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Volcanoes

Volcanoes. Most of earth’s crust and mantle is not molten. Magma is produced locally when conditions melt solid rocks. Temperature – 800-1600 º C Geothermal gradient (5-80 º C/km) avg 25 º C/km Pressure – a decrease in pressure favors melting pressure increase kbar/km

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Volcanoes

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  1. Volcanoes

  2. 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 ºC/km) avg 25 ºC/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 ºC

  3. Ice While ice (solid) is less dense than water, In most substances the solid is more dense.

  4. Where do rock melt? • Spreading zones • Subduction zones • Hot Spots

  5. Partial Melting Geologic jargon felsic = silicon-oxygen rich (>60%) mafic = silicon-oxygen poor (<55%)

  6. 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”

  7. Low viscosity: high temp low Si-O  High viscosity: low temp high Si-O + trapped gases 

  8. Volcanic Products Tephra - ash

  9. Volcanic Products Tephra – cinders, bombs

  10. Volcanic Products Lava – Low silica

  11. Volcanic Products Lava – High silica

  12. Low Si High temp Quiet Explosive High Si Low temp

  13. How does plate tectonics relate to volcano type? depends on what’s being melted and what it passes through Spreading Centers & Hot spots: partial melting of mantle yields low Si-O magma with few volatiles - quiet unless it passes through a continent and gains Si-O - explosive to very explosive Subduction Zones: partial melting of ocean floor (w sediments) and overlying mantle yields higher Si-O with lots of volatiles – explosive unless it passes through a continent and gains Si-O - very explosive

  14. Iceland Spreading center (w Hot Spot?)

  15. Hawaiian Islands Hot Spot

  16. April 23 - August 30, 1902 Final event was nuee ardente Pyroclastic cloud 1000 C Killed 30,000 All but Louis-Auguste Cyparis and Léon Compère-Léandre

  17. Mount St. Helens

  18. Yellowstone Hot spot and Spreading Center beneath a continent = “supervolcano”

  19. Range of potential total destruction

  20. What part do volcanoes play in Plate Tectonics? Create new crust Change composition of atmosphere Affect climate Influence society Tambora, 1815 – caused “year without a summer” in 1816. Affected Mary (Godwin) Shelley’s and John Polidori’s (lord Byron’s doctor) summer plans. Resulted in “Frankenstein” and “The Vampyre”.

  21. Mons Olympus - Mars Io – moon of Jupiter

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