Volcanoes
Overview
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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 Source
• Areas Where Magma Forms (need heat!)
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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 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: Basalt
Ultramafic: Peridotite
Source: http://www.tmm.utexas.edu/npl/mineralogy/Blowups/Olivine_in_peridotite_xenolith.htm
Felsic-mafic: andesite
Source: http://www.otago.ac.nz/geology/features/rocks-minerals/rocks.html
Felsic: Rhyolite
Source: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/
Magma 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?
Lava Flows on Kilauea in Hawaii
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
Hawaiian Lavas: mafic basalts
Source: Courtesy of Carla W. Montgomery.
Volcanic Breccia (felsic)
Source: Courtesy of Carla W. Montgomery.
Kinds and Locations of
Volcanic 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
Volcanic Activity
• Shield Volcanoes: Hawaii
– Mafic lavas, low, flat, ‘shields’
• Volcanic Domes
• Cinder Cones
• Composite Volcanoes
Low-Angle View of Mauna Loa
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
Satellite View of
Hawaii
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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
Dome Formation,
Mount St. Helens
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
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
Paricutín Volcano Erupting
Source: Photograph courtesy of USGS Photo Library, Denver, CO.
Paricutín Showing
Form of Cinder Cones
Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.
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
Source: http://www.enchantedlearning.com/subjects/volcano/gifs/volcanodiagram.GIF
Composite
Volcano in the
Aleutian Islands
Source: Photograph by R.E. Wilcox, USGS Photo Library, Denver, CO.
Hazards Related to Volcanoes
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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.
Pyroclastics Ejected
During Eruptions
Source: Data from U.S. Geological Survey.
Hazards Related to Volcanoes
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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
AftermathMt. 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.
Abacan River
Mudflows, Philippines
Source: Photograph by T.J. Casadervall, U.S. Geological Survey.
Hazards Related to Volcanoes
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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.
Nuée Ardente from Mont Pelée, 1902:
*25,000 – 40,000 people died
Source: Photograph by Underwood and Underwood, courtesy Library of Congress.
Hazards Related to Volcanoes
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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 Volcanoes
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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
Mt. Pinatubo Eruption, 1991
Source: Photograph by K. Jackson, U.S. Air Force.
Source: http://eos.higp.hawaii.edu//
Source: http://volcanoes.usgs.gov/Imgs/Jpg/Pinatubo/16112441-008_large.jpg
The atmosphere: different levels
Source: http://pubs.usgs.gov/publications/text/tectonics.html#anchor10693467
Stratospheric Aerosol, 1991: April 15 - May 25
Source: http://eos.higp.hawaii.edu//
Stratospheric Aerosol, 1991: June 14 – July 26
Source: http://eos.higp.hawaii.edu//
Stratospheric Aerosol, 1993: Feb. 13 – March 26
Source: http://eos.higp.hawaii.edu//