A volcano is a location where magma, or hot melted rock from within a planet, reaches the surface. It may happen violently, in a massive supersonic explosion, or more quietly, as a sticky, slow lava flow.
Volcanoes have been a part of earth's history long before humans. Compare the history of human beings, a few million years in the making, to that of the Earth, over four billion years in the making. Volumes of Some well- Known Volcanic Eruptions
Eruption Date Volume in km^3 -------- ---- -------------- Paricutin, Mexico 1943 1.3 Mt. Vesuvius, Italy 79 A.D. 3 Mount St. Helen, Washington 1980 4 Krakatoa, Indonesia 1883 18 Long Valley, California pre-historic >450 & <700 Yellowstone, Wyoming pre-historic 2400