n.
State in which water-saturated sand loses its supporting capacity and acquires the characteristics of a liquid.
Quicksand is usually found in a hollow at the mouth of a large river or along a flat stretch of stream or beach where pools of water become partly filled with sand and an underlying layer of stiff clay or other dense material prevents drainage. Mixtures of sand, mud, and vegetation in bogs often act like true quicksands. Any sand may become "quick" if its effective weight is being carried by water between the grains. In that case, even a footstep may collapse the loose structure. The sand-water suspension is denser than an animal or human body, so the body cannot sink below the surface, but struggling may lead to loss of balance and drowning.