Through The Sandglass

Ten things we don't know about sand: Number 2

2009-11-08T14:59:13+00:00

It just won't stop cropping up. After I returned from giving the talk in Manchester, checking through the news in the world of science, not only did I come across impressive progress in coastal research (my number 6 unknown ), but there, in Wired Science, was a report titled "Baffling Patterns Form in Scientific Sandbox." It began "With nothing more than beads in a glass box, physicists have revealed yet another mysterious property of granular solids, now recognized by scientists as a unique state of matter, like solids or gases" - my number 2 in the ten things we don't know about sand: "What is it?"

The report describes work by Ralf Stannarius and Frank Rietz of the Otto von Guericke-University Magdeburg in Germany; using, as is so often the case when investigating the bizarre behaviours of granular materials, very simple apparatus, they have produced some quite astonishing results. Results that demonstrate, yet again, that we don't really know how to describe granular materials - they are not consistently solids or liquids, but rather a state of matter in their own right. We don't really know how many states of matter there are - in addition to the solids, liquids, and gases, there are numerous other candidates, including liquid crystal, amorphous, Bose-Einstein condensates, and, of course, the notorious quark-gluon plasmas (all this, I will readily admit, from Wikipedia, where I also discovered something called a "superglass" - but the article was categorised as an "orphan"). As Heinrich Jaeger, the granular guru, remarked when talking about his recent work on the nano-scale forces causing droplet formation in falling streams of sand, these "experimental results open up new territory for which there is currently no theoretical framework."

The fact that granular materials do not like to remain mixed has long been observed, and Stannarius and Rietz describe earlier experimental work which their latest research continues. Put a granular mixture in a container and vibrate, shake, rotate, or otherwise disturb it and it will perpetrate an act of self-segregation. Stannarius and Rietz have shown that such a mixture not only self-segregates, but convects. In the image at the top of this post (from their publication), it almost seems as if the material is mocking us, saying "hey, you'll need better spectacles than these through which to understand what we're up to" (OK, blogger's poetic license). "On the Brink of Jamming: Granular Convection in Densely Filled Containers" by Rietz and Stannarius was first published last year, but last month they released an update with compelling and extraordinary videos of granular convection. The apparatus was, indeed, simple, but clever. As shown below, they used a simple mix of two sizes of glass sand-sized beads in a container that is essentially a Hele-Shaw cell, just like the home-made one I have used in my kitchen physics experiments. Once filled (and it is important that the cell is filled beyond a critical level), it's placed in a mechanism that simply rotates it, slowly, for hours. The cell is back-lit and photographed periodically.

The results are staggering. The movies, of various runs of the experiment and at various resolutions, can be found at the Magdeburg website (caution: if you go to the MIT Technology Review report, the movie link embedded there is for a 150 mb version - better to check out the link I've just mentioned). The movies are dramatic and well-worth watching, but just to whet your appetite, I've assembled a time-series of stills, shown below.

In a completely unpredictable (and unpredicted) way, the grains develop a graceful series of dynamically sustained convection rolls. As the authors wrote, "Known mechanisms for granular convection could not be applied." Another echo of Heinrich Jaeger's comment that "Physicists have a rich toolbox for dealing with solids, liquids and gases. But we don’t have a manual for when the old categories don’t apply." Whatever next in the mysterious world of granular materials?

Arenaceous sporting trivia - the baseball World Series

2009-11-05T17:30:43+00:00

My daughter and her grandfather, both in Philadelphia, will probably, to put it mildly, have less than kind words for me when they see this post. For the Phillies (last year's champions) were beaten in the baseball World Series last night by the New York Yankees - of all teams, it had to be the Yankees (for non-North American readers, I have appended some brief explanatory notes at the end of the post). Angst, tears, and rage in Philadelphia, exuberant celebration in New York. But, for Through the Sandglass, it's just another opportunity, to point out the ubiquity of my topic - in the continuing tradition of my daughter's Simpsons challenge.

