At some places the molten rock,ash,steam or hot gases find their way from the core or mantle out of the earth's surface. This molten rock on reaching the surface is known as lava. The hole or the crack in earth's curst through which lava comes out is the birthplace of a volcano. Lava may comes out with an explosion or quietly. The molten rocks,dust and ahses fall back to earth and in time built up a volcanic mountain around the opening or the hole in the crust.
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