Through The Sandglass

Streams of grains - some more amazing granular research

As I'm sure I've said before, to watch the sands of an hourglass in action is to observe all kinds of natural phenomena at work - and all kinds of questions to which we have no answers. It's not just the cascades and avalanches, but the liquid stream of grains itself that holds mysteries, interactions and behaviours too minute and too rapid for the eye and the brain to grasp. Traditionally, we have to resort to statistics, to averages, to clumps and groupings - to model at the level of individual grains is just too complex and there are too many of them. But now we are beginning to be able to peer into the nano-world of an individual grain and to simulate its interactions with its colleagues, thanks to the continuing, revelatory, research into granular materials. Friends have recently drawn my attention to two specific examples that I'll mention here.

The University of Chicago has long been a fluidised bed of granular behaviour research, with Sidney R. Nagel and Heinrich M. Jaeger as the uber-gurus of the bizarre (remember the Brazil nut effect and then the reverse Brazil nut effect), and now Jaeger, together with his students and colleagues, has yet again achieved something extraordinary. Look again at the flowing stream of sand grains in the hourglass: until recently, studies of so-called "free falling granular streams" tracked shape changes in flows of dry materials, but were unable to observe the full evolution of the forming droplets or the clustering mechanisms involved. But, as recently reported in Science Daily, with the aid of a very expensive and very high-speed camera, Jaeger has been able to track the formation of "droplets" in the granular stream and show that surface tension effects 100,000 times smaller than those that operate in liquids are at work. The dry material behaves as if it were a liquid with very low surface tension - as suggested in the graphic at right, above, and a short but dramatic video is available at the NSF site here.

"At first we thought grain-grain interactions would be far too weak to influence the granular stream," said John Royer, a graduate student on the team. "The atomic force microscopy surprised us by demonstrating that small changes in these interactions could have a large impact on the break up of the stream, conclusively showing that these interactions were actually controlling the droplet formation." So streaming sand not only looks like a liquid, but actually behaves like one, once again raising the question of exactly what form of matter this is. And, as with all this kind of research, it's not just of academic interest - the efficient filling of pharmaceutical capsules is but one (important) industrial process that could benefit. And it's also a further wonderful example of the deeper we look, the more complex things become and the more the questions that are raised. As Jaeger says, these "experimental results open up new territory for which there currently is no theoretical framework."

So Jaeger is breaking new ground in the experimental observation of individual grain interactions, but are we doomed to be unable to computationally model these things, overwhelmed by the sheer numbers, the scale of the problem in a different sense? Well, no, not if Dan Negrut, Toby Heyn, and Justin Madsen at the University of Wisconsin have anything to do with it. Working at the Simulation-Based Engineering Laboratory in Madison, they have developed both the theoretical and mathematical basis, and the power of parallel computing, for modelling the movements of huge numbers of grains. There's a report on their work on Science News, but the best thing to do is to go to their website and enjoy some of their simulations (you'll need to download the VLC viewer for which instructions are given). Not surprisingly, my favourite is their virtual hourglass (illustrated at left at the top of this post); this uses the relatively modest number of 25,000 individual "objects", i.e., grains, but it's incredibly realistic. There are other simulations involving hundreds of thousands of grains and the capability is growing all the time - Negrut hopes his simulation will analyze millions of grains in a single day, if not a matter of hours. To model the interactions of individual grains requires a firm theoretical foundation and the team has made great progress in establishing this; a planned collaboration with Professor Alessandro Tasora from the University of Parma will further refine this. Negrut kindly supplied me with a preprint of the group's forthcoming paper, A Parallel Algorithm for Solving Complex Multibody Problems with Stream Processors. Unfortunately, I have to confess that it's entirely beyond me, even the abstract outstripping my modest mathematical and computational capacity. Here's an extract - I recognised two sand grains in Figure 1 and was then terminally lost:

 

But among the simulations viewable on their website is one of work they are doing on a Mars rover moving over granular materials. This, as I recently noted (Stuck in the Sand) is currently a major problem for the Mars Rover Spirit, and its engineers back on earth. Thanks to being again alerted by a reader, I now find that the Rover's dilemma (sounds like the name of a pub) is being used to good effect to study details of the diverse granular materials revealed by its spinning wheel. As reported in Science Daily, "One of the rover's wheels tore into the site, exposing colored sandy materials and a miniature cliff of cemented sands. Some disturbed material cascaded down, evidence of the looseness that will be a challenge for getting Spirit out. But at the edge of the disturbed patch, the soil is cohesive enough to hold its shape as a steep cross-section." Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the science payloads on Spirit and its twin rover, Opportunity, said "We are able here to study each layer, each different color of the interesting soils exposed by the wheels," adding that "The layers have basaltic sand, sulfate-rich sand and areas with the addition of silica-rich materials, possibly sorted by wind and cemented by the action of thin films of water. We're still at a stage of multiple working hypotheses." Below is an image of the revealed materials (NASA/JPL-Caltech/Cornell University).

 

There is, literally, no end to the extraordinary journeys that granular materials can take us on, so next time you watch an hourglass in action, think of low surface tension liquids, parallel computing and Spirit.

[I have to thank Richard Cathcart and Dominion Rognstad for drawing my attention to these topics - my theme for this blog is so wide-ranging that I can't possibly keep track of all the items of interest and I very much appreciate any suggestions and links that readers might send me.]

I just couldn't resist: Michael Jackson and sand

My daughter has long been a devoted fan of The Simpsons, and sometimes puts her encyclopedic knowledge to the test by challenging us to find any random topic for which she can't cite an episode that includes or addresses it; so far she has succeeded in all challenges. In recent times it has occurred to me that the same game can be played with sand and I thought that the subject of the recent and ongoing world headlines would be an interesting test. Now I will readily admit that a comprehensive inventory of the works of Michael Jackson is not something that I devote a lot of my increasingly precious brain cells to, and so this required a little research (cheating, by my daughter's standards). The image below was easy, since it's all over the net, a tribute sand sculpture by the Indian sand artist, Sudarsan Patnaik, on Orissa’s Puri beach and created in four hours with the help of students of his Golden Sand Art Institute and a couple of tons of sand. But this is a tribute, a posthumous creation - what about the classic works, surely some sand references there?