For a start, like many sporting surfaces, the construction of a world-class baseball field relies on first-class sand. The iconic diamond, its grass and its surrounding "dirt," are made from specialty materials. Go to the website of the Beam Clay company of Great Meadows, New Jersey ("Your 'one-stop source' for America's baseball and sports turf surfaces and supplies!") and you will be bewildered by the choice of over 200 products for the construction, care, and maintenance of your dream infield - for example, their "Premium infield mix":

Made from uniform orange sand and red Beam Clay® with our special binding process that reduces wind and water erosion. Doesn’t separate and blow away! Doesn’t become dusty in stadiums! With proper maintenance, provides firm traction without tracking, good drainage while retaining playing moisture, distinctive reddish/orange color, works up readily, no separation of ingredients, long lasting, safe to slide on - for safe, attractive, consistent professional quality baseball diamonds.

The nature and performance of the materials used for the batter's and catcher's boxes are particularly important, but as in the action of a game, the pitcher's mound has to be a focus of attention. A good history of the pitcher's mound and how to construct one can be found here; the ingredients and recipes vary little - although the climatic environment of the stadium is important. This particular summary is from http://www.baseball-almanac.com/:

The mix used to build the pitcher's landing area (and often the batter's box and catcher's box) should have a significant concentration of clay to provide the necessary stability to resist degradation from increased traffic. A good material will be about 40% sand, 20% silt, and 40% clay. If necessary, you can mix individual components together. Just be sure that individual components are evenly distributed throughout the material.
A quality infield material will have a lower concentration of clay than the pitcher's mound. The infield skin should be moist and firm, not hard and baked dry. To achieve firmness, an infield mix should not be too sandy. An infield mix with greater than 75% sand causes unstable footing for ballplayers and increases infield skin maintenance problems. A sandy infield will create low spots more quickly and is more likely to create lips at the infield skin/turf interface. Ideally, the infield mix should be between 50% and 75% sand and 25% to 50% clay and silt. A combination that has been successfully used is a 60% sand, 20% silt, 20% clay base mix (sandy clay loam to sandy loam). The silt and clay give the mix firmness. If the mix contains too much silt and clay, compaction and hardness become a problem.

So, a skilful (and well-paid) pitcher can stride out to his patch with confidence that its consistency will provide a reliable foundation for his art. And, in the case of Mariano Rivera ("Mo"), who finished off the Phillies last night and has been called "the best closer in the history of the game," his appearance on the field - if the game is in New York - is accompanied by a loud rendition of Metallica's "Enter Sandman" - "we're off to never-never land." It is said that this is by no means Mo's favourite song, but that it is played on his entry because when he comes into a game, you can pretty much put it to bed. If you wish, you can see a video of this from last night's game at http://www.wikio.com/video/1925785.

And then, of course, there's sand lot baseball. And plastic baseball-shaped bottles that can be filled with coloured sand - but one example of a wide range of such things; I couldn't possibly comment on their artistic merit - but I suspect that Andrew Clemens will not be rolling in his grave.....

Notes for non-American readers:

The "World Series" has been widely derided by non-North Americans as being no such thing, since no countries other than the USA and Canada can compete for it. In order to combat such accusations of sporting arrogance, it has often been declared that the name originates from the original sponsorship of the championship by the newspaper, The New York World, early in the last century. Indeed, my (American) wife firmly corrected me to this effect a long time ago. But it's a myth - the "World Series" is, and always has been, exactly that (see Snopes). Not that I would in any way revert to my earlier derisive remarks ..... Always remember that the other life of Steve Gould, the extraordinary and revered evolutionary biologist and writer, was as a devoted and passionate baseball fan - of the Yankees.
I would no more attempt to explain baseball to non-Americans than I would cricket to baseball fans (both are challenges equivalent, in Shakespeare's words, to "numbering the sands and drinking the oceans dry.") Suffice it to say that both games are very much like the classic description of a soldier's life - long periods of boredom interrupted by brief moments of terror (well, generally not exactly terror, but action, something to actually engage the senses and the emotions).
In the later stages of a game, the starting pitcher is often replaced by a specialist finisher - a "closer" like Mariano Rivera.
A baseball signed by Mo and with the words "Enter Sandman" can be purchased from http://www.mlbfansite.com/ for a mere $399.99 (knocked down, so to speak, from the original price of $501.86).
Herewith, from http://www.baseball-almanac.com/stadium/baseball_field_construction.shtml, a simple illustration of the layout of the diamond and the infield. From now on, you're on your own.

