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Unformatted text preview: Si and O in magma tend to “clump” together and begin to form terahedra, causes magma to become “lumpy” and have higher viscosity Viscostity—defined as resistance to flow water—low viscosity (easily flows) Harder to get higher viscosity magmas to erupt at surface—instead of flowing out, must be “ejected” during an eruption Low viscosity magma, tends to flow out in passive eruption High viscosity magma, thrown out in violent eruption (pyroclasts) Amount of silica (Si and O) and amount of dissolved gases in magma have dramatic impacts on style of eruptions Gases in magma are in dissolved (liquid) form under high pressures (confined in magma—surrounded by rock) When eruption occurs, pressure released and gases rapidly change (explosively to gas form) Two types of major magma Basaltic (mafic) and silicic (felsic) Felsic has more silica Mafic has more gases Types of volcanoes Shield Volcano—large, 100’s of km’s across, 5-10 km high, gentle slopes, lava flows, passive eruption of basaltic magmas EX: Moana Loa & Mauna Kea in Hawaii, Mt Kilimanjaro, Tanzania Cinder Cone volcanoes—small km’s across, 100’s of m’s high, steep slopes, pyroclasts,...
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- Fall '08
- Geology, eruptions