How does quicksand work?

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by Brian Griffin (whyzz writer) >> more about the author

Quicksand shows up a lot in movies. It’s actually a pretty cool substance, though it can be dangerous. What is it? It’s sand with a lot of empty space or air in it or sand with a lot of water in it.

People often say quicksand is like a house of playing cards. Have you ever built one of those? You have to balance the cards very carefully or else they will all fall down. Think of a really tall tower of cards. How much of the space in the tower is actually made of cards? How much is just air? What would happen if you tried to stand on it?

Sometimes sand can settle just like a house of cards, very delicately stacked. The grains do not land tightly packed, so there is a lot of air or water in between them. When pressure is put on the sand, all of its support falls apart. If someone is standing on it, they will begin to sink. If someone moves around a lot in quicksand, they are actually shaking up the sand and causing it to lose its support even faster. It gets quicker. That’s why they say people should stay calm and not struggle if they accidentally step in quicksand.

Luckily, people usually only sink so far, and then they will float in the quicksand. It can still be dangerous though, so it isn’t a safe place to play or explore.

Shifting Sands

If you happen to be on a trip to the beach or have some sand around your home and a pale too, you can experiment with some quicksand on a small and safe level.

Fill the pale half way with sand, and add just a tiny bit of water. What does the water do to the sand? Just a little water should actually make sand stronger. You may even be able to build a sandcastle with it.

Next (or after you are done building the castle) fill the pale 3/4ths of the way up with water and mix up the water and the sand. How does the water affect the sand now? What happens if you drop something light like a seashell onto it? What happens if you drop something heavy, like a rock?