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| A <b>volcano</b> is a place where the ] crust is weak, and seismic activity leads to expulsions of ], ] and ] during ]. Volcanoes are usually situated either at the boundaries between ] or over ]s. Volcanoes may be either dormant (having no activity) or active (near constant expulsion and occasional eruptions), and change state unpredictably. | A <b>volcano</b> is a place where ] is extruded from the surface of a planet. the ] crust is weak, and seismic activity leads to expulsions of ], ] and ] during ]. Volcanoes are usually situated either at the boundaries between ] or over ]s. Volcanoes may be either dormant (having no activity) or active (near constant expulsion and occasional eruptions), and change state unpredictably. | ||
| Volcanoes on land often take the form of flat ], as the expulsions build up over the years. Under ], volcanoes often form rather steep ] and in due time break the ] surface in new ]. | Volcanoes on land often take the form of flat ], as the expulsions build up over the years. Under ], volcanoes often form rather steep ] and in due time break the ] surface in new ]. | ||
Revision as of 05:58, 29 March 2002
A volcano is a place where magma is extruded from the surface of a planet. the earth's crust is weak, and seismic activity leads to expulsions of lava, gases and brimstone during eruptions. Volcanoes are usually situated either at the boundaries between tectonic plates or over hot spots. Volcanoes may be either dormant (having no activity) or active (near constant expulsion and occasional eruptions), and change state unpredictably.
Volcanoes on land often take the form of flat cones, as the expulsions build up over the years. Under water, volcanoes often form rather steep pillars and in due time break the ocean surface in new islands.
Science has not yet been able to predict with absolute certainty when a volcanic eruption will take place, but significant progress in judging when one is probable has been made in recent time.
Volcanic activity is often accompanied by earthquakes, hot springs and geysers. Famous volcanoes include Mount Aetna, Mount Hekla, Vesuvius, Mount Fuji, and Mount Saint Helens
Public domain picture from NASAof Tambora, Indonesia.