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What determines the violence of an eruption?

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What determines the violence of an eruption?. Composition of the magma determine the “violence” or explosiveness of a volcanic eruption. Composition of Magma . Temperature: most rock melt at 800-1200C

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what determines the violence of an eruption
What determines the violence ofan eruption?

Composition of the magma

determine the “violence” or explosiveness of a volcanic eruption

composition of magma
Composition of Magma
  • Temperature: most rock melt at 800-1200C
  • Pressure: increases with depth, as pressure increases temperature rock melts increases
  • Dissolved gases: H2O vapor, CO2, SO2, H2SO4

As amount increases, exclusivity increases

The above three factors control

the viscosity of magma

what is viscosity
What is Viscosity?
  • measure of a material’s resistance toflow

Think of Syrup & Water

factors affecting viscosity
Factors affecting viscosity

Viscosity – dependent on both silica content and temperature.

• Temperature - Hotter magmas are less viscous

(Compare difference between cold & hot syrup)

factors affecting viscosity1
Factors affecting viscosity

• Composition - Silica (SiO 2 ) content

More silica, > viscosity : (thick & stick) gases trapped, explosive eruptions (Rhyolitic Lava)

Less silica, < viscosity : (thin & runny) flow easily, nonexplosive eruptions (Basaltic Lava )

generalized types of lava
Generalized Types Of Lava

Basaltic Lava

Andestic Lava

Rhyolitic Lava

basaltic lava
Basaltic Lava
  • low viscosity
  • flow rapidly for great distances
  • nonexplosive eruption
  • primarily from shield volcanoes (Example Hawaiian Volcanoes)
  • Subdivided into flow types
    • A'a lava: rough, jagged blocky texture
    • Pahoehoe Lava: resembles a twisted or rope texture
andestic lava
Andestic Lava
  • 50-60% Silica
  • Massive explosions, huge volumes of ash & debris
  • generally produces blocky lava
  • Composite (stratovolcanoes) forming the Aleutian islands in Alaska, the crest of the Cascade Mountains in the Pacific Northwest
rhyolitic lava
Rhyolitic Lava
  • More than 60% Silica
  • high viscosities and high gas contents
  • generally ooze out of the volcano's
  • The best known examples Yellowstone
  • Most recent eruptions 640,000 years ago