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Volcanoes
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Overview Magma Sources and Types Kinds and Locations of Volcanic Activity Hazards Related to Volcanoes Issues in Predicting Volcanic Eruptions Present and Future Volcanic Hazards in the United States
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Magma Source Areas Where Magma Forms (need heat!) –Upper mantle: asthenosphere –depths of ~ 50 to 250 km –High temps (800-1100 C), medium pressure –Rocks melt, or partially melt –Divergent plate boundaries –Above subduction zones –Hot spots
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Plate tectonics: Asthenosphere is where melting occurs Source: http://www.geol.umd.edu/~jmerck/gal04/GEOL388/lectures/02.html
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Wahalua Visitors’ Center Aflame in Hawaii Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
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Ruins of the Visitors’ Center After Lava Cooled Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
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Magma Types Composition: –Magmas: >Fe, Mg (mafic) vs >SiO 2 (felsic) Dependent on tectonic setting (1) Ocean spreading ridges and hot spots: Mafic rocks (basalt) (2) Continental rifts: felsic (rhyolite, andesite) (3) Subduction zones: mafic + felsic
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Mafic: Basalt Ultramafic: Peridotite Source: http://www.tmm.utexas.edu/npl/mineralogy/Blowups/Olivine_in_peridotite_xenolith.htm
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Felsic-mafic: andesite Source: http://www.otago.ac.nz/geology/features/rocks-minerals/rocks.html
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Felsic: Rhyolite Source: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/
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Magma properties Volcanic Gases: CO 2, SO 2 Pressure builds up as magmas rises to surface –Felsic (more SiO 2 ): viscous + thick = explosive –Mafic (less SiO 2 ): fluid, gases escape *What kind of volcano is safest to live by?
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Lava Flows on Kilauea in Hawaii Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Hawaiian Lavas: mafic basalts Source: Courtesy of Carla W. Montgomery.
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Volcanic Breccia (felsic) Source: Courtesy of Carla W. Montgomery.
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Kinds and Locations of Volcanic Activity Individual Volcanoes–Locations Seafloor Spreading Ridges, Fissure Eruptions Shield Volcanoes Volcanic Domes Cinder Cones Composite Volcanoes
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Volcanoes of the World Source:After R. Decker and B. Decker, Volcanoes, 1981, W.H. Freeman and Company, New York, NY.
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“Hot Spots” Around the World Source: Modified after map in online text This Dynamic Earth, U.S. Geological Survey.
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Kinds and Locations of Volcanic Activity Shield Volcanoes: Hawaii –Mafic lavas, low, flat, ‘shields’ Volcanic Domes Cinder Cones Composite Volcanoes
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Low-Angle View of Mauna Loa Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Satellite View of Hawaii Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Kinds and Locations of Volcanic Activity Shield Volcanoes: Hawaii –Mafic lavas, low, flat, ‘shields’ Volcanic Domes: Mt. St. Helens –Rhyolite, andesitic lavas. –Thick, viscous lavas (domes) Cinder Cones Composite Volcanoes
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Dome Formation, Mount St. Helens Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Kinds and Locations of Volcanic Activity Shield Volcanoes: Hawaii Volcanic Domes: Mt. St. Helens –Rhyolite, andesitic lavas. –Thick, viscous lavas (domes) Cinder Cones: common –Release of gas pressure (pop bottle) –Produces pyroclastics Composite Volcanoes
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Paricutín Volcano Erupting Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Paricutín Showing Form of Cinder Cones Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.
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Kinds and Locations of Volcanic Activity Shield Volcanoes: Hawaii Volcanic Domes: inside Mt. St. Helens Cinder Cones: common –Release of gas pressure (pop bottle) –Produces pyroclastics Composite Volcanoes (stratovolcanoes) Calderas
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Source: http://www.enchantedlearning.com/subjects/volcano/gifs/volcanodiagram.GIF
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Composite Volcano in the Aleutian Islands Source: Photograph by R.E. Wilcox, USGS Photo Library, Denver, CO.
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Hazards Related to Volcanoes Lava Pyroclastics (rocks and lava) Lahars (mudflow of ash and water) Pyroclastic Flows–Nuées Ardentes Toxic Gases Steam Explosions Secondary Effects: Climate and Atmospheric Chemistry
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Formation of “Lava Trees” Near Kilauea Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
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Map Showing Lava Filling Harbor in Iceland Source: Data from R. Decker and B. Decker, Volcanoes, Copyright © 1981 by W.H. Freeman and Company.
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Lava-Flow Control Efforts on Heimaey Harbor Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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Pyroclastics Ejected During Eruptions Source: Data from U.S. Geological Survey.
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Hazards Related to Volcanoes Lava Pyroclastics (rocks and lava) Lahars (mudflow of ash and water) Pyroclastic Flows–Nuées Ardentes Toxic Gases Steam Explosions Secondary Effects: Climate and Atmospheric Chemistry
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Aftermath- Mt. St. Helens Eruption, 1980 Source: Photograph by M.M. Brugman, USGS Photo Library, Denver, CO.
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Ash and Rains Cause Structure Collapse Source: Photograph by R.P. Hoblitt, courtesy U.S. Geological Survey.
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Mudflow and Flood Damage from Mt. St. Helens Source: Photograph by C.D. Miller, USGS Photo Library, Denver, CO.
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Abacan River Mudflows, Philippines Source: Photograph by T.J. Casadervall, U.S. Geological Survey.
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Hazards Related to Volcanoes Lava Pyroclastics (rocks and lava) Lahars (mudflow of ash and water) Pyroclastic Flows–Nuées Ardentes –‘Glowing cloud’ Toxic Gases Steam Explosions Secondary Effects: Climate and Atmospheric Chemistry
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Pyroclastic Flow from Mount St. Helens Source: Photograph by P.W. Lipman, USGS Photo Library, Denver, CO.
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Source: Photograph by Underwood and Underwood, courtesy Library of Congress. Nuée Ardente from Mont Pelée, 1902: *25,000 – 40,000 people died
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Hazards Related to Volcanoes Lava Pyroclastics (rocks and lava) Lahars (mudflow of ash and water) Pyroclastic Flows–Nuées Ardentes Toxic Gases Steam Explosions Secondary Effects: Climate and Atmospheric Chemistry
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Toxic gases: CO 2 ? Cameroon, 1986 Source: http://wps.prenhall.com/wps/media/objects/476/488316/ch13.html
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Carbon Dioxide Cloud Over Lake Nyos, Cameroon Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.
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Animal Carcasses From Deadly Cloud: 1700 people died Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.
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Hazards Related to Volcanoes Lava Pyroclastics (rocks and lava) Lahars (mudflow of ash and water) Pyroclastic Flows–Nuées Ardentes Toxic Gases Steam Explosions Secondary Effects: Climate and Atmospheric Chemistry
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Mt. Pinatubo Eruption, 1991 Source: Photograph by K. Jackson, U.S. Air Force.
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Source: http://eos.higp.hawaii.edu//
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Source: http://volcanoes.usgs.gov/Imgs/Jpg/Pinatubo/16112441-008_large.jpg
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Source: http://pubs.usgs.gov/publications/text/tectonics.html#anchor10693467 The atmosphere: different levels
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Source: http://eos.higp.hawaii.edu// Stratospheric Aerosol, 1991: April 15 - May 25
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Source: http://eos.higp.hawaii.edu// Stratospheric Aerosol, 1991: June 14 – July 26
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Source: http://eos.higp.hawaii.edu// Stratospheric Aerosol, 1993: Feb. 13 – March 26
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