The formation of new oceanic crust at mid-ocean ridges requires a complementary mechanism by means of which lithospheric plates are consumed. The required destruction of lithospheric plates takes place in subduction zones located in the oceans and along the margins of some continents. Subduction zones are places where oceanic lithosphere sinks or is dragged back into the mantle and where magma is produced by partial melting within the mantle wedge above the descending lithospheric plate and/or in the plate itself. The resulting volcanic activity in the ocean basins is manifested by the formation of island arcs, whereas continental margins along which oceanic lithosphere is subducted under continental crust are uplifted and contain volcanic mountain ranges. All active subduction zones are sources of earthquakes that originate primarily within the Benioff zone associated with the down-going slab.