How Mountains Form

Take a good look. That's Mount Everest. Eight thousand eight hundred and forty-eight metres tall — the tallest place on Earth. Climbers spend months getting up it. But here's the strange part. That mountain wasn't always there. Fifty million years ago, the spot where Everest stands today was at the bottom of a warm ocean. So how does an ocean floor become the tallest rock on the planet? That's our story today. How mountains form.

Here's a secret about Earth. The ground you stand on — the rock crust — is not one solid skin wrapped around the planet. It's cracked, like a hard-boiled egg dropped on a table. Big slabs of crust, called tectonic plates, sit on top of a layer of red-hot, slowly-flowing rock far underneath. The plates drift around, very slowly. About as fast as your fingernails grow. Most of the time you don't notice — but at the edges, where two plates meet, things get interesting.

Now imagine two of those plates drifting toward each other. They're both made of solid rock. Solid rock can't just slide through solid rock. So when they push together — for thousands and thousands of years — the rock between them starts to crumple. Like a tablecloth shoved across a table from both sides, it bunches up into folds. Some folds go down, into the Earth. But a lot of them go UP. Pile after pile of crumpled, folded rock — slowly, surely, climbing into the sky. That pile is a mountain.

Here's the catch. This crumpling isn't fast. One year of plate push barely bumps the ground. A thousand years gives you a hill. A million years gets a small range. Fifty million years — and you have the Himalayas. India crashed into Asia about that long ago, and the rock has been piling up ever since. Even today, Everest gains a few millimetres of height every single year. So when you look at a mountain, you're looking at deep, deep, deep time. Patient pressure. The Earth doesn't hurry.

Not all mountains form the same way. Most of the famous ones — the Himalayas, the Alps, the Andes — are FOLD mountains. Two plates squeezed, rock crumpled, peaks rose. But there's a second recipe. Sometimes the crust just cracks. One huge block of rock slides UP along a crack, while the block next to it stays put. That's a BLOCK mountain. The Sierra Nevada in California is one — a giant tilted slab of granite. Same idea, different motion. Both make peaks. Both took millions of years.

Now you try. You've got two sliders. One is collision SPEED — how fast the plates push into each other. The other is TIME — how many millions of years you let them push. Pick your settings, hit GO, and watch what happens. Want a small hill? Tiny speed, short time. Want to beat Everest? Crank both up. There's a yellow line on the height bar showing how tall Everest is — try to match it. What did you have to do to get there?

Let's put the whole story together. Two plates of Earth's crust drift toward each other. Slowly. Patiently. Where they meet, the rock has nowhere to go but up — so it folds, and folds, and folds again. A few millimetres a year. For tens of millions of years. And eventually you get the Himalayas, the Alps, the Andes — the roof of the world. Next time you see a mountain — even a tiny hill — remember: every one of them is Earth, in the middle of doing something. So what built the mountain near YOU?