Planet Earth Exam 2 Study Guide

Planet Earth Exam 2 Study Guide - Derek Ho Planet Earth...

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Derek Ho Planet Earth Study Guide Chapter 9: Volcanoes Viscosity What is viscosity? Viscosity – Resistance of lava to flow What controls viscosity? Amount of silica [less silica means less viscous since less molecules will tangle each other: less viscous means it will flows more] Temperature [hot lava is less viscous] Intrusive Igneous Rock When magma inside the magma chamber freezes and transforms into intrusive igneous rock Types of Volcanoes Shield volcanoes , so named because they resemble a soldier’s shield lying on the ground, are broad, gentle domes. Most shields form from low-viscous basaltic lava flows Cinder cones , consist of cone-shaped piles of tephra. The slope of the cones approaches the angle of repose of tephra, meaning the steepest slope that the pile can attain without collapsing from the pull of gravity (around 30 to 35 degrees like a sand pile) Stratovolcanoes , also called composit volcanoes, are large and cone shaped and consists of alternating layers of lava and tephra. Tend to be steeper near the summit (ex: Mt. Fuji) Mineralogy Intensity of weathering Types of Eruptions Effusive eruptions , produce mainly lava flows [usually low-viscosity balastic lavas]. Creates Shield volcanoes Explosive eruptions, eruptions produce clouds and avalanches of pyroclastic debris [fragmented material]. Sometimes can blast the volcano apart and leave behind a large caldera Creates Cinder cones [small explosions] and Stratovolcanoes [usually large explosions] Other: Phreatomagmatic eruptions, pyroclastic eruptions involving the reaction of water with magma
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Plate Tectonic Settings of Volcanoes Most volcania activity on Earth occurs along divergent or convergent plate boundaries, or in rifts Mid-Ocean Ridge Volcanism Mid-ocean ridge volcanoes, which develop along fissures parallel to the ridge axis, are not all continuously active. Each one occurs every tens to hundreds of years Erupts basalt, which because it’s underwater forms pillow-lava mounds [Iceland was formed from mid-ocean ridge volcanism] Convergent Boundary Eruptions Most of the subaerial volcanoes on Earth lie along convergent plate boundaries (subduction zones) Volcanoes form when volatiles compounds such as water and carbon dioxide are released from the subducting plate and rise into the overlying hot mantle, causing melting and producing magma that then rises through the lithosphere and erupts Continental Rifts Eruptions Magma comes from partial melting of the crust Explosive rhyolitic volcanoes Active today in East African Rift Volcanic Hazards Lava Flows Buried roads, housing developments, cars Turns things into FLAMES Threat of Ash and Lapilli Ash and lapilli can smash and crush roofs or buildings Ash buries crops, spread toxic checmicals that poison soil Threat of pyroclastic flows Cloud can be hot and poisonous Moves so fast, it can flatten buildings and forests Other Threats: Blast, Landslides and Floods, Earthquake, Lahars, Tsunamis, Gas
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This note was uploaded on 02/15/2012 for the course GEOLOGY 460:103 taught by Professor Feigenson during the Fall '10 term at Rutgers.

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Planet Earth Exam 2 Study Guide - Derek Ho Planet Earth...

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