The creation of Stratovolcanoes

Stratovolcanoes are common in subduction zones,forming chains along plate tectonic boundaries where oceanic crust is drawn under continetal crust(Continental ARc Volcanism, e.g. Cascade Range,central Andes) or another oceanic plate (Island arc Volcanism, e.g. Japan,Aleutian Islands).The magma that forms stratovolcanoes rises when water trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust,is released inyo mantle rock of the asthenosphere above the sinking oceanic slab. The realised of water from hydrated minerals is termed "dewatering, '' and occurs at specific pressures and tempreratures for each mineral,as occurs at specific pressures and temperture for each mineral,as the plate descends to greater depths.The water freed from the rock lowers the melting point of the overlying mantle rock, which undergoes partial melting and rises due to its lighter density relative to the surroundings mantle rock, and pools temporarily at the base of the lithosphere. The ,magma then rises through the crust, incorporating silica-rich crustal rock, leading to a final intermediate composition (see Classification of igneous rock).When the magma near the top surface,it pools in a magma chamber under or within the volcano.There,the relatively low presure allows water and other other volatiles(mainly CO2 ,SO2, CI2and H2O) dissolved in the magma to escape from solution, as occurs when a bottle of carbonated water is open ,releasing CO2.Once a cirtical volume of magma and gas accumulates, the abstacle (mass blockage) of the volcanic cone is overcome , leading to a sudden explosive eruption.