Too much, too little, and often in the wrong place

2009-11-02T16:17:27+00:00

It rose out of the omnipresent sand of a natural island, and there remains a thin layer of the ocher substance almost everywhere: on the canopied grandstands, on the brilliantly lighted hotel at the edge of the track, on the seats and in just about every corner of the Yas Marina Circuit in Abu Dhabi.

So went the start of a New York Times article on yesterday's finale to the Formula One Grand Prix season. Small armies of workers were sweeping the sand right up to the last minute and yet, as The Walrus and The Carpenter observed, it's essentially an impossible task. Holding an extravaganza of highly sophisticated but delicate technology in this kind of environment brings many challenges. As the article went on to comment

It may play havoc with the engines of the cars and it will change the grip, lap by lap, for the drivers, even affect the lenses and other camera mechanisms belonging to the hundreds of photographers and journalists who will document the final race

For races in neighbouring Bahrain, it's long been a problem, as explained by Red Bull’s technical director Gunther Steiner:

You have to be aware that it can get in to every part of the car. It literally sandblasts the car every time it goes on track and gradually erodes all the surfaces and the cooling fins on the radiators.

Unique measures are taken to protect exposed suspension and other parts of the cars, and specially designed air filters have to be used. And then there's the problem with grip and tyre selection - after all, a motor race in which the drivers have to go slowly in order to stay on the track - and avoid whole sections of it because it's covered in sand - detracts somewhat from the sporting attraction. David Coulthard, the now-retired driver, was quoted before the race as saying

It does seem to be very sandy. When I followed a car the amount of stuff coming out the back was incredible. What that does is two things: one, it makes the driver pay the price if he goes a bit off line, which is good because it favours ability, but it is also makes people not want to take the risk in overtaking. Sand on your tyre takes a good lap to be cleared out.

And so it proved. It was largely a risk-avoidance race with drivers clearly sticking very closely to a single driving "line," conspicuously steering clear of the rest of the track - and often running into problems when they didn't. Grains of sand influencing a sporting spectacle and, as The Times Online concluded, "Whoever wins the inaugural Abu Dhabi Grand Prix on Sunday will be fêted in a nation that can afford to buy its heroes — but the victorious driver might feel his name is not written in history, but in the sand."

But if the sport was less than inspiring, the setting made up for it. This was the inaugural race at Abu Dhabi's latest example of construction extravagance. Ras Island, just down the coast from the preposterous artificial island developments of Dubai, was but a sandy expanse a mere 30 months ago (see the Google Earth image at left of the image at the head of this post). It hardly seems to have been a natural island, but rather 25 square kilometers of coastal desert, sandbanks, and sabhka (salt flats) carved out and isolated from the mainland by manmade waterways. After several tens of billions of dollars, and the efforts of tens of thousands of workers, things have changed. The image below is of the hotel complex across the track (as night falls, as it did for the Grand Prix, the whole thing glows in a succession of changing colours) and at the right in the image at the top is the way the whole place will look when finished.