It didn't take me long, and I draw your attention to the 1992 video of "Remember the Time," an extravagant production set in ancient Egypt in the times of the cruel but song-'n-dance-loving Pharaohs and their glamorous consorts. Jackson performs some impressive magic disappearing tricks, including his final exit, with granular materials, but most impressive is the introduction which, after a brief homage to the angle of repose, resolves itself (above) into a swirling storm of sand grains - and a sandglass. 

 

Oh, and yes, Michael Jackson did guest star in an episode of The Simpsons.

All that glitters ...

 

At the end of my last post on granular segregation and placer mineral deposits, I included a photo of a sand sample from Yosemite that is reputed to contain flakes of gold, with a slightly enigmatic candidate grain. Lockwood at Outside the Interzone and the Lost Geologist kindly commented with testing advice - press the grain with a needle and, because gold is relatively soft and malleable, it will deform, the needle leaving an imprint; mica, being flaky and brittle, will split apart. I couldn't find the same grain, but found a similar one, and gave it a poke with a needle. The point left a dent - aha, I thought, my hopes rising. But, on applying further pressure, the grain fragmented, flying apart into tinier flakes. It was muscovite, a mica, coloured in this case yellow, and slightly rotten from the processes of weathering - hence the dent, and its deceptively lustrous appearance. I should have known - these are really young sand grains, the recent sawdust of the crumbling Sierran granites, and the mica minerals (including an almost perfectly hexagonal biotite grain, left) form a significant membership of this granular tribe - they'll rot out of existence as time goes by.

So, all that glitters is not gold. Of course, pyrite, the shiny yellow iron sulphide mineral, is the traditional "fool's gold" (left in the photo above) but I'm not that foolish: if I found something that looked like the placer gold shown on the left, below, I like to think that I might have leapt to the correct conclusion. But the little muscovite grains (above, right) do sparkle in a most alluring way - I came across the second photo, below right, which purports to show placer gold nuggets and, while I'm no mineralogist, they look a bit suspicious. But then most prospectors know a lot more about what they're doing than I do.

 

My wife would agree. When we got married, she found the old picture below and felt that, with a geologist for a husband, this would be illustrative of the way her life would evolve (note the contents of the woman's bag). We still, ever-hopefully, have this picture on the wall, but alas, so far ......  

Granular segregation and the Gold Rush

Anyone walking on the beach or through the dunes will often notice areas of dark gray smeared across the surface, often outlining ripples, as if an artist had highlighted the sand's topography with charcoal. I encountered many examples of such designs recently at the dunes of Kelso (above) and Oceano, and on California's beaches. Look closely, and you'll see that these patterns are characterised by concentrations of dark grains, gathered together in a much higher proportion than elsewhere in the sand. Look even more closely, down a microscope, and there they are, little black nuggets nestling among the glittering quartz grains (the example below is from Kelso).

 

As my messing around with kitchen physics showed, sand, like all granular materials, dislikes being mixed and will find endless ways of sorting itself out into its components. Pouring and shaking cause it to segregate by size and shape, transporting it by wind and water differentiates grains by weight (as well as by size and shape), and that's what's going on in the dunes and the beaches. The black nuggets are grains of a mineral much denser than the quartz grains of the same size, and they are therefore slightly less easily moved. With time, the lighter grains are winnowed out and the heavier ones left, concentrated. In the case of the Kelso sand, the heavier mineral is magnetite, an iron oxide; I suspected this, and repaired, again, to the kitchen, to get a fridge magnet which I applied to the sand with the result that the fine black grains flew onto the magnet, piling themselves up into minute towers (see the photo at left; warning - removing the grains from the magnet is far more difficult and can result in scratched white goods).

The natural concentration of minerals by wind, waves and currents is economically important - large deposits of iron were formed this way, today and in the geological past. Such a natural concentration was the cause of one of Thomas Edison’s many business failures. On a fishing trip with friends off the coast of Long Island, Edison put into shore for lunch and found the beach covered with a layer of black sand. He took some home (perhaps to his kitchen) and discovered that the black grains were magnetite. Edison’s enthusiasm ran, as it often did, ahead of his business sense, and he immediately arranged for the purchase of the beach and the manufacture of separating machinery. Unfortunately, by the time he and his colleagues returned to Long Island, a winter storm had reworked the beach and completely removed the black sand.

These kinds of mineral deposits are called placers - in addition to iron, platinum, tungsten, titanium, tin, niobium, zirconium, and other vital elements are all sourced from placers - plus other treasures. The composition of sands betrays their origins, and if they came from the crumbling of precious mineral deposits, then they will contain precious minerals, often more easily accessible than by mining the hard rocks of their origins. Diamonds, rubies, sapphires, garnets, and gold are mined from placer sands in many parts of the world; in places like Namibia, beaches have been stripped to bedrock in the search for precious gemstones. Gold, being heavy and un-reactive, makes for an ideal placer mineral, and such deposits have been exploited for as long as we have been obsessed with gold. An ingenious early method (probably used in ancient Egypt) employed a fleece bag, the woollen side facing inward: water and sediment were passed through the bag, and the heavy gold flakes became embedded in the wool, remaining behind when the bag was emptied of lighter sand and gravel. A similar method was still being used in the mountains of the Caucasus in the 1930s; it also explains Jason and his Golden Fleece.

California was founded on placer sands: forty-niners during the Gold Rush sought the metal not only in subsurface mines, but in the streams and rivers that drained the gold-bearing ores. Panning the stream sediments was backbreaking work, and so a technological breakthrough was called for. It happened in the form of hydraulic mining: miners used high-powered water hoses to erode the valley sides (photo below, USGS). The gold, being heavier than the rest of the dirt, collected in sluices, and everything else drained away; mercury was commonly used to further concentrate the gold. It has been estimated that over a twenty-year period 750 million dump truck loads of sand, mud, and gravel, together with mercury, were flushed into the Central Valley—with dire environmental consequences. The Yuba Valley is just one of the watersheds that remains physically and chemically scarred today, and it can be argued that the environmental movement in the US has its roots there. A few years ago, the New Scientist had a fascinating piece on this - it's only available to subscribers, so I have reproduced it in full at the end of this post. And for further details, go, as usual, to the wonderful USGS search box and put in "hydraulic mining." And where did all this sedimentary debris from hydraulic mining end up? Well, a lot of it is in San Francisco Bay, moving out into the Pacific and forming some remarkable sedimentary features on the way - but more of that in a later post.

