Volcanism - - the eruption, or intrusion, of molten rock...

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-- the eruption, or intrusion, of molten rock at, or near, the earth's surface --- extrusive vs intrusive volcanism Extrusive: -- volcano : forms at the end of a central vent or pipe that rises from the asthenosphere and the upper mantle through the crust into a volcanic mountain * magma originating in the asthenosphere, collects in a chamber below the volcano before being expelled through the conduit & out the vent * crater = circular depression forms at or near the summit * volcano may be active, dormant, or extinct * 75% of volcanoes are on the sea floor * plate boundaries have high volcanic activity * BUT also occur over hot spots Magma chamber- where magma originating in the asthenosphere collects in an opening below the volcano before being expelled through the conduit and out the vent --- lava : the molten rock issued from a volcano; mafic vs. felsic * mafic : Basaltic lava, more magnesium and iron Ma(Magnesium) Ferric (iron) <50% silica thus less viscous= flows redily, traps less gas=less explosive * felsic : Feldspar and silica- Feldspar (Fel)- Silicon( Sic), flows slower, acidic, traps more gases=more explosive
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Volcanism - - the eruption, or intrusion, of molten rock...

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