What happens to the continental crust under a mountain as the mountain erodes and becomes less massive?

Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountainsproduced, and two continents sutured together. Continental collision is known only to occur on Earth.

Continental collision is not an instantaneous event, but may take several tens of millions of years before the faulting and foldingcaused by collisions stops. The collision between India and Asia has been going on for about 50 million years already and shows no signs of abating. Collision between East and West Gondwana to form the East African Orogen took about 100 million years from beginning (610 Ma) to end (510 Ma). Collision between Gondwana and Laurasia to form Pangea occurred in a relatively brief interval, about 50 million years long.