well as some un-paralled exposures of aeolian dune sets in the Slickrock member of the Entrada Formation. It's a truly world-class field location and has been used in a number of publications and texts, including the following figure in Haakon Fossen's structural geology textbook.

Figure 8.11 in Structural Geology by Haakon Fossen (Cambridge University Press)

One of the key aspects of this location is the 100% exposure of deformation bands in the footwall of the fault and their relationship to fluid flow. Students can measure and plot deformation band density in the footwall of the fault and it's a great location to discuss their influence of fluid migration. Anyway, this (formally) pristine outcrop is now missing a few of the deformation bands in Haakon's photo due to some mindless geo-vandalism (see below)

Photo taken by Roy Luck on September 29th 2011.......note the rock powder spread around the outcrop showing evidence of very recent cutting

[end of quotation]

The exact coordinates of the affected area are 38° 43' 00.09" N 109° 47' 17.85" W:

View Larger Map

This act of vandalism took place between 25th and 29th of September 2011. The following picture portraits Bruce on the 25th, early evening:


Bruce Trudgill in the intact outrop. Red circle shows the area later on vandalised by unknown people.

If you know who has done that, you should contact Bruce (http://geology.mines.edu/faculty/btrudgil/) or Becky Doolittle (rdoolitt at blm (d.o.t.) gov) at the Bureau of Land Management. Vandalism is an act of crime.

Why people do that? Reasons (excuses?) are not short. Some people do it for an economic interest: Nice primary or secondary structures, fossils, minerals, etc, are aesthetically attractive, and they can be sold for good money. Researchers need to take samples. But things can be done right, or wrong. Cutting off a cube of rock with an electric saw in an outstanding outcrop, in such a visible place, is plainly wrong.

If the responsible guys of this act of vandalism are researchers, sooner or later others will know. They will be the ones who spoilt Bartlett Wash. For future researchers, think twice what you do on the field, and think how would you like to find an outcrop if you would be the next person to arrive. You are scientist, full stop. Preservation of nature has to be your main objective, always.

Thanks Bruce for raising the voice about this sad issue. Many of us have never been there, or even near, but that doesn't mean we don't feel something has to be done. Thanks also for the pictures and the permission for the quotations!

Thursday video: The Magic Toilet Paper

2012-04-26T06:30:00.000+01:00

Thursday video will be a fixed section in this blog where we will link toYouTube clips (or other sites, of course!) related with tectonics and structural geology. If you want some video displayed here, please feel free to let me know and I will do it.

Let's start with this video from the Structural geology, Tectonics and Geomechanics Research Group of the University of Aachen (Germany). It shows a toilet paper roll being compressed, and behaving like a multilayer. It develops some chevron folds and kink bands, and what it is very interesting, you can do that at home with some DIY skills...

Ladies and gentlemen... "The Magic Toilet Paper"!

You can subscribe to their YouTube channel, or follow them in Twitter. Anyway, you can be sure they will be regularly featured here, as they have been doing for some time very nice and cool stuff.

USGS make available topographic maps online

2012-04-19T13:30:00.002+01:00

USGS has just announced that their historic collection of topographic US maps goes digital. More than 161,000 maps have been digitased and made available online here: http://nationalmap.gov/historical/

If you are a student in the US, that should be good news for you, as you won't have to spend a dollar in maps for working in your own doing geological mapping. Which you should do, as practise makes perfection! ;-)

Extensional grabens in our shrinking Moon

2012-02-28T21:54:00.001Z

The largest of the observed grabens with the
Narrow Angle Camera (NAC) of the LRO spacecraft.
It is about 500 m wide, and nearly 20 m deep.
(Credit: NASA/Goddard /
Arizona State University/Smithsonian Institution)

Who has not read a thousand times that our Moon is a death body without any activity? Well, it turns to be the opposite: The Moon has been active at least until very recent times, and very likely this activity continues now.

