11 - Nats Volcanoes and Other Mountains 2/11/2008 2:59:00...

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Nats 11/02/2008 16:59:00 Volcanoes and Other Mountains 1,500 active volcanoes worldwide. Most active volcanoes are found near convergent plate boundaries. Viscosity=Resistance to flow (gooeyness) Viscosity varies with composition Low viscosity fluids flow more easily that high viscosity fluids Viscosity of materials decreases with increasing temperature Escaping gases drive volcanic eruptions How easily gases escape from magma is controlled by magma viscosity Magma- Molten rock below the surface Lava- Molten rock at the surface More viscosity = more violent eruptions Gases escape easily during mild eruptions with low viscosity magma Gases escape from high viscosity magma Andesitic magma Partial melting of mantle rocks (with water) at the subduction zone. The three types of magma are defined by silica content
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11 - Nats Volcanoes and Other Mountains 2/11/2008 2:59:00...

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