 Subduction. Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into mantle. Regions where this process occurs aren't known as subduction zones. Rates of subduction are typically in centimetre per year, with the average rate of convergence being approximately 2-8 cm per year along most plate boundaries. Plates include both oceanic crust and continental crust. Stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the subducted lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that usually have a high rate of volcanism and earthquakes. Furthermore, subduction zones develop belts of deformation and metamorphism in the subducting crust, whose exhumation is part of Orogyner and also leads to mountain building in addition to collisional thickening.