Quicksand can kill, but seldom does. Its few victims don’t get sucked in over their heads, but people trapped for long periods can die of exposure, thirst or drown in incoming tides.
Wet quicksand occurs when water wells up underneath sand and clay. The clay and water forms a gel that acts like yogurt. When undisturbed it’s solid. However, like tilting a yogurt pot, it flows when shaken. A person walking on it can make it move, an earthquake shaking waterlogged sediments has a similar effect.
A person walking on quicksand sinks downwards, pushing the sand grains together. The sand eventually forms a solid bed, usually when the person is trapped to their waist. The densely packed sand grains hold their legs tightly, preventing them from escaping. To pull them out vertically would need the power of a car.
Dry quicksand is loosely packed sand that’s been carried in the air or had air flowed through it. When someone steps on it, the sand grains pack closer together, causing the person to sink in.
How quicksand works
1. Water wells up
Water flows upwards, saturating the sand and clay.
2. Water pressure increases
If the water can’t escape, its pressure increases. Earthquakes shaking the sand can also increase water pressure.
3. Liquefying the sand
The water pressure reduces friction between the sand particles and pushes them apart making the sand behave like a liquid.
4. The role of salt
Salt allows clay particles to pack closer together. Salty water makes quicksand more unstable, fluid and dangerous.
5. Dry on top
The upwelling water rarely reaches the surface so quicksand looks dry from above and is almost impossible to spot.
6. Add a weight
Any object placed on the liquefied sand and clay will sink downwards, as it would in a liquid.
How to escape from quicksand
1. Go back
Carefully retrace your steps if the sand under your feet feels like custard
2. Don’t panic
If you get stuck, stay calm. The more you flounder, the deeper you’ll sink
3. Strip off
Leave wellies in the quicksand and cut shoelaces. Big rucksacks can act as solid ground
4. Lie down
If you’re sinking deeper, sit or lie in the quicksand to spread your weight
5. And roll
Try to roll out the quicksand, perhaps using a rucksack as an aid
Discover more amazing facts in the latest issue of How It Works magazine. It’s available from all good retailers, or you can order it online from the ImagineShop. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, make sure you subscribe today!
Plus take a look at: