Quicksand is loose, water-logged soil that yields easily to weight or pressure. It can be formed when sand, silt, clay, or other grainy soil is saturated or supersaturated by water flowing from below ground (such as from an underground spring) with enough pressure to separate and suspend the grains. The undisturbed sand often is or appears to be solid until some shock or sudden increase in pressure, such as a person stepping on it, causes it to liquify and lose its friction.