Quicksand

This article is about the geological feature. For other uses, see Quicksand (disambiguation).

Quicksand and warning sign at a gravel mine.

Quicksand is a colloid hydrogel consisting of fine granular matter (such as sand or silt), clay, and water.

Water circulation underground can focus in an area with the optimal 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, and the sand remains a generally solid mass. The water lubricates the sand particles and renders them unable to support significant weight. Since water does not usually go up to the surface of the sand, the sand on top appears solid and can support leaves and other small debris, making quicksand difficult to distinguish from the surrounding environment.

Properties

Quicksand is a non-Newtonian fluid: when undisturbed, it often appears to be solid ("gel" form), but a minor (less than 1%) change in the stress on the quicksand will cause a sudden decrease in its viscosity ("sol" form). After an initial disturbance — such as a person attempting to walk on it — the water and sand in the quicksand separate and dense regions of sand sediment form; it is because of the formation of these high volume fraction regions that the viscosity of the quicksand seems to increase suddenly. Someone stepping on it will start to sink. To move within the 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 .01 m/s would require the same amount of force as "that needed to lift a medium-sized car."

Because of the higher density of the quicksand, it would be impossible for a human or animal to completely sink in the quicksand, though natural hazards present around the quicksand would lead people to believe that quicksand is dangerous. In actuality the quicksand is harmless on its own, but because it greatly impedes human locomotion, the quicksand would allow harsher elements like solar radiation, dehydration, or tides to harm a trapped person. The way to escape is to wiggle the legs.

Prevalence

Quicksand may be found inland (on riverbanks, near lakes, or in marshes), or near the coast.

In fiction

People falling into (and, unrealistically, being submerged in) quicksand or a similar substance is a trope of adventure fiction, notably movies. According to Slate, this gimmick had its heyday in the 1960s, when almost 3% of all films showed someone sinking in mud, sand, or clay, but it has since gradually fallen out of use. The proliferation of quicksand scenes in movies has given rise to an internet subculture scene dedicated to the topic.

See also

• Dry quicksand

External links

Media related to Quicksand at Wikimedia Commons

• Howstuffworks.com - How quicksand works
• "What is quicksand?". Scientific American. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)