Through The Sandglass

Street cred (a belated contribution to “dune week”)

 
So, I ask myself, how could this blog possibly miss the “dune week” celebration on the geoblogosphere, an arenaceous festival if ever there was one? The great thing about asking yourself is that a credible answer should be forthcoming – feeble though it may be in this instance: “distracted, pressures of work, general indolence… but better late than never, eh?” I am not convinced, but, anyway, offer this:

In the great deserts of the world, the sand seas made up of the long, towering edifices of seif dunes, elongate, shape-shifting mountainous ribbons of sand, named after the Arabic word for “sword,” are invariably characterised by intervening “streets.” These are the lanes between the long dunes, mysteriously swept free of sand, covered instead in pebbles and cobbles – as in my example from Egypt’s Western Desert, above. There are, at least, two explanations for these “streets”:

1. Ralph Bagnold, the man who figured out how deserts work, offered a clear model, based on physics, experiment, and meticulous science, that showed how the saltation of sand grains driven by the wind was much more energetic over pebbles (bouncing) than over a sand surface (splashing). This led to a removal of sand from a rocky surface and, inevitably, to its self-accumulation into dunes.

2. The Walmajarri people of Australia’s Great Sandy desert believe that their streets (below) were swept clean by mythical snakes journeying westward.

 
Please don’t choose between these explanations – both are equally acceptable.

 

[For some great dune reading, see Dana Hunter’s post and round-up of the geoblogosphere’s eponymous week.]

Sunday sand critter: stargazing

Cute, huh? Astroscopus y-graecum, the southern stargazer (hence the astroscopus bit), is, in reality, hardly the romantic that its name implies, never mind incapable of actually perceiving any celestial objects; but is just about as nasty as it looks. It not only packs a good jolt of electricity, but is venomous to boot; however, it is extremely clever – here’s the description from the Florida Museum of Natural History:

This fish has many adaptions to life under the sand. Its pectoral fins act as shovels, allowing the fish to bury in a matter of seconds. The body is designed so that the eyes, nostrils, and most of the mouth are above the sand when the fish is under the sand. Scales are absent on head, but are present on body, extending onto fleshy area of caudal fin. The eyes are capable of protruding for a short distance, appearing stalked, so that the stargazer can see above the sand. It brings in water through its nostrils to breathe. Most fish species bring in water through their mouths. The nostrils are protected from sand grains by fleshy, comb-shaped fringes. The mouth also has these fringes around it to keep sand out while the fish is buried. The gill slit is narrow and drawn backwards and upwards into a baggy tube. This tube carries waste water away from the fish and outside the surrounding sand. This fish possesses a special talent: it is able to create electrical currents from a specialized organ located in a pouch behind the eyes. The rate of electric discharge depends upon the temperature, with a maximum of 50 volts. It is used primarily to fend off aggressive, threatening fish rather than for prey capture.

The southern, inhabiting the floors of the Western Atlantic, is but one of fifty species of stargazers that can be found all around the world’s oceans, all belonging to the family Uranoscopidae (implying a seriously long-range scoping ability). For a sense of a stargazer in action – definitely in the category of “nature red in tooth and claw” – see this video; here’s the opening scene, one of deceptive marine tranquillity – but look carefully in the sand….

[Header image from the BBC, Fabio Liverari]

 

Helpful arenaceous Thanksgiving tips

The following are entirely reputable and independent pieces of advice for managing a safe and environmentally benign holiday culinary process:

Partially frozen turkeys will cause the oil to bubble over, possibly covering the entire deep fryer in flames......If the fryer does bubble over or tip and spill hot oil, get away from it and don’t try dousing it with cold water. Move objects away from the oil and any fire and smother it with dirt or sand. Having a few buckets of these materials on hand helps you stay prepared in case something does go wrong.

Safe disposal of leftover cooking oils: Mix the cooking oils with unscented kitty litter, sawdust or sand to solidify the oil. Dispose of it in the trash. Avoid scented or disinfectant types of kitty litter as they can react with the oil and cause a fire (so ensure that a few buckets of sand are to hand).

A VERY HAPPY THANKSGIVING TO ALL!

