Through The Sandglass

Sandstone-making microbes, tafoni - and an extraordinary design idea

I love connections. Those unexpected and wonderful threads of stories that link and flow from one subject to another, subjects that would have seemed to have had nothing in common whatsoever. So here's one such story. The thread is earthquakes-bacteria-desertification-tafoni-sustainable design.

Shake waterlogged sand, and liquefaction occurs: the grains move apart and the friction and adhesion between them is lost, destroying the stability of the material, which then flows and compacts, expelling the water. Earthquakes are particularly good at doing this, with catastrophic consequences. The earthquake that devastated the region around Bhuj in northwestern India in 2001 was one of the most damaging in the country’s history. Twenty thousand people were killed and the havoc caused more than $3 billion of damage. Because the vibrations provoked the sand and soil into liquefying, buildings no longer had a foundation, causing them to sink, tilt, and collapse. Huge cracks in the earth appeared, and water and sand erupted in volcanic fountains as the ground collapsed back on itself. This is a common result of earthquakes: more damage is done by liquefaction than by the tremors themselves. This was the case in Anchorage in 1964, the great San Francisco event of 1906, and in the Loma Prieta earthquake in 1989, where some buildings in San Francisco sank until their third floors were at ground level, and sand volcanoes or “boils” erupted from the ground. Liquefaction was also amply demonstrated in the most powerful series of earthquakes to strike the lower 48 in recorded history—not in California, but in New Madrid, Missouri, between 1811 and 1812.

It is therefore no surprise that liquefaction is the focus of intense research by engineers, physicists, and lovers of granular materials. Is one solution to try to glue the grains together so that they can’t liquefy? In spite of the scale of the challenge, the answer is yes, and we may be able to seek help in this from a seemingly unlikely source. Currently, engineers can inject chemicals, such as epoxies, into sandy soil, but the chemicals may be toxic. The unexpected help comes from Bacillus pasteurii, a natural bacterium that lives between sand grains and in soils. Research by Professor Jason DeJong and his colleagues at the University of California at Davis and the University of Massachusetts have shown that the bacterium causes calcite, or calcium carbonate, to precipitate, which glues the grains together. Inject sand with cultures of these bacteria, feed them well, provide oxygen and a source of calcium, and they will turn loose sand into solid rock. As DeJong says, "Starting from a sand pile, you turn it back into sandstone." The remarkable scanning electron microscope images below are from Eric Seagren, Chiung-Wen Chou and co-workers at the University of Maryland who are also inducing bacillus pasteurii into lithification activities (see the full set of images here).

 

Now, desertification. An evocative word, conjuring up apocalyptic images of the spread of aridity and the destruction of habitable and agricultural lands. It is indeed happening, but often as much as the result of human activity - the massive destruction of forests and other vegetation in China, for example - as climate change. But the edge of the desert shifts, as it always has, sometimes simply because dunes inevitably move on, and sometimes because climate fluctuates. The semi-arid sahel region of North Africa has always had a complex and delicate relationship with the Sahara, suffering drought (as well as excessive rainfall) and dune encroachment; it is in may parts heavily populated and livelihoods are vulnerable to shifting sands and climate change, the current effects of which appear to result not necessarily in less rain, but in less predictable, and periodically more torrential, rain. Massive projects are underway to create immense barriers of vegetation - the "Great Green Wall" of North Africa, 7000 kilometers long and 15 kilometers wide (China has its own version).

But what has this to do with bacteria? I recently came across (initially because it quoted from my book) a compelling report on BLDGBLOG, an eclectic and fascinating collection of writing on "Architectural Conjecture, Urban Speculation, and Landscape Futures" by Geoff Manaugh in San Francisco. This particular report was on the design project that last year won first prize in the Awards for Sustainable Construction by the Holcim Foundation, based in Switzerland. The project is by Magnus Larsson, a student, and it is staggering in its imagination, creativity and scope. Titled  " DUNE: Arenaceous Anti-Desertification Architecture, An Adaptive Proposal for Sahel/Sokoto/Northern Nigeria" it proposes that “maybe there’s a way to sculpt the desert into living spaces.” The sculpture would cross the northern edge of the Sahel, supporting and complementing the Great Green Wall, and would be sculpted by bacillus pasteurii.