And, while I'm at it, I was given by a friend a sand sample from a Yosemite lake, a sample that was reported as containing flakes of gold. I've had a quick look; it's full of the hardly surprising debris of the weathering of the Sierran granites, including many flakes of yellowish mica, red herrings in the search for gold. But, in the middle-right of the photo below is a single grain that looks different - it's still a flake, but more chunky than the typical micas and with a different surface lustre. I'm no mineralogist, and certainly not a precious mineralogist, so if anyone has a view as to whether or not this might be gold, then I'd like to hear from you - but can't yet afford to offer a reward!

  

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From the New Scientist, 12 November, 2005, by Richard Lovett

Histories: The day the gold rush stopped

Although American environmentalism did not begin to flourish until the 1960s, the movement's roots date back to 1878 and a town meeting in Yuba City, California. Not that the assembled townsfolk saw themselves as doing anything so altruistic as protecting nature. Their concern was to save their land and livelihoods from torrents of mud unleashed on them by gold mines upstream. Angry and desperate, they formed the Anti-Debris Association, hired lawyers and went on the offensive. The fight that followed was so bitter it's amazing no blood was spilled. At one point, the association armed an anti-debris militia of 70 men - but law prevailed, and in a decision nearly a century ahead of its time a federal judge decreed that an estimated 45 tonnes of gold must remain in the ground.

IN FEBRUARY 1852, a Connecticut Yankee called Edward Matteson was working his gold claim at a place called American Hill in the Sierra Nevada foothills. There was plenty of gold in the compacted gravel of his claim, but it was widely dispersed and would take months to dig out with a pick and shovel. Perhaps, Matteson thought, there was a better way.

Matteson, like other miners in the early years of the California gold rush, had been using techniques that had hardly changed in millennia. The concept was simple: if you shovelled gold-bearing soil into a sluice box and scoured it with fast-moving water, the lighter sand, gravel and mud would be washed away, leaving the precious metal behind.

Unfortunately, shovelling dirt into a sluice box is hard, time-consuming work - and dangerous if you are digging into the base of a steep cliff. Matteson's brainwave was to attach a canvas hose to a tank of water high above him. Then he could stand safely back and direct the hose so that the water did the excavating and then channelled the debris along a system of ditches into his sluice box.

The Romans had much the same idea: they built dams and ditches to direct water where they wanted it, breaking the dams to create artificial flash floods along the channels. Matteson's innovation was to send the water through a nozzle, magnifying the force of the flow and allowing him to direct it precisely where he wanted.

Thanks to his high-pressure hoses, Matteson's operation became so efficient he could do several weeks' worth of work in a single day. But the new technique, called hydraulic mining, also sent weeks' worth of sediment downriver each day.

Word spread and soon hydraulic mining was booming. Most of the early mines were small and their environmental effects predominantly local. And in the early 1860s severe drought forced many to close. But when the rains returned, so did the miners, this time backed by wealthy investors from as far away as England.

"Hydraulicking" worked best along an 80-kilometre belt of the Sierra Nevada at elevations between 1200 and 1500 metres, where huge deposits of gold-bearing sediments had accumulated in ancient streambeds. There were mines everywhere, but by far the largest was Malakoff Diggins, which was so efficient that it could profitably mine sediments containing only a few pennies' worth of gold per cubic metre.

The mine was run by the well-financed North Bloomfield Gravel Mining Company, which ploughed $3.5 million into the operation. The Diggins eventually produced more than 6 tonnes of gold.

Today all that's left at the site is a 250-hectare pit 200 metres deep. But at the peak of operations, crews laboured day and night in the red-tinted gravels with hoses whose "Little Giant" nozzles could shoot 20-centimetre-thick jets at speeds of up to 50 metres per second - enough force to kill any miner who got in the way. In 1879 a reporter from the San Francisco Bulletin spoke of huge rocks being washed away "like chaff", with "a cloud of red foam" hanging above the points where the water hit the cliff. When water wasn't enough to do the job, entire hillsides were loosened with gunpowder - sometimes 15 to 20 tonnes of rock in a single blast.

When a US federal judge called Lorenzo Sawyer visited the site in the 1880s, he too was impressed. "The excavating power of such a body of water, discharged with such velocity, is enormous," he wrote. He was particularly amazed by the mine's night-time operations, conducted under "brilliant" lights that ran on hydroelectricity. "A night scene of the kind, at the North Bloomfield mine, is in the highest degree weird and startling, and it cannot fail to strike strangers with wonder and admiration."

By 1880, 'hydraulicking' had buried 6000 square kilometres of farmland

But Sawyer wasn't there to admire the scene. He was there because of where all that water, mud and silt was going. The first part of its journey was along a 3-kilometre tunnel through a mountain. The tunnel was effectively a vast sluice box that caught as much as 90 per cent of the gold. The debris, however, carried on into the Yuba river and towards the farmlands below.

In 1880, California's state engineer had estimated that 6000 square kilometres of farmland had been buried by mining debris. Sand bars had sprung up in rivers all the way to the coast. Hardest hit were the towns of Marysville and Yuba City, directly below the mines. As debris built up in the riverbed, the water rose so fast that the levee builders could hardly keep pace. But by now the people of Yuba City were fighting back. In 1878 they had banded together to form the Anti-Debris Association and sued the owners of the mine. Six years later, a panel of judges headed by Sawyer decided the case.

Judge Sawyer's 56-page ruling is a litany of environmental horrors, but the worst were his projections for the future. So far, the North Bloomfield mine had dumped 90 million cubic metres of debris into the Yuba river. About a quarter of that had reached the lowlands. The rest was still perched upstream, clogging some canyons to depths of up to 50 metres and creeping downward with each spring flood. If there was a really big flood, there was a chance the whole lot would come sliding downriver.

Worse, Sawyer estimated that there were 500 million cubic metres or more of gravel still to excavate. There was no choice but to shut down the mine under the ancient law of nuisance, which prohibits using your property in ways that damage someone else's.

