ISP 203B Lecture Notes - Lecture 3: Viscosity, Andesite, Dacite
22 Sep 2016
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Document Summary
Volcanoes are formed by the eruption of magma: magma=liquid rock(molten rock) + gases(h20, co2, so2, composition similar to that of rocks from the crust: silica (>50% of magma) A minor, but critically important component of magma is gases aka volatiles. Magma forms in the mantle, a depth with intense pressure where magma forms and gases are dissolved. Magma is less dense than the solid of same composition is buoyant, and ascends to the surface. Gases start to form bubbles within the magma. Gas is much less dense (more buoyant) than liquid and gas bubbles ascent quicker than the magma. Viscosity is the resistance of a material to flow. Viscosity matters for eruptive styles, then associated hazards. More viscous magma usually cannot let gas escape, and gas bubbles accumulate in the volcano subsurface. Pressures from these gas bubbles build up over time as more gas arrives from depth.