Larsson espouses "aggregation as a design strategy":

in one way, all design is aggregation. even the most austere minimalistic design usually produces an aggregation of elements that weren't there before. on one level, it is hard to do anything in the world without adding something to it: a trace, a movement; something.

sand is the very epitome of aggregation. a single grain of sand is almost nothing: a splinter of rock, something that once was something, but has now become a memory of that thing. but put myriad grains together and you get entire landscapes, deserts, the earth. you get fascinating forms and emergent patterns. you get possibilities, potentials, a fluid material from which to build our structures. and you get a force to do it for you: as the sand is carried by the wind, "all" we have to do is make sure we design with this in mind. work with the aggregation, not against it. allow the aeolian forces to put the sand in motion, allow saltation to do its thing, and then, when the sand has aggregated into a shape that we like, use an intelligent strategy for how to solidify it, petrify it, freeze it into a solid state that speaks of that one moment in time.

To me, of course, that is poetry.

Among the patterns and forms that inspired Larsson (and Gaudi - see previous posts) are tafoni, "a cavernous rock structure that formally ties the project back to notions of aggregation and erosion." He describes how bacillus pasteurii could be harnessed to sculpt the desert into those forms that speak of one moment in time, but endurably, sustainably, providing not only a barrier against desertification, but habitable and cultivatable envrionments:

I researched different types of construction methods involving pile systems and realised that injection piles could probably be used to get the bacteria down into the sand – a procedure that would be analogous to using an oversized 3D printer, solidifying parts of the dune as needed. The piles would be pushed through the dune surface and a first layer of bacteria spread out, solidifying an initial surface within the dune. They would then be pulled up, creating almost any conceivable (structurally sound) surface along their way, with the loose sand acting as a jig before being excavated to create the necessary voids. If we allow ourselves to dream, we could even fantasise about ways in which the wind could do a lot of this work for us: solidifying parts of the surface to force the grains of sand to align in certain patterns, certain shapes, having the wind blow out our voids, creating a structure that would change and change again over the course of a decade, a century, a millenium.

The resulting forms of Larsson's vision are staggering, both in their scale and in their aesthetics:

 

Yes, this is a vision, a design fraught with practical challenges, questions, and difficulties in the real world, not to mention ethical aspects. But "if we allow ourselves to dream" (and we must), then beautiful, visionary, creative, and challenging ideas will result, and wondrous stories will be told.

Update: thanks to J.M. Landim Dominguez (his blog is at http://geologiamarinha.blogspot.com/), a fascinating  video of Magnus Larsson talking about this project can now be found at http://www.ted.com/talks/magnus_larsson_turning_dunes_into_architecture.html

[for details of Magnus Larsson's project, see http://www.flickr.com/photos/bldgblog/sets/72157612777908074/ and http://bldgblog.blogspot.com/2009/04/sandstone.html. For the work of Jason DeJong and his colleagues, see  http://www.sil.ucdavis.edu/projects-bsi.htm and, for example, this Discovery Channel article. Images copyright Magnus Larsson, Eric Seagren et al.]

Landscape plagiarism again: Alberta-on-Sea

A while ago, I picked up on the odd need of tourism promoters to expropriate other people's landscapes in their advertising (Spain's Costa Brava boasting a Bahamas beach); now its happened again, this time perhaps even more bizarrely. The last time I checked the condition of the earth's geography, the Canadian province of Alberta was a long way from the sea. But what's wrong with a little re-branding exercise? As part of a $25 million promotional campaign, the Alberta Government has conjured up a major marine transgression and committed an ethical one themselves, using an image of a young girl, clearly having fun, but on a British beach. We all know that there are lakes in Alberta, but this is ridiculous. And so it has been viewed by the rest of the world  - "derision" is the word most used in the Canadian media. The location is actually on the northeast English coast (hence the need for a wooly sweater) near the town of Bamburgh and the scene-stealing was discovered by Peter Bailey who knew that Alberta had plenty of lakes with sandy shores but no coast. He tracked down the real setting after pestering the Canadian government and tourist authorities with e-mails. And here's the good stuff: under the headline "We screwed up," various Albertan government representatives have been quoted as saying (feel free to laugh out loud as you read - I did):

There had been “no attempt to make people think that the place pictured was Alberta”

"We all knew that every single image we put out to represent Alberta had to be of Alberta, or we would be roasted. Then we screwed up.… We're sorry."

“This slide represents Albertans’ concern for the future of the world”

Tom Olsen, the director of media relations for Stephen Harper, the Canadian Prime Minister, said: “There’s no attempt to mislead. That picture fitted the mood and tone of what we were trying to do. Children are a symbol of the future. They symbolise that Albertans are a worldly people.”

