Geography 2152F/G Lecture 8: Geo 2152 Week 8 Lecture-Volcanoes
14 Feb 2019
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Document Summary
Subduction zones and mid-ocean ridges allow molten rock to reach the surface: most volcanoes are located near plate boundaries, nearly 2/3 of all volcanoes are found on the ring of fire" surrounding the pacific ocean. Types of molten rock: magma: it is found deep within the crust and 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. Rhyolitic and dacitic magmas produce explosive eruptions: volcanic rocks are named based on the amount of silica present, an explosion with a lot of ash is high silica. Basalistic and andesitic magmas produce eruptions that tend to flow rather than explode. Viscosity: magma also contains small amounts of gases (water vapor and carbon dioxide, volcanoes have different shapes based on the chemistry and viscosity, magma viscosity is determined by silica content and temperature.
