Dry Quicksand

Click this video, then if you'd like to know more,

click this link and onwards to the Nature article.

"Sand supports weight. Force chains are known to play a prominent role therein. We considerably weaken the force chain structure by letting air flow through very fine sand. Even when the air is turned off and the bed has settled, the prepared sand does not support weight: Balls sink into the sand up to five diameters deep. We call this state of sand dry quick sand. The state is not to be confused with the normal quick sand which is a mixture of sand, clay, and water. The final depth the ball reaches scales linearly with its mass and above a threshold mass, a sand jet is formed which shoots sand straight and violently into the air. – Read all about it in the 9 December 2004 issue of Nature."