How Things Work: Quicksand

“Beware of the ground for which you stand, the floor is quicker than the sand.”

Making appearances in Jumanji, The Mummy, and The Princess Bride, quicksand is no stranger to the silver screen. In real life, however, this natural hazard is not the stuff of Hollywood. Quicksand is slow, usually shallow, and rarely fatal. Dry quicksand — a distant, sinister cousin — makes for a more interesting story.

Though an unfortunate roll left Jumanji’s Judy and Peter scrambling for solid ground, quicksand’s natural formation is slightly less theatrical. It is often associated with swampy or tropical climates, but a relatively simple set of circumstances can turn sand into quicksand in almost all environments.

Water rising from an underground source can disrupt an otherwise steady region of sand. Often this process occurs unprovoked, though sometimes it is caused when earthquakes aggravate subsurface waters. Common hotspots for quicksand include seashores, riverbanks, locations near springs, and marshes.

Under normal conditions, the frictional forces between individual grains of sand combine to form a force chain, which is what enables sandy surfaces such as beaches and deserts to hold large amounts of weight.

When enough water enters the system, this friction is disrupted and the grains of sand enter a state of suspension that is far less stable. Though weak below the surface, the sand’s uppermost layer almost always maintains a deceptively dry appearance, making it possible for an unsuspecting traveler to stumble into a region of quicksand.

Even without a copy of The Worst-Case Scenario Survival Handbook in tote, a victim of quicksand is seldom in any real danger. That being said, extricating oneself from such a watery pit is still something of a production.

Quicksand takes hold of a sunken body the same way thick mud can suction a boot on a rainy day. Motion only strengthens its grasp, creating a vacuum pressure. Thus, the most effective way to escape the clutch of quicksand is to make slow and subtle movements.

Even if it’s only a few feet deep, being stranded in quicksand can result in other perils. The struggle out can lead to heat exhaustion. Moreover, victims of quicksand are vulnerable to environmental hazards such as a rising tide or predatory animals.

Deeper pits of quicksand, though more dangerous, are still far from life-threatening. Humans are able to float in water, which has a density of one gram per cubic centimeter, one-half that of quicksand. Thus, buoyant force would prevent any unlucky traveler from sinking beneath the surface.

Since motion increases suction, the best course of action is to remain still and lie back. It would be nearly impossible to drown in a pit of quicksand, unless a victim was to enter one headfirst.

Unlike quicksand, dry quicksand lives up to its name. Similar to a house of cards, dry quicksand under pressure will collapse instantaneously.

When air flows through a body of sand, the grains loosen, creating a system of dry quicksand unable to support even small amounts of weight.

Dry quicksand has only ever been documented in a lab setting, though there is no scientific reason that it could not exist in nature; desert winds would achieve the same effect as the air currents used by scientists to manufacture dry quicksand. If it does exist, dry quicksand would explain the various legends of desert travelers and even entire caravans disappearing beneath the sand.

Such a possibility was taken so seriously that the legs of the Apollo missions’ Lunar Module were equipped with large plates to protect against a descent into unsteady soil. As it happened, the addition was not needed; the surface of the moon turned out to be solid.

In labs, when objects such as ping-pong balls are released onto dry quicksand, the energy associated with the collapse causes a stream of sand to shoot into the air. Though dry quicksand didn’t make it into Jumanji, a vanishing caravan of travelers immediately followed by a jettison of sand would certainly be worthy of Hollywood.