Quicksand n. : Sand easily moved or readily yielding to pressure; especially, a deep mass of loose or moving sand mixed with water, sometimes found at the mouth of a river or along some coasts, and very dangerous, from the difficulty of extricating a person who begins sinking into it.

Example:
What is Quicksand? Why is it different from normal sand?

Taxonomy
quicksand, sand, Dry quicksand, free encyclopedia, sand particles, viscosity, water and sand, sink, presence, clay, stress, sediment, underground sources, search, geological feature, warning sign, gravel, mercury.

Defination from the web:
quicksand, a person or object must apply sufficient pressure on the compacted sand to re-introduce enough water to liquefy it. The forces required to do this are quite large: to remove a foot from quicksand at a speed of one cm per second would require the same amount of ...