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Unformatted text preview: VOLCANISM * The process by which magma and gases are transferred from the Earth's interior to near or on the surface. * 2 basic types: extrusive vs intrusive volcanism Extrusive: when magma (lava) flows out onto the Earths surface and then cools to form igneous rock ** volcano : a landform with a vent , or fissure (crack) on the surface which is the end of a conduit originating from below the crust in the Asthenosphere * Often a mountain landform (fissures usually do not form features of high relief or volcanic peaks) * Magma originating in the asthenosphere is expelled through the conduit & out the vent * Magma collects in a magma chamber below the volcano before being expelled * crater : the surface depression at the summit of the volcano * A volcano may be categorized as: Active: currently erupting, or has erupted during recorded history Dormant : an active volcano that is in repose but is expected to erupt in the future Extinct : a volcano that is not expected to erupt again * 75% of volcanoes are on the sea floor * Most convergent and divergent plate boundaries have high volcanic activity * Hot spots are also areas of high volcanic & earthquake activity * Lava : the molten rock issued from a volcano; the term used for magma once it has erupted onto the Earht's surface * May be two types of material: mafic or felsic * Mafic or basaltic lava : high in Mg & Fe, < 50% silica thus less viscous which means it flows readily, and thus less gas is trapped within leading to a less explosive eruption * Felsic : richer in silica thus more viscous meaning it floes slower: it is also more acidic, and more gases are trapped leading to more explosive eruptions * pyroclastics or tephra : solidified magma fragments expelled explosively from a volcano, quite common with felsic magma (explosive eruptions) * bombs (> 1 m), pumice, scoria, cinders (1-2 in),...
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This note was uploaded on 03/23/2009 for the course GEOG 1111 taught by Professor Hopkins during the Fall '08 term at University of Georgia Athens.
- Fall '08