Chapter6_post - Chapter 6 outline Generation of magmas...

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Chapter 6 outline Generation of magmas (magmas are usually generated in the mantle) Increase T in mantle Lower P in mantle add water to mantle Key properties of magma that control the style/magnitude of eruption Viscosity (controlled by magma chemical composition) Volatile content Volume of magma Controls and classes of magma/lava chemical composition Basalt Andesite Rhyolite Plate Tectonic Settings of Volcanoes Volcanism at spreading ridges Developed spreading ridges (mid-ocean ridges) Continental divergence Volcanism at subduction zones Volcanism at hot spots (intraplate volcanism) Volcanic Eruption Products Lava (aa, pahoehoe) Pyroclastic materials (ash, glass, pumice) Eruptive Styles Hawaiian Strombolian Vulcanian Plinian Volcanic Explosivity Index Volcanic landforms (cinder cones, shield volcanoes,stratovolcanoes,lava domes, calderas)
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Volcanism Definitions: 1. Volcanic force or activity. 2. The phenomena associated with volcanic activity. Volcano : the word comes from Vulcano, the name of an island in Italy. Legend has it that the Roman god Vulcan worked inside Vulcano (or Etna). His nasty temperament and fits of rage were greatly feared. Vulcan forged weapons of war for the gods, and without provocation, he could destroy people and their property, with fire and lightning, lava flow, or volcanic explosions.
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Generation of Magmas Magma : molten rock below the Earth’s surface When it has traveled from the magma chamber to the surface, the magma becomes lava . Where does magma come from? mantle
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Generation of Magmas Melting of rock is promoted by either: 1. increasing T (temperature) 2. lowering P (pressure) 3. increasing water content
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Movement of Magmas—how do they get to the surface? Magmas ascend to surface because they are lower density than solid rock
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Properties of magma that control style/magnitude of eruption 1. Viscosity 2. Volatile content 3. Volume of magma chamber
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Magma Viscosity A physical property of magma - Definition: The resistance of a fluid to flow - The lower the viscosity of a magma, the more fluid its behavior - Low viscosity lava flows like melted ice cream; other low viscosity substances: water, oil - High viscosity lava flows like toothpaste, or doesn’t flow much at all; other high viscosity substances: honey, glacier Magma viscosity is controlled by: Temperature Silica content
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Key physical property that determines magma viscosity is silica content (4 O, 1 Si) Higher silica content higher viscosity Lower silica content lower viscosity – Silica tetrahedra link up to each other, creating chains, sheets, pyramids, that inhibit flow of magma Magma Viscosity
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The volatiles (dissolved gases) of a volcano is mostly water vapor, that can result in explosive behavior. CO 2 is also present. High viscosity
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This note was uploaded on 02/02/2010 for the course GEO 107 taught by Professor Stidham during the Fall '08 term at SUNY Stony Brook.

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Chapter6_post - Chapter 6 outline Generation of magmas...

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