Through The Sandglass

Of Mice and Sand - Evolution in Action

This is the year of the great Darwinfest and, inevitably, sand makes its contribution. The immediate reference would be to the "sand walk" at Down House in the Kent countryside, Darwin's "thinking path" that he walked every day. A visit to Down House (appropriately under consideration as a World Heritage site) is, for many of us, an intellectually spiritual experience. Walk the sand walk, and the sense of place is resonant. What is arguably the greatest idea ever was formed here. It is the place where our understanding of ourselves and our place, and the place of every living thing in the natural world, was born.

The process of natural selection, illuminated today so brilliantly and so subtly by genetics, is a natural wonder, the place where the scenes of life's history, as revealed through geology, develop into the dramas of today's biosphere.  Sand, being the ubiquitous and hyperactive player in the games of our planet's past has, of course, always influenced evolution. Granular materials, whether in the desert or the surf zone, are not the easiest places to live, and the challenges have driven endless adaptations. But what I want to focus on here is an example of evolution in "real time," changes that are happening at a pace that we can comprehend on our timescale.

The coastline of Florida as we see it today is young. Quite apart from the fact that the coast today is not what it was yesterday, the major features, however they are constantly changing, were sculpted a few thousand years ago as sea levels rose after the last Ice Age. The barrier islands of the Gulf Coast and the sweeping beach and dune systems of the Atlantic side are works in progress. As are their populations of mice. Peromyscus is the most widespread mammal in North America, a species that has adapted to and enjoys a wide range of habitats, including the mainland of Florida, its Atlantic beaches, and its recently formed barrier islands off the Gulf Coast. But the mice that live on the light sand beaches and among the dunes have distinctly lighter fur than their relatives who inhabit the dark soils of the mainland, and  Hopi E. Hoekstra, John L. Loeb Associate Professor of the Natural Sciences in Harvard's Faculty of Arts and Sciences, together with her colleagues at the University of California, San Diego, and Leipzig in Germany, have demonstrated that this is evolution at a dramatic pace. A paper in this month's Molecular Biology and Evolution (http://mbe.oxfordjournals.org/cgi/content/abstract/26/1/35?etoc) reports the latest results from a project that has been going for some time. Not only does their work reveal some of the complexity of genetic switches, nucleotides, and amino acid mutations that choreograph evolutionary change, but it importantly sheds new light on the thorny and much-debated topic of convergent evolution, showing that, like so many things, it's not as simple as we might like to think. Now, when I say "we," I am not really referring to myself - as a geologist, the time it takes me to be out of my depth in the field of molecular biology can be measured on the nanoscale, so I shall return to the influence of sand.

Hoekstra's project has studied beach mice in diverse habitats, among them Santa Rosa Island, one of the longest barrier islands in North America, and the site of a Civil War battle. The mice forage on the white sands and among the dunes, eating mainly sea oats, and trying to avoid predators from the skies - owls, herons, and hawks. And, nature being red in tooth and claw, mice with lighter-coloured coats are less visible and more likely to survive. As natural selection, it's as simple as that (putting aside the complexity of the genetic mechanisms that actually allow it to happen). Completely distinctive subspecies have evolved and it's all happened in just a few thousand years - as Hoekstra says, “It’s a large effect mutation. And what it says is that adaptation does not always occur gradually, but may happen in these relatively large jumps.” The barrier island beach mice are genetically more similar to (but still different from) their Atlantic Coast relatives hundreds of kilometers away than they are to their nearby mainland cousins.

Unfortunately, avian predators are not the only threats that the beach mice have to deal with. Our lunatic obsession with beach front property development is destroying their habitats, and, barrier islands being where they are, hurricane damage is frequent and extensive; Hurricane Ivan excavated a completely new breach in Santa Rosa Island as seen in the image below - a great example for fans of storm-generated overwash sand deposits.

 

The beach mice are disappearing rapidly - since Hoekstra's project began, one subspecies has become extinct and six of the seven remaining are endangered.

There are other examples of sand habitats actively driving evolutionary change. The gloriously named bleached earless lizard lives among the stark white gypsum dunes of the White Sands National Monument, again formed only a few thousand years ago. The lizard is thus named because it is bleached - compared to its darker relatives beyond the dunes, it has lost its colour as a protective adaptation (it has been shown that this adaptation is not driven by temperature regulation). Spiders, scorpions, toads, and mammals living in the dazzling dunes are all paler than their brethren beyond the sand. 

