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Introduction

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
How
discovered		 Eruption Date Volume in km3
eruptions
observed
by humans		 Patricutin, Mexico 1943 1.3
Mt Vesuvius, Italy 79 A.D. 3
Mount St Helens
Washington		 1980 4
Krakatoa, Indonesia 1983 18
inferred
by studie
of deposits		 Long Valley, California pre-historic >450 & <700
Yellowstone, Wyoming pre-historic 400
Note that the volcanic eruptions occurred before historic times were several orders of magnitude larger (more than 1000km3 in erupted volume) than ones observed by humans.
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Last modified: April 8, 1999

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