Chapter 7. Natural Disasters. Volcano Case Histories: Killer Events. Tenth Edition 7-1

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1 Natural Disasters Tenth Edition Chapter 7 Volcano Case Histories: Killer Events Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-1

2 Volcanism at Spreading Centers: Iceland (1 of 3) Rifting at spreading centers worldwide creates 20 km 3 of new oceanic crust each year Iceland Volcanic plateau built of basaltic lava erupted from hot spot underlying mid-atlantic Ocean spreading center 13% covered by glaciers 33% covered by active volcanoes Volcanic eruptions (mostly peaceful fissure eruptions) occur about every 5 years Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-2

3 Volcanism at Spreading Centers: Iceland (2 of 3) Iceland Lava Flows of 1973 Vestmannaeyjar fishing port, harbor built by volcanism Fissure opened 1 km from town, emitted 230 million m 3 lava and 26 million km 3 pyroclastic material, increased size of island by 20% Destroyed 370 buildings and began to fill in harbor Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-3

4 Volcanism at Spreading Centers: Iceland (3 of 3) Iceland Lava Flows of 1973 To divert flows, Icelanders bulldozed lava and ash into barriers, sprayed flows with seawater to harden into walls Used heat from flows to heat town Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-4

5 Figure 7.1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-5

6 Figure 7.2 Lava ignites buildings, Vestmannaeyjar, Iceland Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-6

7 Figure 7.3 Volcanism at Spreading Centers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-7

8 Volcanism at Subduction Zones Most of world s famous volcanoes are subduction zone volcanoes Many regions around subduction zone volcanoes are heavily populated Erupt directly into atmosphere (not underwater) so have direct impact on worldwide climate Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-8

9 Volcanism at Subduction Zones: Cascade Range (1 of 2) Cascade Range, Pacific Coast United States and Canada Subduction of Juan de Fuca plate under Pacific Northwest is responsible for Cascade Range volcanoes Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-9

10 Volcanism at Subduction Zones: Cascade Range (2 of 2) Cascade Range, Pacific Coast United States and Canada Subduction Upper mantle (asthenosphere) is melted (aided by water released from sediments on top of subducting plate) and mixes with melted crustal rock into rising andesitic magma Some magma cools at depth into plutonic rocks Some magma erupts explosively at surface Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-10

11 Figure 7.4 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-11

12 Figure 7.5 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-12

13 Volcanism at Subduction Zones: Eruption Frequency Eruption frequency: Mt. St. Helens Every century or so for last 2500 years 1975 study predicted eruption before major eruption Photo left in 1974; Photo right in late 1980 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-13

14 Figure 7.6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-14

15 Figure 7.7 Eruption Histories of Cascade Range Volcanoes Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-15

16 Volcanism at Subduction Zones: Mount St. Helens Mount St. Helens, Washington, 1980 Dozens of magnitude 3 earthquakes as magma pushed toward surface, expanding northern side outward Landslide occurred (recorded as 5.1 M earthquake) on north side of mountain, traveling great distance as mudflows (lahars) Landslide released pressure on magma and blast followed pyroclastic flows Blast opened throat of volcano for vertical column eruption (Plinian phase) lasting nine hours Continued pyroclastic flows and ash falls from eruption cloud Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-16

17 Figure 7.10 (a) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-17

18 Figure 7.10 (b) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-18

19 Figure 7.10 (c) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-19

20 Figure 7.10 (d) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-20

21 Figure 7.10 (e) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-21

22 Figure 7.10 (f) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-22

23 Figure 7.12 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-23

24 Figure 7.13 Mount St. Helens, Washington, 1980 Building of lava dome continues today Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-24

25 Figure 7.11 Map of Materials After Mount Saint Helens Eruption Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-25

26 Volcanism at Subduction Zones: Lassen Peak Lassen Peak, California, Lassen Peak: not a volcano itself but lava dome (one of largest known) in remnants of enormous Mt. Tehama Formed from lava too viscous to flow away so solidified as plug : eruptions each May (probably initiated by melting of snow) of ash clouds and collapse of overtopped lava dome pyroclastic flows and lahars Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-26

27 Figure 7.16 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-27

28 Figure 7.17 Mount Shasta, California Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-28

29 Volcanism at Subduction Zones: Mount Shasta Mount Shasta, California Active volcano 11 eruptions in 3,400 years, last in 1786 Lower slopes are broad and smooth Pyroclastic flows spread widely as they move downhill Settled with three towns and one large reservoir Risk is low when comparing eruption recurrences to lifetime of person or building, but settlements persist for centuries Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-29