[see Hopi Hoekstra's site: http://www.oeb.harvard.edu/faculty/hoekstra/Links/ProjectsPage.html. Beach mouse photo from

http://www.oeb.harvard.edu/faculty/hoekstra/Links/ProjectsPage.html, credit J.B. Miller, Santa Rosa hurricane damage photo from

http://coastal.er.usgs.gov/hurricanes/ivan/photos/florida.html. For more on evolution at White Sands, see http://www.nps.gov/whsa/naturescience/white-animals.htm; lizard photo from that site.]

The Urban Stratum

The Urban Stratum is the provocative stratigraphic name that Jan Zalasiewicz gives to our remains in The Earth After Us - What legacy will humans leave in the rocks? Perhaps reflecting the current global issues that cause us to contemplate our mortality and vulnerability as a species, there are several books around (Year Million, The World Without Us) that focus on the post-human earth. However, this one is written by a geologist, a paleontologist and stratigrapher, and it perhaps addresses the question I raised in the earlier post on science writing by professional geologists (December 29). His perspective is from 100 million years hence - without doubt long post-human. The structure is from the point of view of future geologists/archeologists/anthropologists - re-evolved editions of ourselves or alien, it doesn't matter - attempting to discern and reconstruct the nature of the species which dominated the planet for a brief time in the distant past. Along the way, there is a highly readable narrative of the methodologies and the trials and tribulations of stratigraphy and paleontology.

To geologists, the fact that this account is a humbling one will come as no surprise, but the poverty of our legacy, thoroughly thought through and documented in the book, is, nevertheless, exactly that. While, in this year of Darwin festivities, the imagery of the "tree of life" is under profound revision, our view of our superiority and dominance at the head of that tree is enduring, the arrogance of our species seemingly in-built (if cockroaches were to construct their tree of life, guess who would be perched at the top). Zalasiewicz cleverly examines our understanding of life 100 million years in the past - and its many limitations - to shed light on how thin, paltry, discontinuous and incomplete the "Urban Stratum" will be. Even if we assume, heroically, that our species will accomplish more than few thousand years on the planet, how thick will the stratum representing that period be in the stratigraphic section of 100 million years hence?

Essentially none of our infrastructure, creations, and artifacts will survive 100 million years of erosion, burial, diagenesis, and tectonics in their original compositional and structural form, and we ourselves, inhabiting the erosional land rather than the depositional marine realms are poor fossil candidates - think of the extent (or lack of it) of the record of our ancestors in the African Rift Valleys. And, given that the final circumstances of personkind may well have led to the mass evacuation of cities, there will be relatively few of us potentially preserved in the arguably more durable cellars, basements, and subways of today's subsurface levels. And direct evidence of our social structures, our thinking, our arts will be entirely lacking - what, after all, do we really know of the daily life of a dinosaur family? Furthermore, as Zalasiewicz points out, while we may regard the mighty dinosaurs as icons of the Jurassic, there was much more to life at that time and perhaps the future investigators will take a similar view: "They may well regard the myriad tiny invertebrates, or the bacteria of the world as much more important to that (in planetary terms) rare phenomenon, a stable, functional, complex ecosystem. ... Take away humans, and the present world would also function quite happily ... Take away worms and insects, and things would start seriously to fall apart. Take away bacteria and their yet more ancient cousins, the archaea, and the viruses too, and the world would die." 

Zalasiewicz entertainingly explores the idea that trace fossils, the evidence of creatures' activities rather than the creatures themselves, will be potentially preservable and informative. The remains of an interstate highway might be fragmented and discontinuous in a future outcrop, but they will have stories to tell. And, an intriguing idea: perhaps the most durable trace fossils will be the thousands of deep oil and gas wells, lined with corrosion-resistant steel and penetrating deep into the geology - equivalents of fodinichnia or domichnia? Trace fossils fall into various classifications, depending on whether they represent tracks, burrows, feeding paths and so on, but all reflect the Greek for a track or a trail, ikhnos. Zalasiewicz proposes a new class: frivolichnia, pleasure traces of movie theatres, baseball diamonds and cricket grounds, museums, libraries, all of which might be completely inexplicable to our future investigators. Given that this blog is primarily about sandy topics, what might be made of the traces of a golf course? Strange, isolated bodies of sand distributed unnaturally in a soil horizon. And I must point out, as the book does, that, while much of our concrete will physically and chemically disintegrate over a hundred million years, the quartz sand grains will endure - because quartz sand grains, more often than not, do.

