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Igneous Structures and Field Relations-CH4

Ovingvitvolcanolo gyvulcanismotuff conesringshtm 15 5

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Unformatted text preview: Landforms - central vent eruptions f) lava dome - schematic corss section of lava dome These are typically Si-rich magmas (e.g. dacite or image source: Winter (2010) rhyolite) with high viscosity, and generally form late in Crater/Dome image Mount St. Helens. USGS photograph taken on October 1, 2004 eruptive cycle image source: John Pallister 16 Landforms - central vent eruptions g) Caldera - large-scale collapse features that typically form at central vent, …. Image source: http://volcanoes.usgs.gov/Products/Pglossary/caldera.html Aerial view west across Pinatubo caldera (Philippines) showing fumaroles and crater . lake U.S. Geological Survey Photograph taken on May 18, 1992, by Willie Scott. 17 Landforms - central vent eruptions g) Caldera Development of Crater Lake caldera 7015-6850 ybp image source: Winter (2010) 18 6 8/27/2012 Landforms - central vent eruptions h) lava lake - large volumes of molten lava, usually basaltic, contained …. http://www.swisseduc.ch/stromboli/perm/erta/ movies-en.html Image source: http://www.swisseduc.ch/stromboli/index-en.html Lava lake with convection currents and one lava fountain (Erte Ale, Ethiopia) 19 Landforms – fissure eruptions distinctive landforms develop from fissure eruptions issuing from fracture, or system of dikes - the most multiple flows build up to form immense lava plateaus; e.g. Snake River Plain Basalts, ID; Columbia River Basalts, OR, WA, ID Flood basalts of the Columbia River Plateau image source: Press and Siever (2001) extensive system being at the mid ocean ridge 20 Landforms – fissure eruptions example of fissure eruption Grande Ronde Basalt of the Columbia River Basalt Group. Thick stacks of laterally extensive lava flows typify this flood basalt province. Photo by Thor Thordarson Location of the exposed feeder dikes (heavy lines) and vents (V's) of the southeastern portion of the Columbia River Basalts. image source: Winter (2010) 21 7 8/27/2012 Landforms – lava flows Basaltic flows are clas...
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