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Quicksand myth exposed

Quicksand is not the bottomless pit portrayed in Hollywood films that sucks in unsuspecting victims and swallows them whole.

It is true the more people struggle, the deeper they sink into the soupy mixture.

But its buoyancy makes it impossible to be completely submerged, scientists report today in the journal Nature.

"Everybody thinks, thanks to Hollywood, that you can drown in quicksand. Basically if you do a simple buoyancy calculation, the Archimedes force, it is immediately evident that you can't drown completely," says Professor Daniel Bonn, a physicist at the University of Amsterdam.

Quicksand consists of salt, water, sand and clay. It is the water content that makes quicksand, which is found near estuaries, beaches and rivers, so dangerous.

"If you tread on quicksand, or liquify it by moving, it goes from something that is almost completely solid to something that is almost completely liquid," Bonn says.

He and his colleagues showed that Hollywood had got it wrong by measuring the viscosity, the resistance to flow, of quicksand and its sinking ability.

They also calculated the amount of force necessary to get a trapped foot out and found it was 100,000 Newtons, the equivalent needed to lift a medium-sized car.

If someone falls into quicksand they begin to sink and the sand packs densely around the feet, forming a type of trap.

In films people sinking in quicksand usually grab onto an overhanging tree branch or are pulled out just as they are about to disappear under the mucky surface.

But Bonn and his team say in real life the victim would sink halfway into the quicksand but would not disappear.

The scientists advise people trapped in quicksand not to panic.

"All you have to do to get your foot out is to introduce water into the sand and if you can do that along your leg by wiggling your leg around, that is the best way to get out," Bonn says.