Creating a dry variety of quicksand: Granular physics

An aerated form of sand engulfs objects instantaneously, shooting out a jet of grains. Sand can normally support a weight by relying on internal force chains 1 , 2 , 3 . Here we weaken this force-chain structure in very fine sand by allowing air to flow through it: we find that the sand can then no longer support weight, even when the air is turned off and the bed has settled — a ball sinks into the sand to a depth of about five diameters. The final depth of the ball scales linearly with its mass and, above a threshold mass, a jet is formed that shoots sand violently into the air.