Factors affecting Volcanic Eruptions

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History (British History) Mind Map on Factors affecting Volcanic Eruptions, created by keistajupiter on 07/14/2014.

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Factors affecting Volcanic Eruptions
1 Dissolved Gases in Magma
1.1 Dissolved gases such as water vapour and carbon dioxide are present in magma.
1.1.1 These gases expand near the surface.
1.2 Vents = openings near the surface through which molten gases / rock are released.
1.3 Eruption violence related to how easily gas escapes from magma.
1.3.1 Gas escapes easily from less viscous magma.
1.3.2 More viscous magma = more explosive eruption.
1.4 Therefore the more viscous the magma, the more difficult it is for gas to escape the magma, and the more explosive the volcano.
2 Magma Temperature
2.1 Hotter magma is less viscous = less explosive.
2.2 Basaltic volcanoes are very hot - 1200°c.
2.3 Andesitic volcanoes are quite hot - 1000°c.
2.4 Rhyolitic volcanoes are cooler - 700°c.
2.5 The cooler the magma, the less viscous the lava, and therefore the more explosive the volcano.
3 Magma Composition
3.1 Low silica content magma is less viscous = less explosive.
3.2 Basaltic volcanoes have a low silica content - 42 to 52%.
3.3 Andesitic volcanoes have a medium silica content - 50% or more.
3.4 Rhyolitic volcanoes have a high silica content - 70% or more.
3.5 Therefore the higher the silica content, the more viscous the magma, and the more explosive the volcano.
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