30 Figure 7.18 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-30

31 Figure 7.21 Eruption Volumes of Some Events Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-31

32 Figure 7.22 Volcanic Processes and Killer Events Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-32

33 Figure 7.23 Historic Record of Volcano Fatalities About 275,000 people killed during last 500 years by about a dozen volcanic processes Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-33

34 Table 7.1 Volcanic Causes of Deaths 275,000 Deaths 530 Volcanic Events Pyroclastic flow 29% 15% Tsunami 21% 5% Lahar 15% 17% Indirect (famine) 23% 5% Gas 1% 4% Lava flow <1% 4% Pyroclastic fall (bombs) 2% 21% Debris avalanche 2% 3% Flood 1% 2% Earthquake <1% 2% Lightning <1% 1% Unknown 7% 20% Data Source: Simkin,T.,Siebert,L.,and Blong,R., Volcano Fatalities in Science 291:255,2001 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-34

35 Volcanic Processes and Killer Events: Pyroclastic Flows In pyroclastic flows, the superhot, high speed turbulent cloud of ash, gas and air is deadly they result in about 29% of volcanic deaths Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-35

36 Figure 7.24 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-36

37 Volcanic Processes and Killer Events: Eruption Column Collapse Pyroclastic Flow Mount Mayon, Philippines, 1984 Vulcanian eruptions sent ash clouds 10 km high, collapsed into pyroclastic flows down mountain Columns are more likely to collapse and form pyroclastic flows when eruptions are weaker and eruption column is cooler Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-37

38 Figure 7.27 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-38

39 Volcanic Processes and Killer Events: Pyroclastic Surges El Chichon, Mexico, 1982 Dormant for 550 years, then month of earthquakes led up to six- hour-long Plinian eruption, followed by five days of inactivity Pyroclastic surge flowing radially outward from volcano Overran nine villages, killed 2,000 people Plinian column up to 20 km high, two more pyroclastic surges Eruption changed (cooled) global climate Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-39

40 Figure 7.28 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-40

41 Volcanic Processes and Killer Events: Dome Collapse Dome Collapse: Mount Unzen, Japan, 1991 Unique in steady magma supply and topography chunks of lava dome frequently break off creating pyroclastic flows 7,000 pyroclastic flows between 1991 and 1994 Cities and towns near the volcano, and farming villages on lower slopes, evacuated when threat grew 44 observers killed in 1991 by larger than usual flow, including famed volcano photographers, Maurice and Katya Krafft Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-41

42 Volcanic Processes and Killer Events: Mount Pelee (1 of 2) Mount Pelee, Martinique, 1902 Many pyroclastic flows occur from hot ash and gas overspilling crater rim Few deadliest pyroclastic flows generated by directed blasts Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-42

43 Volcanic Processes and Killer Events: Mount Pelee (2 of 2) Mount Pelee, Martinique, : Small pyroclastic flow killed 40 people and raised tension, but mayor of St. Pierre (town of 25,000) used militia to prevent people from leaving before election Enormous pyroclastic flow enveloped town, killing 29,000 people Area is fully settled again now Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-43

44 Figure 7.25 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-44

45 Figure 7.26 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-45

46 Volcanic Processes and Killer Events: Pyroclastic Flows Over Water Krakatau, Indonesia, 1883 Blast on August 27 generated pyroclastic flow that traveled across 40 km (25 mi) of sea surface in Sunda Straits to Katimbang on Sumatra and was still hot enough to kill more than 2,000 people on Sumatra Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-46

47 Volcanic Processes and Killer Events: Tsunami Volcano-generated tsunami have been responsible for 21% of volcano-caused deaths 1883 Krakatau caldera collapse killed more than 36,000 people Less than 10% directly killed by eruption More than 90% killed by volcano-caused tsunami Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-47

48 Volcanic Processes and Killer Events: Lahars (1 of 2) Lahars are volcanic mudflows and volcanic debris flows that are fluid when moving, but then solidify Water flowing downhill mixes with old pyroclastic debris from previous eruptions to form huge mudflows Lahars can flow at velocities of 65 km/hr, tens of kilometers from volcano Lahars are responsible for about 15% of deaths by volcano May be primary events during volcanic eruptions or occur later due to addition of water such as from heavy rain or melting glacial ice Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-48

49 Volcanic Processes and Killer Events: Lahars (2 of 2) Nevada Del Ruiz, Colombia, 1985: Very high volcano in the Andes Mountains has a large ice cap Initial Plinian eruption sent pyroclastic debris falling onto ice cap, melting ice, creating lahars flowing down mountain, killing 1,800 Later eruptions melted more ice, creating bigger lahars, finally reaching town of Armero (27,000 residents), killing 22,000 people Lahars were repeat of 1845 events, when 1,000 people were killed (fewer residents) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-49

