What is a quicksand?

-Karthik Gurumurthy

So, quicksand isn’t quite the dramatic trap you see in movies, but it’s still pretty fascinating. It’s basically just a mix of sand and either water or air. At first, it looks totally solid — but the moment you disturb it, it turns into this unstable mess.

The thing is, the grains of sand in quicksand are usually more stretched out instead of being round, which means they don’t pack together tightly. Instead, there’s a ton of empty space between them — sometimes 30 to 70 percent of the whole thing is just air or water! It’s like a house of cards: it looks fine until you put a little pressure on it… and then it all collapses.

When you step on quicksand (or if there’s any kind of vibration or water movement), it messes up the fragile structure. Water gets pushed upward, the sand loses its grip, and suddenly it can’t hold your weight anymore — that’s when you start sinking.

In normal sand, the grains are packed in really tight with way less empty space (only around 25 to 30 percent), so it doesn’t collapse under you like that.

You’ll usually find real quicksand in places where water is hanging around — like along riverbanks, beaches at low tide, or at the bottom of alluvial fans where rivers spread out after coming down from mountains. Sometimes you even get it in deserts, on the loose side of sand dunes, but that’s super rare. And honestly, even when you do find it, you’re not going to get sucked under like in the movies — usually, you’d only sink a few centimeters before the sand firms up again because the air gets squeezed out and the grains settle tighter together.

The amount of sinking in quicksand is usually limited to just a few centimeters, as the grains eventually settle too close together to allow further compaction.