Well, the Albertans are proud of their "freedom to create".......

Of course, the Northumberland tourism folk, whose beach it is, are quite pleased: “We think it's quite funny — a landlocked province in Canada presenting an image of itself as an island,” said a marketing executive, “But Northumberland Tourism is actually really thrilled that a picture of a beach in our area is being used for the Alberta campaign. We see it as promoting the beauty of the North of England, which is often neglected. I hope that when people in Alberta realise where the beach is, they’ll come to visit.”

This is the real beach (the Albertans clearly did not want to include the caravan - mobile home - parks) which is indeed a great sweep of sand backed by dunes.

 

The Canadians were also hijacking some great (but inappropriate geology). This is the coast where the Lower Carboniferous comes down to the sea, the marine, estuarine, fluvial and deltaic sediments that inundated the worn-down Devonian Old Red Sandstone continent. The sculpture of the coast reflects the underlying stratigraphy, and Bamburgh Castle, just to the north, is built on the Whin Sill, a late Carboniferous igneous intrusion whose scarp today winds across the country and forms the foundation for great stretches of Hadrian's Wall. For yes, we are close to the Scottish border here, just a little south of Siccar Point where James Hutton had his flash of inspiration and the unconformity named after him. From its origins in the 11th century, Bamburgh Castle had a torrid history, given its location, but its various sieges and battles were historically predictable, unlike today's Canadian invasion.

 

And, while we're at it, there have been other examples of landscape plagiarism - the English city of Birmingham has used images of its namesake in Alabama, the northwest England industrial town of Rochdale has  expropriated images of the industrial city of Manchester, and Bamburgh Castle has been used to attract folk to Scotland (which has many spectacular castles of its own).

[Bamburgh Castle and beach photo, Gemma Longman, Creative Commons License] 

Guest Photographer - nature's sand designs

I was recently contacted by Larry Deemer, who is lucky enough to live in Breezy Point, a coastal neighborhood in Queens, the borough of New York City. Larry spends time on the beach, observing - obviously with great pleasure and in meticulous detail - what is going on, particularly after a high tide. He sent me some of his photographs, and I was captivated. As he says

Most people don't stop to notice the beautiful patterns, or believe that they would be found on a beach in New York City. The variety of patterns are intriguing...from the ones that repeat simple patterns over a large area to the ones that are strangely abstract to the ones that look like a Japanese landscape painting or a dental x-ray. The best photos do not come from expensive cameras or digital ones. The simple Ricoh lens captures the warmest feeling of the sand.... It's nice to know that others stop to look at sand.I make my time on the beach a blend of art and science. There is always something new to see and wonder over.

I asked Larry if I could use the blog to post some of the photos and he kindly agreed, sending me a selection of his favourites (or favorites). Here's a selection - enjoy and wonder over them.

 

 

 

[all photographs copyright Larry Deemer]

Kitchen physics continued

Some further observations, and hints for readers who wish to try this at home (or in the classroom).

I was, as you could probably tell, flushed with the success of making cross-bedding in the comfort of my own kitchen, and eagerly awaiting the arrival of colourful granular materials from the aquarium supplies place. I had, much to my wife's appreciation (and, indeed, mine, since, much as I like sand, grains in your dinner are a step too far), removed my lab from the kitchen. The substantial box of supplies was delivered and I set up to enthusiastically scatter granular materials around a different room in our apartment. Not being familiar with aquarium interior design and therefore not knowing quite what to expect, I had ordered quite a variety of materials, both in terms of colour and grain character; furthermore, I had happened upon a "buy one, get one free" offer and so was surrounded by a rainbow of pots of grits. The variety and volume available turned out to be a good thing.

Given that a simple mixture of sugar and play sand had immediately produced such dramatic results, I had blithely assumed that, with a little thought as to mixtures of grain size and angularity (with appropriately different angles of repose), I would easily generate even more dramatic structures, the colour variations picking out in fine detail the segregation and stratification in a visually satisfying way. But this was not to be. Given even my qualitative understanding of the unpredictability and fickleness of granular materials, I should have anticipated that it would not be that simple to induce them to cooperate. My first couple of mixtures essentially produced no internal structure at all, and then I succeeded in producing segregation, but not stratification. By this I mean that different families of grains would spontaneously separate, with smaller grains at the top of the pile, larger ones towards the base, as in the image at the top of this post; this was an interesting demonstration but hardly what I was looking for.

