By Jessica Duke, MD
Two hikers were recently hiking the remote Subway Trail in Zion National Park, Utah, when, believe it or not, they became trapped in quicksand! The first hiker stepped in the colloid suspension and when the second hiker attempted to rescue her, he too became caught and buried up to his knee. The first hiker was able to escape, but no amount of effort from either of them could pry the second hiker loose. He was not only stuck in the frigid quicksand, but also exposed to the elements. There was no cell service in the area and with no chance of extracting the second hiker on her own, the first hiker was forced to leave the second hiker with their warm weather gear and head out in search of help. After hiking alone for hours, the first hiker was finally able to call for help. A search and rescue team found the second hiker several hours later, but they were not able to free him from the quicksand until late into the night. They had to spend the night out in the park until a helicopter crew was able to extract them the following day. Thankfully, both hikers recovered fully from their misadventure.
We’ve all seen the action films where quicksand swallows its victims whole. In reality, quicksand doesn’t suck people under the way it always seems to in the movies, but it is difficult to get out of and can be extremely dangerous. Quicksand is a mixture of sand or silt and water that is typically found on riverbanks, near lakes, in marches, or near coastal areas. It is not usually a problem at Zion, but quicksand can form there when there the conditions are right.
At rest, quicksand appears solid, but it becomes unstable when exposed to a sudden shock or stress, like the weight of a hiker. The higher the stress, the more fluid it becomes. A person will start to sink when they step on quicksand, but even a person moving in quicksand will never sink all the way as the human body isn’t dense enough. Objects in quicksand sink to the level at which the weight of the object is equal to the weight of the displaced quicksand. Quicksand has a density of about 2g/mL, while the density of the human body is only about 1g/mL. At that density level, you would only sink in to about your waist. However, panicked movement causes a person to sink further and makes extraction by the victim or a rescuer more difficult.
While it isn’t possible for a person to sink entirely in quicksand, that doesn’t mean it isn’t dangerous. The real danger with quicksand is the environment. Weather exposure, dehydration, hypo/hyperthermia, tides, and carnivores may all harm a trapped person. If you do step in quicksand, it is not only important to stay calm so that you don’t sink in further, but also to get out of the quicksand as quickly as possible so that you don’t become a victim of the environment.
So how do you escape from quicksand? Well, to move within quicksand, a person must apply enough pressure on the compacted sand to re-introduce water to liquefy it. Sounds easy enough, but the forces required to do this are quite large. For example, the force needed for someone to pull their foot out of quicksand at a speed of 1cm/s would be equivalent to that required to lift a medium sized car (about 100,000N). Therefore, even if just your foot were stuck in quicksand, it would not be helpful to have someone try to pull you out as this method requires immense force and also puts the rescuer at risk of becoming a victim. If there are multiple rescuers, they could potentially pull the victim to firm ground using a rope, belt, or strap, but this is still extremely difficult and potentially risky. Your best chance is to slowly wriggle your leg to create a space between your foot and the quicksand to allow water to flow down and loosen the sand. If you are wearing a pack, remove it immediately and throw it to firm ground to reduce your weight on the quicksand. If you are submerged to your waist, try to flatten out with your arms and legs extending so as to float in the supine position and then swim to firm ground.