Quick sand


When I was a kid, I was always intrigued by quicksand with the idea of getting caught in it and never getting out.

The story of quicksand

A natural phenomenon, quicksand is an area of ground that feels solid but ultimately cannot hold a certain weight. In reality, there are two kinds of quicksand.

Dry quicksand

In deserts, dry quicksand, very fine grains of sand lifted in large quantities by the wind, have an unstable and very aerated structure. If you step on it you sink immediately.

Damp or wet quicksand

With a very fragile structure, its formation requires a mixture of running water, which pushes the sand upwards, and clay, which keeps the sand on the surface. When you press on the mixture (sand, salt water, clay), the clay is diluted in the water and the structure collapses. Although it looks solid, wet quicksand is viscous. When it is subject to stress, this viscosity becomes fluid, a process referred to as thixotropy (fluid mixture of liquids and solids, sand + water). Several suspended substances dispersed regularly in another substance are referred to as a colloid.

How to get out of quicksand

No matter what the movies say, you don't sink into wet quicksand completely because the density of the body is similar to the density of water. When a body becomes caught in quicksand, it floats better than in water. The viscosity keeps the body immobile. According to the Archimedes' principle, if you sink into wet quicksand, in order to decrease the suction that holds your body trapped in the sand, you should gently rotate your foot to displace the water so that you can get out. With pressure being greater on the lower part of the submerged body, the result is a generally a vertical upward thrust. The force encountered by the part of the body submerged in the quicksand is subject to a field of gravity. It is even advised to lie down.

Adopt the right method

To get out of wet quicksand, you have to aerate the grains of sand by creating spaces between them. Gently rotate your leg to allow the water to seep between the grains of sand, aerate the spaces between them and expand the mixture.

Another kind of wet quicksand

Often after an earthquake, water seeps in under pressure and the ground can turn to liquid and start to move as a result of the action of the water currents that flow from the bottom upwards. Regardless of whether the water is fresh or salty, the grains of sand start to separate from each other, the environment becomes unstable and you sink into it.

Quicksand in movies

Quicksand - American film by Irving Pichel (1950)
Quicksand - French film by Paul Carpita (1995)
Knock on Wood - French film by Francis Veber (1981)

Quicksand at Mont Saint-Michel

Without an experienced guide, crossing the beaches of Mont Saint-Michel bay is dangerous even though this large, practically flat expanse of shoreline really makes you want to take a walk. Subject to silting, the sandy sections comprise several areas of quicksand. The ground gives way under the movement of the channels and becomes blocked if you do not move. Normally, if the channel fills up, you are supposed to float but if you are unable able to free yourself with your arms, it is likely that you will succumb to hypothermia. It is even impossible to tow a person who has become stuck in this way because, in this case, they have become as heavy as a car.

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