Stratovolcano the Composite Cones Essay Example | Topics and Well Written Essays - 500 words

Stratovolcano the Composite Cones - Essay Example Stratovolcanoes are common at subduction zones forming a chain of volcanic features along plate tectonic boundaries where the oceanic crust is drawn under continental crust. The magma that is responsible for stratovolcanoes formation rises when water that is trapped both in the porous basalt rock and in hydrated minerals of the upper oceanic crust layer. It is then released into the mantle rock of the asthenosphere of earth’s crust that is above the sinking oceanic slab. After the occurrence of dewatering at high pressures and temperatures for each mineral, the plate descends to greater depths. The released water from this rock then lowers the melting point by cooling the temperatures of the overlying mantle rock. This in turn makes the rock to undergo partial melting and then rises due to its lighter density relative as compared to the surrounding mantle rock and the pools that form temporarily at the base of the lithosphere. The magma then rises thought the earth’s cr ust, carrying silica-rich crustal rock leading to a final intermediate composition. On reaching near the top surface, it then forms a pool in the magma chamber within the volcano, due to low pressure, water and other compounds such as chlorine sulphur and carbon dioxide dissolve in the magma to escape from the solution. Once a critical large volume of magma and gases accumulates the rock that acts as an obstacle is then overcame leading to a sudden explosive eruption (Biley ). Stratovolcanoes are rated as the most hazards to civilians as they cause large numbers of death when they occur. Many deaths are caused by mud and the pyroclastic flow that fast-moving mixture of hot volcanic debris ash and gases that can travel at high speed of about 160km/h. The eruption of Mt Pel’ee on Martinique Island in the Caribbean, El Chi chon volcano in Mexico which killed thousands of lives, the Pinatubo volcano that erupted in 1991 in Manila and the Unzen volcano on the island of Kyushu. Stratovolcanoes mainly form at the convergent plate margins usually where one plate descends beneath an adjacent denser plate at the site of a subduction zone.