QUICKSAND
Quicksand forms in saturated loose sand when the sand is suddenly agitated. When water in the sand cannot escape, it creates a liquefied soil that loses strength and cannot support weight. Quicksand can form in standing water or in upwards flowing water (as from an artesian spring). In the case of upwards flowing water, forces oppose the force of gravity and suspend the soil particles.
The saturated sediment may appear quite solid until a sudden change in pressure or shock initiates liquefaction. This causes the sand to form a suspension and lose strength. The cushioning of water gives quicksand, and other liquefied sediments, a spongy, fluid-like texture. Objects in liquefied sand sink to the level at which the weight of the object is equal to the weight of the displaced soil/water mix and the submerged object floats due to its buoyancy.
Quicksand may be found on riverbanks, near lakes, in marshes, or near coastal
areas. When undisturbed, it often appears to be solid, but a less than 1% change in the stress on the quicksand will cause a sudden decrease in its viscosity. A human is unlikely to sink entirely into quicksand due to the higher density of the fluid (assuming the quicksand is on dry ground and not under water, but even if underwater, sinking is still improbable), Quicksand has a density of about 2 grams per milliliter, whereas the density of the human body is only about 1 gram per mililiter. At that level of density, sinking beyond about waist height in quicksand is impossible.
areas. When undisturbed, it often appears to be solid, but a less than 1% change in the stress on the quicksand will cause a sudden decrease in its viscosity. A human is unlikely to sink entirely into quicksand due to the higher density of the fluid (assuming the quicksand is on dry ground and not under water, but even if underwater, sinking is still improbable), Quicksand has a density of about 2 grams per milliliter, whereas the density of the human body is only about 1 gram per mililiter. At that level of density, sinking beyond about waist height in quicksand is impossible.
With quicksand, the more you struggle in it the faster you will sink. If you just relax, your body will float in it because your body is less dense than the quicksand. Continued or panicked movement, however, may cause a person to sink further in the quicksand. Since this increasingly impairs movement, it can lead to a situation where other factors such as weather exposure, dehydration, hypothermia, tides or carnivores may harm a trapped person,
The best thing to do is to make slow movements and bring yourself to the surface, then just lie back. You'll float to a safe level.
sources :
https://science.howstuffworks.com/environmental/earth/geology/quicksand2.htm
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