Magma types magma compositions vary in sio 2 iron

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Magma Types Magma compositions vary in SiO 2 , iron, magnesium, and volatile gases Mafic magma – low in SiO 2 (45-50 %) but high in iron, and magnesium (dark) Felsic magma – high in SiO 2 (up to 75 %) but low in iron, and magnesium (light) Intermediate magma – intermediate range of SiO 2 (50-65 %), iron, and magnesium Amount of volatile gases will affect explosive characteristics of eruptions
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Magma Types and Magmatic Rock Mafic magmas produce basalt lavas – Intrusive equivalent is gabbro Intermediate magmas produce andesite lavas – Intrusive equivalent is diorite Felsic magmas produce rhyolite lavas – Intrusive equivalent is granite
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Subduction zones = andesite, stratovolcanos Rifts = basalt/andesite/rhyolite, (cinder cones, domes) Plumes = basalt, shield volcanos
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Types of Volcanoes Shield volcanoes – Very large, flat, with abundant thin basalt flows – Basalt is less viscous than andesite or rhyolite – Shield like shape - larger area relative to height – Examples: Hawaiian Island chain
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Basalt Flow – Shield Volcano
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Hawaii - shield volcanoe
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Types of Volcanoes Volcanic Domes – Composed of more viscous andesite or rhyolite • these lavas do not flow much – Ooze out onto surface from a tube and pile up close to the vent – Compact, small, and steep sided volcano – Various locations around Pacific Ring of Fire
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Volcanic domes (plug domes) - Mono Craters
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Types of Volcanoes Cinder Cones – Minor explosive volcano – Batches of lava shot into the air as pyroclastics – Size of pyroclastics range from ash (very fine), cinders, bombs, or blocks (very coarse) – Pyroclastics fall close to the vent creating a cone shaped volcano – Example: Particutin, Mexico
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Cinder Cones = Piles of Pyroclastics (tephra)
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  • Fall '19
  • Volcano, Mantle, Cascade Volcanoes, Cinder Cones, • Pyroclastics, Volcanoes Formation

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