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OverviewOverview
• 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
Magma SourceMagma 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
Plate tectonics: Asthenosphere is where melting occurs
Source: http://www.geol.umd.edu/~jmerck/gal04/GEOL388/lectures/02.html
Wahalua Visitors’ Center Aflame in Hawaii
Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
Ruins of the Visitors’ Center After Lava Cooled
Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
Magma TypesMagma Types
• Composition: – Magmas: >Fe, Mg (mafic) vs >SiO2 (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
Mafic: BasaltMafic: Basalt
Ultramafic: PeridotiteUltramafic: PeridotiteSource: http://www.tmm.utexas.edu/npl/mineralogy/Blowups/Olivine_in_peridotite_xenolith.htm
Felsic-mafic: andesiteFelsic-mafic: andesite
Source: http://www.otago.ac.nz/geology/features/rocks-minerals/rocks.html
Felsic: RhyoliteFelsic: Rhyolite
Source: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/
Magma propertiesMagma properties
• Volcanic Gases: CO2, SO2
• Pressure builds up as magmas rises to surface– Felsic (more SiO2): viscous + thick = explosive
– Mafic (less SiO2): fluid, gases escape
*What kind of volcano is safest to live by?
Kinds and Locations of Kinds and Locations of Volcanic ActivityVolcanic Activity
• Individual Volcanoes–Locations
• Seafloor Spreading Ridges, Fissure Eruptions
• Shield Volcanoes
• Volcanic Domes
• Cinder Cones
• Composite Volcanoes
Volcanoes of the World
Source:After R. Decker and B. Decker, Volcanoes, 1981, W.H. Freeman and Company, New York, NY.
“Hot Spots” Around the World
Source: Modified after map in online text This Dynamic Earth, U.S. Geological Survey.
Kinds and Locations of Kinds and Locations of Volcanic ActivityVolcanic Activity
• Shield Volcanoes: Hawaii– Mafic lavas, low, flat, ‘shields’
• Volcanic Domes
• Cinder Cones
• Composite Volcanoes
Kinds and Locations of Kinds and Locations of Volcanic ActivityVolcanic 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
Kinds and Locations of Kinds and Locations of Volcanic ActivityVolcanic 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
Paricutín Showing Form of Cinder Cones
Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.
Kinds and Locations of Kinds and Locations of Volcanic ActivityVolcanic 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
Composite Volcano in the Aleutian Islands
Source: Photograph by R.E. Wilcox, USGS Photo Library, Denver, CO.
Hazards Related to VolcanoesHazards 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
Formation of “Lava Trees” Near Kilauea
Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.
Map Showing Lava Filling Harbor in Iceland
Source: Data from R. Decker and B. Decker, Volcanoes, Copyright © 1981 by W.H. Freeman and Company.
Lava-Flow Control Efforts on Heimaey Harbor
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
Hazards Related to VolcanoesHazards 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
Aftermath-Mt. St. Helens Eruption, 1980
Source: Photograph by M.M. Brugman, USGS Photo Library, Denver, CO.
Ash and Rains Cause Structure Collapse
Source: Photograph by R.P. Hoblitt, courtesy U.S. Geological Survey.
Mudflow and Flood Damage from Mt. St. Helens
Source: Photograph by C.D. Miller, USGS Photo Library, Denver, CO.
Hazards Related to VolcanoesHazards 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
Pyroclastic Flow from Mount St. Helens
Source: Photograph by P.W. Lipman, USGS Photo Library, Denver, CO.
Source: Photograph by Underwood and Underwood, courtesy Library of Congress.
Nuée Ardente from Mont Pelée, 1902:
*25,000 – 40,000 people died
Hazards Related to VolcanoesHazards 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
Toxic gases: CO2?
Cameroon, 1986
Source: http://wps.prenhall.com/wps/media/objects/476/488316/ch13.html
Carbon Dioxide Cloud Over Lake Nyos, Cameroon
Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.
Animal Carcasses From Deadly Cloud: 1700 people died
Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.
Hazards Related to VolcanoesHazards 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
Source: http://pubs.usgs.gov/publications/text/tectonics.html#anchor10693467
The atmosphere: different levels