Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Regions where this process occurs are known as subduction zones. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately 2 to 8 cm per year.

Plates include both oceanic crust and continental crust. Stable subduction zones involve the oceanic crust of one plate sliding beneath the continental crust or oceanic crust of another plate. That is, the subducted crust is always oceanic while the overriding crust may or may not be oceanic. Subduction zones are often noted for their high rates of volcanism, earthquakes, and mountain building.

Orogenesis, or mountain-building, occurs when large pieces of material on the subducting plate (such as island arcs) are pressed into the overriding plate. These areas are subject to many earthquakes, which are caused by the interactions between the subducting slab and the mantle, the volcanoes, and (when applicable) the mountain-building related to island arc collisions.