Overall, it's a great, beautifully written and thought-provoking book, but, while each chapter is introduced by a fragment from the reports of our future investigators, I found myself wishing that it had concluded with an outright foray into science fiction - a longer selection from those journals, illustrating the challenges and pitfalls involved in the reconstruction of things long gone. What if, for example, the most likely survivors of our artistic efforts would be stone statues (made, as they are, from already long-lasting geological materials)? What if, as a result of differential preservation and the general serendipity of discovery, rather than an idealized human form from classical Greece, our future investigators excavated one of the figures below? How would this influence their other interpretations? Or what if they unearthed a Henry Moore or Salvador Dali statue?

 

Now that we are firmly in the realm of science fiction, here's another thought experiment, an opportunity for geological speculation. Plate tectonics will grind to a halt, probably not in the next hundred million years, but eventually. The earth's engine will seize up, for any number of reasons. Internal radioactive heating will diminish, thickening and immobilising the lithosphere. Or, changes to the atmosphere and the sun's thermal activity will drive off all water from the planet and the lubrication of plate tectonics will be gone. Or, plate tectonics may cause its own demise, adding sufficient new continental crust that, eventually, there will be no more room for manoeuvre. Or, as Ray Siever pointed out in his book on sand, atmospheric toxicity will kill off land plants, the continents will be rapidly eroded, the oceans will fill up with sand and ..... Or, any conspiracy of the above.

So, here's the question, given that our appreciation of plate tectonic processes was a long time coming, difficult, and highly controversial even while their work was going on all around us, in a post plate tectonics world, how would we discern that those processes had ever happened? What would be the evidence revealed to and by geologists of the future that plate motions and plate margin dynamics had sculpted the appearance of our planet? Something to think about as we gaze more closely at other planets?

[images of the Venus of Willendorf and the Easter Island Moais reproduced under creative commons license, thanks to  Matthias Kabel and Paweł Drozd. Ray Siever's Sand, published by the Scientific American Library in 1988, is unfortunately no longer in print. Peter Ward and Donald Brownlee's The Life and Death of Planet Earth is another good read on this entertaining topic.]

Sediment Budget Busting

Sometimes you have to wonder. And the good tax-paying citizens of Bournemouth are certainly wondering. An article in yesterday's UK Guardian newspaper highlights the latest episode of another sorry story of expensive coastal meddling: "Shifting sands swell the cost of UK's first artificial surf reef."

Bournemouth, and its sandy suburb of Boscombe (pictured), is a classic British seaside holiday resort on the south coast, with piers, Winter Gardens, beach huts and many of the other weird and wonderful cultural manifestations of the coastal resorts that flourished in Victorian times when the therapeutic value of sea water and air were much-heralded. But Bournemouth is determined to participate in the 21st century, and a couple of years ago it proudly declared that "Europe’s first artificial surf reef is being built in Boscombe, Bournemouth this year and is set to put the holiday resort firmly on the UK surf map." The "UK surf map"? Well, yes, there are places around the UK, particularly further west in Cornwall which faces the full force of Atlantic weather, where surfing is feasible and popular, but the map is not a densely annotated one, and Malibu we certainly are not. But the officials of Bournemouth were determined, and approved construction of an artificial reef to amplify existing surf and generate surfer-seducing waves, together with onshore redevelopment (including "surf pods," whatever they might be, and a "surfing academy") that would bring people and money pouring in.

Other such reefs have been constructed - in Australia and New Zealand - and a company from down under was contracted for the construction. The reef itself is built of gigantic sand bags, made from specialty "geotextiles" and each weighing around 2500 tons. Sand (brought from the Isle of Wight further along the coast) is piled up onshore, processed, and then pumped and piped offshore to barges which fill the bags and place them on the sea floor, 200 meters from the beach - which has, therefore become a rather large construction site for some time. The small building in the left hand photo, below, is the same as seen in the bottom left of the picture above.

The project was scheduled to be completed last year, but was, of course, dependent on reasonably good weather. However, this being the British Isles, the weather last summer was distinctly uncooperative, the work had to be suspended and the contractors returned to more balmy southern hemisphere climes (although their accommodation is still being paid for). Inevitably, thousands of tons of unused sand remains stockpiled on the beach, an eyesore for residents; but at least the eyesore is diminishing as, during the course of British coastal winter, the sand is being, shall we say, redistributed.

