Did you know that in the 1960s, 1 in 35 films, give or take, featured someone dying from being trapped in quicksand? From "Lawrence of Arabia" and "Ice Cold in Alex" to more recent films like "Indiana Jones and the Kingdom of the Crystal Skull", the idea that quicksand is a quick ticket to the afterlife has become ingrained in many people's minds.
But, how dangerous is quicksand, really? Let's find out.
What is quicksand?
Quicksand is defined as "a deep mass of loose sand mixed with water into which heavy objects readily sink," according to the Merriam-Webster dictionary. In this sense, quicksand is a type of colloid made up of fine granular material, like sand, silt, clay, and water.
A colloid is a special kind of mixture of microscopically dispersed insoluble particles (clay, sand, silt for example) suspended in another substance, like water. It tends to form when saturated loose sand is suddenly agitated and the suspension water cannot readily escape.
Scientifically classified as "shear-thinning thixotropic non-Newtonian fluid", colloids like quicksand do not follow the normal laws of physics associated with liquids and/or solids. Interestingly, there are plenty of examples of similar non-Newtonian fluids in your home too.
Toothpaste, some syrups, and hair gels are all other examples of them you'll meet every single day. Just like quicksand, they may appear solid initially but are able to flow when an increase in pressure or force is applied to them — like squeezing a toothpaste tube for example.
For this to happen, enough stress or force must be applied to enable the substance to flow like a liquid. This is called its "yield stress", which, in the case of quicksand, is fairly low, at around a 1 percent increase in the weight on top of the quicksand.
This is exactly what can happen when an unfortunate individual accidentally stumbles upon some quicksand and steps into it. This sudden "shock" disrupts the careful balance of sand and/or clay or mud and water. This causes the body of sand to liquefy resulting in the water and particulate matter separating.
This leaves a layer of densely packed wet sand that cannot support your weight and causes you to sink. This is primarily because the frictional forces between sand grains that would normally be able to resist your weight are temporarily lubricated.
If you take our advice and stay calm, eventually the equilibrium of the quicksand will be restored, preventing you from sinking further. If, however, you do struggle, you will continue to disrupt the system, worsening your problem fairly quickly.
There are other materials that have the exact opposite properties of "shear-thinning thixotropic non-Newtonian fluids", appropriately called "shear-thickening thixotropic non-Newtonian fluids." One example is cornstarch in water (also known as oobleck). Such materials are ideal for impact protection for things like bullet-proof vests and motorbike armor.
Instead of weakening and thinning, like quicksand, these materials react to a sudden addition of stress of force by rapidly stiffening, providing a form of a shock absorber.
Certain places are prone to quicksand formation like, for example, hollows at the mouths of large rivers, along flat stretches of stream, beaches where pools become partially filled up with sand, and where an underlying layer of stiff clay or other dense material prevents drainage. Quicksand can also be found where sand, mud, and vegetation mix together in bogs.
Contrary to popular belief, however, you can never actually completely become submerged in quicksand. This is because quicksand, while a hazard, cannot defy other basic laws of physics — namely buoyancy.
The density of sand and water that make up a body of quicksand exceeds that of a human body, and so, you cannot easily completely sink within it. Water's density, for example, is 62.4 lbs/ft3 (1 kg/L). In other words, 1 kilogram of water takes up 1 liter of space.
While the human body is primarily made of water (about 60%), it has other denser materials within it, like muscle, that can increase the average density of the human body. However, even with these denser materials, the human body has a density close to, but still less than water at around 8.3 lbs/gallon (1,010 kg/m3).
For this reason, if you were unfortunate enough to accidentally step into quicksand, you should only sink up to about your waist if no effort were made to escape. On top of this, quicksand pits are rarely more than a few feet deep, allowing most adults to touch bottom while still only waist deep.
However, it is theoretically possible to be killed by quicksand if you lose your balance and fall in such a way as to drown. It is thought, though nobody really knows why, that this is where quicksand gets its public reputation for being incredibly dangerous.
Interestingly, some scientific experiments have been conducted in the past to attempt to simulate and study quicksand under more controlled conditions and without risking anyone's life. One particular example was conducted by Daniel Bonn from the University of Amsterdam.
While on a trip to Iran, he came across a body of quicksand near a lake. Bonn took some samples and analyzed them back in his lab.
He found that this particular example was a specific mixture of clay, saltwater, and sand, and decided to make more of it synthetically. To test what happens when people step into it, he used a series of aluminum beads that have the same density as a human being.
He then simulated people flailing around by shaking the beads and waiting to see what would happen. As you've probably already worked out, the beads sunk a little but didn't completely submerge. Eventually, as the water and sand begin to remix, the beads actually began to float back on the surface.
Bonn went further and tried various other objects and found that so long as their density was roughly similar to a human, they would usually only ever sink to roughly half their height. Satisfied with these results, he then went on to find out how much force is needed to free objects — like your foot.
Bonn found that with this particular quicksand mixture, you'd need to use about 22,481 pounds (100,000 newtons) of brute force. That is roughly the force needed to lift a medium-sized car.
Unless you are Superman, this is not very likely.
How many people are killed by quicksand every year?
In short, and not to sound flippant, nobody is actually killed by quicksand. As we've previously highlighted, you cannot be completely consumed by quicksand due to the differences in density of your body and the quicksand.
However, what normally happens is that people tend to panic and become trapped in quicksand. This limits their mobility, leaving them exposed to the elements or, in the case of coastal bodies of quicksand, prone to incoming tides and drowning if the tide is high enough. This is how, tragically, a mother of two was killed in Antigua in 2012. She became stuck in a patch of quicksand close to the shoreline and drowned when the tide came in.
