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[[Image:Volcano.jpg|thumb|300px|Snow-covered Kanaga Volcano in Alaska erupts a small column of tephra, gas, and steam. Kanaga is a stratovolcano. View is toward the west.]]A '''volcano''' is a vent of some kind in the earth's crust through which [[magma]] is ejected.  The magma frequently builds up in layers, resulting in the formation of mountains.  Different types of magma produce different kinds of structures.  Hot basaltic [[lava]], which has low viscosity, tends to produce flat shield volcanoes because it can flow long distances before cooling.  [[Andesite]] and [[dacite]] lava generally produce cones, like those seen in the cases of [[Mt. Fuji]] and [[Mt. Rainier]], because the higher viscosity lava flows build up more dramatically near the vent

[[Image:Volcano.jpg|thumb|300px|Snow-covered Kanaga Volcano in Alaska erupts a small column of tephra, gas, and steam. Kanaga is a stratovolcano. View is toward the west.]]

A ''volcano'' forms when [[magma]], in the form of [[lava]], is able to breach the surface of the [[Earth]]. Many volcanoes tend to resemble [[mountains]], although some are so large that they form entire [[Island|islands]], as is the case of [[Mauna Loa]]. Volcanoes come in three main types, stratovolcano (also composite cone), shiled volcano, and cinder cone.

[[Category:Volcanology]]

[[Category:Volcanology]]