Depending on the type of plates that collide, they either lift or subduct. When an oceanic plate collides with a continental plate, it typically slides underneath it. If two like plates collide, they crush together at the collision point and lift up broken material from both plates.
Tectonic plate collisions generate tremendous force, and the results of the impact form major geological features. Some of the features are obvious to the eye, while others may remain hidden.
Oceanic plates are typically heavier, and more dense, than continental plates, so when they collide the oceanic plate is forced down under the edge of the continental plate creating a subduction zone. Subduction zones create two significant geologic formations, magma chambers and fault lines.
Once a subduction zone is created, the pressure pushing the two plates together still exists. When it builds up too much energy, the oceanic plate slips further underneath, creating violent earthquakes that can also trigger tsunamis. When the edge of the oceanic plate is pushed down far enough, it melts from the heat of the earth's core and rises through the broken plates to form volcanoes.
Continental plates have similar densities, so when they collide, they crush and lift up creating mountain ranges such as the Himalayas and the Appalachians. These plates continue to slide and create earthquake fault zones.