GEOG 1290 Lecture Notes - Lecture 29: Krakatoa, Subduction, Volcanism
29 Nov 2014
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Document Summary
Small, medium piece of lithosphere that is too buoyant to subduct. Extrusive volcanism: magma expelled while molten. Intrusive volcanism: magma solidifies in shallow crust near surface. Pyroclastic material: magma solidifies far beneath surface, solid rock fragments, dust, lava bombs thrown in the air by explosions. Us has 10% of active volcanoes, pacific ring of fire has 80% of world"s: considered active if it has erupted once historically and probably will volcanoes andesite line again. Convergent boundaries: volcanoes form due to subduction. Krakatau 1883: huge eruption, blew itself up. High silica content (felsic magma), more polymerization, thick magma, more gas pressure builds up, high explosively index. Low silica content (mafic content), less polymerization, thin magma, less gas pressure builds up, low explosively index. Role in mineral cycles (ca, k, mg, s, p) Shield volcanoes: hawaiian islands: manna loa largest area; kilauea tallest, low viscosity: lava flows easily, flood basalt plateaus (india"s deccon and the us columbia plateau)