Sawyer didn't ban hydraulic mining outright, though. He ruled that if the miners were to continue, they must find a way to keep the debris on their own property - and prove in advance that it worked. The miners appealed for leave to experiment with remediation techniques while continuing their operations. But Matthew Deady, one of Sawyer's fellow judges, gave that idea short shrift. Asking the people in the valley below to put up with that, he said, "may be likened, at least, to living in the direct pathway of an impending avalanche".

Sawyer's judgement was remarkable because it pre-dated America's best-known environmental rulings by more than 80 years. The stakes were enormous: the judgement would determine California's future as either an agricultural state or a mining state. But Sawyer didn't seem to see it as a trailblazing decision. He was simply applying established law, albeit on an unprecedentedly large scale.

It took years to force out miners who flouted the ruling, but the court's decision effectively killed off hydraulic mining in the California goldfields. Hydraulicking itself has never died: it has been used elsewhere to mine everything from coal to rubies and even aluminium. The difference is that today's mines exploit higher-grade ores, which make it economical to trap the tailings and recirculate the water in closed loops.

The hydraulic miners' legacy still surfaces from time to time in California's courts. In 1986 a flood breached levees built nearly 100 years earlier out of debris washed down from the North Bloomfield mine, resulting in lawsuits over whether such materials were adequate for flood protection. And in 1995 the California supreme court took on the tricky question of who owns those sandbars created by the shifting sediments from the old mines, some of which are now prime sites for urban development.

But nobody ever found an environmentally sound way to reopen the Malakoff Diggins. Today it's a little visited state historical park, even though, if Sawyer's back-of-the-envelope estimate is correct, gold worth $650 million remains in the ground.

Father's Day, sand and culture

I was delighted to see this morning that Google UK had elected to celebrate the joys of paternity with the image above. I was surprised, however, on going to Google.com that no such celebration seemed to be in order. Having spent a chunk of my life living and working in the US, and being married to an American, cultural contrasts have always been of interest ("two nations separated by a common language", hoods, bonnets, trunks, and boots, sidewalks and pavements and the completely different meanings if anyone were to say "I'm mad about my flat") - but I always thought thought that the Brits were supposed to be the dour, reserved ones compared with the more exuberant Americans. So why the Googles are behaving counter-culturally is beyond me.

This is also a reminder that the holiday (vacation) season is upon us, and, along with that, the season of sand sculpture festivals around the world. The Queen (of England) has just visited our south coast to see, amongst other things, a gigantic sand sculpture of her even more gigantic home of Windsor Castle - she apparently remarked that it "looked just like the real thing" (which is, after all, largely built out of sandstone). And these days you don't even have to be at the beach for such festivals - Berlin is not renowned for its coastal location and glorious beaches, yet it is right now the home of this year's Sandsation and Philadelphia is celebrating its World Series champions, the Phillies, (currently heading up the National League East) with a sculpture in Franklin Park (scene of an Egyptian extravaganza a couple of years ago). If you were to visit one of India's beaches, your enjoyment might be dampened but your health awareness raised by a sand sculpture warning on the threat of swine flu. All in all, the silly season is upon us - but then why not?

And, in preparation for relaxation on the beach, sand castle building and a general intimacy with granular materials, there's a great book I would recommend that you take along .......

 

[Phillies sculpture photo via creative commons license, Samjcohn's flickr photostream]

Of reptiles and robots - locomotion in sand

Anyone who clambers up the slip face of a dune becomes rapidly, and agonizingly, aware that locomotion in sand is a challenge. Even walking on the beach often requires a different kind of gait. Granular materials just make life difficult for humans, other critters, and vehicles (see the problems for Spirit, bogged down in the sands of Mars, Humphrey Bogart's encounter with the angle of repose, or the travails of participants in the Marathon des Sables). For us, simply walking on sand requires around two-and-a-half times as much energy as on a hard surface - we're actually better off running, which only takes one-an-a-half times as much effort (although my knees are reluctant to put this to the test). Yet there are large numbers of our companions in the world that are exquisitely adapted to locomotion on and in granular materials - at least under the right conditions. The complex networks of tracks and trails in the sands of the Kelso dunes reminded me of this (as I paused for breath), together with the impossibility of photographing fleet-footed lizards dashing effortlessly for cover at speeds that the eye can barely follow. 

The ghost crab, so-named because of its ability to disappear instantly into the sand, and whose genus, Ocypode means "swift-footed," is one of the record-holders in the granular olympics; in the right conditions, it can scoot across the surface at speeds in excess of five miles an hour, its small body becoming a blur. However, if the conditions are not just right and the sand is soft, the ghost crab runs into trouble and is swiftly overtaken by the zebra-tailed lizard who, although surprisingly does not spend a great deal of time in the sand, nevertheless can cope with widely varying granular conditions, even quicksand. It would seem that the lizard's talents derive from clever foot-design and actions, but the fact is that we're not entirely sure (see http://www.sciencemag.org/cgi/content/full/315/5810/325). The variety of critters who are good at moving around in sand is equalled by the variety of ways in which they do it. Think of the snakes, the sidewinder for example, whose waving, looping motion leaves such unique and beautiful designs; or another lizard, the sand skink, also known as the sand swimmer or sand fish, which seems to have taken a kind of nanotechnology approach, the microscopic design of its scales reducing friction and minimizing abrasion as it swims effortlessly beneath the surface of the sand for much of its existence. The sand skink's motion is also unique, and enables it to treat the sand as a viscous fluid through which it can swim (http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003309). Or consider the charmingly named itjaritjari, a strange little marsupial mole that lives throughout Australia’s deserts. It seems to have no eyes or ears, but put it down on the sand and it will disappear, as the Aboriginal people say, “like a man diving into water.” No one knows how the itjaritjari navigates or senses, but it has a hard nose and front feet well adapted to excavating, the back ones being webbed to help push through the sand; the young are carried in a pouch that cleverly faces backward so as not to fill up with sand. And then there are the insects.

