Quicksand is a colloid hydrogel consisting of fine granular material (such as sand or silt), clay, and water. Quicksand forms in saturated loose sand when the sand is suddenly agitated. When water in the sand cannot escape, it creates liquefied soil that loses strength and cannot support weight. Quicksand can be formed in standing water or in upwards flowing water (as from an artesian spring). In the case of upwards flowing water, seepage forces oppose the force of gravity and suspend the soil particles. The saturated sediment may appear quite solid until a sudden change in pressure or shock initiates liquefaction. This causes the sand to form a suspension and lose strength. The cushioning of water gives quicksand, and other liquefied sediments, a spongy, fluidlike texture.
Contributions by Vsmith, 184.108.40.206, and Mikenorton.