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E are runnier silica poor runnier silica rich magmas

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Unformatted text preview: poor magmas tend to have lower viscosities ( i.e., are “runnier”) Silica-poor “runnier”) Silica –rich magmas tend to have higher viscosities (i.e., are “stiffer”) Silica “stiffer”) Temperature: For a given magma, the higher the Temperature: temperature, the lower the viscosity This means… This Higher temperature magmas tend to have lower viscosities ( i.e., are Higher “runnier”) “runnier”) Lower temperature magmas tend to have higher viscosities (i.e., are Lower “stiffer”) “stiffer”) How these factors work together to determine eruption style style …So there are many factors that determine eruption style Thankfully, these factors work hand-in-hand (which Thankfully, simplifies things substantially) simplifies Consider the main plate tectonic environments in which Consider volcanoes occur… volcanoes Divergent plate boundaries Convergent plate boundaries Hot Spots (intraplate environments) Plate Tectonic Environments and Volcanism Plate Non-random distribution: Volcanoes that follow divergent plate boundaries Volcanoes Volcanoes that follow convergent plate boundaries Random distribution: Hot Spots (intraplate environments) In General (Although a Little Oversimplified)… In Divergent plate boundary plate Hotspot/plume (within plate) Convergent Convergent plate boundary plate decompression decompression melting melting hydration hydration melting melting Localized Localized heating, heating, decompression decompression melting melting Divergent Hot Spot (Intraplate) Convergent Magma composition Mafic (low silica) *Mafic (low silica) *Intermediate to felsic Temperature High High Low Viscosity Low Low Intermediate to High Volatile content Low Low Intermediate to High Explosive Tendency Low Low High * With some exceptions Volcanism at Divergent Plate Boundaries Volcanism (e.g. Mid-Ocean Ridges and Continental Rifts) Much of the Earth’s volcanism occurs at divergent boundaries. Somewhat lacking in the “wow” department (nonexplosive and largely un...
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