When you walk around on land, you are walking on top of Earth’s rocky crust. Below the crust is another thick layer of rock. These layers form Earth’s tectonic plates and when those plates collide with each other, they often form mountains.

Julie Menard

To find out more about how mountains form, I visited my friend Julie Menard, a professor in environmental sciences at Washington State University who is very curious about geology.

“When the collision happens, one plate will not simply go on top of another,” she said. “The plates will just push against each other and over a long period of time a mountain will form.”

Menard told me that these tectonic plates are huge. The plates are about 77 miles thick, and they move very slowly—just about 2 to 3 inches a year. When the two plates come together, they push the rock upwards. It can take ten millions of years for the mountain to rise up.

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