The original budget for the reef was impressive - £1.4 million. With the delays and the estimated costs of replacing the redistributed sand (the council has, with some precision, set aside £169,000 for this), the costs are now exceeding £3 million. The financial budget is busted, and one has to question the effects on the sediment budget. Every segment of coast anywhere in the world has a natural (or unnatural) sediment budget, incomings and outgoings, net profits, net losses, a granular balance sheet. Excavating the sand from the Isle of Wight will have altered the budget there. And, as the work of Rob Holman has demonstrated (see my January 6 post), the nearshore environment is even more dynamic and shifting than we had realized, dramatic sand movements varying with the season. Now it would seem to me, looking at it in a simple-minded way, that we have absolutely no idea what an artificial reef of this magnitude will do to the local sedimentary budget for Bournemouth - but that it will certainly do something. Similar structures both trap sand and stimulate scouring, and the very fact that the reef is designed to modify the waves might surely mean that it will also modify their effects?

One can only wonder - in a dynamic economic environment and a dynamic sedimentary environment, is this really the best use of public money? The taxpayers of Bournemouth are certainly wondering. 

[coastal photograph: http://commons.wikimedia.org/wiki/File:Boscombe_Pier_November_2005.jpg; construction photographs: http://www.bournemouthsurfreef.com/tag/construction/]

The man who figured out how deserts work

Among the many things that are intoxicating about the desert, the things that draw us back, I find the silence perhaps the most compelling. In a world where noise bombardment is the norm, the complete absence of sound is a shock and a fascination, the auditory equivalent of turning off your headlamp deep underground and experiencing, literally, a complete inability to see your hand held up in front of your face. Sit in the desert in the morning or at night and you can sense yourself straining to detect a sound, any sound - but there is nothing. Wilfred Thesiger, one of the great desert explorers and writers, wrote of "a silence in which only the winds played, and a cleanness that was infinitely remote from the world of men." It is only the wind that breaks the silence, gently and subtly as the day warms up and the air is on the move, sometimes expressing itself with the fury of a sandstorm. Watching the first breaths of wind gather momentum and begin their game with the sand is hypnotizing - at first a few tumbling grains, then more, gathering themselves into swirling, shape-shifting, fluid sheets dancing over the desert surface. This is the desert at work, the wind is the engine and the sculptor, and, as Thesiger observed, the only thing that breaks the silence.

We can wonder at the glorious diversity of the results of the engine's efforts - ripples, ridges, dunes in all their variety, sand seas, sandstorms, sand blasting - but our understanding of how the engine works is owed to one man, Ralph Bagnold.  Born in 1896, Bagnold was one of those extraordinary people whose skills became renowned in entirely different fields of endeavor - in his case, a military and a scientific career, united only by sand. Having survived the First World War, he was posted to Egypt in 1926 and arrived in time to watch the Great Sphinx being disinterred from its sand tomb. For a soldier in Egypt, R&R time offered many opportunities, but for Bagnold it was a chance to explore the desert - not on foot or by camel, but in Model T Fords (somewhat modified), and, later, Model A's. He pioneered the means for extended automobile expeditions, desert navigation, and driving across sand - including the giant dunes of the Great Sand Sea.  As a civilian in the late 1920s and early 1930s, he accomplished journeys that no-one had thought possible, and, along the way, became fascinated by what we didn't know about the desert:

“In 1929 and 1930, during my weeks of travel over the lifeless sand sea in North Africa, I became fascinated by the vast scale of organization of the dunes and how a strong wind could cause the whole dune surface to flow, scouring sand from under one’s feet. Here, where there existed no animals, vegetation or rain to interfere with sand movements, the dunes seemed to behave like living things. How was it that they kept their precise shape while marching interminably downwind? How was it they insisted on repairing any damage done to their individual shapes? How, in other regions of the same desert, were they able to breed “babies”, just like themselves that proceeded to run on ahead of their parents? Why did they absorb nourishment and continue to grow instead of allowing the sand to spread out evenly over the desert as finer dust grains do? More basically, what kind of upward physical force must be exerted on the mineral grains to make them rise against the force of gravity, lifting them to such a height that they can strike one’s face like little hammers? No satisfactory answers to these questions existed. Indeed, no-one had investigated the physics of blown sand. So here was a new field, I thought, one that could be explored at home in England under laboratory-controlled conditions.”

And explore under laboratory-controlled conditions is exactly what he did. He was a highly-skilled engineer and designed and built his own wind tunnels and delicate measuring apparatus from scratch. He meticulously measured sand, its ranges of grain sizes and how they influenced (and were influenced by) transportation by his laboratory winds. He documented saltation, the process by which flying sand grains land and kick yet more grains into the air, and demonstrated that this is the main way in which desert sand moves, quantifying the physics and the aerodynamics. In 1938, he returned to the Sahara as a leader of a multi-disciplined expedition to the Gilf Kebir in the southwesternmost corner of Egypt, an area he and his colleagues had explored earlier. His aim was to take field measurements of moving sand and dune dynamics to test his laboratory results, an aim he accomplished with dramatic success. This was the first time that the desert's engine had been scientifically measured and documented - many questions remain today, but the basis was set out by Bagnold.

