volcanoes. 1. increase temperature 2. decrease pressure 3. alter composition (to decrease melting...
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VOLCANOES
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1. Increase Temperature
2. Decrease Pressure
3. Alter Composition (to decrease melting temperature)
Melting the Mantle
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1. Mid Ocean Ridges (decompression)
2. Hotspots (high temperature + decompression)
3. Subduction zones (add water, decrease melting temperature)
Where Does Melting Occur?
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Magma: result of melting rocks
Lava: magma that flows out over the surface
Pyroclastic rocks:Rock fragments resultingfrom explosive volcanism, depositedby sedimentary processes.
Volcanic Products
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Pu'u O'o, Hawaii
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Fire Fountain
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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
Controls on Eruptive Style
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2. Volatiles H2O and CO2
“Dry” mantle rocks generate mafic magma “Wet” mantle rocks generate felsic magma
Volatiles decrease magma viscosity when dissolved
Controls on Eruptive Style
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1. Fissure eruption2. Shield volcano3. Pillow basalts4. Domes & Cones5. Strato-volcano
Subaerial eruption,low viscosity magma
Submarine eruption,low viscosity magma
Subaerial eruption,high viscosity magma
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Eruption Style
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Fissure eruption:Krafla, Iceland
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Hexagonal cooling joints in basalt: Devil's Postpile, California
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Hexagonal cooling joints in basalt,e.g. Giant’s Causeway, Antrim
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Sunset Crater, Arizona
Bonito Flow
Cinders
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Cerro Negro, Nicaragua1947 eruption
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