Geol111_Volcanology2007B

Geol111_Volcanology2007B - Volcanology Mt St Helens-Cascade...

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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 Earth’s 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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This note was uploaded on 10/26/2009 for the course GLY 123 taught by Professor Vogl during the Spring '09 term at University of Florida.

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Geol111_Volcanology2007B - Volcanology Mt St Helens-Cascade...

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