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VOLCANOES

VOLCANOES. Melting the Mantle. 1. Increase Temperature 2. Decrease Pressure 3. Alter Composition (to decrease melting temperature). Where Does Melting Occur?. 1. Mid Ocean Ridges (decompression) 2. Hotspots (high temperature + decompression)

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VOLCANOES

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  1. VOLCANOES

  2. Melting the Mantle 1. Increase Temperature 2. Decrease Pressure 3. Alter Composition (to decrease melting temperature)

  3. Where Does Melting Occur? 1. Mid Ocean Ridges(decompression) 2. Hotspots(high temperature + decompression) 3. Subduction zones(add water, decrease melting temperature)

  4. Volcanic Products Magma: result of melting rocks Lava: magma that flows out over the surface Pyroclastic rocks: Rock fragments resulting from explosive volcanism, deposited by sedimentary processes.

  5. Pu'u O'o, Hawaii

  6. Fire Fountain

  7. Controls on Eruptive Style • 1. Viscosity • Depends on SiO2 content • “Mafic” magmas: poor in SiO2, rich in Mg, Fe low viscosity • “Felsic” magmas: rich in SiO2, poor in Mg, Fe high viscosity

  8. Controls on Eruptive Style 2. Volatiles • H2O and CO2 • “Dry” mantle rocks generate mafic magma “Wet” mantle rocks generate felsic magma • Volatiles decrease magma viscosity when dissolved

  9. Eruption Style } 1. Fissure eruption 2. Shield volcano 3. Pillow basalts 4. Domes & Cones 5. Strato-volcano Subaerial eruption, low viscosity magma Submarine eruption, low viscosity magma } Subaerial eruption, high viscosity magma

  10. Fissure eruption: Krafla, Iceland

  11. Hexagonal cooling joints in basalt: Devil's Postpile, California

  12. Hexagonal cooling joints in basalt, e.g. Giant’s Causeway, Antrim

  13. Sunset Crater, Arizona Cinders Bonito Flow

  14. Cerro Negro, Nicaragua 1947 eruption

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