It is also theoretically possible to be killed by "dry" quicksand. While not actually quicksand, the dangers commonly associated with quicksand have been observed in the past in grain elevators and silos. However, the very specific environmental factors needed to create this in nature have never been observed.
Technically called "grain entrapment" or "grain engulfment", several people are killed each year when they become submerged in grain and cannot escape without assistance. If completely engulfed, victims either die from suffocation or by being crushed to death by the mass of grain above and around them.
This is exactly what happened to a farmhand in Germany in 2002. Firefighters were called to the scene and when they did find the man, he had sunk up to his armpits in the grain.
"Each time he exhaled, the volume of his chest reduced, causing [the] grain to rush to fill the gap and making it progressively harder for him to breathe," explained the BBC.
To save the man's life, firefighters lowered a cylinder to surround the man's body. Once installed, they used an industrial vacuum cleaner to suck out the grain in the immediate vicinity of the victim preventing the grain from further crushing his chest.
Mercifully, this man actually survived the ordeal to fight another day. For many others around the world, however, if no immediate help can be provided, the outcome can be very tragic. A truly horrific death, and one that is completely avoidable.
There is also a very dangerous natural form of what is commonly referred to as quicksand that can, and often does, kill people. This is something called liquefaction.
This is a very special case that occurs when a natural disaster like an earthquake stirs up soil and/or sand with water. Liquefied soils then rapidly lose their structural integrity and flow like a liquid, severely weakening foundations to buildings and other structures.
This often results in buildings collapsing, killing their occupants outright. Such events have happened regularly throughout history, with one infamous example occurring during the 1964 Niigata earthquake, killing about 36 people.
Another, more recent event occurred during the 1989 Loma Prieta, California earthquake. Liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco. This tragic event killed about 63 people.
Quicksand, or rather the liquefaction of sediment, is also a major headache for some major civil engineering works — like building a dam. This is a complex enough undertaking and they need to be incredibly tough structures.
However, if precautions are not taken to mitigate the potential for liquefying sediment around or below the main dam structure, the dam can be undone in very short order.
This is where something called "Darcy's Law" comes in very handy. Developed by a French hydraulics expert in the 1800s, the law is “an equation that defines the ability of a fluid to flow through a porous media such as rock.”
Since dams are specially designed to hold back millions of tons of water, there is always the potential for that water to penetrate sediment around the dam if the design of the dam is not 100% attached to solid rock or is of an earth-fill design.
This is exactly what happened to the Teton Dam in Idaho back in the 1970s. An earth-fill dam, water was able to seep into the dam's main structure, eventually liquefying the part of the main dam wall and causing a catastrophic collapse.
The disaster resulted in the tragic death of eleven people, destroyed thousands of homes, and businesses, and wiped out entire agricultural communities in the area. The cost of damage has since been estimated to have been about $2 billion at the time.
A detailed investigation later discovered that the cause of the collapse was found to be the hydraulic piping or internal erosion caused by water seeping through the soil, weakening the overall structure. to prevent a similar problem from occurring today, most new dams are built with "walls" below the surface to prevent, or at least slow down, soil liquefaction and maximize the life span of the dam.
How do you get out of quicksand?
So, in the highly unlikely event that you accidentally fall into a body of quicksand, how, exactly, do you get yourself unstuck?
Your first reaction needs to be to keep calm. This is vital, as the more you struggle to escape, the more you'll get trapped in the quicksand.
This is because once you've disturbed and temporarily liquefied the quicksand, you'll sink to around your waist or mid-chest level (if it is that deep). Once the sand grains in suspension begin to settle under gravity, they'll begin to compact around your submerged body parts — namely your legs.
If you do attempt to aggressively free yourself, you will simply liquefy more sand, making your situation progressively worse the more you stress and strain to escape.
Try to control your breathing too. If you breathe more deeply than usual, this will greatly increase your relative buoyancy and also doubles as a way to calm you down and think clearly.
If you are carrying heavy loads, like a bag, jacket, etc., try to remove these and toss them onto solid ground. Everything, that is, except for things like trekking poles, or, if you are inclined to use one, a wooden walking stick.
These items can prove incredibly useful for helping you escape a body of quicksand. A wooden pole or stick is obviously a great buoyancy aid, but a regular trekking pole can also be useful to help you break free of the quicksand.
To do this, lay the stick down behind your back, and lower your back onto it. This will help stabilize your body, and greatly assist you when attempting to free your legs.
At all times, try to keep your head and arms out and above the quicksand, so you can grab hold of solid things like branches, roots, or other people's hands to help wrench you free. If you are able to get rapid assistance from other people, ensure they pull you out slowly and steadily, not yank you out like they are attempting to win a tug-o-war contest.
And, never, we repeat never, attempt to "float" belly down in the quicksand. This will dramatically increase the likelihood that you will be suffocated! Not good.
If no assistance is immediately available, and if you are able, try to lie down on your back as slowly as you can. Once in a supine, or close to supine, posture, gently wiggle your legs in tiny movements. This will allow you to slowly but surely free your legs from the compacted sand.
Eventually, you should be able to fully recline on the surface of the sand. Once in this position, you should be able to gently crawl or "swim" to the edge of the quicksand body to reach more solid ground and pull yourself out.
However, when moving over the surface of the quicksand keep your arm movements small, controlled, and as close to your core as possible. You don't want to create more liquefaction of the quicksand more than you have already. And that is your lot for today quicksand skeptics.
That being said, horses are more likely to panic when under stress.