Because they stack on top of each other like playing cards, very little water can flow between the particles. Resistance to the flow of a fluid between solid particles increases enormously as the space between the particles becomes very small, as in clay. Sand particles, on the other hand, are more rounded, creating much larger gaps between particles. Sand particles deposited in water will be almost completely surrounded by water, so water can flow up through sand with relative ease. Some people and most animals panic when caught in quicksand.
Animals frequently die of exertion or starvation.
However, a dangerous situation arises if the upward flow of water slows so that water pressure no longer lifts each sand particle. Stepping into such loose sand or mud might be like stepping into a deep pit filled with powder. The distance you sink depends on how firmly the particles compact below you as you drop. Experiments have demonstrated this phenomenon as well. 250, December 1952, pp.