Trying to understand the skills of these expert critters is the focus of research around the world, for efficient locomotion in granular materials is critical in the realm of robotics, particularly for extraterrestrial explorers (as Spirit's problems so dramatically illustrate).  Daniel Goldman at the Georgia Institute of Technology in Atlanta was one of the researchers chasing ghost crabs and zebra-tailed lizards across laboratory sands in his pioneering work in the field of biomechanics, and he has now turned his attention to robotics. As reported earlier this year, Goldman, together with colleagues from the University of Pennsylvania and Paul Umbanhowar at Northwestern (who was extremely helpful to me as I was writing the book, trying to comprehend his extraordinary work on oscillons - no doubt the subject of a later post), has made real progress on designing a robot that doesn't get bogged down. Their laboratory test bed track consisted of an eight-foot-long container filled with poppy seeds and with holes in the base so that granular material could be aerated and turned into variable types of fluidized bed with different densities. "We used poppy seeds as the granular material because they were large enough not to get into the SandBot motors but light enough to be manipulated with our air blowers," explained Goldman. "We have done experiments with small glass beads, which more closely approximate desert sand, and found no qualitative change in the results." The photo below shows the SandBot at rest and churning through the poppy seeds. The robot's "legs" are C-shaped and their rotation characteristics variable. The ability of the robot to keep moving is highly sensitive to the density (and therefore the packing) of the sand and the frequency with which the wheels rotate. It will hardly be a surprise to any of us who have buried the wheels of a 4WD in the sand that the looser the material and the faster the wheels are rotating, the more easily will the robot bog down. As Goldman said, "changes in volume fraction [packing and density] of less than one percent resulted in either rapid motion or slower swimming. We saw similar sensitivity when we changed the limb rotation frequency."

The Georgia Tech news release concludes with the following: Goldman "also plans to use the information to help roboticists design devices with the appropriate feet and limb motion to move well in complex terrain - including sand. Future robots may have the ability to sense the type of material they are walking across, allowing them to adjust their limb motion accordingly. Such smart robots would advance the exploration of other planets, as well as search-and-rescue missions in disaster settings." This is important - and fascinating - stuff, worth contemplating next time you're struggling up the face of a sand dune, gazing enviously at that lizard.

[The report on Goldman's work linked above also contains some videos of the SandBot's efforts, enjoyable viewing. Ghost crab image via Creative Commons license at mmhaffie's flickr site, zebra-tailed lizard image, Madalyn Berns and ScienceMag, sand skink image credit Matt Gunner at flickr, sidewinder and cricket images, National Geographic]

A thematic departure - in the interests of science and free speech

Readers will probably have sensed that I did not set up this blog as a vehicle or a forum for controversy; it's designed to be interesting (and, I hope, fun). It's not that I don't have strong opinions on many topics (ask my wife) but if I need to express them or grind axes, I'll find other ways of doing so. However, once in a while, something comes up that can't be ignored and that deserves as much attention and broadcasting as possible. As someone who modestly attempts to translate science for interested non-specialists, I have a lot of respect for the skills and energy of many professional science writers, among them Simon Singh. But Singh is currently being sued for libel by the British Chiropractic Association, with whom the law has so far sided.  This case, and the bizarre way in which British libel laws purport to work, have been taken up in a campaign by Sense About Science, an independent charitable trust established in the interests of "Promoting good science and evidence for the public." And quite rightly so - as the campaign states, "This is an issue that affects anyone who cares about science, journalism and free speech."

Having added my name to the list of now over 10,000 signatories of the Sense About Science statement, I shall simply copy below the update e-mail I received from them today. This may be, in the first instance, an issue about my country's idiotic libel laws, but it would seem that anyone is liable to being sued in British courts, and in today's world the implications are broader and indeed potentially impact "anyone who cares about science, journalism and free speech." For further background on the case, see this and other pieces in The Guardian (where the initial offense was committed), Singh's website and his recent statement; there are numerous other blogosphere posts, including one by Pharyngula. Read on and have a think:

Dear Friends

In a strangely quiet ten minutes, I’m glad finally to find time to send this quick update on Keep Libel Laws out of Science to all who have signed the statement to support Simon Singh and seek a review of the libel laws.

Today, thanks to all your efforts, we are sending that statement again to the Department of Culture, Media and Sport, but now with 10,000 signatures! And still they are pouring in. We’ve also had great comments, examples of similar cases, offers of help, and urgently needed donations for the campaign.  Please keep them coming. We’re working through offers of help and ideas as quickly as we can.

Signatories are going up more quickly, thanks to Andy Lewis’ speedy rescue with an automated system and the patient volunteers who have worked long days to help. You can view signatories via a link from the main page on www.senseaboutscience.org/freedebate and lots of other related material. If you twitter, you can follow short updates at twitter.com/freedebate.

Simon’s case and the chilling effects of libel threats have been covered by The Guardian, The Times, Daily Mail, The Independent, Nature, BMJ, The Economist, Times Higher Education, Sunday Times, FT, Wall Street Journal, Private Eye, The Observer, Channel 4, BBC, among others. Links to these and some of the many blogs about the case are on the website. Do tell me if you see more, especially outside the UK. The statement has been translated into French (thanks to Jean-Paul Krivine) and we know of coverage in Sweden, Germany, Spain, India and America, but there may be things we’ve missed. Also, if you write for any publication, can you write about the campaign and the issues raised by Simon Singh’s case?

You can now buy Keep the Libel Laws out of Science T-shirts, mugs, bags, badges and caps online from Spreadshirt. The lovely logo is thanks to Hamish Symington, and thanks also to everyone else who offered design ideas. If you send us photos of you wearing them outside the Royal Courts of Justice, or similarly relevant venue, we’ll put them up!

Keep Libel Laws out of Science got in its Mini and went to the Cheltenham Science Festival. The organisers were really supportive (thank you) and let me roam. It was wonderful to hear all the support for Simon and the campaign, but very difficult to stop the speakers from stealing all my badges! A few pictures are on the website. Dara O’Briain, Robin Ince and Ben Goldacre took part in an event alongside Simon and all stressed the importance of freedom of speech.

Great to see the logo link to the campaign on many websites but there must be hundreds more that should be carrying it. Please cajole and harangue those you use.

On the issue of chiropractic claims, some of you will have seen the cumulative effect of interest in the case on the blogosphere over this past weekend; hundreds of chiropractic websites were taken down following questions by bloggers and urgent instructions from chiropractic organisations to avoid breaking the rules on medical claims for chiropractic. http://www.quackometer.net/blog/2009/06/chiropractors-told-to-take-down-their.html A few other links are on our website; there seems to be a lot happening so do send us links to anything you think relevant.

