Volcanoes. Overview Magma Sources and Types Kinds and Locations of Volcanic Activity Hazards Related...

Volcanoes Volcanoes

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


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?

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 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.


• Shield Volcanoes: Hawaii– Mafic lavas, low, flat, ‘shields’

• Volcanic Domes

• Cinder Cones


Low-Angle View of Mauna Loa


Satellite View of Hawaii



• Shield Volcanoes: Hawaii– Mafic lavas, low, flat, ‘shields’

• Volcanic Domes: Mt. St. Helens– Rhyolite, andesitic lavas. – Thick, viscous lavas (domes)

• Cinder Cones


Dome Formation, Mount St. Helens



• 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


Paricutín Volcano Erupting


Paricutín Showing Form of Cinder Cones

Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.


• 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 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


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


Pyroclastics Ejected During Eruptions

Source: Data from U.S. Geological Survey.


• Lava




• Toxic Gases



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.

Abacan River Mudflows, Philippines

Source: Photograph by T.J. Casadervall, U.S. Geological Survey.


• Lava



• Pyroclastic Flows–Nuées Ardentes– ‘Glowing cloud’

• Toxic Gases



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


• Lava




• Toxic Gases



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.


• Lava




• Toxic Gases



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

Source: http://pubs.usgs.gov/publications/text/tectonics.html#anchor10693467

The atmosphere: different levels


Stratospheric Aerosol, 1991: April 15 - May 25


Stratospheric Aerosol, 1991: June 14 – July 26


Stratospheric Aerosol, 1993: Feb. 13 – March 26

Volcanoes. Overview Magma Sources and Types Kinds and Locations of Volcanic Activity Hazards Related...

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