The strange red object in the centre of the header image is "Ferrari World," the largest indoor theme park on the planet, "like a megalomaniac’s pleasure dome" in the words of the NYT. Yas Island will boast 20 hotels, 3 theme parks, a "Super Regional mall", golf courses, several marinas, and commercial and residential developments. You can read the full specs at the developer's website, but in case you don't here's a sampling of the exuberance on this "island of dreams":

There will be a Super Regional Mall that will house famous retail brands from
around the world in over 500 stores and 4 floors including lifestyle, fashion &
boutiques.
• There will also be room for a complete town centre concept, contained in a
number of adjacent buildings and built under a 88,100m2 roof
• The Yas Mall will have one of the largest free standing roofs in the world,
showcasing 296,000m2 of the world’s best retail space
• Adjoining the Yas Mall will be will be Abu Dhabi’s first Multi-purpose Retail
Park (100,000m2)
• Three major department stores will be accommodated.
• A large hypermarket covering an area of 17,000 m2

What I have not been able to determine is how much concrete goes into this monster (one hotel used 45,000 cubic metres of it, the racetrack 225,000) or, indeed, where all the sand came from for that concrete; presumably, as in neighbouring Dubai, local sources of non-desert sand were used (the windblown stuff being too rounded and smooth for good concrete), and the local natural sand budgets consequently profoundly changed. But it's not just the natural sand budgets. Although sand prices around the world have fallen during the economic crisis, they peaked in 2007 at more than $40 per ton, and sand supplies were becoming difficult. The Economist recently ran an article (pleasingly titled "The hourglass effect") that began:

“LOOKING for sea-sand for reclamation project in Singapore. Prompt reply is greatly appreciated.” Many such pleas can be found on Alibaba.com, a popular Chinese trading-website. Malaysia banned sand exports as long ago as 1997. Indonesia followed suit in 2007 on environmental and, some say, political grounds. Ever since, it has become harder for Singapore to secure supplies for its booming construction industry and sea-fill plans.

Singapore has turned to Cambodia and then Vietnam for its sand, but both have now banned exports. It seems that Myanmar may be the replacement supplier, so I will see my favourite material propping up, through, of course, western contractors, a loathsome dictatorship. The need is clear for a more widespread development and use of advanced forms of concrete that not only use less sand, but also can be manufactured without the associated emissions. And considering that every man, woman, and child on the planet "consumes" forty times their own weight in concrete every year, the sooner the better.

And finally, still on sand budgets and still in the news, today's Guardian newspaper carries a piece titled "Tide turns again for Cancún in shifting sands row." The 800,000 cubic metres of sand that were used to replace beaches washed away by Hurricane Wilma a few years ago lasted only a few months, and the current project is only the latest in a series of failed attempts at beach nourishment.

A huge project to replenish eroded beaches in Mexico's main Caribbean coastal resorts, including Cancún, has been suspended after legal action by environmentalists.

Campaigners claim the $75m (£45m) plan – involving taking 6.2m cubic metres from a sandbank just off Cozumel island, 50 miles from Cancún, to hotel beaches – is based on incomplete assessments.

Critics say dredging the sandbank will alter currents and damage ecosystems, including coral reefs and breeding grounds for species such as the queen conch. They also fear Cozumel will become more vulnerable to hurricanes. "It's absurd. We understand it is necessary to fill out the beaches but it needs to be done without sacrificing other places," said Alejandra Serrano of the Mexican Centre for Environmental Law.

But Rodrigo de la Pena, president of the Hotel Association, criticised the delay: "We cannot sell ourselves as a place of sun and sand, if we don't have the sand."

Alejandra Serrano is right - it's absurd. But then so many things are, including much of what I've just written about .....

Coastal change and saving sand - the state of the art

2009-10-29T22:53:02+00:00

In my talk earlier this week, Ten Things We Don't Know About Sand, number 6 was "How coasts work." Now of course we know the basics, but coastal systems are so complex and dynamic that the details elude us. I used my postcards of French sandbanks and the fascinating work of Rob Holman at Oregon State University and his Argus program movies to show just how dynamic our coasts are and how difficult it is to describe or model them in a way that not only creates a detailed understanding of their processes, but therefore a means of sensibly managing them and planning for the future. And then I read the announcement of a new USGS publication, Saving Sand: South Carolina Beaches Become a Model for Preservation, in which the introduction includes the following:

Changes in the morphology of coastal landforms and patterns of sediment movement have been studied for over a century, but, in general, scientists have only a rudimentary understanding of the processes that drive coastal change.

