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- Aug 18, 2002
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Its great that they are showing the possibility of a dismissed anomalous event:
Source
The paper is:
Lohse, D., Rauhe, R., Bergmann, R. & van der Meer, D. (2004) Granular physics: Creating a dry variety of quicksand. Nature. 432 (7018). 689 - 90.
I have to say that from the pictures in the paper the jet of sand is very odd indeed. The conlusion is the bit that references Lawrence of Arabia:
Lawrence of Arabia's wikipedia entry:
http://en.wikipedia.org/wiki/T._E._Lawrence
and the 7 Pillars of Wisdom:
http://en.wikipedia.org/wiki/Seven_Pillars_of_Wisdom
Available here.
This longer report casts more doubt on Lawrence's link to this topic:
Source
Swallowed by 'dry quicksand'
Thursday December 9, 2004
The Guardian
There can't be many citations of TE Lawrence's Seven Pillars of Wisdom in the annals of fluid dynamics. But Detlef Lohse and colleagues at the University of Twente, Netherlands, nod to the 1926 account of the Arab revolt against the Ottoman empire as they report the creation of "dry quicksand" which may render stories of travellers and whole vehicles being swallowed instantly more credible.
The team made dry quicksand by forcing air through a deep layer of sand in a miniature pit and then allowing the sand to settle. In doing so, they broke up what they call the "force-chain structure" of fine sand.
To see how the dry quicksand behaved, the researchers suspended a ping-pong ball partly filled with bronze grains above the pit. They then burnt through the thin rope holding the ball. To their surprise, it disappeared beneath the sand instantaneously. Though the expected splash did not happen, a more dramatic effect was seen. "A straight jet of sand shot violently into the air after about 100 milliseconds," the team writes in the journal Nature today.
Source
The paper is:
Lohse, D., Rauhe, R., Bergmann, R. & van der Meer, D. (2004) Granular physics: Creating a dry variety of quicksand. Nature. 432 (7018). 689 - 90.
Sand can normally support a weight by relying on internal force chains. Here we weaken this force-chain structure in very fine sand by allowing air to flow through it: we find that the sand can then no longer support weight, even when the air is turned off and the bed has settled — a ball sinks into the sand to a depth of about five diameters. The final depth of the ball scales linearly with its mass and, above a threshold mass, a jet is formed that shoots sand violently into the air.
I have to say that from the pictures in the paper the jet of sand is very odd indeed. The conlusion is the bit that references Lawrence of Arabia:
In nature, dry quicksands may evolve from the sedimentation of very fine sand after it has been blown into the air and, if large enough, might be a threat to humans. Indeed, reports that travellers and whole vehicles have been swallowed instantly7,8 may even turn out to be credible in the light of our results.
...........
7. Lawrence, T. E. Seven Pillars ofWisdom
(Anchor, New York, 1926).
8. Bagnold, R. A. The Physics of Blown Sand and Desert Dunes
(Methuen, London, 1941).
Lawrence of Arabia's wikipedia entry:
http://en.wikipedia.org/wiki/T._E._Lawrence
and the 7 Pillars of Wisdom:
http://en.wikipedia.org/wiki/Seven_Pillars_of_Wisdom
Available here.
This longer report casts more doubt on Lawrence's link to this topic:
December 09, 2004
Tales about sand that swallows people may have a grain of truth
By Nigel Hawkes
TRAVELLERS’ tales about being suddenly swallowed by the desert sands may not be so fantastic as they appear.
Dutch scientists have recreated conditions that may sometimes arise when very fine sand is blown by the wind and settles to form a mass so loosely packed that it behaves like a liquid, swallowing up travellers and even vehicles whole.
This “dry quicksand” could be a threat to humans, they suggest, citing T.E. Lawrence’s Seven Pillars of Wisdom as a literary source for just such an event. If so, it would be one of the few factual statements in a book full of poetic flights of the imagination.
Detlef Lohse, of the Physics of Fluids Group at the University of Twente in the Netherlands, and colleagues blew air through very fine sand in a container with a perforated base. They then allowed the sand to settle. In doing so, it trapped a lot of air which separated the grains. When they put a ping-pong ball full of bronze grains on the surface of the sand, it disappeared instantaneously.
"Objects often make a splash as they hit sand,” the team reports in Nature. “In this case, there was no splash, as expected, but a straight jet of sand shot violently into the air after about 100 microseconds.”
The final depth reached by the ball depended on its mass, and a jet of sand was produced only by a ball weighing more than 28.5 grams (1oz). Typically, a ball reached a depth more than five times its diameter, more than deep enough, were it a vehicle, to swallow it without trace.
Granular materials such as sand behave sometimes like solids and sometimes like liquids. Imagine a tipper truck filled with gravel. As it drives along, the gravel remains solid; but when it is tipped, there comes a moment when it turns into a fluid and pours from the truck.
In a famous demonstration at the Royal Institution in London a lecturer showed the same effect by blowing air through a barrel of sand that had a steel ball lying on its surface, and a tennis ball submerged at the bottom.
As the sand was turned into a fluid, the steel ball sank and the tennis ball “floated” to the surface. Professor Lohse and colleagues have gone a stage further by showing that once fluidised, sand can appear solid but behave like a quicksand.
Whether that ever happens outside the laboratory remains conjectural. While Professor Lohse cites T. E. Lawrence, he says that his acquaintance with the book comes from the film Lawrence of Arabia, where Daud, the Arab companion of Peter O’Toole’s Lawrence, does indeed disappear as they cross the Sinai Desert.
In fact, this scene was inserted by the screenwriter Michael Wilson, or so he later claimed when his credit on the movie was denied in favour of Robert Bolt, who had produced the final rewrite.
All that Lawrence had ever claimed in Seven Pillars was that Daud had died of cold.
Despite this, travellers who encounter what the Egyptians call nafash are advised to take care. Its surface can look just like ordinary sand or gravel, but warning is given by rising clouds of dust. If the nafash is more than a few centimetres thick, vehicles can quickly be bogged down and there is no way of telling how deep it is by its appearance. Whether it can actually swallow one is perhaps doubtful.
The best advice is to keep going at a good speed, making a broad unhurried U-turn to escape. The worst is to stop.
Source