What causes quicksand to form?

Question

What causes quicksand to form?

Answer 1

Quicksand is a colloid hydrogel consisting of fine granular matter (such as sand or silt), clay, and salt water. In the name, as in that of quicksilver (mercury), "quick" does not mean "fast," but "alive" (cf. the expression the quick and the dead).

Water circulation underground can focus in an area with just the right mixture of fine sands and other materials such as clay. The water moves up and then down slowly in a convection-like manner throughout a column of sand under optimal conditions, and the sand remains a generally solid mass. This lubricates the sand particles and renders them unable to support any significant weight, since they move around with very little friction, behaving more like a liquid when exposed to stress. Since the water does not usually go all the way up through the sand, the sand above does not appear to move at all, and can support leaves and other small debris, making quicksand difficult to distinguish from the surrounding environment.