eli5 do mountain ranges like the himalayas recede over millions of years during tectonic movements? Is it just the reverse proces of what created them?
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M.S. in geology here. There are a couple reasons mountain ranges disappear after a while. First, as others have mentioned, erosion will remove a *lot* of material from a mountain range. But tectonic forces also play a role in the destruction of mountain ranges. Mountain ranges like the Himalayas result from the continental crust being compressed and therefore thickened by colliding plates. Rock is forced both upward into the mountains but also downward forming a so-called “crustal root” that sticks down into the mantle. After this compression ends, the thickened crust becomes unstable. It is unable to support its own weight. The crustal root is also unstable as continental crust is considerably less dense than the mantle (it’s a bit like trying to hold a balloon underwater). The compressed crust therefore starts to extend back outward and the mountain range essentially collapses over time.
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