Volcano Facts

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Plural volcanoes, or volcanos, any vent in the crust of the Earth or other planet or satellite, from which issue molten rock, pyroclastic debris, and steam. Volcanism (vulcanism) is the name given to the processes and phenomena associated with the surficial discharge of such material from volcanoes, geysers, and fumaroles.

Volcanoes figure prominently in the mythology of many peoples who have learned to live with eruptions, but science was late in recognizing the important roleof volcanism in the evolution of the Earth.One major 18th-century school of thoughtheld that molten rock and volcanoes were simply accidents caused by burning coal seams. Geologists today agree that volcanism is a profound process resultingfrom the thermal evolution of planetary bodies. Heat does not easily escape from large bodies by conduction or radiation. Instead, partial melting and buoyant rise of magma are major contributors to the process of heat flux from the Earth's interior. Volcanoes are the surface manifestation of this thermal process, which has its roots deep inside the Earth and which hurls its ashes high into the atmosphere.

The term volcano can either mean the vent from which magma erupts to the surface, or it can refer to the landform created by the solidified lava and fragmental volcanic debris that accumulate near the vent. One could say, for example, that large lava flows are erupted from Kilauea Volcano in Hawaii, the word volcano here signifying a vent. By contrast, one could say that Kilauea is a gently sloping volcano of modest size as Hawaiian volcanoes go, the reference in this case being to a landform.

Broadly defined, all igneous rocks are the result of volcanism. If igneous rocks solidify from magmas that have not reached the surface, they are called intrusive igneous rocks, and this process in a more restricted sense is termed plutonism. Igneous rocks that cool and solidify at the Earth's surface are known as extrusive igneous rocks, and these are...
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