Abrasive Sunday Sand

 
All in all, it’s been an abrasive week. No, I’m not referring to my day job, but rather an emerging theme that started with my last post on the stories of three indefatigable women and a mystery Gobi sand. So far, there have been two very interesting responses to my question of what the mineral content of this “special sand” might be that made it so prized for polishing jade (and I’m also following up on other suggestions): Howard Allen helpfully defines some constraining criteria in terms of hardness and density (we must be dealing with something heavy enough to form a placer deposit, and hard enough – but not too hard – to polish a tough material like jade). Richard Bready – knowledgeable and stimulating as always – points to the work of a researcher at The British Museum whom I should contact, and sources that mention corundum, quartz, and garnet.

Earlier in the week, I heard from Siim Sepp, a graduate student of geology at the University of Tartu in Estonia, who alerted me to his areno-blog, Sandatlas, which he has been expanding into a wide-ranging and informative source for a variety of geo-topics. Browsing around Siim’s site, I was struck by one of the images in his gallery, above. This stunning sand is from the area of the Emerald Creek garnet district in the panhandle of Idaho, where garnets from sand- to golf ball-size occur in placer deposits that, organised by the Forest Service, can be visited by the public for a “mine your own garnets” day out. Garnets have been used since antiquity as both gemstones and abrasives, and the latter continues to be a widespread application today; Emerald Creek, in addition to being a Forest Service recreational area, is still one of the leading sources of industrial garnets in North America, producing a range of product sizes for everything from serious sand-blasting to fine polishing via water-jet cutting.

There are quite a few different “species” of the mineral group collectively referred to as garnet; they are all silicate minerals (strictly, nesosilicates or orthosilicates), but their composition (and colour) varies, with different sites within the crystal structure being occupied by iron, magnesium, calcium, aluminium, and chromium. Nevertheless, they all belong to a single group because they all have the same crystal form – the crystals are isometric, their internal structural symmetry being that of a cube. In garnets, these highly symmetrical internal building blocks most commonly organise themselves into the overall shape of a dodecahedron, but other related shapes can also form. The combination of colour and symmetry produces some truly stunning crystals, such as this one from Emerald Creek, the big one being 2.5 centimetres across (image from Exceptional Minerals):

 
One particular form, the star garnet, is the State Gem of Idaho; these extremely rare specimens are examples of asterism, the appearance of a luminous star shape as a result of tiny fibrous crystals of the mineral rutile (titanium dioxide) being included in the structure:

Garnets have a torrid geological history, born at high temperatures and pressures deep in the earth’s crustal kitchen, and, as a result, showing up at the surface in metamorphic, or, less commonly, igneous rocks. The garnets of the Emerald Creek district originate from sediments deposited around 1.5 billion years ago, buried, cooked, and rudely ejected back to the surface; weathering has liberated the tough garnet crystals to be concentrated in the stream placer deposits, but the original hard rock has also been extensively mined for not only garnets but a wide variety of minerals and metals.

So, not a solution yet to the Gobi mystery, but, for me at least, an interesting detour from the daily grind.

Extraordinary women–and a Gobi sand question

 
For one reason or another, I have been reading The Gobi Desert by Mildred Cable and Francesca French. In the history of exploration and enquiry into far-flung parts, it’s easy to overlook that regiment of indefatigable women – particularly Victorian - who played extraordinary roles. Perhaps the most celebrated was, of course, Gertrude Bell, whose middle-eastern exploits changed politics and history. But in China, in the first couple of decades of the last century, there were three women, Mildred, Francesca, and the latter’s sister, Eva (Evangeline), who documented the landscapes and culture of that part of the world through quite remarkable travels. Yes, they were missionaries, but they pursued their goals with linguistic skills and a deep cultural sensitivity that resulted in accounts that are distinctly and fascinatingly different from the typical travel writing of the times and have become classics. And the classic of the classics is their description of their thirteen years in the Gobi, “following trade-routes, tracing faint caravan tracks, searching out innumerable by-paths and exploring the most hidden oases. ... Five times we traversed the whole length of the desert, and in the process we had become part of its life."

The story begins as they set out from the fort at what is today called Jiayuguan, the westernmost bastion of the Great Wall. Leaving the western gate, they passed a great mound of earth whose role was to keep out the evil spirits of the desert, and a stone tablet on which were inscribed the forbidding words “Earth’s Greatest Barrier.” Following the Silk Road westwards, they stopped at isolated and insular oases – Shachow, “City of Sands,” Shamen, “Gates of Sand.” These even before they reached the Taklamakan Desert proper.