A couple of years ago, I was lucky enough to be invited to join an expedition retracing, as far as we could, Bagnold's 1938 itinerary - I was the sort of token geologist. And what an extraordinary experience that was - I became completely hooked on the desert. A visit to the site of his base camp revealed the extent to which his much-studied dune had overridden the scene. Challenges of logistics, navigation and vehicle travel in 2007 only emphasized how extraordinary had been Bagnold's achievements nearly eighty years previously.

The Second World War saw Ralph Bagnold back in his military role. Exploiting his desert expertise, he established the legendary Long Range Desert Group, a highly mobile raiding force that wrought havoc by appearing out of nowhere behind enemy lines after journeys that were thought impossible. After the war, he returned to refining and compiling his work on desert sand, the result being The Physics of Blown Sand and Desert Dunes, a work which remains a classic reference today. He later published with Carl Sagan on the sands of Mars and provided advice to NASA in preparations for the first mission to the Red Planet. And, having exhausted what could be done at the time on windblown sand without reliable long term wind data, now Brigadier Bagnold turned his attention to revolutionizing our understanding of sand transport by rivers and waves.

There is much to say about Ralph Bagnold, and I shall say more in later posts. But for now to conclude with a return to the engine, the desert wind.... I took Bagnold's writing with me through the Gilf Kebir and across the Great Sand Sea - an inspiration in an inspirational landscape, not just the science and the observations, but the resonance of his palpable love of the desert. I watched sand on the move, skittering across the desert floor under a gathering wind, avalanching spontaneously down the steep slope of a dune - and hurtling chaotically, viciously in a raging sandstorm. We had experienced minor sandstorms already, but the one that hit us in the White Desert was a monster. I have just now opened my notebook from that evening, scribbled in pencil because a pen became instantly non-functional, and some sand grains fell from between the pages. As I was blasted by the onslaught of flying sand, I felt a resonance with Ralph Bagnold who had written:

"A dense, stinging fog of low-flying sand grains wholly obscured not only our cars but ourselves up to our shoulders, while our heads stuck out against a clear blue sky. One after the other, our feet dropped an inch as sand was scoured from beneath.

The whole landscape was on the move."

On this occasion, my head did not stick out above the sand and there was no blue sky visible - until the following, incredible, morning which revealed "a cleanness that was infinitely remote from the world of men."

 

[For further reading, Ralph Bagnold's autobiography, Sand, Wind, and War - Memoirs of a Desert Explorer is fascinating and characteristically modest - but, sadly, out of print. The Physics of Blown Sand and Desert Dunes was reprinted in paperback by Dover in 2005. Bagnold photographs above by kind permission of Stephen Bagnold; other photographs are my own. More can be found on Bagnold throughout my own book, Sand: The Never-Ending Story, University of California Press - just published - only a few remaining - hurry!] 

Strange and beautiful quartz grains - confessions of an arenophile

Back in London, and time to catch up a little on documenting the examples of the world's sands that friends have sent. Yes, I confess, I'm an arenophile (or psammophile if you prefer not to mix your classical languages). Given the dazzling variety and unique character of every sand, it's no wonder that collecting it is a global occupation. I succumbed in the process of writing the book, an old friend starting me off by providing the examples which eventually formed the first color plate, and then I was fortunate to receive the enthusiastic help of Loes Modderman, a Dutch collector, one of whose stunning images formed the second plate and who generously gave me a large selection of her sands (see http://www.scienceart.nl/ for some superb examples).

The old friend had also sent me some particular treasures that I must now return to him, and I spent some time ensuring that I had good enough photographs. One example struck me again as being beautiful and mysterious - coarse quartz grains that he had plucked out from river sands in East Kalimantan. Here are a couple of photographs of these (amateur, I'm afraid, simply a home microscope and a camera adapter). They are all doubly-terminated little diamond-like crystals, but the odd thing is that they appear to be zoned, this internal structure being picked out by abrasion during transport. But I am no expert mineralogist - can anyone shed light on the origin of these extraordinary natural works of art?

 

And, while I'm organizing sands here's a crittur that illustrates my last post - a foram that constructs its shell out of sand grains.

And, what the hell, while I'm at it, here are a few more examples of the stunningly beautiful world of the microscopic.

