Here's what happens:
* Denser oceanic crust is forced beneath the less dense continental crust.
* The subducting oceanic plate melts as it descends into the mantle.
* This melted rock rises to the surface, creating volcanoes on the continental side of the boundary.
* The process also forms deep ocean trenches and mountain ranges.
This process is responsible for many geological features, including the Andes Mountains in South America and the Cascade Range in the western United States.