I then had a brilliant idea: I would actually re-read the original paper by Makse and his colleagues (available here); this proved - surprise, surprise - to be be extremely informative. To begin with, they used a combination of two grain types, initially white glass beads (repose angle 26 degrees) and sugar crystals (roughly cubic and with an angle of repose of 39 degrees); this produced spontaneous segregation and stratification. They then used a mixture of fine and coarse sand and achieved the same result (indicating that grain density was not a critical factor). They wrote:

In all the above experiments we used mixtures composed of two types of grain with different shape, and therefore with different angles of repose. In particular we obtain stratification (plus segregation) when we use larger cubic grains and smaller spherical grains: the angle of repose of the large species is then larger than the angle of repose of the small species. Otherwise we obtain only segregation and not stratification when the large grains are less faceted than the small grains, i.e., the large grains have smaller angle of repose than the small grains.

They continued with further experimental variables and concluded:

These results suggest that the phenomenon of segregation is always expected when pouring a granular mixture of grains of different sizes, no matter the values of the angles of repose of the species. However, the phenomenon of stratification is only expected when the large species have larger angle of repose than the small species. Additionally, we performed a series of experiments in which we find similar stratification by using different mixtures of differing size ratio between large and small grains (1.66, 2.1, 2.25, 3.25, and 6.66), suggesting that the phenomenon occurs for a broad regime of grain size ratios. We find a similar stratification when we double the gap between the vertical plates of the cell and simultaneously double the flow rate of grains.

They then moved on to mixtures of three grain types (a close-up of this stratification is shown at right):

The experiment results in stratification with three layers, with the finest grains on the bottommost of each triplet of layers and the coarsest grains on the topmost layer ..... Experiments using a continuum size distribution are ongoing, since geological rock formations (which also display stratification) generally occur in the presence of a continuum distribution of grain size.

I was relieved that density was not a major factor (since, until I have a look with a microscope, I have no idea exactly what my aquarium decor is made of); I also followed their advice of cleaning the perspex with an anti-static cleaner - electrostatic effects between the grains can be important (indeed, it would seem to be influential in natural movement of sand by saltation, a phenomenon known as triboelectrification - perhaps more on that another time). I then repaired to, yes, the kitchen, and, on a series of plates, poured out a selection of my materials into heaps to determine grain size versus angle of repose. Selecting a coarse, black, angular, material (strictly more of a gravel than sand) with a steep angle of repose and fine, golden, semi-rounded grains (gloriously titled "imperial yellow") that formed a distinctly more gently sloping pile. I mixed up these materials, fully expecting to produce a sort of dramatic bumblebee effect - but they refused to cooperate, segregating somewhat but not really stratifying. As a result of this and my previous experiments, I was now surrounded by pots, tupperware etc., stolen from the kitchen and containing a wide variety of colourful, but non-performing mixtures. I added some fine, almost spherical "diamonique green" and tried again: hints of stratification. Becoming more desperate and, as if it were possible, less analytical, and having great faith in natural sand, I then mixed in a large proportion of the play sand (still, I believe, with some sugar) and poured. The result was dramatic and not unlike the illustrations in Makse's paper:

 

Both segregation and stratification appeared, and each stratified layer was clearly beginning to show sorting by grain size:

 

 

So, what is it about natural sand that seems to make it self-stratify more spontaneously than the artificial materials? Clearly, my "kitchen physics" is not conducted under strict laboratory conditions, I have not quantitatively evaluated the grain size, sorting, and shapes of my materials, and I have not rigorously recorded the many permutations and combinations now occupying the small army of tupperware containers on the floor; I am, in short, overwhelmed by my variables. But here are my amateur conclusions:

1. Using an anti-static cleaner is probably important.
2. Artificially coloured materials are valuable in offering a range of grain types and in highlighting internal structure of the pile.
3. Natural sand is probably a key ingredient in most easily producing stratification.
4. Adding sugar is, pragmatically, likely to produce results.
5. Varying the rate of pouring produces different outcomes.

I shall continue (it is, after all, an excuse to play), but if anyone has recommendations and further experiences to contribute, I would be delighted to hear them.

Another arenophile

I've just been contacted by Betsy Kimak who works as an independent web designer out of Denver and who had nice things to say about this blog. Betsy is a self-confessed arenophile - as she describes herself:

I’ve always liked dirt. I was one of those kids who played with bugs, searched for fossils, buried things in the backyard, collected rocks, and panned for gold. I’m not a geologist, but I am a bit of a science geek who has an unhealthy relationship with sand. I suppose that’s what happens when a Florida baby is plucked from beach bliss and carried off to a geologically-fascinating, but landlocked state.

