PT4-Academy

PT4-Academy - Volcanoes Most of earths crust and mantle is...

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Volcanoes
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Most of earth’s crust and mantle is not molten. Magma is produced locally when conditions melt solid rocks. Temperature – 800-1600 ºC Geothermal gradient (5-80 º C/km) avg 25 º C/km Pressure – a decrease in pressure favors melting pressure increase kbar/km Composition – water, carbon dioxide, silica favor lower melting temperatures 0.8% water lower melting temp 100 º C
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Ice While ice (solid) is less dense than water, In most substances the solid is more dense.
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Where do rock melt? 1. Spreading zones 2. Subduction zones 3. Hot Spots
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Partial Melting Geologic jargon felsic = silicon-oxygen rich (>60%) mafic = silicon-oxygen poor (<55%)
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Viscosity – resistance to flow temperature – hotter = less viscous volatiles – more = less viscous silicon-oxygen – more = more viscous due to polymerization Viscosity is important because it determines “explosiveness”
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High viscosity: low temp high Si-O + trapped gases Low viscosity: high temp low Si-O
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Volcanic Products Tephra - ash
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Volcanic Products Tephra – cinders, bombs
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Volcanic Products Lava – Low silica
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Volcanic Products Lava – High silica
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Low Si High temp High Si Low temp Quiet Explosive
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This note was uploaded on 10/23/2011 for the course GLY 1000 taught by Professor Parker during the Spring '11 term at FSU.

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PT4-Academy - Volcanoes Most of earths crust and mantle is...

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