A note from Simon Singh: “I’ve met so many passionate, supportive people at talks I’ve given, most recently Skeptics in the Pub in Oxford and Cheltenham. The responses, with all the blogs and comments too, suggest this is a campaign gathering the momentum necessary to reform the libel laws. Please continue your support in any way you can, and tell others about it.”

Campaign next steps are commitments and publicity from organizations and publications, finding funds to keep the campaign going (ideas please?) and meetings to discuss a parliamentary timetable and commitments; Simon is out speaking to lots of people; and please ask everyone you know who cares about scientific debate and free speech to sign (we need a printed banner for the events we are going to – can anyone provide or help with the cost?).

I hope to write a less hurried update soon, and let you know more about likely milestones in the court case and in seeking parliamentary review and legal reform, but meantime do check the website (yes, we’d like to sort out RSS feeds -  help please?)

The Monterey Submarine Canyon - continued

A couple of weeks ago, on the road in California, I did a brief post reflecting on the dramas going on beneath the waves of Monterey Bay. Given the complexity of the Monterey Submarine Canyon, and the scope of the work done on this huge and dynamic feature, that post was the briefest of introductions; among the comments, Diggitt very reasonably asked about the origin of the canyon, since the corresponding onshore feature, the estuary of the Elkhorn Slough (great name) is a puny drainage, hardly capable of sculpting the submarine topography of the canyon. What with getting distracted by other things, but particularly by becoming diverted into the fascinating literature on the many studies of the canyon, it's taken me rather longer to follow up than I had intended. But here, still only scratching the surface of the material available, are at least some answers - still brief highlights, but I'll include some references for readers who would like to look deeper (so to speak).

It was only fifty years or so ago that Francis Shepard, the first geologist to devote his life to marine geology and an internationally renowned figure in the science, began to define and unravel the mysteries of submarine canyons. But one of the key mysteries remained unsolved for some time - many canyons are clearly related to onshore drainage systems, but, even allowing for a more exaggerated erosional capability during the dramatically lower sea levels of the Ice Ages, most of today's onshore rivers are dwarfed by the scale of their offshore equivalents and, like Elkhorn Slough, seem totally incapable of creating such submarine topography  - the Monterey Canyon is, after all, equivalent in scale and relief to the Grand Canyon. Today, we know much more about the origins and processes, but many mysteries, enticingly, remain. For example, it was long thought that, given the inadequate capability of Elkhorn Slough, the Monterey Canyon must be essentially inactive, a mere shadow of its former self with little or no sediment movement down its axis, little erosion, little activity at all - and that therefore it would be a relatively safe one to examine from the point of view of threats to expensive instrumentation. The canyon quickly demonstrated how wrong this view was, and that regular massive torrents of turbulent, gravity-driven, flows of sand, mud and rocks hurtle down the canyon at speeds in excess of a hundred miles an hour, sweeping away everything before them. The image below (from MBARI, the Monterey Bay Aquarium Research Institute) shows a heavyweight steel base for instruments that was carried fifty meters down the canyon floor from where it was originally placed.

 

There are two basic questions that have formed the basis for extensive studies over recent years: what are the workings of the canyon today and what is its history and origin? The first question is, in many ways, easier to answer than the second, but I must point out that sand (of course) tells us tales that allow us to address both. Submarine canyons behave in many ways just like their surficial, subaerial relatives: the geometries of tributaries and channels are similar, and at any one point in the canyon system at any given time, erosion, sediment transport and deposition may be occurring, serving to create an ever-evolving complex. As sediments are flushed out of the lower reaches of a canyon, the transport velocity drops and therefore so must the sediment - on land, the canyon may end in in a lake and a large delta will form; in the submarine realm, a canyon will end on the wide expanses of the relatively flat sea floor and, shaped very much like deltas, submarine fans will be deposited. It is the history and interactions of successive flushes of sediment and deposition of fans that provides us with part of the story of a canyon's history. For the Monterey Canyon, there are two distinct groups of fan deposits, the older group further out than the younger one. The older sediments seem to have started accumulating perhaps as long as 20 million years ago, fed by a system of canyons, not just the ancestor of today's Monterey Canyon. But we must remember what a tectonically turbulent setting this is, caught between the San Andreas and parallel fault zones offshore - a lot has changed in 20 million years, including moving a long distance northwestward. The younger stack of fan sediments originated within the last million years and continues its activity today; those million years include dynamic changes to the tectonic architecture and topography of this part of California, and the huge fluctuations in sea level during the the Ice Ages - no wonder it's a complex system.

Around a million years ago, California's geography was quite different: much of the Central Valley was a vast freshwater lake, Lake Corcoran, that drained at its southern end into the ancestor of the Salinas River, a much mightier feature than its descendant, cutting through the Coast Ranges and draining into Monterey Bay; it is proposed that it was this river and its massive cargo of sediment torn from the Sierras that initiated the Monterey Canyon as we see it today, quite possibly aided by ever-recurring fault movements. Around 500,000 years ago, upheavals along the San Andreas permanently closed off the river's route - the Monterey Bay drainage system would be emasculated and Lake Corocoran would find a new outlet northward into San Francisco Bay. Elkorn Slough and today's Salinas River, while still players in the canyon's game, are not what they used to be. For today's dynamics, I've annotated a Google Earth image:

 

The Monterey Canyon forms, understandably, the boundary between the Santa Cruz and the Southern Monterey Bay littoral cells - it's the "sink" that permanently sucks sand out of both(for more on littoral cells, see "Beach Nourishment and Sediment Budgets"). General littoral drift, the direction sand transport along the shore, is shown with the orange arrows. For the Santa Cruz cell, sand is transported generally down the coast, all the way from Half Moon Bay (west of the El Corte de Madera Creek tafoni of another earlier post), only to pour over the sides of the canyon and be swept out to sea. South of the canyon, transport along the shore is more complex - in part as a result of the canyon's topography influencing waves and currents. Three "sub-cells" have been identified, with different senses of sediment transport, influenced too by the Salina River. Interestingly, before 1910, the Salinas flowed northward, parallel to the shoreline, and emptied into Elkhorn Slough, but it then broke through the dunes separating it from the ocean to flow essentially along its current route, where we keep it firmly in place. But the shape and size of the sand accumulation of its mouth suggest that this may have been its preferred long-term itinerary during the ice ages.

