Geography 2152F/G Lecture Notes - Lecture 1: Pyroclastic Rock, Dacite, Stratovolcano
19 Jan 2015
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Document Summary
Most are located near plate boundaries 2/3 of all volcanoes found on ring of fire surrounding pacific subduction zones and mid-ocean ridges allow molten rock to reach the surface. Magma found deep within the crust and upper mantle. Lava it is found flowing from an erupting volcano basically magma that has reached the earth"s surface. The most abundant elements in magma are silicon and oxygen; when combined referred to as silica. Volcanic rocks are named based on the amount of silica present. Basalt (lowest silica, most flowing type of magma, found in hawaii), andesite, dacite, Types of volcanic rock (in increasing silica content: Low silica content: hotter, less viscous, fewer gases. High silica content: cooler, more viscous, more gases. Volcanoes with high silica magma produce the most explosive eruptions. As magma approaches the surface, the pressure lowers allowing gases to bubble up and escape: gases typically released from vent of volcano prior to eruption.
