Quicker sand

Here's something even scarier than quick sand.   Quick sand at least usually looks a little different because it's a bit wet.  This new type of trap is completely dry.

Traditional deathtrap quicksand is a slurry of sand, water and clay. The water keeps the sand from sticking together to support weight, and a person who steps in slowly sinks.

Now Dr. Lohse, a professor of applied physics, and his colleagues at the University of Twente in the Netherlands show that it is possible to vanish into a pile of completely dry sand as well. Worse, their sand looks the same as the normal, weight-supporting variety.

What you can see in the panel at right (click to enlarge) is a ping pong ball, weighted with bits of bronze, completely -- and quickly -- disappear into the sand.  The current issue of Nature describes how the researchers were able to puff dry air through sand and make it rearrange itself into a structure that is so precarious -- like a house of cards -- that it is unable to support weight and collapses around anything set on it.

Dr. Lohse said the findings could explain reports of travelers' being swallowed up in the desert.

"The U.S. Army is very interested in this," he said, "because these days, the U.S. Army tends to go to desert states."