50 Figure 7.29 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-50

51 Volcanic Processes and Killer Events: Mount Rainier Mount Rainier, Washington On Alert: Considered very dangerous by volcanologists because of: Great height Extensive glacial cap Frequent earthquakes Active hot-water spring systems Mountain may fail in massive avalanche and/or melted ice may cause floods or lahars, even without eruption Osceola mudflow, 5,600 years ago, spread more than 120 km from mountain and over enormous area, now densely populated Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-51

52 Figure 7.32 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-52

53 Volcanic Processes and Killer Events: Debris Avalanches Stratovolcanoes are riddled with fractures Hot water and gases chemically decompose volcanic rock over time Sector collapses flow downslope as debris avalanches, as at Mount Shasta in California Debris avalanches are responsible for 2% of volcano-caused deaths Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-53

54 Volcanic Processes and Killer Events: Indirect - Famine Laki, Iceland Fissure Eruption of 1783 Greatest lava eruption of historic times Fissure eruption with lava flow of 5,000 m 3 /sec (1/3 volume of Mississippi River) over 50 days Accompanied by enormous volume of gases Haze of SO 2 and fluorine killed Iceland livestock about 20% of human population died of famine Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-54

55 Volcanic Processes and Killer Events: Tambora Tambora, Indonesia, 1815 Most violent and explosive eruption of last 200 years Two extremely violent Plinian eruptions tore open the volcano so that 50 km 3 of magma erupted in pyroclastic flows over one week Reduced elevation of mountain from 4,000 m to 2,650m Created 6 km wide, 1 km deep caldera Eruption caused 117,000 deaths 10% directly by eruption 90% from famine or disease, after pyroclastic fallout damaged crops Affected global climate so that 1816 was known as the year without a summer Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-55

56 Death at Ashfall, Nebraska 10 million years ago: savanna waterholes, migrating wildlife Eruption at Yellowstone 1,300 km away blanketed Nebraska with 0.3 m thick layer of volcanic ash, dumped by wind in waterholes Volcanic ash is tiny, sharp pieces of glass and rock, dangerous to inhale deprived animals of adequate oxygen over long term Animals very well preserved in ash after death fossils excavated at Ashfall Fossil Beds Historical Park in Nebraska Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-56

57 Figure 7.34 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-57

58 Figure 7.33 Volcanic ash Tiny pieces of sharp glass that are easy to inhale but do great damage to respiratory systems, including causing death Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-58

59 Volcanic Processes and Killer Events: Gas (1 of 3) Killer Lakes of Cameroon, Africa East African Rift Valley failed rift with string of crater lakes Lake Nyos is young, high crater formed by explosion few hundred years ago, filled with rain water 1986: gigantic volume of gas burst out of Lake Nyos and swept down valleys, 50 m thick, up to 45 mph Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-59

60 Volcanic Processes and Killer Events: Gas (2 of 3) Killer Lakes of Cameroon, Africa Four villages overwhelmed by cloud of gas in 1986 Residents lost consciousness only four awoke 1,700 people killed, 3,000 cattle died, all local wildlife died Gas was carbon dioxide Abundant carbon dioxide killed fauna but did not affect flora Carbon dioxide had leaked up from basaltic magma underlying lake, part of Cameroon volcanic line of East African failed rift Lake water is stratified, with densest water at bottom absorbing leaked carbon dioxide and trapping it there Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-60

61 Volcanic Processes and Killer Events: Gas (3 of 3) Killer Lakes of Cameroon, Africa Lake eventually became unstable (triggered by unknown disturbance, overturning of water layers), and CO 2 burst out in huge bubble, flowing down mountainsides in dense cloud along ground About 1/3 of gas was left in lake, more is continually being added 20 years for lake water to become oversaturated in CO 2 again Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-61

62 Figure 7.35 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-62

63 Figure 7.36 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-63

64 Figure 7.37 Degassing pipe allows high-pressure, gas-rich water to escape before building to a catastrophic volume. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-64

65 Volcanic Processes and Killer Events: Lava Flows Nyiragongo, Zaire, 2002 Some stratovolcanoes like Nyiragongo of East African Rift Valley have lava lakes in summit crater In 2002, lava with exceptionally low viscosity flowed very fast down volcano slopes Killed 45 people living on the mountain Flowed through city of Goma (500,000 residents plus Rwanda civil war refugees), destroying buildings and forcing evacuation Lava flows are responsible for less than 1% of volcano deaths. Although they are frequent, the lava usually flows quite slowly. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-65

66 VEIs of Some Killer Eruptions Does energy of eruption correlate to number of fatalities? VEI is semi-quantitative estimate of magnitude of volcanic eruption, using volume erupted and eruption-column height Some deadly events have low VEI Frequency of different VEI magnitudes is inverse correlation Bigger eruption, less frequent occurrence Smaller eruption, more frequent occurrence As population grows, more people live in volcano hazard zones Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-66

