eli5 We are told mountains were created by tectonic plates squeezing together, so why aren’t they just rubble?


When you crush a rock it doesn’t bulge, it shatters. So why are mountains solid rock?

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>When you crush a rock it doesn’t bulge, it shatters. So why are mountains solid rock?

Tectonic plates are not rams crashing headlong into each other. One plate will either move 1. alongside, 2. over or 3. under another one. There’s definitely lots of rubble, but only where the plates meet – dozens of kilometers **under** the mountains.

Under sufficient heat and pressure, rock becomes plastic. The upper layers *do* fracture.

But they don’t just stand there and get crushed. When plates collide — at a “convergent plate boundary” — the lower rock smooshes, or one plate goes under the other. The upper layers ride up on top of that.

Answer: They *are* rubble, just a lot of the pieces are huge.

You’re thinking on Human scales when you should be thinking on continental-level scales.

On large scales (hundreds of km, hundreds of years), continental crust acts like clay or playdough – it deform. Sure, there might be fracturing or rubble in small places, but on large scale it’s not unlike smushing two sheets of clay together.

There are many places where you can see layers of rock piled one on the other, like a layer cake. The U.S. Grand Canyon is a famous example. There, they are mostly sedimentary, and laid out flat and horizontally, like mud layers on the bottom of a lake.

However, tectonic pressures pushing against the side of such a rock pile can literally bend those stacks of layers into curves, even flip them over like layers in kneaded bread dough. This works best if the rocks are deeply buried (thousands of meters) because then the pressures result in plastic flow instead of crumbling. Uplift and erosion can later expose them to our view.

Such “folded” rock can also be seen all over. The canyons of southern Crete, for example, have many beautiful exposures of folded rock.