Betsy drew my attention to her sandy website, http://www.sandrific.com/. She is building a sand collection, and has developed a very satisfying and accessible way of displaying this via a Google Maps mashup (see the screenshot above): simply click on the location for images of the sand, the place, and further information.

I remember that a while ago there was a discussion with Robert Huber at Stratigraphy.net on ways of linking and compiling geoblogosphere posted images and content with global locations. Now I am technically fairly hopeless, and am not quite sure how to mash things up, but clearly Betsy has this well in-hand, and this might be worth some further thought; she wrote about the process in her blog, http://www.umaitech.com/cms/?p=41. Her sandrific blog is now listed in my blogroll.

I should also note that Sandrific is up for a Webby People's Voice Award - see  http://pv.webbyawards.com/ for more information and the opportunity to vote. And Betsy is looking to populate the map - any arenaceous samples out there?

A little light relief - sandglass uses

[thanks to Private Eye]

Kitchen physics - making cross-bedding

It will be obvious to those who have read items on this blog that I find the bizarre behaviours of granular materials fascinating. It was only as I was working on the book that I encountered just how weird and wonderful these behaviours are, how much extraordinary research in physics and engineering is being done, how important these things are, and how often we unwittingly encounter them, in our daily lives. One of the signature characteristics of any granular material, whether it's sand, nuts, or the contents of your pharmaceutical capsule, is its extreme dislike of being mixed. A mixture of different types of grains will take advantage of the slightest opportunity to un-mix itself, to self-segregate; when shaken, stirred, rattled, vibrated, rotated - and even just poured - that's what granular materials do, they self-segregate. And one result of self-segregation is the formation of patterns, patterns that we can easily recognize in nature.

One of the deceptively simple demonstrations of this behaviour was the focus of research by Hernán Makse, published in Nature back in 1997. The paper by Makse, then at Boston University, and his colleagues, was titled "Spontaneous stratification in granular mixtures," and one of the illustrations is shown (with permission) at the top of this post. They demonstrated that a mixture of sand and sugar would separate into its components if you simply poured it slowly and evenly into a pile. “A miracle occurs,” said Eugene Stanley, one of the collaborators. “It’s like throwing a deck of cards on the table and having all the blacks fall on one side and the reds on the other.” Makse, Stanley, and their colleagues conducted a series of experiments using different materials - sand, glass beads, sugar crystals - and the results were clear. Typically, larger grains will have a steeper angle of repose than smaller ones, and they will roll down the slope more energetically. The smaller grains tend to get stuck at the top of the pile, the larger ones at the base—they spontaneously segregate. But things become more complicated. As the different angles of repose of different grains are reached and exceeded, successive avalanches will be made up of different-sized grains. The cascades of smaller grains will stop first, to be then covered by a layer of the larger grains still on the move. The process repeats itself over and over, creating a layered pile. Different (and unpredictable) results can be achieved by varying the size, density, and shape of the grains and therefore their angle of stability or repose.

The result is a very distinctive pattern. Philip Ball, the superb science writer, is fascinated by patterns in nature, and his book on the subject, The Self-Made Tapestry is one of my favourites. He has just updated the book into a series of three, Nature's Patterns: A Tapestry in Three Parts, the parts being Flow, Branches, and Shapes, and last month gave a talk at the Royal Institution in London, an event that I couldn't miss. It was riveting stuff, but I was particularly fascinated by the fact that, in the middle of the talk, he repeated Makse's experiment, like magic trick, before my very eyes. The device used is a Hele-Shaw cell, first developed (not a surprise, this) by the engineer Henry Selby Hele-Shaw in the early part of the last century to experiment with various kinds of fluid flow (Hele-Shaw invented, amongst many other things, the variable-pitch propeller). For granular flow experiments, it's a simple narrow box with perspex (plexiglass) sides, and, after his talk, Ball kindly showed me just how easy it is to make, and how he used a simple mixture of sugar and sand for his trick.

I resolved to try this for myself - the drama of the demonstration being ideal for the occasional talk that I give; not being confident about sawing perspex in my apartment garage, I once again sought the help of Trevor (who had built my arenophile shelves). When he arrived with the device, I was like a kid with a new toy - but nervous as to whether it would work. I had prepared a mixture of "play sand" and granulated sugar, and set up (my wife again long-suffering) in the kitchen. With a slightly shaking hand and an envelope with the corner cut off as a makeshift funnel, I poured the mixture into the cell (and on to the kitchen counter, floor, etc.). To my amazement (and that of my audience), it worked!

