Competitive Exams: Volcanoes
In the weaker parts of the earth's crust sometimes the molten, rock finds its way to the surface and is poured out to form a volcano. A volcano is a vent or an opening in the earth's crust through which rock fragments, lava, ash and clouds of gases come out. In course of time, the lava, ashes and other material accumulate around the vent and form a cone-shaped hill or mountain. The cup shaped hollow in the centre of a volcano is called a crater. Volcanoes which are no longer active are called extinct volcanoes. A volcano which is only sleeping and may become active is called a dormant volcano. The volcanoes which erupt frequently are active volcanoes. Distribution of Volcanoes: There are several thousand volcanoes in the world. They are distributed in several belts across the continents. The most important belt runs right and round the Pacific Ocean. Another, rather less important, are from Iceland, just touching the British Isles, through the Azores across the Atlantic to the west Indies, with a branch running through the Mediterranean Sea.