<P> Stratovolcanoes are sometimes called "composite volcanoes" because of their composite layered structure built up from sequential outpourings of eruptive materials . They are among the most common types of volcanoes, in contrast to the less common shield volcanoes . Two famous stratovolcanoes are Krakatoa, best known for its catastrophic eruption in 1883 and Vesuvius, famous for its destruction of the towns Pompeii and Herculaneum in 79 CE . Both eruptions claimed thousands of lives . In modern times, Mount Saint Helens and Mount Pinatubo have erupted catastrophically . </P> <P> Existence of stratovolcanoes has not been proved on other terrestrial bodies of the solar system with one exception . Their existence was suggested for some isolated massifs on Mars, e.g., Zephyria Tholus . </P> <P> Stratovolcanoes are common at subduction zones, forming chains along plate tectonic boundaries where oceanic crust is drawn under continental crust (continental arc volcanism, e.g. Cascade Range, central Andes) or another oceanic plate (island arc volcanism, e.g. Japan, Aleutian Islands). The magma forming stratovolcanoes rises when water trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust is released into mantle rock of the asthenosphere above the sinking oceanic slab . The release of water from hydrated minerals is termed "dewatering", and occurs at specific pressures and temperatures 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 then undergoes partial melting and rises due to its lighter density relative to the surrounding 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 . When the magma nears the top surface, it pools in a magma chamber under or within the volcano . </P> <P> There, the relatively low pressure allows water and other volatiles (mainly CO, SO, Cl, and H O) dissolved in the magma to escape from solution, as occurs when a bottle of carbonated water is opened, releasing CO . Once a critical volume of magma and gas accumulates, the obstacle (rock blockage) of the volcanic cone is overcome, leading to a sudden explosive eruption . </P>

Where are stratovolcanoes commonly found what type of plate boundary are they near
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