The Movement of Continental Plates:
subduction When two continental plates collide (at a convergent plate boundary like the Ring of Fire), some crust is destroyed in the impact and the plates become smaller. The results differ, depending upon what types of plates are involved.
Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this phenomenon is called subduction.
Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming undersea volcanoes in the vicinity.