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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 similarly to normal quicksand, but it does not contain any water and does not operate on the same principle. Dry quicksand can also be a resulting phenomenon of contractive dilatancy.
Historically, 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. In 2004, it was created in the laboratory, but it is still not clear what its actual prevalence in nature is.
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:
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 program 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 did not encounter dry quicksand.
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