Everything You Know About Quicksand Is Wrong

“Quicksand is a mix of sand, mud and water and depending on the viscosity it’s not as dangerous as people sometimes think.” —Indiana Jones, Indiana Jones and the Kingdom of the Crystal Skull (2008)

In A Nutshell

We’ve all seen the movies where the hero (or hapless sidekick) falls into quicksand and is ever so slowly swallowed by it. Unfortunately for Hollywood, that just not how it happens. Quicksand is a mixture of sand, water, clay, and salt that doesn’t so much suck someone into a bottomless pit as it does trap them. It turns out that you won’t drown in quicksand, but pulling you out with all your appendages intact is very, very tricky.

The Whole Bushel

It’s a popular obstacle thrown in front of heroes and sidekicks in adventure movies. Someone stumbles into quicksand, and they’re warned not to struggle and not to move, lest they get sucked all the way under. Invariably, whoever is left on solid ground finds a way to pull them out with a handy vine or tree limb; unfortunately, absolutely every part of that scenario is absolutely wrong.

We’ll start at the beginning. Quicksand is a mixture of sand, water, air, clay and salt; it’s put together in such a way that, unlike regular sand, there’s quite a bit of water in between the grains of sand and it’s held together by the lumps of clay. When it’s disturbed, the clay doesn’t so much hold the whole thing stable as much as it dissolves into a runny, watery mess. The solid stuff sinks to the bottom, and the water floats to the top. When there’s enough salt involved, though, it changes the charge of the particles and makes them adhere to each other.

This all makes for an extremely dense mass of clay and sand that allows you to step into it, but by the time you try to step out, it’s solidified around your foot.

Sounds pretty legit as far as Hollywood goes, right?

The problem with their take on quicksand happens when you factor in density. Quicksand is, on average, twice as dense as a person’s body—so you just don’t sink into it. At most, a person might find themselves up to their waist or so in the mucky sand, but that’s about as far as they’ll go.

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The other problem comes with getting pulled out. According to Hollywood, our hero just needs to find a tree branch or vine, and the person will be able to pull themselves out. But unless they have the upper-body strength to pull with a force that would move a decent-sized car, that’s just not going to happen.

After quicksand liquefies and pulls the person in, the subsequent reaction solidifies the mixture. A lot.

So much so that holding onto a rope and having a car try to pull the person out would tear them in half before the quicksand would let go.

Ironically, it’s doing what you’re absolutely told not to do that will get you unstuck. Gradually struggling against the hold of the quicksand will change the makeup of the substance yet again, introducing water into the space around your trapped appendages and gradually loosening the quicksand’s grip on you.

Freeing yourself from quicksand can take a while, and it’s thought that this time investment could be what led to the whole myth about drowning in quicksand in the first place. Quicksand is often found near coastal areas, and those that haven’t successfully freed themselves by the time the tide comes in will face the danger of drowning from a completely different threat than the quicksand that caused their problems in the first place. The other danger of quicksand comes when it’s formed spontaneously by earthquakes or damage to underground water sources. When it suddenly appears near populated areas, it can spell disaster for nearby man-made structures.

Show Me The Proof

Featured image photo credit: Matthew Bargo
Nature: Quicksand can’t suck you under
The Naked Scientists: What is Quicksand?
National Geographic: Quicksand: Why It Traps, How To Escape

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