Quicksand

Quicksand is sand or silt so soaked with water that it behaves like a liquid when disturbed. In films, people who step into it sink steadily until only a hat remains. In reality a person cannot sink completely: quicksand is about twice as dense as the human body, so a person floats in it, usually sinking no deeper than the waist.^[1] The hat, in other words, was always going to be fine.

Getting out

The difficulty with quicksand is not sinking but getting out. Once disturbed, the sand settles and grips, and pulling a leg straight up takes a very large force. A 2005 study found that the trick is to wiggle the legs slowly, letting water seep down around them to loosen the sand, while leaning back to spread out the weight and float.^[2]

Experts recommend moving slowly and calmly. This is the only emergency in which the official advice is to take your time.

Where it is found

Quicksand can form near riverbanks, beaches, marshes and springs, anywhere that water flows up through sand. It is often found on tidal flats, where the real danger is being held in place while the tide comes in, so people walking on such flats are advised to check tide times and stay on marked paths.

• Films: sink completely.
• Reality: float at about the waist.
• Advice: move slowly, lean back, check the tide.

See also

• Sand – the dry version
• Mud – a cousin
• Tide – the real thing to watch

References

1. Sinker, S. (2005). “You Float”. Granular Matter Letters 2: 1.
2. Wiggle, W. (2009). Slowly Does It. Estuary Press.
3. Hat, H. (1962). Only the Hat Remained. A film critique.