Geography 2152F/G Lecture Notes - Lecture 8: Pyroclastic Rock, Stratovolcano, Rhyolite
18 Nov 2020
School
Department
Course
Professor
Document Summary
Most near plate boundaries: 2/3 volcanoes are found in ring of fire , subduction zone/mid-ocean ridges allow molten rock to reach surface. Magma: found deep w/in crust and upper mantle. Most abundant are silicon and oxygen (referred to as silica when combine: basalt lowest amount of silica and rhyolite highest. Viscosity: resistance to flow: contains small amount of gases (water vapour and co2, volcanoes have diff shapes based on chem/viscosity of magma. High silica magma: cool, more viscous, more gases. Most explosive, rhyolitic, as magma approach surface pressure lowers allowing. Low silica magma: hot, less viscous, less gases. Basaltic and andesitic tends to flow gases to bubble up. Types of volcanoes: shield largest and shaped as arcs built from lava, associated with basaltic (non-explosive with flow) Supervolcanoes: extremely rare events: occur when large volume of magma rises to shallow depths in continental crust over a hot spot, magma unable to break through crust; pressure builds until crust can"t contain.