But one of the things that intrigues me is the following account from their overnight stay in Huei-huei-pu, the “Moslem Tomb Halt,” whose location today I have yet to figure out. While wandering around the village, Mildred stopped at the local shop, where

There was something different here, however, for, in addition to the dull stock of the oasis shopkeeper, this man had a variety of articles made from a fine-grained, light-grey stone which was found near at hand. These were slabs on which to rub down the hard sticks of Chinese ink, and little pots to hold water with which to moisten them. The chief demand, however, was for small pieces to be used as whetstones for knives, razors or scissors, and many a carter passing that way added a hone to his small outfit of traveller’s necessities.

Having made some purchases, Mildred sat down and chatted with the shopkeeper about this and that, but then

I turned to go, and just as I was leaving, I noticed on his counter a jar of coarse grey sand. Taking some of it in my hand, I rubbed it between my fingers testing the quality of the grains, and as I did so I felt there was something unusual about it. “What do you keep sand for?” I asked. “Is there not enough of it by the roadside?”

“This is special sand, Lady,” he said. “It comes from near here but is not found elsewhere in the Gobi.It is so heavy that the wind does not blow it about, and it is the only sand which can be used for one process in the polishing of jade.Though it is hard enough to use even on jade, yet it never scratches the surface. It is very highly valued, and jade polishers send here to get it.”

So there’s my question – does anyone have an idea as to exactly what this highly valued sand might be?

Nikon’s Small World – and other images

 
Each year, Nikon holds its Small World microphotography competition and the results can always only be described as stunning. This year is no different – but with the added element of sand appearing as the 14th place winner, the image above by Yanping Wang of the Beijing Planetarium.

Browsing through the galleries of winners, Honorable Mentions, and “Images of Distinction,” one of the (many) things that is striking is the art of nature’s patterns and designs, a theme superbly covered in the books by Philip Ball, Nature’s Patterns – A Tapestry in Three Parts. Scale has little role in all this, and I found it entertaining (not to mention awe-inspiring) to flip between the microscopic and the huge – specifically, the glorious gallery published earlier this year by Time, “Our Beautiful Planet: Images from Space by an Astronaut Photographer.” The images were taken by Paolo Nespoli:

European Space Agency Astronaut Paolo Nespoli — who first traveled to space aboard the Space Shuttle Discovery in 2007 — photographed a unique and stunning image of the space shuttle Endeavour docked with the International Space Station on a recent Soyuz mission. During a 159-day mission aboard the International Space Station, Nespoli managed to find time, despite his full schedule of duties, to capture footage for a documentary film, First Orbit. Combining historic voice recordings of cosmonaut Yuri Gagarin’s first manned spaceflight, the documentary charts the view that Gagarin saw during his historic mission. In addition to this footage, Nespoli also took many still images of Earth. LightBox presents a selection of these photos that show our planet as a beautiful abstract canvas.

“A beautiful abstract canvas” indeed; but then put some of these images together with the Small World – the viewer can be hard-pressed to determine scale at all:

Salar de Uyuni, Bolivia, Mar 2, 2011; Douglas Moore, University of Wisconsin - Stevens Point, Agatized dinosaur bone cells, unpolished, ca. 150 million years old (42x)

 
Dr. Juan Carlos Izpisúa, CMRB - Center of Regenerative Medicine in Barcelona, Neurons growing over astrocytes in a human stem cell embryo body (20x); Desert, Somalia, January 30, 2011

And then the “abstract canvas” is on display in quite extraordinary ways in the microscopic world:

Dr. Michael M. Raith, Steinmann Institut, University of Bonn, leucite crystal from volcanic rock showing polysynthetic lamellar twins formed by the cubic- tetrago (40x); Dennis Callahan, California Institute of Technology, Department of Applied Physics & Materials Science, Cracked gallium arsenide solar cell films (50x)

But, this being the blog that it is, I shall finish with the following image of sand dunes in Saudi Arabia – or is it actually a biological photomicrograph?

Sand bottle houses

 
Once in a while, out of curiosity, I just go to Google News and enter “sand.” More often than not, among the reports of the latest exploits of one of the Junior High School basketball teams from Sand County, Nebraska, are a couple of items of interest, not to say surprises. Here’s one from a recent report from BBC News:

Nigeria's plastic bottle house

By Sam Olukoya BBC Africa, Yelwa

Nigeria's first house built from discarded plastic bottles is proving a tourist attraction in the village of Yelwa. Hundreds of people - including government officials and traditional leaders - have been coming to see how the walls are built in the round architectural shape popular in northern Nigeria.The bottles, packed with sand, are placed on their side, one on top of the other and bound together with mud.

