EOSC 114 Study Guide - Final Guide: Yellowstone Hotspot, Shield Volcano, Rhyolite
31 Jan 2013
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Density: less mass/volume so magma (melted rock) rises above solid rock. Viscosity: how runny, fluid magma is; low viscosity (runny, flowing) will rise through crust; dependant on sio2 content and temperature more sio2, higher viscosity (stronger bond = more solid) For magma to rise through crust, it must have lower density than crust, low viscosity, and hot enough to stay liquid. Intrusive rocks magma that cools slowly underground, crystals visible. Extrusive rocks magma cools quickly on surface, crystals too small to see. Mafic magma: low sio2 content, low viscosity, less explosive (ex. form basalt rocks) Felsic magma: high sio2 content, high viscosity, more explosive (ex. form rhyolite rocks) Lava: low gas content, low viscosity, flows as pahoehoe or a"a (see 4) Volcanic glass: magma cools quickly before crystallization obsidian if solid or pumice if bubbles. Pyroclastic material: high gas content, high viscosity more explosive. Shield volcano flat, broad (100s of km wide) basalt lava flows; low explosivity.