Sometimes I think that there must be something to the idea of synchronicity...

The full report, downloadable from the USGS link above, is a case study of the state of the art of our evaluation of how a single stretch of coast works. It's the summary of a six-year multidisciplinary study of the northeastern coast of South Carolina by the USGS in cooperation with the South Carolina Sea Grant Consortium (SCSGC). "The main objective of the study was to determine the geologic and oceanographic processes that control sediment movement along the region’s shoreline and thereby improve projections of coastal change." The stretch of coast studied is the "Grand Strand" segment, three headlands south from Cape Hatteras (where the lighthouse was heroically moved after decades of futile attempts to stop natural processes). It's only a 100 km length of coast, but it's a complex system of beaches, barrier islands, back barrier lagoons and tidal inlets. The variation of shore types is illustrated in the figure below, from the report.

And the dramatic rates of shoreline change, both long-term and short-term, are shown in the figure below. Note that the scale is in meters per year, ranging from +10m/yr to -10m/yr, over just this short length of coast.

The study is truly interdisciplinary, and employed a wide-ranging set of tools. Sidescan sonar, and the acoustic back scatter that it generates, allowed mapping of sediment types. Ground penetrating radar and different sub bottom profiling techniques revealed the structure and sedimentological/geomorphological history of the sub-seafloor geology. Current meters, sediment traps, wave-height sensors, and other instruments were attached to sturdy metal frames and anchored to the seafloor to record constantly changing environmental conditions and sediment flux. The operations (below, right) were clearly more successful than those of the traverse and triangulation party of L. P. Raynor in 1924 (below, left, photo from http://www.photolib.noaa.gov/).

I won't attempt to describe here the results of this extraordinary programme of research, but they are fascinating. Substantial contrasts in coastal processes arise from sand supply and availability. Sand-starved segments of the coast are characterised by exposure of older sediments and sedimentary rock (as old as Cretaceous in age, from 70 million years ago) and respond to wave and storm action very differently from sand-rich segments. Beach profiles and the dramatic changes to those profiles vary enormously both with sand availability and with exposure to seasonal change and storm events. Sediment budgets and individual littoral cells, along with their specific sediment sources and sinks, change rapidly along the coast and on a scale smaller than we have previously been able to define. Sediment flux is hugely variable with the time of year and wave and weather conditions, displaying complete reversals of transportation direction. The illustration below is just one example of the detailed analysis of shallow offshore processes, sand ridges in this case lying just oceanward of the popular resort of Myrtle Beach.

And popular - never mind populous - describes this entire stretch of coast, and the work described in this publication attempts to address the thorny issues of future management of a coast that has seen profound changes as a result of human activity. The entire profile - and the associated sedimentary processes - of much of this shoreline has been fundamentally changed by development and all the sea walls, beach armouring, and attempts at "beach nourishment" that go along with it. But look at the rates of shoreline change illustrated above, and the scale of the challenge becomes clear. Shorelines move - that's what they do. And they do it on our time-scales. And they'll do it regardless of our puny bits and pieces of engineering. They may do it slowly but inexorably, day-in, day-out, or they may do it overnight - for example, as a result of Hurricane Hugo in October 1989 (another anniversary this month, along with the Loma Prieta earthquake), illustrated dramatically in the "before and after" photos of the aptly named Folly Beach, down the coast from Myrtle Beach, shown below (again from the amazing resource that is the photo library at the NOAA).

In a 2002 report titled Coastal Sprawl: The Effects of Urban Design on Aquatic Ecosystems in the United States (written, very appropriately, by Dana Beach of the South Carolina Coastal Conservation League), we read the following:

Coastal counties cover 17 percent of the land area of the United States. Coastal watersheds, as described by the Department of Agriculture, represent just 13 percent of the nation’s acreage. By any measure, the coastal zone is a small part of the country, but it is home to more than half of America’s citizens. Moreover, today’s coastal populations are just the tip of the iceberg. Over the next 15 years, 27 million additional people—more than half of the nation’s population increase—will funnel into this narrow corridor along the edge of the ocean.

