Geography 2152F/G Lecture Notes - Lecture 8: Pyroclastic Rock, Magma Chamber, Pyroclastic Flow
22 Apr 2016
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Document Summary
Subduction zones and mid ocean ridges allow molten rock to reach the surface. Magma: found deep within the crust and upper mantle. Most abundant elements are silicon and oxygen silica. Rocks name based on amount of silica present: basalt, andesite, dacite, rhyolite (low high silica) Viscosity: magma contains small amounts of gas, volcanoes have different shaped based on chemistry and viscosity of magma, determined by silica content and temperature. High silica: cooler, more viscous, more gases (more explosive) As magma approaches the surface, the pressure lowers allowing gases to bubble up and escape. Basaltic and andesite magma produce eruptions that tend to flow rather than explode. Classification based on shape, appearance and style of eruptions. Eruptions are non-explosive and consist of gentle flows. Some eruptions contain tephra (general term for fragmented material expelled during an eruption) Accumulations of tephra are referred to as pyroclastic deposits. Built from combination of lava flows and pyroclastic deposits.
