Quicksand

Quicksand formed when the water reduce the friction between sand particles.Therefore, the sand started to "move".The quicksand happen more frequently in few places,such as riverbank, beach, shoreline, near underground springs and swamps.



Resources:http://science.howstuffworks.com/environmental/earth/geology/quicksand1.htm

In some action movies,when a person drop into the quicksand,then person will sink into the sand and after than die.Movies give us a wrong concept.The density of human is 1g/ml,and the density of quicksand is 2g/ml.Compare to both density,human will not sink until cover the head but will
sink until the waist then stop.The situation that a person die in quicksand might probably because of too afraid and struggle try to go away from quicksand.Must remember the more you struggle in it the faster you will sink.So just relax yourself and try to move slow motion.This can reduce viscosity.Besides,extend arm and band down leg to increase surface area can lead to float up.



Reference: science.howstuffworks.com/environmental/earth/geology/quicksand.htm