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Volcanoes. Overview Magma Sources and Types Kinds and Locations of Volcanic Activity Hazards Related to Volcanoes Issues in Predicting Volcanic Eruptions.

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Presentation on theme: "Volcanoes. Overview Magma Sources and Types Kinds and Locations of Volcanic Activity Hazards Related to Volcanoes Issues in Predicting Volcanic Eruptions."— Presentation transcript:

1 Volcanoes

2

3 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

4 Magma Source Areas Where Magma Forms (need heat!) –Upper mantle: asthenosphere –depths of ~ 50 to 250 km –High temps ( C), medium pressure –Rocks melt, or partially melt –Divergent plate boundaries –Above subduction zones –Hot spots

5 Plate tectonics: Asthenosphere is where melting occurs Source:

6 Wahalua Visitors’ Center Aflame in Hawaii Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.

7 Ruins of the Visitors’ Center After Lava Cooled Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.

8 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

9 Mafic: Basalt Ultramafic: Peridotite Source:

10 Felsic-mafic: andesite Source:

11 Felsic: Rhyolite Source:

12 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?

13 Lava Flows on Kilauea in Hawaii Source: Photograph courtesy of USGS Photo Library, Denver, CO.

14 Hawaiian Lavas: mafic basalts Source: Courtesy of Carla W. Montgomery.

15 Volcanic Breccia (felsic) Source: Courtesy of Carla W. Montgomery.

16 Kinds and Locations of Volcanic Activity Individual Volcanoes–Locations Seafloor Spreading Ridges, Fissure Eruptions Shield Volcanoes Volcanic Domes Cinder Cones Composite Volcanoes

17 Volcanoes of the World Source:After R. Decker and B. Decker, Volcanoes, 1981, W.H. Freeman and Company, New York, NY.

18 “Hot Spots” Around the World Source: Modified after map in online text This Dynamic Earth, U.S. Geological Survey.

19 Kinds and Locations of Volcanic Activity Shield Volcanoes: Hawaii –Mafic lavas, low, flat, ‘shields’ Volcanic Domes Cinder Cones Composite Volcanoes

20 Low-Angle View of Mauna Loa Source: Photograph courtesy of USGS Photo Library, Denver, CO.

21 Satellite View of Hawaii Source: Photograph courtesy of USGS Photo Library, Denver, CO.

22 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

23 Dome Formation, Mount St. Helens Source: Photograph courtesy of USGS Photo Library, Denver, CO.

24 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

25 Paricutín Volcano Erupting Source: Photograph courtesy of USGS Photo Library, Denver, CO.

26 Paricutín Showing Form of Cinder Cones Source: Photograph by K. Segerstrom, courtesy of USGS Photo Library, Denver, CO.

27 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

28 Source:

29 Composite Volcano in the Aleutian Islands Source: Photograph by R.E. Wilcox, USGS Photo Library, Denver, CO.

30 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

31 Formation of “Lava Trees” Near Kilauea Source: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO.

32 Map Showing Lava Filling Harbor in Iceland Source: Data from R. Decker and B. Decker, Volcanoes, Copyright © 1981 by W.H. Freeman and Company.

33 Lava-Flow Control Efforts on Heimaey Harbor Source: Photograph courtesy of USGS Photo Library, Denver, CO.

34 Pyroclastics Ejected During Eruptions Source: Data from U.S. Geological Survey.

35 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

36 Aftermath- Mt. St. Helens Eruption, 1980 Source: Photograph by M.M. Brugman, USGS Photo Library, Denver, CO.

37 Ash and Rains Cause Structure Collapse Source: Photograph by R.P. Hoblitt, courtesy U.S. Geological Survey.

38 Mudflow and Flood Damage from Mt. St. Helens Source: Photograph by C.D. Miller, USGS Photo Library, Denver, CO.

39 Abacan River Mudflows, Philippines Source: Photograph by T.J. Casadervall, U.S. Geological Survey.

40 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

41 Pyroclastic Flow from Mount St. Helens Source: Photograph by P.W. Lipman, USGS Photo Library, Denver, CO.

42 Source: Photograph by Underwood and Underwood, courtesy Library of Congress. Nuée Ardente from Mont Pelée, 1902: *25,000 – 40,000 people died

43 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

44 Toxic gases: CO 2 ? Cameroon, 1986 Source:

45 Carbon Dioxide Cloud Over Lake Nyos, Cameroon Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.

46 Animal Carcasses From Deadly Cloud: 1700 people died Source: Photograph by M.L. Tuttle, USGS Photo Library, Denver, CO.

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48 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

49 Mt. Pinatubo Eruption, 1991 Source: Photograph by K. Jackson, U.S. Air Force.

50 Source:

51 Source:

52 Source: The atmosphere: different levels

53 Source: Stratospheric Aerosol, 1991: April 15 - May 25

54 Source: Stratospheric Aerosol, 1991: June 14 – July 26

55 Source: Stratospheric Aerosol, 1993: Feb. 13 – March 26


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