Quicksand is a non-Newtonian fluid : when undisturbed it often appears to be solid ( `` gel '' form ) , but a minor ( less than 1 % ) change in the stress on the quicksand will cause a sudden decrease in its viscosity ( `` sol '' form ) . After an first disturbance -- such as a person attempting to walk on it -- the water and sand in the quicksand separate and dense regions of sand sediment form ; it is because of the formation of these high volume fraction regions that the viscosity of the quicksand seems to increase suddenly . Because of the higher density of the quicksand , it would be impossible for a human or animal to completely sink in the quicksand , though natural hazards present around the quicksand would lead people to believe that quicksand is dangerous .