[for professional and expert microphotography of sand grains, see Gary Greenberg's dazzling illustrations in A Grain of Sand: Nature's Secret Wonder]

Nostalgia and Building Stones

Earlier this week, I went on one of my occasional pilgrimages back to my alma mater, on this occasion to give a talk to the Friends of the Sedgwick Museum on a topic that you can probably guess. The grand and imposing building is home to the Earth Sciences Department at Cambridge as well as the museum, and it is always with a range of emotions that I re-enter it. For the ground (first) floor has changed hardly at all since I was there as a student in the late Pliocene, and the pleasure of meeting old friends and mentors is mixed with a sense of unreality, a time-warp - and, yes, nostalgia. There are, of course, many ways in which things there have changed (including the pleasing statistic that more than half of the students there today are female), but there are good reasons for the enduring ambiance of the ground floor. The large space is lined on three sides with magnificent glass-fronted wooden cabinets containing a unique collection of building and decorative stones, installed in 1911 not long after the building was opened, and the space is clearly and unalterably the collection's home. I may have moved around and onward in the intervening years, but the same solid chunks of Millstone Grit remain in the same place and unchanged since I walked past them every day a long time ago.

The collection is one of the treasures of the museum and is a unique reference collection, of continuing value to architects and building conservation experts. It  contains around 2,500 specimens, largely from Great Britain, but several cases advertise "Colonial and Foreign" examples. It was put together for the Sedgwick by John Watson, himself a building stone merchant, whose son was a student at the university. Each example is a perfect cube, around 20 cms on a side, and dressed or polished in a way typical of its use, and each with its original label. Many of the stones revel under exotic names reflecting the local origin and nomenclature: you can study examples of the Bastard and Windy Nook Freestones, Kentish Rag, Stink Stone, Blue Liver Rock, and Clunch.

And, naturally, many of the samples are of the classic sandstones. The Devonian Old Red Sandstone stars widely, including the Caithness Sandstone from the northernmost reaches of Scotland, out of which the Sedgwick's fine external double staircase is built. John Watson's entire catalog of the collection can be found, thanks to the American Universities Internet Archive and the University of California, on the web (http://www.archive.org/details/britishforeignbu00watsrich), and in it, the Caithness Sandstone is described as follows:

Still further north is found the celebrated Caithness Flagstone, which is one of the most important economic products

of this[the Devonian] system. It is used locally for general building, but it is in special repute more as a material

for flagging,and for staircases, both external and internal, for which purposes it has long been employed not only in 

the British Isles but all over the world. Baron Liebig's great establishment on the River Plate, in South America, for 

the manufacture of his well-known meat extract, is floored throughout with Caithness flags. Sir Roderick Murchison, in 

his third edition of Siluria published in 1858, writes, "The Flag-stones of Caithness, which were first described by me 

in the year 1827 under the name of Bituminous Schists … are in many places impregnated with bitumen, chiefly resulting 

from the vast quantity of fishes embedded in them. The most durable and best qualities, as flagstones, are derived from 

an admixture of this bitumen, with finely laminated, siliceous, calcareous, and argillaceous particles, the whole forming 

a natural cement more impervious to moisture than any stone with which I am acquainted." A good practical illustration 

of this useful stone, employed for steps, can be seen in the staircase leading from the ground floor to the first floor 

of the Sedgwick Museum, Cambridge, connecting the economic and palaeontological sections. This example, as well as other 

specimens, shew that by no means all the rocks of the Old Red Sandstone are "red." 

The collection includes a modest sampling from North America, including the Potsdam Sandstone and the "Warsaw Bluestone," a classic representative of North American Old Red building stones, a field trip for which can be easily accomplished by a stroll around Yale University or some of the classic buildings of Manhattan, including the Dakota Building, home of John Lennon and the scene of his death.

Mark Twain seems to have had a great fondness for the Old Red, describing in an 1868 newspaper article, “that poor, decrepit, bald-headed, played-out, antediluvian Old Red Sandstone formation which they call the Smithsonian Institute.” In actual fact, Twain had his old, red, sandstones mixed up - the Smithsonian is built from the "New Red" Triassic Seneca Sandstone [thanks Callan Bentley for the comment pointing this out].In his 1903 essay, Was the World Made for Man?, Twain wrote:

So the Old Silurian seas were opened up to breed the fish in, and at the same time the great work of building Old Red Sandstone mountains eighty thousand feet high to cold-storage their fossils in was begun. This latter was quite indispensable, for there would be no end of failures again, no end of extinctions—millions of them—and it would be cheaper and less trouble to can them in the rocks than to keep tally of them in a book.

