The process of an oceanic plate colliding with and descending underneath a continental plate

The correct answer is - subduction.

When an oceanic plate is colliding with continental plate and is descending underneath is the process known as subduction. This process occurs on places where there's convergent plate boundaries between a continental plate and oceanic plate. The oceanic plate is lower, thinner, and has higher density of its crust, while the continental is higher, thicker, but has lower density of its crust. The oceanic crust, as the plates collide, moves bellow the continental crust, thus subduction bellow it. As the oceanic plate moves more and more bellow the continental plate, it reaches the mantle, and the high temperatures and pressures of the mantle layer star to melt the crust from the oceanic plate. As a result of this process there's lot of volcanic activity along the boundary, as well as earthquakes, and the formation of mountain ranges.