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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. Volcanoes were important contributors to the early earth atmosphere by releasing gases such as nitrogen (N2), carbon dioxide (CO2), and ammonia (NH4).

Volumes of Some Well-Known Volcanic Eruptions
Eruption Date Volume in km3
by humans
Paricutin, Mexico 1943 1.3
Mt. Vesuvius, Italy 79 A.D. 3
Mount St. Helens,
1980 4
Krakatoa, Indonesia 1883 18
by study
of deposits
Long Valley, California pre-historic >450 & <700
Yellowstone, Wyoming pre-historic 400

Note that volcanic eruptions that occurred before historic times were several orders of magnitude larger (more than 1000 km3 in erupted volume) than ones observed by humans.

Volcano Web : Introduction

created by Ithara Phlong,
Volcanic Studies, Montgomery college

last modified: September 18, 2000