Through The Sandglass

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.

Arenophile genetics, Jedi, and another submarine canyon

Geology doesn't exactly run in my family. My parents weren't geologists, I married someone to whom dip and strike will eternally remain an arcane concept, and neither of my kids are geologists. Geology has, however, touched, so to speak, them all, and rubbed off most on my daughter. She's the one who has always loved the outdoors and adventures. She became, involuntarily, intimately familiar with the major faults of the Atlas Mountains during our trek there together when she turned fifteen (she was, according to our guide, the youngest western female to climb Jebel Toubkal, the highest mountain in North Africa). And her recent activities would suggest that arenophilia may be genetic.

Earlier this summer, on a well-deserved vacation/holiday in southern California, where was her first  destination after arrival? The Imperial Sand Dunes - in the distinctly uncomfortable temperatures of July. The area, also known as the Algodones Dunes, is the largest landscape of sand in California, covering its intersection with Mexico and Arizona. And there she collected, secured, and labelled in detail, plastic bags of sand for her arenophile father - mad dogs, Englishmen, and their daughters. En route, she came across the strange sight of a small group of Star Wars figures, for it was here, in 1982, that a massive set for Return of the Jedi was constructed. And, in the same way that the archaeology of the Ten Commandments has become an attraction of the dunes at Oceano (see my earlier post), so the Imperial dunes are a place of pilgrimage for devoted Star Wars fans who re-enact and dig. This phenomenon was covered by a highly entertaining article earlier this year in Harper's Magazine, " Raiders of the lost R2: Excavating in a galaxy far, far away." As one of the pilgrims is quoted as saying, “As a kid, you can only go so far playing with action figures. As an adult, you don’t play with action figures anymore. You become the action figure.”

Escaping from the desert heat, my daughter then sought refuge on the beaches around San Diego - and continued to assiduously collect and catalogue sands for her deranged father. And, in the process, she made an interesting and geologically significant, observation. The beaches of La Jolla Shores and La Jolla Cove are immediately next to each other, the Cove being located in the rocky headland that juts out at the southern end of the Shores. Yet their sands are dramatically, visibly, different. Between your toes on La Jolla shores is a fine sand (upper image, below), quartz grains shot through with dark rock and mineral fragments; at the Cove (lower image, same magnifications), the sand is coarse but poorly sorted, made up of a wide range of grain sizes, with shell fragments clearly visible, along with dark minerals, oranges, pinks, and purples. This contrast seem bizarre - until we look at the geology and what's going on along this stretch of coast.

 

First, the setting of the Cove is distinctive. It's backed by sandstone cliffs shown in the photo, weathering and eroding away at a rapid rate. The sandstone was formed around 70 million years ago as the tectonic turbulence that has long characterised southern California raised the Sierra Nevada mountains. The Sierras were formed as a series of gigantic bodies of originally molten rock, plutons, emplaced deep within the earth's crust, but rapidly jacked up to the surface by the tectonic turbulence. Once there, they were worn away by the relentless forces of weathering and erosion, the sedimentary debris forming the sandstones of La Jolla Cove. Now those sandstones are themselves providing much of the sedimentary debris for this segment of the coast - you can almost sense the sand pouring off the lower part of the cliff onto the beach - local ingredients.

 

Second, and even more importantly, if you were to pull the plug in order to see the landscape beneath the ocean along this stretch of shoreline, then an extraordinary topography would emerge. Just a few hundred yards offshore from the southern end of La Jolla Shores is the head of a huge submarine canyon. Similar to the Monterey Canyon further north (that I wrote about here), this feature is deep and sinuous, winding its way far out across the Pacific Ocean floor. And it's a sand-sucker - any sand that is carried down the coast along La Jolla Shores from the north is inevitably and irrevocably swept down the canyon and out to sea. The La Jolla canyon forms the boundary between two segments of coastline that are distinct with respect to their sedimentary processes and the transport and deposition of sand - two different littoral cells (see my "Beach Nourishment and Sediment Budgets" post). 

 

No wonder the sands of the Shores and the Cove are so different. This is a dynamic stretch of coast and the submarine canyon has long been a laboratory in which we have learned something of the dramas that are played out in these landscapes. And it's perhaps no wonder that one of the world's foremost centres of oceanographic research, Scripps Institution of Oceanography, is located (on land) at the head of the canyon.