67 TABLE 7.2 VEIs of Notable Volcanic Disasters (Volcanic Explosivity Index) VEI Volcano 8 Yellowstone, 600,000 years ago; Toba, 74,000 years ago 7 Tambora, Vesuvius, 79; Krakatau, 1883; Pinatubo, St. Helens, Pelée, Nevado del Ruiz, Lake Nyos, 1986 Toba eruption almost drove humans into extinction Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-67

68 Volcano Monitoring and Warning: Long Valley (1 of 2) Long Valley, California, 1982 Abundant crustal melting (no hot spot), including colossal eruption 760,000 years ago, created Long Valley caldera and erupted pyroclastic debris (Bishop Tuff) 100 s of meters thick Giant continental caldera Rare giant eruptions Frequent small eruptions Long Valley 600 years ago Mono Lake ~200 years ago Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-68

69 Volcano Monitoring and Warning: Long Valley (2 of 2) Long Valley, California, (few weeks after Mt. St. Helens eruption) Numerous earthquakes, including four magnitude Resurgent dome rose 25 cm U.S.G.S. issued Notice of Potential Volcanic Hazard, lowest level alert House prices dropped 40%, tourism slowed Residents erupted volcano did not erupt Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-69

70 Figure 7.38 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-70

71 Figure 7.40 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-71

72 Volcano Monitoring and Warning: Mount Pinatubo (1 of 3) Mount Pinatubo, Philippines, 1991 Volcano-warning success story Largest eruption in 20 th century near populated area Nearly one million people (20,000 U.S. military) in danger zone After 500 years of quiet, magma moved toward surface Thousands of small earthquakes Intense monitoring program by U.S. and Philippine scientists began Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-72

73 Volcano Monitoring and Warning: Mount Pinatubo (2 of 3) Mount Pinatubo, Philippines, 1991 June 7 Degassed magma reached surface, formed lava dome June 12 (Philippine Independence Day) Large explosive eruptions began Evacuation removed almost everyone; military base closed June 15 Cataclysmic eruption More than 5 km 3 magma and rock, blasted up to 35 km height in atmosphere Pyroclastic flows 200 m deep Typhoon (hurricane) arrived and washed volcanic debris downslope as lahars Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-73

74 Volcano Monitoring and Warning: Mount Pinatubo (3 of 3) Mount Pinatubo, Philippines, 1991 Assessment: 300 people killed but a million moved out of harm s way (20,000 estimated deaths without evacuation) $500 million property saved (include military aircraft) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-74

75 Figure 7.41 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-75

76 Volcano Monitoring and Warning: Signs of Impending Eruption (1 of 3) 1. Seismic Waves Magma rising toward surface causes rocks to break, sends off short-period seismic waves Magma rising through opened conduits sends off long-period seismic waves For two weeks before Mt. Pinatubo eruption, 400 long-period events were recorded daily from 10 km deep magma moving into place for eruption Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-76

77 Volcano Monitoring and Warning: Signs of Impending Eruption (2 of 3) 2. Ground Deformation Ground surface rises and falls in response to magma movement Measured with tilt meters, strain meters, distance-meters, satellites Three Sisters volcanoes in Oregon Bulged upward 10 cm as about 21 million m 3 magma moved Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-77

78 Volcano Monitoring and Warning: Signs of Impending Eruption (3 of 3) 3. Gas Measurements Magma approaching surface loses gas as pressure drops Mammoth Mountain, California CO 2 from magma kills trees Declining CO 2 levels have relieved worry Galeras Volcano, Colombia Decrease in gas emissions relieved worry Volcano was plugged by sticky magma, gas pressure building Eruption killed seven volcanologists collecting data in crater Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-78

79 Figure 7.42 LIDAR LIDAR image shows ground deformation as magma moves below ground at Three Sisters volcanoes in Oregon Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-79

80 Volcano Monitoring and Warning: Volcano Observatories In 20 th century, U.S. had powerful eruptions in Alaska, California, Hawaii and Washington At least 65 active or potentially active volcanoes in U.S. U.S. Geological Survey established Volcano Hazards Program with five volcano observatories: Alaska, Cascades, Hawaiian, California, and Yellowstone Each with own website to report current activity Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-80

81 TABLE 7.3 Volcanic-Alert Levels, US Geological Survey Normal Advisory Typical background activity of a volcano Elevated unrest above known background activity Watch Heightened/escalating unrest with increased potential for eruptive activity or minor eruption underway Warning Highly hazardous eruption underway or imminent Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-81