Dry quicksand
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Dry quicksand is loose sand whose bulk density is reduced by blowing air through it and which yields easily to weight or pressure. It acts similar to regular quicksand, but it does not contain any water and does not operate on the same principle. Dry quicksand is an interesting example of a granular material.
Until recently, the existence of dry quicksand was doubted, and the reports of humans and complete caravans being lost in dry quicksand were considered to be folklore.
[edit] Scientific research
Writing in Nature, rheologist Detlef Lohse and coworkers of University of Twente in Enschede, Netherlands allowed air to flow through very fine sand (typical grain diameter was about 40 micrometers) in a container with a perforated base. They then turned the air stream off before the start of the experiment and allowed the sand to settle: the packing fraction of this sand was only 41% (compared 55–60% for untreated sand).
Lohse found that a weighted ping pong ball (radius 2 cm, mass 133 g), when released from just above the surface of the sand, would sink to about five diameters. Lohse also observed a "straight jet of sand [shooting] violently into the air after about 100 ms". Objects are known to make a splash when they hit sand, but this type of jet has never been described before.
Lohse concluded that
- 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 instantly may even turn out to be credible in the light of our results.
(data and quote from Nature 432, 689 - 690 (09 December 2004); doi:10.1038/432689a)
[edit] Occurrences in literature and otherwise
During the planning of the Project Apollo moon missions, dry quicksand on the moon was considered as a potential danger to the missions. It was not known if the surface of the moon was solid or a mile-deep layer of dust that would swallow the astronauts and their craft. The large plates at the end of legs of the Apollo Lunar Module were designed to reduce this danger, but the astronauts did not encounter dry quicksand.
Dry quicksand was occasionally featured in literature. The 1966 movie African Gold (released abroad as Ride the High Wind) shows an actress being trapped in dry quicksand. Mindwarp (1990) also has an actress wandering into dry quicksand before being rescued. The movie 12 to the Moon (1960) shows a crew member being lost in moon dust similar to dry quicksand. In the film Lawrence of Arabia, a servant of T. E. Lawrence drowns in dry quicksand (this was never claimed to have happened in real-life).
Perhaps the most well-known instance of dry quicksand in popular culture is the movie The Princess Bride, in the form of the "Lightning Sand", one of the three horrors of the Fire Swamp. Dry quicksand was also featured in the movie Mad Max: Beyond Thunderdome and in the 2004 Chinese film, Kekexili: Mountain Patrol.
