Is there really such a thing as quicksand?

Is there really such a thing as quicksand or is it just a make-believe sand trap found in Tarzan movies? If it does exist, where is it usually found, can it actually pull you down and under, and how can a person escape from it? — Barbara R., Normal, Illinois

Dear Barbara:

It's real, all right. "Quicksand" is the name given to a mass of sand particles that are supported by circulating water rather than by each other. It can be found wherever sand and water can be found--especially near streams, beaches, and the mouths of rivers.

Contrary to popular belief, quicksand cannot suck you down and under. Its density is greater than the density of most things, including human bodies; in other words, you can float in it. If you struggle, though, you'll only succeed in digging yourself deeper in.

If one of your excursions around normal is interrupted by quicksand, keep yourself still until you stop sinking (you will). Use slow swimming motions to get yourself into a horizontal position and then roll yourself to terra firma.

— Cecil Adams

From: http://www.straightdope.com/