"I wanted to see this building for myself as I was surprised to hear it was built from plastic bottles," said Nuhu Dangote, a trader who travelled from the state capital, Kaduna, to see the house. "They were saying it in the market that it looks like magic, that you will be amazed when you see it, that is why I have come here to feed my eyes. The whole world should come and look at it."

The real beauty of the house is its outside wall as the round bottoms of the exposed bottles produce a lovely design. But for those behind the project, its environmental benefits are what are most important.

Twenty-five houses, which will be available to rent, are being built on this estate on land donated by a Greek businessman and environmentalist. Each house - with one bedroom, living room, bathroom, toilet and kitchen - uses an estimated 7,800 plastic bottles. This "bottle brick" technology started nine years ago in India, South and Central America, providing a cost-effective, environmentally-friendly alternative to conventional building bricks.

Yahaya Ahmed of Nigeria's Development Association for Renewable Energies, estimates that a bottle house will cost one third of what a similar house made of concrete and bricks would cost. It is also more durable.

"Compacted sand inside a bottle is nearly 20 times stronger than bricks," he says. "We are even intending to build a three-storey building." The bottle houses are also ideally suited to the hot Nigerian climate because the sand insulates them from the sun's heat, helping to keep room temperatures low. And because of the compact sand, they are bullet-proof - which may also prove another attraction in more insecure parts of the north.

A firm concrete foundation is laid to ensure that the structure is firm and stable - and the sand is sieved to make sure it is compact. "You need to sieve it to remove the stones otherwise it will not be nice and it would not be able to pass through the mouth of the bottle," explains Dolly Ugorchi, who has been trained in bottle house building. Bottles for the houses are mainly sourced from hotels and restaurants

Some have expressed concern about the amount of sand needed for the new houses. "My fear is that this building method will increase the demand for sand and even lead to an increase in the price of sand," says Mumuni Oladele, a mason in the southern city of Lagos. "At the moment people looking for sand to build houses dig everywhere to get the sand. You can imagine what will happen when the demand for sand goes up to build bottle houses."

According to market research company Zenith International, most water in Nigeria is sold in small plastic bags, but it says the bottled water market is growing - accounting for about 20-25% of official sales, the equivalent of up to 500m litres a year. This means discarded plastic bottles are actually sought after in Nigeria where they are often used for storage or by street vendors to sell produce like peanuts. The bottles for these houses are currently being sourced from hotels, restaurants, homes and foreign embassies.

The project is also hoping to help to remove children who do not go to school from their life on the streets.

"I don't want to be a beggar, I want to work and get paid - that is why I am doing this job," says 15-year-old Shehu Usman, who is working on the building site. "When I grow old I want to build myself a house with bottles," he says.

After the 25 houses have been completed, the next construction project for the Development Association for Renewable Energies will be a school on the estate, which street children like Shehu will be able to attend.

Children making money filling bottles may one day be able to attend a school to be built on the estate

Seems to me that this creative idea addresses all sorts of issues - but then, of course, I would think that.

[See also a report with some more details here.]

Sunday sand: Komodo pink

No, these photos are not photoshopped – these are the real colours of this beach on Komodo Island:

 
Simply spectacular, macroscopically and microscopically, and a place to just wander, as I did – for some time. And what’s going on under the waves I described – with movies – in an earlier post.

The sand, when dry, has a light pinkish tan colour, but the dramatic hues are on display when it’s wet. The colour comes from tiny fragments of bright red coral which, when mixed with grains of quartz, shell fragments, our old friends foraminifera, and other biogenic detritus, create this glorious overall pink sand. Beachcomb a little, and there are the coarser fragments of coral, and, in the storm zone at the top of the beach, genuine chunks:

This is one of the so-called soft corals, the alcyonarians, specifically, and for obvious reasons, the “organ pipe coral,” Tubipora musica. From ARKive.org:

Unlike most corals, it is not colourful polyps that make organ pipe corals attractive, but instead, their dark red coloured skeleton. The skeleton is composed of thin tubes, or pipes, (hence its common name), which are two millimetres in diameter and cemented together by horizontal plates at intervals of several centimetres. Unless the colony has been damaged, a mass of greenish-brown or grey polyps, each with eight tentacles, obscures the skeleton. These colonies can form mounds up to 50 centimetres in diameter and may dominate large patches of reef. There are at least two species, only one of which is named; Tubipora musica. The structure of the tentacles of different colonies of T. musica varies greatly; some have broad feather-like pinnae (tiny projections) down the sides of the tentacles, whilst others have no pinnae at all.

