Physics Concepts and Definitions

What exactly is quicksand and how does it work?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. Quicksand has earned its deadly reputation mostly from fiction, movies and TV, where it does, one would have to admit, usually make an enjoyably familiar plot device or obstacle. Some of the most memorable and horrifying quicksand scenes come from the quicksand-obsessed cinema of the 1960s, including classics like "Lawrence of Arabia" (1962) and Disney's adaptation of the "Swiss Family Robinson" (1960). In fact, quicksand was such a popular silver-screen menace at the time that it appeared in literally 3 percent of all theatrical releases in the year 1960 [source: Engbar]. Since then it has lurked everywhere in movies, from the comedy of Mel Brooks to the "Nightmare on Elm Street" franchise.

    In real life, however, quicksand is not the fearsome morass that's pictured by Hollywood; rather, it's plain sand or any grainy soil that has had the friction between the grains reduced by water. Since moisture is usually a necessary condition to create quicksand, you are most likely to find it in muddy, watery areas, such as riverbanks, swamps and marshes, but Denise Dumouchelle, a geologist with the United States Geological Survey, reports that quicksand can really be found anywhere, as long as the right conditions exist. Two things may create the conditions to form quicksand. Underground water may seep up and saturate the sand, thereby reducing the friction between the sand grains and giving the sand a liquid nature. Or, sand or another soil may be sifted by the force of an earthquake so that friction is lessened and the earth becomes unsteady.

    The idea that quicksand will pull you down if you fall into it is a fallacy. It is actually the wild movements people make in the quicksand that cause them to sink deeper. Slow, angled movements, on the other hand, will bring you to the surface, and then you can lie back and float to safety. When a person finds that he has a foot stuck in quicksand, he often reacts by shifting his weight back and forth to free it. This worsens the problem; instead, you should fall forward to spread your body weight over a large area of the quicksand and, using slow movements, attempt to free your foot. Once freed, you should roll away from the quicksand area and run to solid ground. Sometimes, people get both legs caught in quicksand and need two people or a rescue squad to free them.

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