Travels meme - and a mad idea for the geoblogosphere

OK, time to contribute to the circulating fun of the geoblogosphere's travels. First, the US - the majority of states, but that's not surprising since I lived, taught, and generally worked there for many years. The blank states are slightly odd, now I look at them, but then again.....

 

And now, the world

I had to colour in Spitsbergen/Svalbard myself since I didn't find it in the list. And there are, of course, distortions, not just projectional. I've been as far east in Russia as western Siberia, but not Kamchatka, and I certainly haven't roamed around the entirety of China. In the opposite sense, I have strayed into Libya and Sudan, but shouldn't admit it, and, given the areas of red that would be generated, it would be highly misleading, never mind brazen, to include them.

It makes me realize how many places are still high on my list - African Rift Valleys, most of South America, New Zealand......but here's an idea: we could all knock one ambition off our lists by selecting a country that nobody has been to and holding The First International Geoblogosphere Conference and Field Trip there in 2010. It would have to be a geologically provocative and politically sensible country, and I know it's crazy and impractical, but it would sure as hell be fun.

On a completley different side note, thanks to All of My Faults are Stress-Related for pointing out the upcoming blogfest Carnival of the Arid - it should make for some good reading.

Granular stuff, earthquakes, and power laws - again

Back in November, in my post on the sandglass, I commented that watching avalanches of sand in a sandglass is to witness one of nature's most fundamental laws in action. The relationship between avalanche size and frequency is an example of a power law. A single grain falling on the pile may simply nudge another further down or set off a catastrophic avalanche - the system is dominated by large numbers of small events and occasional large ones. Prediction is impossible, but the size versus frequency relationship is consistent and follows a power law. Power laws are everywhere: gravity is an example and these relationships can be found in biological systems and communities, the stock market, population behaviours - and, perhaps most famously, earthquakes. The Gutenberg-Richter relationship between earthquake magnitude and frequency is a power law.

The weird and wonderful world of granular materials seems dominated by power laws and here (thanks, again, to Jules) is another fascinating example, shedding light (quite literally) on the details of seismic events. Two post-doc researchers at Duke University, Nick Hayman and Karen Daniels, created an innovative means of modelling and quantifying small-scale events along a moving fault, looking at the way in which granular materials determine fault zone development. They took tiny plastic discs and put them, one layer thick, in between two Plexiglas plates, the lower of which was split, one side being incrementally displaced by a weighted spring to mimic fault displacement. The experimental events obeyed a power law. But the really clever thing, the experimental magic, was that the optical properties of the discs changed according to how much strain they were undergoing and putting the whole contraption on a light table and imaging it through a polarizing filter, yielded some extraordinary results (http://www.jsg.utexas.edu/news/resspotlights/2009/tabletop_earthquakes.html). The image at right is one clip from a fascinating movie which can be viewed through this site: the "fault" runs through the middle of the array of discs and the sinuous patterns of bright threads show the locations of greatest strain, each one forming a "force chain." With each displacement, these patterns change, chains appearing and disappearing, linking and separating. Force chains are common in granular materials - the distribution of stress inside a sand pile is not uniform, being lower (counter-intuitively, below the center of the pile) and this may account for the sudden, catastrophic, failure of grain silos and allow the sand in the sandglass to flow smoothly.

This direct imaging of micro-processes and deformation in a fault zone is amazing, and the technique will undoubtedly produce further suprises. And it allows quantitative analysis of what is going on - Hayman and Daniels describe how subtracting one image before an event from one immediately after, allows measurement of exactly what changed - the illustration below (taken from their paper at http://www.agu.org/journals/jb/jb0811/2008JB005781/) shows an example of this "image differencing" technique; "the image is white where a force chain strengthened, black where a force chain weakened, and gray where no change occurred. A chain that is lined with a white strip on the left side and dark on the right slipped sideways as a unit; a chain structure that is completely white formed during the slip event; a chain structure that is completely dark disappeared during the slip event. Finally, particles that slipped sideways appear as faint rings."

“What our experiment is showing is that some of the fundamental distributions of earthquakes that are known in nature can be mimicked using just granular materials,” said Hayman. “And the fact that we can observe the state of stress enhances the point of view that these materials are important in faults.”

Tabletop experiments, direct imaging of geological processes, granular materials, power laws - what fun!

