Dry quicksand is loose sand whose bulk density is reduced by blowing air through it and which yields easily to weight or pressure. It is similar to regular quicksand, except that it does not contain any water, and an interesting example of a granular material.

Up to 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.

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 2cm, mass 133g), 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)

Occurrences in literature and otherwise

Dry quicksand was occasionally featured in literature. The movie African Gold from 1966 (released abroad as "Ride the High Wind") shows one actress being trapped in dry quicksand. Mindwarp (movie) (1990) also has one actress wandering into dry quicksand before being rescued. The movie 12 to the moon (1960) shows one crew member being lost in moon dust behaving like dry quicksand. One of T. E. Lawrence's servants in the most acclaimed film Lawrence of Arabia also drowns in dry quicksand.

During the planning of the Project Apollo moon missions, dry quicksand on the moon was also a 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.

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.

External links

• Pictures of the quicksand experiment by Lohse et al