plate tectonics Tools A B the earths crust is divided into a number of these tectonic plates. the outer layer of the earth the crust layer of molten rock on which the plates float magma a boundary where the plates are moving apart ocean ridge the deepest part of the ocean a trench where ocean plate is melted subduction zone the driving force of the tectonic plates convection currents created when two continental plates collide fold mountains created when two continental plates move apart an ocean name given to volcanoes in the pacific ring of fire where new crust is being made constructive plate margin explosive volcanoes often happen here destructive plate margin mountains created when indian plate collided with asian plate himalayas fold mountains found along the western coast of south america andes