[For an entertaining and accessible discussion of sand piles, power laws, self-organized criticality etc., read Per Bak's How Nature Works]    

Grain-by-Grain (2): the amazing sand bottles of Andrew Clemens

Sand has always provided a medium, a muse, an inspiration in many ways, but the way in which it inspired Andrew Clemens was extraordinary - and unique. Clemens was born in Dubuque, Iowa, in 1852 (or 1857, reports vary), one of the six sons of German and Prussian parents whose shipboard romance began as immigrants to the U.S. His father was a locksmith and wagon-maker who moved the family to McGregor, Iowa, to take advantage of the business provided by the gold-rush and settlement of the west. At the age of five, Andrew was struck by "brain fever," encephalitis as we now know it; lucky to survive, he lost his hearing and speech. He was sent to the Iowa Institute for the Education of the Deaf and Dumb in Council Bluffs, but as a young teenager he most enjoyed his time in McGregor, working in his father's business - and visiting Pictured Rocks. 

In what is today Pikes Peak State Park, the classic Paleozoic formations of the central U.S. form bluffs and gullies along the Mississippi River, among them the Ordovician St. Peter Sandstone. This classic sandstone is famously pure and white, its well-rounded quartz grains providing the raw material for glass-making and other applications. But at Pictured Rocks, waters percolating down through the overlying limestones, charged with a variety of minerals, have stained the St. Peter with a dazzling palette of natural colours (photo from Iowa Geology 2001, 26, Iowa Department of Natural Resources).

Clemens loved this place, and collected a spectrum of sand samples of subtly different hues, greens, reds, browns, yellows, grays and blues. Back home, he would carefully sort the grains by both colour and size, and then go to work. In bottles of different sizes and types, he would, grain-by-grain, construct small works of art. Using specially devised tools - fish hooks and wands made of hickory - he would sort and position his fine-grained sands into, at first, geometrical designs and later, as he developed his incredible craft, meticulously detailed images (photos courtesy of the State Historical Society of Iowa, Des Moines).

The image of George Washington on his horse is perhaps the most famous, but the designs range from personalized greetings to dramatic eagles, via ships, floral designs and documentation of local events, often with words and mottoes. His pieces, of necessity, were constructed upside-down, each bottle later sealed; he used no glue, no pigments, nothing except naturally-coloured sand grains and his patience and genius. How many bottles he made is unknown, for they are fragile and many have been broken over the years, a work of art becoming just a pile of coloured sand on the floor. Indeed, for a while Clemens worked at the South Side Museum in Chicago, constructing simple designs as the public watched, which were then dramatically smashed with a hammer to demonstrate that no magic was involved; understandably, Clemens did not find this activity to his liking and soon returned home.

Clemens's extraordinary skill and creativity became recognized, but only modestly. The Editor of the North Iowa Times wrote in 1888 that "McGregor has an artist nowhere equaled in this world in his line of artistic work. He invented and became skilled in an artistic work all unaided and alone. He invented and made his own tools. He has thus brought to a surprising perfection an art of which he alone is the inventor, the master. We refer to the pictures wrought from sand from Pictured Rocks by Andrew Clemens. Our people do not properly appreciate this art. The master doesn't seem to know its worth nor does he seem to realize his exalted position among the inventors of the world. Mr. Clemens lately completed what may be regarded as a masterpiece. He has made many fine efforts before. This last one is a perfect picture of General Washington on horseback. The artist has surpassed the copy, he gives the coloring, shadowing, form, all complete and perfect and all done in sand. The work shows a Mississippi River steamer running at full speed, a group of Indians in camp, the flag of our country, fields, harvest scene, all perfect and wrought with natural colored sands in a glass jar. The jar is open at the bottom and the work is commenced at the top of the picture. But to appreciate this wonderful work one must see it as we have seen it. It is one of the wonders of the age and ought to have a place among the great art of the world."

Clemens died, tragically young, in 1894, probably of tuberculosis. His bottles had sold for fifty cents or a few dollars but today the survivors sell for thousands.

(quotation and information from http://members.tripod.com/clipclop/andrew/, a site which has detailed information and pictures of many of the surviving works. For the geology of Pikes Peak State Park, and further material on Clemens, see http://www.iowageology.org/gb70/stop-05.htm, the source of the picture of Clemens, above).

Coastal geologist at work

Thanks to Jules for posting a comment that drew my attention to a piece in the New York Times Science section on Rob Holman, a coastal geologist at Oregon State. Not only does he run the unique Argus program which allows imaging of sand movement in nearshore environments (demonstrating how little we really understand about these complex systems), but he's also an arenophile. The article, http://www.nytimes.com/2009/01/06/science/06prof.html?_r=1, contains a link to an audio slide show with some examples of Argus imaging. See also the Coastal Imaging Lab website at the University, http://cil-www.coas.oregonstate.edu/.