 

All I had to do was control the rate at which I poured, and the avalanching grains did exactly what they were supposed to do - they self-segregated and spontaneously stratified. In the interests of cleaning up the kitchen, I moved the cell, causing further avalanching and truncation of the underlying original pattern. I then tried it with just the play sand and, lo and behold, the dark grains separated themselves from the light grains. To the geologically-inclined, this pattern will be all too familiar - I had made cross-bedding. The second image below shows my experiment on the left and natural cross-bedding on the right.

 

Cross-bedding is formed when any mixture of sand grains is swept along by a current - whether water or air - and deposited, building up a slope, down which the next surge of grains cascades. Cross-bedding (so-called because it forms at an angle to the main surface of deposition, e.g. the beach) is found in ripples, river sand banks, marine bars, and dunes - essentially anywhere that sand falls out of a current. It tells us a great deal about the nature of the fluid flow, its direction, strength and so on - and the only reason we can see it is because of self-segregation and spontaneous stratification, grains of different colours (and different physical characteristics) picking out the internal structure. And, thanks to Hernán Makse, Philip Ball, my long-suffering wife, and Trevor, I had demonstrated this in my own kitchen.

I was, I suspect fairly obviously, thrilled to bits about this success. I now await delivery of a veritable rainbow of different coloured sands and glass beads with which I can expand my play; this is, of course, possible thanks to the new tradition of exchanging sand at wedding ceremonies and the keepers of aquaria requiring coloured substrates against which the denizens are best displayed. But this is also a simple and terrific way of demonstrating granular physics, natural pattern formation, and geological processes in any classroom. I discovered that Makse has developed a classroom version available here and that there are instructions (in different languages) for making various forms of Hele-Shaw cells on this site. 

[For further exploration of granular material behaviour, Makse's home page is a good starting point; make sure to have a look at the page on the spontaneous stratification experiment and the one on cross-bedding. For a spectacular series of images and animations of cross-bedding and bedforms in general, go to the work of Dave Rubin and Carissa Carter at the USGS: http://walrus.wr.usgs.gov/seds/bedforms/pindex.html]

Sand as motif - further confessions of an arenophile

It was my intention to put together a more technical post on the challenges of measuring the shape of a sand grain - an apparently esoteric endeavour, but in fact of surprising importance in science and our daily lives. However, I not only realised that this would require more time for thought (including a probably vain attempt to comprehend fourier analysis), but I also became otherwise-occupied over the last day or so. 

I suppose, since I have written the book, that, in the strict sense, I have long been an arenophile, but it was only in the course of writing that my arenophilia has extended to collecting my subject matter. Sand collecting is a serious activity for a large community of enthusiasts around the world, and the diversity of sands and the uniqueness of family of grains means that any collection is endless. It was, I suppose, inevitable that, spurred on by two charming and helpful arenophiles, I should start gathering my own collection.  The first was Marco Bonifazi, whom I visited a couple of years ago at his wonderful old house in a village in the Swiss Jura mountains. Marco is a man of many interests and talents, among them collecting sand - he has more than 8000 samples:

 

A few years ago, Marco helped organise an exhibition at the Natural History Museum in Neuchatel (set up by Louis Agassiz before he decamped to the US in 1846), simply titled Sable. The exhibition had to be extended because of popular demand - and is something that I would love to recreate at a museum in the UK or the US (see, in French, the Museum descriptions of the exhibition). Marco provided me with the start of my own collection and today my friends and family never leave home without a few ziplock plastic bags on my behalf. The second sand collector to whom I owe a great deal is Loes Modderman, who lives in the Netherlands and has a superb website on all things microscopic. I was captivated by some of the images on her site that demonstrated the beauty of the endlessly varying hues of natural sand, and she very kindly and enthusiastically allowed my to use one of these images as a plate in the book (the illustration at the top of this post, Sands of South Africa). And then, one day, I received an e-mail from Loes letting me know that I should expect a package; when it arrived, I was astonished and delighted to find that it contained dozens of sand samples from numerous far-flung parts of the world. This completed my conversion to a full-fledged arenophile, and, as further plastic bags arrived from family and friends, and as I filled many of my own, the question was how to do the spectrum of sands justice?

