GEOG 1350 Lecture Notes - Lecture 4: Dacite, Andesite, Rhyolite
9 Dec 2018
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Document Summary
2/3 of all volcanoes are found in the ring of fire surrounding the pacific ocean. Subduction zones and mid-ocean ridges allow molten rock to reach the surface. Magma: is found deep in the crust and the upper mantle. Lava: it is found flowing from an erupting volcano. Essentially, lava is magma on the earth"s surface. The most abundant elements in magma are silicon and oxygen; when combined they are referred to as silica. Volcanic rocks are named based on the amount of silica present. Types of volcanic rocks: basalt, andesite, dacite, rhyolite. Magma also contains small amounts of gases (water vapour and carbon dioxide) Volcanoes have different shapes based on the chemistry and viscosity of their magma. Magma viscosity is determined by silica content and the temperature. Magma with high silica content: cooler, more viscous, more gases. Magma with low silica content: hotter, less viscous, fewer gases. Volcanoes with high silica magma produce the most explosive eruptions.
