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Geology Exam 2 Study Guide (highest grade in class)

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GEOL 1001
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Geology Exam 2 Study Guide Chapter 5Volcanoes are events at which molten rock lava pyroclastic debris gas and aerosols erupt at Earths surfaceA hill or mountain created from the products is also called a volcanoThe characteristics of a lava flow molten rock that moves above ground depend on its viscosity which in turn depends on its temperature and compositionBasaltic lavas can flow at great distancesPahoehoe flows have smooth ropy surfacesAa flows have rough rubbly surfaces jagged Andestic and rhyolitic flows tend to pile into mounds at the ventPyroclastic debrismolten rock that moves over the groundEruptions may occur at a volcanos summit or from fissures on its flanksThe summit of an erupting volcano may collapse to form a bowl shaped depression called a calderaA volcanos shape depends on depends on the type of eruptionShield volcanoare broad gentle domesCinder cones are steep sided symmetrical hills composed of tephraComposite volcanosStratovolcanoescan become quite large and consist of pyroclastic debris and lava Type of eruptions depend on several factors including the lavas viscosity and gas contentEffusive eruptionsproduce only flows of lavaExplosive eruptionsproduce clouds and flows of pyroclastic debris Different kinds of volcanoes form in different geologic settings as defined by plate tectonics theoryEruptions can be predicted by earthquake activity changes in heat flow changes in shape of the volcano and the emission of gas and steamBasaltic mafic lavavery hot low silica and low viscosityLava tubethe insulated tunnellike conduit within a flow through which lava movesColumnar jointingsolidified flows that contract with vertical fractures that are hexagonal in cross section create hexagonal columnsPillow basaltrounded blobs of basalt that cooled underwaterVolcaniclastic depositsgeneral term for accumulations of fragmented igneous materialLapillipea to plumsized materialPyroclastic flows also called nuee ardentesan avalanche of hot ash 200 450C 390840F pulled down the side of a volcano by gravityTephraunconsolidated deposits of pyroclastic grains regardless of sizeTufflithified ash or ash mixed with lapilli formed by burying and transforming into rockIgnimbrite welded tuffsheet of tuff that is deposited while hotBlockschunks of preexisting rock fragments by eruption
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