Quicksand
Definitions
- 1: sand readily yielding to pressure; especially : a deep mass of loose sand mixed with water into which heavy objects readily sink
- 2: something that entraps or frustrates <lead poor people into consumerist quicksand — Robert Wright>
Description
Quicksand is a colloid hydrogel consisting of fine material (such as sand or silt), clay, and water.
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, seepage 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, fluidlike 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.
Liquefaction is a special case of quicksand. In this case, sudden earthquake forces immediately increase the pore pressure of shallow groundwater. The saturated liquefied soil loses strength, causing buildings or other objects on that surface to sink or fall.
Quicksand itself is harmless: a human or animal is unlikely to sink entirely into quicksand at all 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 impractical). Quicksand has a density of about 2 grams per milliliter, while the density of the human body is only about 1 gram per milliliter. At that level of density, sinking in quicksand is impossible. Descending about up to the waist is possible, but not any further. Even objects with a higher density than quicksand will float on it—until they move. Aluminum, for example, has a density of about 2.7 grams per milliliter. But a piece of aluminum will float on top of quicksand until motion causes the sand to liquefy.[2]
Continued or panicked movement may cause the victim to sink deeper, leading to belief that quicksand is dangerous. Because it increasingly impairs human locomotion, it allows harsher elements such as sunlight, dehydration, carnivores, omnivores, hypothermia or tides to harm a trapped person. Quicksand may be escaped by slow movement of the legs in order to increase viscosity of the fluid, and rotation of the body so as to float in the supine position.[1]
