Geoscience Study Guide-exam 3

Geoscience Study Guide-exam 3 - Geoscience Study Guide exam...

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Geoscience Study Guide- exam 3: Chapter 12: Volcanoes Volcanoes transport magma from the lithosphere to form rock at the Earth’s surface and inject gases into its atmosphere (see diagram on second page of chapter 12) o •80% are Andesite volcanoes above subduction zones rim Pacific o •15 % are Basalt volcanoes in rift zones – plate divergence o •5 % are Basalt volcanoes above hot spots - Hawaii, Iceland Volcanism, Magma Type, and Plate Boundaries o •Mid ocean ridge, Ocean island hot spots, Continental rifts - Basalt o •Island Arc and continental arc above subduction zone - Andesite o •Continental interior hot spot - Rhyolite Flow velocity, eruption style and volcano shape – its all about magma viscosity o •Viscosity is resistance to flow o –Low viscosity magma is very fluid – like syrup o –High viscosity magma does not flow easily o •Viscosity function of Magma composition, temperature, Volatile (H 2 O, CO 2 , SO 2 ) content Eruption of low viscosity basalt magma o •Basalt o –50 % SiO 2 o –Low magma viscosity o –“Quiet” eruptions o •Lava fountains o •Cinder cones o •Fluid lava flows Pyroclastic Eruption - expanding steam froths viscous andesite / rhyolite magma o •Andesite o –60% SiO 2 o –High magma viscosity o –“Violent” eruptions driven by expansion of steam o •Pyroclastic flows o •Eruption column o •Lateral blast o •Mud flows = lahar o •Pyroclastic –means broken by fire o •Volcanic ash is silicate glass shards of shattered frothed magma Pyroclastic Ash Flows or “Glowing Avalanche” o •Confining pressure drops as magma rises o •H 2 O expanding in viscous magma froths and shatters glassy magma o –Like popping cork on champagne
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o •“ash” plume 10,000’s ft o •Collapsing eruption column drives pyroclastic flows Living with Geologic Hazards o •Understand geologic processes that pose threat to human life and/or property o •Identify areas likely to be affected o •Control the hazard? – works for some, not others o •Control use of land affected o •Effective response to geologic hazards requires o –public awareness and understanding of risks o –the economic resources and willingness to commit them Lahar is Volcanic Mudflow - Ash + Melted Snow Like wet cement at 100°F •Lahars are the greatest threat to life & property from andesite volcanoes •Ash cloud from small eruption (1 km 3 ) circled the Earth •Deposit 1.8-2.8 inches deep Chapter 13: Earthquakes: Earthquakes caused by slip on faults o •Earthquake = violent ground shaking due to passage of waves transmitting elastic strain energy released as rock masses slip along a fault Rocks deform elastically – until they break o •Stress = force / area o •Strain = change of shape result of applied stress o • Elastic Deformation o –large stress produces small strain (bending) o –Elastic rock “snaps back” to original shape when stress removed
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This note was uploaded on 10/19/2011 for the course GEO 1050 taught by Professor Staff during the Spring '10 term at UConn.

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Geoscience Study Guide-exam 3 - Geoscience Study Guide exam...

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