- Dry quicksand
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 similarly to normal quicksand, but it does not contain any water and does not operate on the same principle. Dry quicksand is an 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.
Writing in Nature, physicist 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 to 55–60% for untreated sand).
Lohse found that a weighted table tennis 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 had 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.
During the planning of the Project Apollo moon missions, dry quicksand on the moon was considered as a potential danger to the missions. The successful landings of the unmanned Surveyor probes a few years earlier and their observations of a solid, rocky surface largely discounted this possibility, however. 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.
In popular culture
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). The plot of the Arthur C. Clarke novel A Fall of Moondust (1961) was based on the perils of working and traveling on a moon surface covered by a deep layer of dry quicksand, based on the actual risks considered during the planning of the Project Apollo missions. In Universal Pictures' 1999 The Mummy, Captain Winston Havelock's biplane and body disappear into dry quicksand after High Priest/Mummy Imhotep summons a sand storm to make the biplane crash.
In the videogame Xenogears the continent of Ignas (the country of Aveh) is covered mostly by a large desert, and several plot events revolve around characters' gears or vehicles being buried by dry quicksand.
The Princess Bride featured dry quicksand (called "Snow Sand" in the book and "Lightning Sand" in the movie) as one of the three terrors of the Fire Swamp. Dry quicksand was also featured in the movies Mad Max: Beyond Thunderdome, and the 2004 Chinese film, Kekexili: Mountain Patrol. In the 1993 film Pure Luck Martin Short's character finds himself sinking in dry quicksand in Mexico before being rescued.
In a 1990 episode of Mission: Impossible, "The Sands of Seth", a minister of the Egyptian government heads a cult that meets in an ancient structure with a dry quicksand pit for disposing of undesirable individuals.
In Indiana Jones and the Kingdom of the Crystal Skull, the title character gets caught in a dry quicksand pit while trying to escape from Soviet soldiers. While sinking, Indiana humorously tries to explain the difference between dry and regular quicksand.
World 2 (Desert World) of Super Mario Bros. 3 features many obstacles that resemble dry quicksand.
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