The Santa Cruz cell has been estimated to deliver, on average, 223,000 cubic yards of sand (12,000 dump trucks) per year, 85% of it from rivers (much diminished under our control); some of this gets caught up behind the structures of the harbour at Santa Cruz. The Southern Monterey Bay cell, although much smaller, includes the input from the Salinas River and shifts 840,000 cubic yards of sand a year, 58% from rivers, the rest blown in off the coastal dunes. Moss Landing sits at the boundary of these two littoral cells, at the mouth of Elkhorn Slough: the head of the canyon yawns only a few hundred meters out to sea, and dredged material dumped near the head disappears quickly - it would seem that the canyon mouth is eroding shorewards, potentially threatening Moss Landing.  

Ongoing processes in the canyon have been studied in many different ways: ROV's (remotely operated vehicles, miniature submarines laden with instruments) roam its topography, seismic profiles enable us to peer through the layers of sediment and reveal the complexity of the fan systems in cross-section, cores of the sediments are taken, and instruments measuring currents and other data are moored (often temporarily) along its length. ROV images are useful for hunting down equipment that has been swept away, but primarily reveal extraordinary details of events in the canyon. Below, from the paper Trail of Sand in Upper Monterey Canyon (see the references at the end) are images of cobbles flushed down the canyon (their rock types easily correlated with the onshore geology) and sand ripples on the floor of the canyon (the black bars are 10 centimeter scales).

 

Perhaps most incredible is the detailed imagery generated by multibeam sonar that creates digital maps of the canyon system at high resolution. Below is one example, from Semiannual patterns of erosion and deposition in upper Monterey Canyon from serial multibeam bathymetry; it shows the upper canyon system in startling detail - the base of the canyon is marked by giant sand waves, several metres high and tens of metres in wavelength, formed by the immensely strong currents. This is one of a time-series of images that have enabled definition of changes day-to-day as avalanches scour the canyon walls, sediment gravity flows deposit sand banks and erode channels, sand waves move on, and meanders change their shape.

 

It has been estimated that around 400,000 cubic yards of sediment is delivered to the canyon head on average each year, to be flushed episodically out to sea. But this is only part of the story - equally huge volumes of sediment are supplied to the canyon by collapse of its walls and by deeper ocean currents. The size of those flushes varies enormously; once again, nature follows a power law - lots and lots of small events, a few massive ones. Truly massive, catastrophic, flows occur only on a scale of years and something sufficient to move sediment all the way down into the far reaches of the canyon seems to take place on a scale of every hundred years or so; the last one of these may have been associated with the 1906 earthquake.

We have much still to learn about this great and dynamic topographic feature, but what we do know hints at the turmoil going on every day beneath waters of Monterey Bay - visit, turn your back on the commercial claptrap of Cannery Row, stare out to sea, and wonder.

[The resources on the Monterey Canyon are vast, many of them originating from the MBARI, the USGS, workers at California State University at Monterey, Stanford, and other research institutions. Brian at Clastic Detritus (who has also posted on the canyon) kindly provided a link to a USGS paper by Fildani and Normark (the latter being one of the long-term canyon workers), http://walrus.wr.usgs.gov/reports/reprints/Fildani_MG_206.pdf; some of the material for this post has also been taken from two Geological Society of America papers: Trail of sand in upper Monterey Canyon: Offshore California, by Paull and others at MBARI (Geological Society of America Bulletin 2005;117;1134-1145) and Semiannual patterns of erosion and deposition in upper Monterey Canyon from serial multibeam bathymetry by Smith and others at California State, Monterey (Geological Society of America Bulletin 2005;117;1123-1133). If any readers are interested, but cannot access GSA journals, please let me know and I can email a copy. General articles can be found at the MBARI site, this one (which includes the images at the top of the post and of the shifted instrumentation package) being particularly good,  and here's a summary of the Trail of Sand paper. Fantastic data on California coastal sediment movement and sand budgets can be found in the report,  http://www.dbw.ca.gov/csmw/pdf/Sand_Budgets_Major_Littoral_Cells.pdf, downloadable from the Coastal Sediment Management Workgroup site that contains all kinds of other goodies.]

Oceano dunes (2) - Egyptian archaeology

The dunes at Oceano that I visited and introduced in the previous post are but the northern tip of the eighteen-mile-long Oceano-Nipomo-Guadalupe dunes complex, the largest landscape of coastal dunes in California. Further south, the dunes are punctuated by lakes, marshes and the river channels that supply the sand to the coast for later redistribution by the wind. We know that coastal dunes differ from their desert relatives, but for movie-makers whose budget does not allow for a trip to the Sahara, California's dunes provide a passable desert-replicating backdrop. They have played this role recently for the third in the Pirates of the Caribbean series, but have hosted many other dramas, including Hidalgo, G.I.Jane, and The Last Outpost with Cary Grant. However, their Hollywood heyday was much earlier - Rudolph Valentino stalked the dunes in the 1920s Sheik movies and Marlene Dietrich was transported across the sand in her car mounted on a sled since she refused to walk in the stuff during filming of Morocco with Gary Cooper in 1930. But the most famous and enduring role that   the Nipomo dunes have played was in Cecil B. DeMille's first version of The Ten Commandments, arguably the first epic film, made in the silent era in 1923. For his 1956 remake with Charlton Heston and Yul Brynner, and Anne Baxter, DeMille went to Egypt, but for his original version the budget didn't extend that far so he went to Nipomo. And there he built a truly epic set for the City of the Pharaohs and the Exodus scenes, and the remains of that set lie beneath the sands today.

The movie had, for the times, an astonishing budget of $1.4 million which DeMille set about spending with abandon - it's reported that, in response to telegrams expressing concern over his extravagance, he asked . "What do they want me to do? Stop now and release it as The Five Commandments?" He employed as his set designer Paul Iribe, a Frenchman who would later return to his native country and become one of the founders of the Art Deco movement. Tribe was certainly the man for DeMille's epic vision. The temple wall, 700 feet wide, towered over a hundred feet above the dunes, decorated with hieroglyphics modelled on those recently discovered in the tomb of Tutankhamun; four 20 ton statues of the Pharaoh and 21 sphinxes were shipped in by train. On site for the month of shooting were 3,500 actors, 1,500 construction workers and 5,000 animals; a huge camp had to be built to provide living quarters. The weather was distinctly cold and actors had to have their skin coated in glycerine so as to appear to be perspiring in the Egyptian sun.