Lunar Reconnaissance Orbiter (LRO) spacecraft has obtained images of the surface of our satellite where extensional faults are clearly visible. NASA estimates that this faults are not older than 150 million years, which is pretty young for what we expected to be the lunar tectonics.

Two years ago, the Lunar Reconnaissance Orbiter mission also detected other young geological features, which where interpretd as compressional uplifts. It was said, at that time, that the Moon is shriking. But the identification of extensional faults shows that this shrinking (due to thermal contractions) is not homogeneus everywhere.

But why not listening directly to Tom Watters from the Smithsonian Institution? (You can also active the subtitles!):

Diagram of formation of a graben with two bounding faults (Credit: Arizona State University/Smithsonian Institution)

Read more here: http://www.nasa.gov/mission_pages/LRO/news/lunar-graben.html

The origins of plate tectonics, with Dan McKenzie and Fred Vine

2012-02-23T23:13:00.000Z

The Geological Society of London opened a few months ago a channel in YouTube with the aim of reaching a larger audience through divulgation videos.

Yesterday, The Geological Society uploaded a very interesting inteview to Dan McKenzie and Fred Vine, where they discuss the early history of development of the theory of plate tectonics. The clip is taken from 'Dan McKenzie and friends: highlights from the Bullard labs'. [Copyright: 2011 Cambridge University (Depart. of Earth Sciences)].

Enjoy it!

http://www.youtube.com/watch?v=MQY-aaXz2c4

Structural Geology Lab Manual by David Allison

2012-02-21T20:03:00.002Z

A structural geology laboratory manual comes always handy to anyone dealing with maps, cross-sections or stereograhic nets. Even those experienced geologists who have left their university days left behind the mist of time need to have one. Many techniques are learnt, but soon leave room in our room for other issues that may be even more important (e.g. telephone number of the canteen waitress, local pubs near an outcrop, and so forth...)

There are methods in structural geology that if one doesn't use them regularly, soon become rusty and we simply need to refresh them from time to time: how to rotate lines and planes with a stereonet, how to solve a three-point problem, etc.

Today I'd like to present you an excellent structural geology lab manual, written by David T. Allison, an associate professor of geology of the Department of Geology and Geography of the University of South Alabama:

http://www.usouthal.edu/geography/allison/GY403/StructuralGeologyLabManual.pdf

The manual contains explanations and exercises on attitude measurements, true and apparent dips, three-point problems, stereographic projections, rotations with the stereonet, stereograms, geologic mapping and cross-section construction, thickness and outcrop problems ans statistical techniques.
It is written in a very approachable style, and completed with good figures that will help anyone to understand and practise the foundations of our profession or studies.

The text makes reference to several spreadsheets that you can find in the homepage of the author:

http://www.usouthal.edu/geography/allison/

I hope you find it useful. Comments are welcomed, as usual!

Vote for my photobook

2012-01-24T09:44:00.000Z

Last winter I created a photobook for my dad. He doesn't have a computer, and I thought it would be nice to show him my pictures together with a (not mine!) poem that reflects my thoughts about each photo.

http://www.bobbooks.co.uk/bookshop/users/JorgeGines/visiones-versos-viajes/

I won the "Best book of March" award, and now I am compiting in the "Best Photobook of the Year 2011" contest. Competition is hard!.

The prizes are a couple of Olympus PEN cameras for the winner and for the runner-up. You know how much I love photography, so... Would you vote for me? :-)

In order to vote...

a) Register at: http://www.bobbooks.co.uk/register.html

b) Vote for me! Just click on "Vote for this book" in http://www.bobbooks.co.uk/bookshop/users/JorgeGines/visiones-versos-viajes/ . It couldn't be easier!

Bobbooks offers, by the way, an amazing quality, great value for money. Highly recommended, and a great idea for a personal present.

Important note: Let me know if you have voted. I will raffle, if I win, a £50 gift voucher from www.bobbooks.com amongst those voting for me!

