Despite it’s not unusual to see bad guys getting swamped in quicksand in movies, drowning in quicksand completely is not possible in real life.
Here is the science behind it.
Analysis of the composition of the “quicksand” showed that there are four key ingedients – sand, obviously, water, clay and salt. Together these materials form a structure resembling a house of cards, with large water-filled gaps between the sand particles, which are loosely glued in place by the clay.
As long as it’s left alone, the structure remains stable. But as soon as it’s disturbed, by stepping on it, the clay changes from a jelly-like consistency to a runny liquid. The effect is the same as stirring a pot of yoghurt. Liquefying the clay makes the quicksand about one million times runnier, and the whole house of cards comes tumbling down, with you inside it.
Very quickly, the sand sinks to the bottom and the water floats to the top. This is where the salt comes in. When there’s enough salt present, as soon as the clay particles liquefy, electrical charges make them begin to stick together to form bigger particles and these also settle with the sand.
The result is a very stodgy layer of sand and clay, which is twice as dense as the original quicksand and packed tightly around the trapped body parts.