[The image of the canyon, along with many others, can be found at http://walrus.wr.usgs.gov/pacmaps/sd-index.html; Scripps put out a news release a couple of years ago that describes some fascinating research on sand movements and budgets along this part of the coast: http://scrippsnews.ucsd.edu/Releases/?releaseID=785; the department of geology at San Diego State University have, brilliantly, put together Google Maps overlays of the geological maps: http://www.geology.sdsu.edu/kmlgeology/kmz/la_jolla/la_jolla.html; and see the comprehensive study of California's coastal processes and littoral cells, Littoral Cells, Sand Budgets, and Beaches: Understanding California’s Shoreline. The photo of the Star Wars set is from http://www.desertusa.com/sandhills/du_sh_star.html. And, finally, thanks to my daughter for her genetic peculiarity and for prompting the basis for this story.]

 

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] 

Dr Who and the Sands of Time

For those non-UK readers who are saying to themselves, "Dr Who?" and suspecting that this might be a version of the "who's on first?" routine, I'm referring to a British science fiction TV series. A distinctly cult series, if ever there was one. The first episodes were back in the early 1960s and it was revived,very successfully, a few years ago after a hiatus. The programme has a huge following, of all ages, and, of course, like all cult things, an industry surrounding it. "The Doctor" is a strange alien time-traveller, immensely old, but always looking like whatever actor is starring in any given series; there have been eleven Doctors over the years, every one of them the ingenious solver of bizarre problems, always able to, in the end, avert imminent catastrophe. As one actor moves on, he mutates, regenerates, into the new one. The Doctor travels about - through space and time - in the Tardis, which looks for all the world like an old UK police callbox (right), but open the door and inside it's huge, filled with all kinds of weird and wonderful  time-travelling propulsion and calculating contraptions.

These days, the programmes go out not on a regular schedule but as periodic, and eagerly awaited, specials. Last month, for Easter, we were treated to Dr Who and the Sands of Time (I know I'm a bit late describing this but I have been otherwise occupied with kitchen physics and proof-reading). It was filmed in February in Dubai - as the producer commented, "We always looked at going abroad. A beach in Wales, especially in February, would have just looked like, well, a beach in Wales." The typically strange story required the presence of a red double-decker London bus in the middle of the desert, so the BBC shipped one out to Dubai. Unfortunately, on arrival, a cargo container was dropped on it so the script had to be rewritten to incorporate its revised appearance. Then shooting was disrupted for some time by a major sandstorm - and in the story, blowing sand penetrates the engine of the bus, causing agonising delay and tension as the voracious aliens (not the poor guy in the picture, who was also stranded but was, sadly, consumed) approach.

 

The show is highly creative and extremely well-written and the latest incarnation of The Doctor, David Tennant, has been superb (at the same time playing a highly-acclaimed Hamlet for the Royal Shakespeare Company). In every series, Dr Who has always been accompanied (platonically, of course, since he's an alien and this is prime-time TV) by a lissome female companion, sometimes just for one episode, sometimes for many. In the desert, this was Michelle Ryan, star of the remake of The Bionic Woman and English TV soap opera, fetchingly attired in a black cat-suit. But everyone knows that David Tennant's time is up, he is due to be regenerated by the end of the year. Everyone knows who his replacement is to be (this is news in the UK) and everyone, including, presumably, his replacement, is apprehensive - Tennant's time-travelling shoes (generally suede) are big ones to fill.

Dr Who and the Sands of Time, was good TV from every point of view, but, naturally, particularly mine given the place and the ubiquitous material. I have read that there is also a classic desert episode (I think I missed it, but then again, my memory...), in which the Tardis arrives in the Gobi Desert, just in time to meet Marco Polo on his way to visit the fabled palace of Kublai Khan. Forced to travel together, they witness "singing sands," the bizarre variety of sounds emitted periodically and spontaneously, by dunes. This is entirely accurate - in his description of his journey, Marco Polo tells of the spirits of the desert and the strange and terrifying musical and drumming sounds that they make. But undoubtedly more of that in a later thrilling Through the Sandglass episode.

[pictures from the Radio Times]