Thanks!

Steno's 374th birthday in Google's doodle

2012-01-11T09:36:00.000Z

Google dedicates today their doodle to Nicolas Steno, who is considered as the father of geology and stratigraphy. Steno was born in Denmark on a 11th of January, in 1638. Happy 374th birthday, Steno!!

Check www.google.com, or your regional version of Google, and you will see the doodle in action.

Isn't nice to see geology portrait in such a colourful way? I love it!

The Girl with the Cross-section Tattoo

2012-01-05T14:04:00.000Z

Yesterday, I was looking for an article in the New Scientist website, and I found this another article by chance: "The best science tattoos and the stories behind them"

What is the first thing you see? A cross-section tattooed on the shoulder of Helen Malanda, a geology postgraduate student.

The tattoo is portraited in the latest book by Carl Zimmer - "Science Ink; Tattoos of the science obsessed". See more about it here and here.

Oh, and happy New Year! This is post 100th, by the way!

(Image by Helen Malanda/Sterling Publishing)

Visible Geology: a visualisation tool

2011-10-27T07:25:00.000+01:00

Rowan Cockett's Visible Geology is an interactive tool for visualising geological structures, ideal for teaching and also for self-study. Visible Geology is highly interactive and web-based, so the only thing you need for using it is a HTML5 compatible browser (basically, not IE). I am really impressed by this simple but complete application.

http://visible-geology.appspot.com/

In Visible Geology you can create block diagrams for illustrating bedding, faulting, folding and intrusions (dykes).You can keep this blocks as a simple cube, or what is really nice, is that you can modify the topography. You can model top surface of the cube with a couple of easy options, drawing contour lines or selecting predefined patterns (like valleys, slopes, mountain tops, etc.).

But it doesn't end there. Once you are happy with your model, you can even do cross-sections!

So, easy to use, quick (very quick), very nice results... I am just looking forward having the chance of using it for some report!

But surely the best thing is to start watching one of the available tutorials in video:

Visible Geology is in a beta status at the moment. I would suggest the following features for future versions:
- Capability for choosing bed thickness.
- Variable scale.
- Folding would improve several orders of magnitude if it would be possible to change basic parameters such as amplitude, wavelength, etc.

It is really a great program, and I am sure it will be soon widely used in education. Go to use it, go!

Thanks Rowan!

Björk, Biophilia and plate tectonics

2011-10-14T06:23:00.000+01:00

Did you ever imagine I would write about music here? No, of course not. And that was because Björk didn't compose before her new "Biophilia" album, a masterpiece of modern music that aims to mix music, technology and science. Actually, the album has been released as a traditional CD but also as an application for your smartphone. I will leave the review and explanation of the album to other people: CultureLab interview with Björk. (Yes! Bjork in "New Scientist"!).

So, why I write about "Biophilia" in this blog, afterall? Well, first, becuase I love this album and anything that comes out of Björk's mind, and second, because the 8th track of the album deals with... yes, plate tectonics! "Mutual Core" is the 9th track of the album. A song with absolutely explicit scientific lyrics, full of metaphors that we, geologists, will love ("As fast as your finger nails grow/the Atlantic ridge drifts","My Eurasian plate subsumed,/ Forming a mutual core"). I find it absolutely hypnoptic, beautiful and, why not, magnificient.

"Mutual Core"

I shuffle around the tectonic plates in my chest.

You know I gave it all,
Try to match our continents
To change seasonal shift,
To form a mutual core.

As fast as your fingernail grows,
The Atlantic ridge drifts
To counteract distance.

You know I gave it all,
Can you hear the effort of the magnetic strife?
Shuffling of columns
To form a mutual core.

This eruption undoes stagnation.
You didn't know i had it in me,
Withheld your love, an unspent capsule.
I didn't know you had it in you,
You hid the key to our continuity.
I didn't know you had it in you.
This eruption undoes stagnation.
You didn't know, you didn't know.

