The area where the Earth's crust goes back down into the mantle is called a subduction zone.

Here's a breakdown of what happens in a subduction zone:

* Convergent Plate Boundaries: Subduction zones occur at convergent plate boundaries, where two tectonic plates collide.

* Denser Plate: One plate, usually the denser oceanic plate, is forced beneath the other, less dense plate.

* Melting and Magma: As the denser plate descends, it experiences intense pressure and heat. This causes the rock to melt, forming magma.

* Volcanoes and Earthquakes: The magma rises to the surface, creating volcanoes. The movement of the plates along the subduction zone also generates earthquakes.

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