Crust crumpling
How Do Mountains Grow?
Mountains rise where plates collide and rock has nowhere to go but up.
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Step 1 of 5
Plates move steadily and cannot stop.
Driven by heat flow in the mantle, plates drift a few centimetres a year. When two head for each other, something has to give.
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Step 2 of 5
Squeezed crust folds upward.
Rock under enormous sideways pressure buckles, exactly like a rug pushed from both ends. The folds are the mountains.
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Step 3 of 5
Rock is stiff over seconds, bendy over ages.
Hit rock with a hammer and it shatters. Push it for millions of years and it folds without breaking. Timescale decides which happens.
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Step 4 of 5
There is a deep root underneath.
Mountains float on the mantle like icebergs on water. A high range has a thick root pushing down, several times the height above ground.
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Step 5 of 5
Erosion fights back the whole time.
Rain, ice and rivers strip rock away constantly. A range only grows while collision outpaces erosion; when it stops, mountains wear down to hills.
The Himalayas still rise about a centimetre a year, because India is still driving into Asia.
The short version
Mountains form where colliding plates crumple the crust upward, and they last only while uplift beats erosion.
Try it yourself
Push a folded towel from both ends. The ridges that rise are folded mountains, made in one second instead of ten million years.
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