Once upon a time, adventurers into unknown lands feared quicksand – a deadly hazard that looked like a sand patch or a harmless puddle. Step in the wrong place, the natives warned, and you would die. This sudden peril became a very useful device in TV and movies from the 1950s to the 90s, and a metaphor for the U.S. war in Vietnam. It’s an old-fashioned trope now but quicksand is a real thing. A curious situation created through soil dynamics makes for some spooky geology.
Quicksand, as a distinct thing and a metaphor for sinking deeper as you try to escape, was once popular in TV, movies, comic books, and adventure stories. It even became a fetish. In the 1960s, the concept of quicksand was invoked frequently whenever people went into unknown areas. It was characterized by immobilization and eventual death. Struggle was futile. The unfortunate victim was sucked down gradually into the goo until only an outstretched hand, and then, finally, a hat, was all that remained floating on the surface.
The quicksand was said to be bottomless.
All of that is untrue. Yet, quicksand is not wholly fiction. It can be a danger today, particularly to animals or people who can’t get out of the trap before a tide rushes in. Let’s unpack this geological hazard.
What is it?
Classic quicksand is a mix of sand and water that looks and acts like a solid but destabilizes and collapses when stress is applied.
Areas of silt and clay can also appear as a stable surface that collapses. There is also dry quicksand – a mix of air and sand – that will not hold weight. You might hear that some unsuspecting traveler through the desert (or fire swamp) will sink into a man-eating natural hourglass, but this is entirely mythical.
Sediment + water
Think about how you moisten sand at the beach to build up a sand castle. A moderate amount of water and sand results in packed grains that are held fairly tightly together and can sustain weight. Additional water reduces friction, the particles separate and the mixture flows. The sand may look stable and can hold light weight but a force such as a foot bearing down disrupts the balance. The sand suddenly loses stability and collapses.
Vibration, such as from an earthquake, can trigger a complex process called liquefaction. Buildings constructed on wet ground can collapse during the shaking when the shear strength is suddenly reduced and the particles flow past each other. The land liquifies.
Natural areas of quicksand can be found where there is upward flowing water, like at the outflow of spring, or near rivers or on beaches where water is present just below the surface.
Silty areas can more easily liquify than sand. Clay deposits can exhibit thixotropic behavior and lose their shear strength suddenly due to vibration. (Add water to corn starch while slowly stirring to make it just liquid. Then let it rest. Is this a liquid or a solid? It’s a thixotropic solution.)
The higher the stress applied to the material, the more liquid it becomes. Therefore, thrashing around will indeed cause you to sink and become more engulfed.
“Quick” suggests the sand comes to life but instead it gives way. “Quick” refers to how easily the sand changes character from solid to liquid. As mentioned, quicksand pits are not bottomless. They are typically not even very deep. No scary creatures live in the sand to consume you.
Quicksand doesn’t suck you down, but you sink into as you would in any liquid. It is always more dense than water alone. The high viscosity of the saturated sand creates resistance and suction. You are almost guaranteed to lose your shoes during a quicksand escape if they aren’t laced tight.
In 2005, researchers published in Nature how they simulated natural quicksand from a location in Iran using sand, clay, and saltwater. The results of the experiment made news headlines. We were assured that quicksand is real but you can’t sink in more than halfway.
Areas of quicksand or dangerously sticky mud or clay are found around the world near sources of water. They can be a fairly permanent feature or appear in response to wet conditions. They can even move locations from one day to the next.
Locally known as “jelly sands”, areas of quicksand occur around the Santa Ana River in California, posing a threat to horses who step onto damp sand only to sink in. Horses may panic and become exhausted trying to escape. It can take special equipment to pull them out.
In 2019, two horses had to be rescued from Merthyr Mawr beach in Glamorgan, South Wales after they sunk into quicksand. A similar event in 2012 in Geelong, Australia required the horse to be sedated to get him out before the tide came in.
In 2014, a 78-year-old woman who frequently hiked alone in Arches National Park, Washington without issue became stuck in quicksand for 14 hours before rescuers helped free her. As with other areas, it was difficult to tell what ground was unstable until you stepped in it.
The Broomway path in the UK is a well-known hazard in Southend-on-Sea, England along the edge of the aptly named Foulness Island. Accessible only during low tide, the trail has claimed some who have gotten stuck in the quicksand and could not escape before the tide returned “faster than a man could run”. The so-called Black Grounds along the land’s edge consist of jelly-like mud.
How to escape
If you discover you are rapidly sinking up to your waist, toss off any extra backpacks and attempt to redistribute your weight by lying back.
Selectively increasing the stress is the key to escape. Stopping can cause the viscosity of the material to increase (like when you stop stirring the corn starch). When you try pulling your leg out of the semi-liquid, you are working against a vacuum left behind. Instead, move a little back and forth to create a space for water to move into. This will loosen the material around your limbs. Don’t panic and move slowly and deliberately towards safe ground. Many people can extract themselves relatively easily provided they can get leverage and move their legs/feet slowly and pull out. Most importantly, don’t hike alone and be aware of hazards in silty wet places. Don’t fear the quicksand, just respect it.
Bakalar, N. (2005). Quicksand science: Why it Traps and How to Escape. National Geographic. https://www.nationalgeographic.com/news/2005/9/quicksand-science-why-it-traps-how-to-escape/
Engber, D. (2010). Terra Infirma: The rise and fall of quicksand. Slate. http://www.slate.com/articles/health_and_science/science/2010/08/terra_infirma.html
Khamsi, R. (2005). Quicksand can’t suck you under. Nature.