What is quicksand made of

If stumbling into quicksand ranks on your list of worries, don't panic. You won't sink in—at least not all the way. Real quicksand is certainly hard to get out of, but it doesn't suck people under the way it always seems to in the movies. According to a study published in the current issue of the journal Nature, it is impossible for a person immersed in quicksand to be drawn completely under. The fact is, humans float in the stuff. Researchers in the Netherlands and France studied quicksand, a combination of fine sand, clay, and salt water.

At rest, quicksand thickens with time, but it remains very sensitive to small variations in stress. At higher stresses, quicksand liquefies very quickly, and the higher the stress the more fluid it becomes. This causes a trapped body to sink when it starts to move. But a person moving around in quicksand will never go all the way under. The reason is that humans just aren't dense enough. Quicksand has a density of about 2 grams per milliliter.

But human density is only about 1 gram per milliliter. At that level of density, sinking in quicksand is impossible.

You would descend about up to your waist, but you'd go no 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.

But a piece of aluminum will float on top of quicksand until motion causes the sand to liquefy. During their study, researchers placed an aluminum bead on top of a container of laboratory-created quicksand. At rest, the bead remained on the surface, despite aluminum's higher density. But then scientists started shaking the container. When they shook it only a little, the bead stayed floating on top. But when they shook the container a bit harder, the ball descended to the bottom. But if quicksand becomes less viscous as you struggle, why is it so difficult to escape?

The reason, explain the study's authors, is that after its initial liquefaction, quicksand's apparent viscosity thickness or flow resistance increases. In normal sand, grains are packed tightly together to form a rigid mass, with about 25 to 30 percent of the space voids between the grains filled with air or water.

Because many sand grains are elongate rather than spherical, loose packing of the grains can produce sand in which voids make up 30 to 70 percent of the mass. This arrangement is similar to a house of cards in that the space between the cards is significantly greater than the space occupied by the cards. The sand collapses, or becomes 'quick,' when additional force from loading, vibration or the upward migration of water overcomes the friction holding the grains together.

Most quicksand occurs in settings where there are natural springs, either at the base of alluvial fans cone-shaped bodies of sand and gravel formed by rivers flowing from mountains , along riverbanks or on beaches at low tide. In such cases, the loose packing is maintained by the upward movement of water.

Quicksand does occur in deserts, but only very rarely: where loosely packed sands occur, such as on the down-wind sides of dunes, the amount of sinking is limited to a few centimeters, because once the air in the voids is expelled the grains are too densely packed to allow further compaction.

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Develop and improve products. List of Partners vendors. Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert. Helmenstine holds a Ph. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. Updated December 04, Key Takeaways: Quicksand Quicksand is a non-Newtonian fluid made of sand mixed with water or air.

It changes its viscosity in response to stress or vibration, allowing you to sink, but making it hard to escape. You can only sink into quicksand up to your waist. Really, the only way to drown from the quicksand is to fall into it head first or face first. A rescuer can't simply pull a victim out of quicksand. However, a person or branch can be used to help reduce the victim's weight, making it easier to work free and float.

Even though you can't sink all the way into quicksand, it's a killer. Death can come in the form of suffocation, dehydration, hypothermia, predators, crush syndrome, or drowning from a river or incoming tide. The best way to prevent a fatality is to keep a charged cell phone with you so you can call for help. If you have to rescue yourself, wriggle your legs to make the quicksand more fluid while trying to sit back into the quicksand to increase your body's surface area.

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