Fortunately, I have a long-suffering wife who has also been infected by arenophilia, whose life has unavoidably been deeply penetrated by sand over the last few years. And I'm also lucky enough to know Trevor, who builds things - extremely well and thoughtfully. The result, a few days ago was the installation in our apartment here in London of a set of shelves (of significant dimensions) specifically to display sands - interior decorating with an arenaceous motif. I had earlier found the ideal glass containers - in bulk, from a medical supplies website (heaven knows what they are supposed to contain). So fourier analysis went out the window and much of my time in the last day or so was devoted to filling and cataloguing the containers - a modest 150 of them. I think (and, wonderfully, my wife agrees) that the result is great - it's certainly unique, it displays the subtle and ever-varying colours and character of the world's sands, it's thematic, and it complements the colour of the room.

  

Now, of course, I'll have to get the microscope out and continue with the exploration of nature's wonderful debris. 

Fundraising and madness in the desert - the Marathon des Sables

It's billed as the toughest footrace one earth, a reputation difficult to dispute - lunacy in a good cause. The 24th Marathon des Sables has just finished in the Moroccan Sahara south of the town of Ouarzazate (at least, I believe everyone who was going to finish has finished). The race, equivalent to five and a half normal marathons, covers 240 kilometers (150 miles) over typically six days (including a rest day) - or more. Water and tents are supplied, but competitors have to carry everything else with them, food, clothes, medical supplies, suncream ...... Medical supplies are dominated by diverse treatments for the feet - photographic reporting of the event includes some truly gruesome images of sand-flagellated feet. And the competitors pay for this masochistic pleasure - if you wish to sign up for next year's event, put aside over $4000. However, the event is a a major means of obtaining sponsorship and it raises significant amounts for a variety of charities.

This year, more than 800 lunatics from all over the world entered the race (I'm not sure exactly how many finished, but it's generally around 80%). But they and the organisers were in for a surprise - torrential rains caused widespread flooding, swamping the camp at the start resulting in the runners being evacuated to hotels in the nearest town. The race eventually got underway, but was shortened. And the rain completely changed the ground conditions, wet sand being a very different material from dry sand. At the start, the eventual winner, the Moroccan Mohamad Ahansal, commented that "because of the rain, the ground is less soft. And, as you know, it is easier for runners to take a clear lead on sand surface. It will be harder than last year...." (which he won also). One surprising consequence was that he and a group of other old hands decided to avoid the sodden wadis and head for the dunes - promptly getting lost. They added several kilometers to their first stage.

Mohamad won the shortened event in a time of 16 hours and 27 minutes, with his older brother Lahcen fighting back but not making it into the top ten. However, Lahcen is truly the old hand - he has won ten of these ultramarathons and had beaten his brother into second place seven times (although they had a habit of crossing the finishing line together - see photo, right). It's Mohamad, however, who holds the record for the event: in 1998 he covered the 137 miles of the Marathon des Sables in 16 hours and 22 minutes, 29 seconds - which seems to me to be an average speed of around eight and a half miles per hour. He is, understandably, in the Guiness Book of Records. This year, for the women, the winner was Touda Didi, also Moroccan, also the winner of last year's race. Incredibly, a 60 year-old, Marco Olmo, came in in 12th place in the general men's rankings; the oldest person ever to complete the race was 78. They do say that it's as much a challenge of mental stamina as a physical one.

It's likely that few of the competitors are geologically inclined, and, even if they were, other priorities might absorb their attention. But the landscapes through which the Marathon des Sables passes are spectacular - here's a Google Earth image of the setting for one of this year's stages.

 

[The photo at the top is from the Royal Air Force Team in an earlier event, http://www.raf.mod.uk/news/archive.cfm?storyid=0BA59D3A-1143-EC82-2ECFDC433CA32B3F; for more on the Marathon (including entry forms for next year, should you wish), see http://www.saharamarathon.co.uk/index.html and http://www.darbaroud.com/index_uk.php]

Granular films - sand the movie star

In the film blog of the British newspaper, The Guardian, a few days ago, the weekly feature called "Clip joint" called on readers to submit movie scenes featuring the desert, to compile "a tour of the best web morsels on Sahara-like expanses." The writer declared that "I can't find the exact quote, but somebody once said of Lawrence of Arabia something like, 'The desert is the screen.' Frankly, with films, that's all I need to hear. Help me to my seat forthwith, usher: I need an extra-large tub of grandeur, and sand in my hair." (For non-UK readers, the "usher" refers to the person in a cinema or theatre who shows you to your seat, and the "tub" is is a - traditionally mediocre, but you do find Baskin Robbins these days - container of ice cream). Now geologists obviously have a unique and idiosyncratic perspective on this; I have spent long periods in movie theatres losing the plot but trying to figure out from the background geology where a scene was actually filmed. And, of course, I'm particularly interested in films which don't simply occur in a desert setting, but which the desert - and, ideally, the sand - is a critical part of the plot, if not an actual character.

