Under his weight, the person then sinks into the sol (liquidised sand). There is a sudden decrease in its viscosity. Quicksand is a non-Newtonian fluid: when undisturbed it often seems to be solid (" gel" form), but a small (less than 1%) change in the stress on the quicksand causes it to turn liquid (" sol" form). This makes it difficult to distinguish quicksand from the surrounding environment. 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. They behave more like a liquid when exposed to stress. This lubricates the sand particles and makes them unable to support any significant weight, since they move around with very little friction. The water moves up and then down slowly in a convection-like manner throughout a column of sand, and the sand remains a generally solid mass. Water circulation underground can focus in an area with just the right mixture of fine sands and other materials such as clay. Quicksand may be escaped by slow movement of the legs in order to reduce viscosity of the fluid, and rotating the body so as to float on one's back (supine). It can be difficult to get out: that is the real problem. A human or animal does not sink entirely into quicksand due to the higher density of the fluid. However, a person does not drown in quicksand. If animals or people stand on it, they sink into it. It has the characteristic of thixotropy: it looks solid, but when pressure is applied it liquifies (acts like a liquid). Quicksand is a mixture of water and sand or silt.
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