A volcano is a mountain which is formed by the eruption of material from the earth's interior through a central opening or groups of openings. Volcanoes are scattered over the world. Volcanoes can be divided into three catagories based on volcano form and type of volcanic activity. They are Shield, Composite, and Explosion volcanoes.
A shield volcano is built chiefly of layers of basalt ( a dark, heavy lava ). A few shield volcanoes are composed of andesite ( a related, less dense type of lava ).
A composite volcano has more frequent and violent explosive eruptions than shield volcanoes do. Lava maybe extruded from either central crater or fissures on a volcano's sides.
Explosion volcanoes are composed of inclined layers of pyroclastic debris and contain no lava. During an eruption, debris are ejected from the crater. Most explosion volcanoes are built during one period of eruption.
2011/01/12
Volcano
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