Basaltic lava less silica and higher temperature, low viscosity, gasses escape at surface low pressures, not explosive



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Basaltic lava - less silica and higher temperature, low viscosity, gasses escape at surface low pressures, not explosive

  • Basaltic lava - less silica and higher temperature, low viscosity, gasses escape at surface low pressures, not explosive

  • e.g. Shield volcanoes, Rifts, MOR, cinder cones

  • Intermediate silica, explosive, composite = stratovolcanoes, Andes, Cascades, Aleutians Japan, Philippines, often pyroclastic clouds = nuée ardente

  • Rhyolitic lava - more silica and lower temperatures, high viscosity, gasses cannot escape, explosive.













Exhalative (gas: H2O, CO2, SO2)

  • Exhalative (gas: H2O, CO2, SO2)

  • Effusive (lava)

  • Explosive (tephra)





Explosive (tephra)

  • Explosive (tephra)



Coarse = close

  • Coarse = close

  • Thick = close







Layered

  • Layered

    • Lava/sediment
  • Jointed

    • Columnar


Columbia Plateau



Projectiles

  • Projectiles

    • Ballistic
    • Wind-borne
  • Divergent Margin +

















Rare, extremely explosive

  • Rare, extremely explosive

  • Size of ash cover = violence

  • Toba and our near-extinction















Is on the mid-Atlantic Ridge,

  • Is on the mid-Atlantic Ridge,

  • 13 volcanoes have erupted since AD 874.

  • most active & volatile is Grímsvötn.

  • Over the past 500 years, Iceland's volcanoes have erupted a third of the total global lava output.

  • One quarter of Iceland ‘s population died due to eruption of the craters of Laki in 1783-84. The craters are a part of a larger volcanic system with the subglacial Grímsvötn as a central volcano. Because most of Grímsvötn’s eruptions have been subglacial, the interaction of magma and meltwater from the ice causes phreatomagmatic explosions





Plugs

  • Plugs

  • Dikes



Laccoliths - Henry Mts.

  • Laccoliths - Henry Mts.

  • Colorado Plateau







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