At the end of shooting, DeMille destroyed (bulldozed, some say dynamited) the set in order to prevent cheap and nimble competitors using it and possibly because he could not afford the removal required in his contract with the landowner. The remains were rapidly buried in the sand, but locals have long described a single dune that didn't move - supposedly because it was anchored by DeMille's debris.

But then the El Nino winter storms of the 1980s arrived and stripped the sand away, revealing scattered fragments of the Pharaoh's City. It was then that a documentary film maker, Peter Brosnan, spurred on by a comment in DeMille's autobiography that future archaeologists might be seriously misled about an ancient Egyptian outpost on the California coast, teamed up with archaeologist John Parker, and began serious investigation. Amongst the scattered wood debris, they found fragments of the plaster statuary (including a Pharaoh's foot), now degraded and fragile, together with tobacco tins and other artifacts from the 1920s. Ground penetrating radar helped them identify other large objects buried in the sand and define the area of the remains. A Pharaonic hand is on display at the Dunes Center in Guadalupe. Funds are still sought for a proper excavation of what is, arguably, a key cultural and cinematographic historic site, the largest movie set ever built at the time, partly exposed to the elements but largely still hidden beneath the California sands.

 

[see Brosnan's site,  http://www.lostcitydemille.com/index.html, from which some of the illustrations above come, The Center for Land Use Interpretation description of the archaeological site, http://ludb.clui.org/ex/i/CA4973/, a good description on Siffblog, and an NPR interview with Brosnan from a few years ago at  http://www.npr.org/templates/story/story.php?storyId=4494713. For other movies starring sand, see my April4 post, Granular films, and thanks to Kevin, our Oceano guide, for bringing this story to my attention] 

California Sands - the dunes of Oceano (1)

Let’s face it, dunes are sensual things, languidly animated, their soft and complex curves ever-changing with the light and with time, their lines and crests shifting in and out of focus, deep shadows, bright sand. They are immensely and compellingly photogenic. Spectacular photographs of dunes are as numerous as the sand on the sea shore, but, to me at least, none can equal those of Edward Weston and his son Brett – just put “Weston” and “dune” into a Google image search and you will (if you are not already in agreement) see what I mean. Such a search will turn up not just stunning black and white images of the sculpture and moods of sand, but also the famous nude studies, an  interplay of sensual forms. I’m lucky to own a copy of Dune, the intoxicating book of Weston photographs and was delighted to find that the location for these was the coastal dune system at Oceano, California – I needed to see where these master photographers worked and Oceano instantly became a key destination for my recent west coast wanderings. I spent time on the internet and Google Earth, trying to figure out how to most effectively fit a walk into the Oceano dunes into the itinerary (my father used to regularly remark that “time spent in reconnaissance is seldom wasted," a maxim from his army days, and I still find these words to live by – greatly facilitated by the resources of the web).

It quickly became clear that the dune system is divided into two very distinct domains, the only State Park where vehicles may drive on the beach and the dunes (the State Vehicle Recreation Area) and the large area of the natural preserve where the environment and ecology of the dunes remain undisturbed (these domains are players in a high-profile political and policy controversy on which more, but not a lot more, later). Since I was unwilling to drive my rental car on the beach (there is undoubtedly something in the small print of the contract), it seems that I would have to allot a fair amount of precious time to parking the car in town and hiking down the beach before trekking down the beach and turning back into the dunes to access the Preserve. But then, just a few days before the planned visit and already on the road, through the serendipitous wonders of the internet and the blogosphere, I got lucky. Out of the blue in my inbox appeared an email titled “Oceano Dunes local resident” and signed off “at your service," a message from Kevin Rice, a self-confessed sand enthusiast from the Oceano area who had found me through my earlier blog post where I had mentioned my intention of visiting the dunes. Kevin very generously offered his experience and knowledge to help with my visit – an offer that I immediately took up with enthusiasm. Kevin is a Los Angeles fire-fighter who lives in San Luis Obispo – a 180 mile commute for a shift. He got off work the morning of my talk at the Long Beach Aquarium and came along that evening; we met up afterwards and organised getting together in Oceano for a couple of days later. Our rendezvous was at the classic Rock & Roll Diner, a converted railroad car, the inside complete with table juke boxes and festooned with movie memorabilia.

Part of our good luck was that Kevin knew the quick way into the dunes and we were able to take a couple of hours walking through their extraordinary landscapes – sand against a backdrop of the Pacific and the green hills of the interior. Kevin is indeed a sand enthusiast and a great spokesman for the Oceano dunes and taking the walk in his company was a great pleasure, far more enjoyable than if we had just arrived on our own. The morning was a typically California coastal overcast one, there were no deep shadows in the folds of the dunes, but nevertheless, it’s a beautiful place. We observed and created avalanches, saw where the funnelling of strong winds creates creates trains of mega-ripples, their amplitudes and grain sizes larger than those of the common ripples, and wondered at the variety of flora flourishing in the sand (but at the same time struggling against the grip of the alien grasses introduced long ago in an attempt to stabilise the dunes).

 

We saw the middens of the Chumash Indians, littered with the shells of the famed Pismo clams, the native inhabitants long succumbed, like the native flora, to alien arrivals, and the clams are nowhere near as abundant as they used to be. Being coastal dunes, these are subject to the salty and damp sea air, and the local water table, so mysterious layers and patches of damp and slightly cemented sand form the medium for bizarre and wonderful granular sculptures.

 

It was a truly memorable experience – dunes (and the Westons’ dunes at that) and good company. Kevin has his feet very rationally in both camps, the environmental and the recreational. It is certainly not for me to pronounce on the public antagonism between them, and this blog was never intended to be a political or an axe-grinding one. I can only comment that on this, as with so many contrasting points of view, the world is not black and white, but rather it is made up of glorious shades of gray that can and should be celebrated, and that a balanced approach is, while sadly rare, something that can be valued by all.  

The dunes at Oceano, in addition to providing great landscapes, have hosted extraordinary people and strange events – more of these in subsequent posts. Meanwhile, thanks again, Kevin.