I must have seen some of these on my snorkelling excursions, but, being no expert, failed to make the correlation with the beach; my excuse is, as the description above mentions, in the living corals the tentacles completely obscure the skeleton:

 
The organ pipe corals are much-prized, particularly for making jewellery and ornaments and by owners of salt water aquaria – for both the easily maintained living corals and for the decorative qualities of the bright red skeletons. As a result, the colonies are routinely harvested and dynamited and Tubipora musica is classified as Near Threatened (NT) on the Red List of the International Union for Conservation of Nature and listed on Appendix II of CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora. So, a slightly sobering thought – does the dramatic debris of Komodo’s pink beaches originate entirely from natural mortality or does the activity of illegal trade make a contribution?

 

[Living coral picture credit]

Sand continuum - a modelling breakthrough

It’s happened again – a topic that I touched on in my Milan talk shows up in a New Scientist report from earlier this year (I only just caught up with it). In the talk, I commented on the profound challenges of mathematically modelling and simulating such an apparently simple material as sand, and referred to the amount of effort and research that had to go in to the stunning special effects for the Sandman character in Spider-Man 3:

 
From wired.com (ignore the reference to “the molecular structure of sand”):

The secret to Spider-Man's success can be found in a single grain of sand. After all, it's not really Peter Parker in latex that makes this film franchise a billion-dollar box office hit. It's the villain, and this time around it's the Sandman, a shape-shifting computer-generated marvel made up of thousands of digitized grains of sand.

But making the villain wasn't easy (nor was it cheap). It all started with director Sam Raimi peering through a microscope to study the molecular structure of sand, and led to two-and-a-half years of visual-effects R&D and a crew of 30 special-effects technicians.

"I had people bring in 12 different kinds of sand -- this is where people think the movie industry is insane -- so I could look at it," says Raimi. "I saw California beach sand, Mojave desert sand. We ended up picking Arizona sand because it looks exactly like ground corncobs. The reason that's important is that when you bury people alive in hundreds and hundreds of pounds of sand, they'll be squished. You need something lightweight like corncobs, so air can get through and the actors and stuntmen won't be crushed."

Computer modelling of sand as individual grains, even with the power of today’s algorithms and processing capacity, is limited to tens of thousands, perhaps a hundred thousand, grains. But now a different approach has yielded impressive results, as reported under the title “CGI tricks: How to make a fake beach look real” in the New Scientist:

From explosions in a desert, to the trickle of an egg timer, animated scenes containing sand are notoriously hard to model. But now Rahul Narain and his team from the University of North Carolina at Chapel Hill have developed a new technique that should make computer animations look more realistic.

Since sand is made up of a collection of tiny grains, its appearance can vary greatly. "It can look like a solid pile you can stand on, to a flowing avalanche, or even a cloud of dust," says Narain. Much work has gone into modeling solids and fluids, but materials such as sand have received less attention, perhaps because of these unique properties. So far, the only way to simulate sand has been to model every grain as an individual object, which can be extremely costly in terms of computation time and memory.

Narain and his colleagues are taking a more holistic approach. They realised that although individual sand grains do move independently, in practice the grains tend to flow together more often than not. So it made sense to make the most of existing fluid-modeling techniques and model sand as one big continuous material.

"This 'continuum based approach' makes it possible to simulate sand in a much faster and more memory-efficient way without sacrificing much in the way of realistic behaviour," he says.

Their new model also includes algorithms to make sure it's simulated realistically in instances when sand behaves differently from liquids. They do this by taking into account the forces on the particles, such as friction. When tested with animated sand clouds forming in an explosion (see video above) the results proved to be true-to-life.

As well as being used in animated films and games, when the technique is refined further it could be used to model real life scenarios such as avalanches and explosions.

The video (from which the image at the top of this post is a screen-grab) is impressive, and can be found on youtube.