Geology 101 Week 5
Geology 101 Week 5 GEO 101
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This 3 page Class Notes was uploaded by Kayla Corbett on Sunday March 6, 2016. The Class Notes belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Dr. Natasha T. Dimova in Fall 2016. Since its upload, it has received 12 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 03/06/16
Kayla Corbett Guest Lecture Volcanoes Volcanoes-place in earth where magma and lava comes out Volcanoes-Mountain constructed by the eruption of molten rock from earths interior Volcanologists study volcanoes-not the most well adjusted folk Volcanoes are inevitable Volcanic gases Three products of volcanism- Volcanic gases (vapors and aerosols), pyroclastic flows (fragments and varying size), lava flows (molten rock) Viscosity-resistance to flow Rheology- the study of flow and the properties of flowing materials Basaltic lava-very hot and very fluid 2 different types: pa-hoe-hoe: skins forms, rolled into ropy ridges and furrows A’a’: cools and thickens more quickly, forming shard/fragments Columnar jointing-contracts into vertical columns Pillow Basalts-blobs cooled underwater Lava pressure ruptures a pillow to form the next blob and repeats Felsic Lava-thick and sticky (viscous), produces explosive eruptions Basaltic Eruptions-Lava fountains, lapilli-pea-size fragments, blocks, bombs Felsic Eruptions-Angular pumice fragments, tephra-deposits of debris of any size, tuff or ignimbrite-lithified ash (welds together due to retention of high heat) Pyroclastic flows-avalanches of hot ash-up to 300 km/hour Temps from 500 c to 1000c Products of volcanism-volcanic gas Rheology affects eruption violence Basaltic, low velocity-easy gas escape, mellow eruption Felsic, high velocity-difficult escape, violent eruption Magma chamber -Some cool to form intrusive rocks -Some erupt to form extrusive rocks Volcanic Architecture Crater-bowl-shaped depression, surface expression of volcano Up to 500mm across and 200 m deep Summit or fissure eruptions Caldera-giant crater, up to tens of kilometers across Magma chamber forms and collapses on itself Types of Volcanoes Shield volcano-broad, slightly domed shaped, like inverted shield Cinder cones-conical piles of tephra Composite or stratovolcano-large, coned-shaped with steeper slopes Alternating layers of lava, tephra, and debris Example: Mount Fuji Effusive vs Eruptive Effusive-produce lava flows Explosive-blow up Effusive-produce vast outpouring of lava Explosive-release pressure (volcanic gases) catastrophically Eruptive style-related to volcano type Shield=effusive Cinder=explosive pyroclastic explosions Mount St. Helens-erupted May 18,1890 at 8:32 a.m. An earthquake-triggered landslide released pressure An initial vertical blast led to a much stronger lateral blast Krakatau-a volcano between Java and Sumatra The 9-km island, 800 m above the sea, erupted May 20, 1883 Continued erupting through June and July Recurrence interval-average time between eruptions -Active-erupting, recently erupted Volcanoes and Civilization Protection Warning signs indicate that an eruption is imminent Earthquake activity-magma flow increases seismicity Heat flow-magma causes volcanoes to “heat up” Changes in shape-magma causes expansion Emission increases-changes in gas and mix in volumes Volcanic types are linked to tectonic settings Mid-ocean ridges-spreading axes MOR-generated oceanic crust covers 70% of the earth Convergent boundaries-subduction zones Convergent boundaries-must subaerial volcanoes Are volcanoes developing on the overriding plates? Continental arcs and oceanic island arcs are common Continental Rifts-many volcano types reflecting Oceanic Hot spot-a plume under and oceanic plate Thousands of thin basalt flows build up through time Building above sea level, basalt can flow long distances. Lava builds upward and outward and the island grows Continental hot spot-thin crust, shallow magma. Flood Basalts-voluminous lava eruption above a plume When a mantle plume intersects base of rifting lithosphere Lava spreads over large areas; great thickness Iceland is a hot spot that straddles the Mid-Atlantic Ridge Kava has built the hot spot/ridge above sea level The island is being torn apart by a divergent boundary People live near volcanoes because that is where the best soil is Volcanic activity evident on the Moon and Planets Lunar Maria (dark “seas”) are regions of flood basalts Olympus Mons-extinct Martian shield volcano The Jovian moon lo has active volcanoes
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