Geol111_Volcanology2007B

Geol111_Volcanology2007B - 10/27/09 Volcanology 10/27/09 Mt...

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Unformatted text preview: 10/27/09 Volcanology 10/27/09 Mt St Helens-Cascade Range, WA 10/27/09 The natur e of volcanic er uptions Factors determining the violence or explosiveness of a volcanic eruption Composition of the magma Temperature of the magma Dissolved gases in the magma 10/27/09 The natur e of volcanic er uptions Factors affecting viscosity continued Lower silica content = lower viscosity or more fluid-like behavior (e.g., mafic lava such as basalt) Dissolved gases Gases expand within a magma as it nears the Earths surface due to decreasing pressure The violence of an eruption is related to how easily gases escape from magma 10/27/09 The natur e of volcanic er uptions Factors affecting viscosity continued In summary Fluid basaltic lavas generally produce quiet eruptions Highly viscous lavas (rhyolite or andesite) produce more explosive eruptions 10/27/09 A pahoehoe lava flow 10/27/09 A typical aa flow 10/27/09 10/27/09 Figure 5.19 10/27/09 Figure 5.A 10/27/09 10/27/09 Figure 5.22C 10/27/09 Figure 5.20 10/27/09 Figure 5.21 10/27/09 Figure 5.B 10/27/09 Mater ials extr uded fr om a volcano Pyroclastic materials fire fragments Types of pyroclastic debris...
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Geol111_Volcanology2007B - 10/27/09 Volcanology 10/27/09 Mt...

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