And population growth is but a subset of a broader problem that results from rising sea levels, the evolving economic and regulatory challenges, and environmental changes. I'll finish this post with a couple of quotes from the press release for the humbly-titled USGS Circular 1339 - I recommend downloading it - it's a cracking read.

“Effective beach preservation requires knowing the beach’s sand budget and understanding the geology that constrains it,” said U.S. Geological Survey lead scientist Walter Barnhardt. “It takes a systematic approach and strong partnerships at all levels of government with neighborhood associations and universities to keep a beach from simply washing away.”

“The comprehensive nature of this study -- considering the geologic framework, behavior and driving processes regionally -- has resulted in a remarkable baseline for better managing our beach and near- shore resources,” said Paul Gayes, Director of Coastal Carolina University’s Center for Marine and Wetland Studies.
“From inventory of potential future beach nourishment sand resources, to distribution of important hardbottom fish habitat, to models of beach behavior, this study forms the starting point for many present and future efforts. This work is regularly cited as a model approach and result for similar studies and efforts around the country,” said Gayes.

To "around the country" I might add "and around the world."

The Bayeux Tapestry - the quicksand scene

2009-10-25T18:10:37+00:00

My daughter is a great fan of The Simpsons (recently celebrating their 20th anniversary), and enjoys challenging anyone to name any topic for which she cannot quote an episode in which that topic featured. Sometimes, I feel as if I'm getting that way about sand, given the diversity of contexts in which it shows up, but I'm really not up to her professional level. However, until recently, if someone had challenged me to link the Bayeux Tapestry (which is not, incidentally, a tapestry, but more of an extravagant piece of embroidery) and sand, I would have been stumped: but not now.

I recently had the experience of seeing the Tapestry for the first time. The word "spellbinding" is not one I use often, but it seems the only way of describing it. The Tapestry, all 70 meters (230 feet) of it, is displayed in low light to preserve its extraordinary colours, and this adds to the magic as you walk along the story. It's an ancient graphic novel, an elongate comic book, almost an animation; you half expect to see Spiderman intercepting the Norman invaders, or the Sandman attacking their fleet. Such thoughts did not detract from my sense of wonder, but my reverence was briefly tested when I spotted Harold riding along with a hawk on his arm (as, I suppose, such noble folk generally did in those days); I was suddenly struck by a memory of my father reciting to me the comic monologue from music hall days (does anyone reading this remember Stanley Holloway?) of the Battle of Hastings, in which Harold was routinely depicted "on his 'orse with his 'awk in his 'and." Chuckling would have seemed entirely inappropriate, so I controlled myself.

But, back to the point. The early scenes depict Harold being captured in France by Duke William and, having sworn allegiance to him and giving his guarantee that he would not declare himself king, taking off on a campaign with William against a revolting member of the local aristocracy. In doing so, they had to pass by Mont St. Michel and cross the River Couesnon. Now in those days, the river was still behaving naturally, since it was long before human interference changed the regional sedimentology (see my piece on the massive experiment underway there). And the river contained quicksands. The scene that I've reproduced at the head of this post shows Norman horses struggling in the quicksand and Harold saving a couple of soldiers by dragging them out by hand (he carries one on his back). The Latin description reads "hic Harold Dux trahebat eos de arena" - "here Duke Harold pulled them from the sand." The round hill with the structure on top of it (upper left of centre) depicts Mont St. Michel.

The story goes on to describe how Harold went back on his word and declared himself King, thereby incurring the wrath of William, who proceeded to invade England and defeat the Saxon army at the Battle of Hastings, in the course of which Harold was shot in the eye by an arrow:

And after the battle were over

They found 'Arold so stately and grand,

Sitting there with an eye-full of arrow

On his 'orse with his 'awk in his 'and.

And thus was our vocabulary doubled - but no need to sweat or perspire over that.