What you resist persists, nuance makes heat
To counteract distance
I know you gave it all,
Offered me harmony if things were done your way.
My Eurasian plate subsumed,
Forming a mutual core

This eruption undoes stagnation.
You didn't know I had it in me,
Withheld your love, an unspent capsule.
I didn't know you had it in you.
This eruption undoes stagnation
You didn't know i had it in me
This eruption undoes stagnation
You didn't know, you didn't know”

DRT2011 fieldtrips - Photoalbum

2011-10-02T19:57:00.001+01:00

DRT2011 fieldtrips, a set on Flickr.

A the end of August and beginning of September, I attended the DRT 2011 meeting in Oviedo. This meeting included two fieldtrips, and these are the pictures I took during this great days back home in NW Spain.

I hope you enjoy them. I will be completing slowly their description, but in the meantime, if you have any question about the pictures, just let me know here in this post and I will try to answer your doubts.

There are nearly 150 pictures, so take it easy!

J.

Flying over planet Earth

2011-09-22T18:17:00.006+01:00

Made by http://infinity-imagined.tumblr.com/, using data from NASA (http://eol.jsc.nasa.gov/sseop/mrf.htm)

Beautiful, isn't it? Pay attention to the thunderstorms visible from 0'20"!!

Short course: Structure, permeability and fluid flow at depth in the Earth's crust

2011-09-20T06:58:00.001+01:00

From October 11th to 13th will take place a short course at the RWTH Aachen University on Structure, permeability and fluid flow at depth in the Earth's crust, given by Prof. Stephen Cox.

You can have more information following this link.

6.9Mw earthquake in India, Nepal and Tibet

2011-09-19T12:20:00.000+01:00

A 6.9 Mw earthquake hast struck India, Nepal and Tibet, causing at least 18 casualties. Much damage has occurred, and landslides have been triggered by the seismic event, blocking remote regions and breaking communication with the most affected areas.

Early calculations locate the hypocentre at 19.7 km depth, underneath the Sikkim region of India. The focal mechanism solution indicates a likely strike-slip movement in a fault which doesn't seem to be directly related with the India-Eurasia thrusting.

This earthquake is related with the convergence of the Indian subcontinent moving towards Eurasia, a phenomenon that causes the uplift of the Himalayan range.

More info at:

http://www.bbc.co.uk/news/world-south-asia-14967812

http://www.bbc.co.uk/news/world-south-asia-14967857

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005wg6/#summary

Callan explains you the Virginia earthquake

2011-08-24T07:30:00.003+01:00

A great post from Callan Bentley's blog, describing the geological background of yesterday's earthquake in Virginia (USA), 5.8-5.9 magnitude:

http://blogs.agu.org/mountainbeltway/2011/08/23/the-mineral-va-earthquake-of-august-23-2011/

Earthquake strikes US east coast

2011-08-23T21:28:00.004+01:00

5.9 magnitude earthquake in the East coast of USA. Some material damages but not casualties reported:

http://www.washingtonpost.com/earthquake-rattles-washington-area/2011/08/23/gIQATMOGZJ_story.html

http://www.bbc.co.uk/news/world-us-canada-14634730

Age of the oceanic lithosphere

2011-08-22T21:11:00.005+01:00

Just a short note... I found the other day (or I should say, refound, as I have used it many times in the last years) this image from

Cool, isn't it? :-) And it makes a great desktop background!

http://www.ngdc.noaa.gov/mgg/ocean_age/data/2008/ngdc-generated_images/whole_world/2008_age_of_oceans_plates.jpg

You can find more here. http://www.ngdc.noaa.gov/mgg/ocean_age/
Enjoy!

How people in science see each other

2011-08-11T18:40:00.001+01:00

How true!

(click on the image to enlarge it)

(reblogged from http://sotak.info)