Hopping out of the truck at the NO VEHICLES signpost, we inspected the cut bank sculpted by the recent flash floods. In ordinary conditions this was a regular 4WD vehicle crossing, so we walked toward the water’s edge on the packed wet sand. Six steps were normal; on the seventh, the sand rippled and vibrated, like shaken Jell-O jigglers; our boots sank several inches, and we beat a hasty retreat. The sand looked exactly the same in both places.
This was my first encounter with quicksand. I am guilty of having the same misconceptions about quicksand as you may have, so today’s post is an attempt to clear this up.
Quicksand is really not any special kind of sand; it is actually a condition, super-saturation, that is happening to a patch of sand. There is an insistent flow of water beneath the surface that agitates the grains of sand, lifting them apart. Each grain of sand is surrounded by a thin film of water, and as they lose friction with each other the solid mass breaks asunder. The water is not strong enough, however, to completely disperse the sand and the resultant soupy pool therefore can look like solid ground.
At rest, quicksand thickens with time, but it remains very sensitive to small variations in stress. At higher stresses, quicksand liquefies very quickly, and the higher the stress the more fluid it becomes. This causes a trapped body to sink when it starts to move.
According to a study published in the journal Nature, quicksand has a density of about 2 grams per milliliter; human density is only about 1 gram per milliliter. It is impossible for a person in quicksand to be drawn completely under. You would descend about up to your waist, but you’d go no further.
Here is a delightfully entertaining 3-minute video clip from the Discovery Channel, in which Bear Grylls shows us how to escape from Colorado River quicksand near Moab. (How appropriate!) Enjoy it — and stay away from jiggly sand!