What Is Quicksand?

A sign warning of the danger of quicksand in multiple languages.
A sign warning of the danger of quicksand in multiple languages.

What is Quicksand?

Quicksand is a mixture of either sand, silt, or clay with water. When undisturbed, this substance appears to have a solid physical state - however, it quickly collapses under outside stress. Quicksand is unique in that it is considered a non-Newtonian liquid, which means it does not fall under the characteristics of Newton’s Law of Viscosity. Unlike regular sand, which is characterized by the presence of less than 30% air, quicksand consists of between 30 and 70% void space between the grains of sand. This high level of space means that additional weight or vibrations are not sustained by the quicksand, making it unstable. When the surface of this substance is disturbed, the water and sand separate, creating a water-like quality. This sudden loss of viscosity causes the person or animal walking across it to sink.

Where Does Quicksand Occur?

Although quicksand can occur anywhere in the world, it is most likely to form in areas with natural springs. These springs are typically found near riverbanks, at low tide on the beach, and in alluvial fans. In these places, the upward motion of water creates extra space between grains of sand or grainy soil, resulting in quicksand. Desert quicksand may also occur in dry areas, although it is less likely. When found in the desert, quicksand generally forms at the base of dunes, where downward moving wind forces space between the grains of sand. Desert quicksand is not usually as thick or deep as quicksand near water sources.

Getting Stuck in Quicksand

Most people are familiar with movie scenes in which a person falls into quicksand, struggles, and sinks. While it is possible to get stuck in a patch of quicksand, completely sinking is unlikely. In fact, if a person relaxes their body once inside, sinking is actually impossible. This is because the density of quicksand is approximately 2 grams per milliliter, whereas the density of a human body is around 1 gram per milliliter. In other words, humans should be able to float on quicksand.

The natural human reaction upon falling into quicksand is not to relax but rather to struggle. This struggling creates a vacuum effect that makes it harder for a person to remove their arms and legs. Slow movements, however, reduces the level of viscosity, informally referred to as thickness. Additionally, experts suggest that rather than pulling arms and legs straight up, a person stuck in quicksand would be better served by slowly working their legs in a small, circular motion. This circular motion creates a space between the body and the quicksand, allowing the space to fill with water, which is much easier to escape. Another approach to escaping quicksand is to spread one’s arms and legs to increase the surface area of the body. An object in quicksand with a larger surface area is more likely to float than sink.

Quicksand has often been considered a dangerous natural occurrence, but this idea is just a popular myth. If an animal or person were to become stuck for a significant amount of time, however, other risks may become a concern, including dehydration, weather exposure, sunstroke, hypothermia, predatory animals, or rising tidal waters.


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