So I've just spent a very enjoyable couple of hours looking through the responses in The Guardian, and checking out many of the YouTube links (I'd already added my own, which I shall come to shortly). The nominations cover a spectrum, from films in which deserts show up, through films which are largely set in an arid place, finally to films in which the desert and the sand are not just the background but a constant theme - they have roles, they provide tension. In the first category of the spectrum, one can move from Casino, Ben Hur, through Paris Texas and There Will be Blood, to Zabriskie Point which starts the next category. Ice Cold in Alex, The Good, the Bad and the Ugly (Clint Eastwood's forced walk through the dunes includes some great granular bits), The Flight of the Phoenix (both versions, the older one the better), Humphrey Bogart in Sahara (see my "angle of repose" post), and, of course, Lawrence of Arabia. Next, there is an obvious group which initiates the final category in the spectrum - Dune, Star Wars (the sand people and the deserts of Tatooine), The Sheltering Sky, and The English Patient (the initial scene of which, with the plane flying over the sunset-illuminated dunes, is staggeringly beautiful - I might, carried somewhat away, argue that dunes are female....).

Which brings us to the extreme sand end of the spectrum. Runner-up is The House of Sand, from which the image at the head of this post is taken. Set in the spectacular landscapes of Brazilian coastal dunes, this 2006 film by Andrucha Waddington won that year's Alfred P. Sloan prize at the Sundance Festival - well-deserved, in my view. The story follows three generations of women (two played by the extraordinary Fernanda Torres and the other by her real-life mother) stranded in the dunes as a result of male dementia. Against the backdrop of this spectacular landscape, and with the ever-shifting sands playing their role, the film follows threads of history: from the 1919 expedition to the dunes to use a solar eclipse to attempt to demonstrate the curvature of space, as predicted by Einstein, through WW II to the moon landings. When her mother asks what they found on the moon, the daughter replies "nothing but sand." Scenery, science, history, drama, stunning cinematography, sex, and great acting, this movie has it all.

But the grand prize, in my personal "best arenaceous movies of all time" list goes to Woman of the Dunes, the 1964 film of Kobo Abe's book The Woman in the Dunes. The slight difference in translation is confusing, but the book title more accurately reflects the story. Hiroshi Teshigahara's film won the Special Jury Prize at the Cannes festival and was nominated for the Best Foreign Language Film at the Oscars. Filmed among Japan's Tottori coastal dunes, this surreal movie features a lost entomologist who finds himself essentially kidnapped and marooned at the bottom of a deep hole in the dunes where a widow is kept by the bizarre local inhabitants to sweep the ever-encroaching sand from her house. If it sounds weird, it is - but it's compelling. The characters - and the viewer - lose all sense of time, which becomes measured only by the movement of sand and the daily routine of their battle against it. There are constant and meticulously observed scenes of the behaviour of granular materials (hardly a common commendation for a film, but I thought they were brilliant). Sand really is a major character - and the concept of "sand and sex" takes on a whole new meaning. The film is wonderful, but the book is well-worth reading too  - one quote:

Because winds and water currents flow over the land, the formation of sand is unavoidable. As long as the winds blew, the rivers flowed, and the seas stirred, sand would be born grain by grain from the earth, and like a living being it would creep everywhere. The sands never rested. Gently but surely they invaded and destroyed the surface of the earth...... While he mused on the effects of the flowing sands, he was seized from time to time by hallucinations in which he himself began to move with the flow.   

As an endnote, the theme of wind, sand, and madness is not a new one. Thanks to one of the comments in the Guardian blog, I came across scenes, evocative of Teshigahara, from the 1928 silent movie, The Wind, in which Lillian Gish (whom I have always thought extraordinary), is, in the end, saved from madness and driving sand. It was filmed, in part, in the Mojave Desert.

[to see the Guardian blog list in full, go to http://www.guardian.co.uk/film/filmblog/2009/apr/01/1; for a taste of The House of Sand, http://www.youtube.com/watch?v=BlxSR1-sErk; Woman of the Dunes, http://www.youtube.com/watch?v=K1mpRGqkpAs; The Wind, http://www.youtube.com/watch?v=I-Q2vDNyqXM&NR=1]