1. Lecture Outlines Natural Disasters, 7th edition
Patrick L. Abbott

2. Volcano Case Histories: Killer Events Natural Disasters, 7th edition, Chapter 9

3. Volcanism at Spreading Centers
Rifting at spreading centers worldwide creates 20 km3 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

4. Volcanism at Spreading Centers
Iceland – Lava Flows of 1973
Vestmannaeyjar fishing port, harbor built by volcanism
Fissure opened 1 km from town, emitted 230 million m3 lava and 26 million km3 pyroclastic material, increased size of island by 20%
Destroyed 370 buildings and began to fill in harbor
Figure 9.2

5. Volcanism at Spreading Centers
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
Figure 9.3
Figure 9.4

6. Volcanism at Spreading Centers
Iceland – Jokulhlaup of 1996
Fissures opened under glacier, melted 600 m of ice
Meltwater accumulating in volcano crater flooded out suddenly as jokulhlaup flood (45,000 m3/sec)
Destroyed Iceland’s longest bridge, telephone lines and roads

7. 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

8. Volcanism at Subduction Zones
Cascade Range, Pacific Coast United States and Canada
Subduction of Juan de Fuca plate under Pacific Northwest is responsible for Cascade Range volcanoes
Figure 9.5

9. Volcanism at Subduction Zones
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
Figure 9.6

10. Volcanism at Subduction Zones
Cascade Range, Pacific Coast United States and Canada
Eruption frequency: Mt. St. Helens
Figure 9.7

11. Volcanism at Subduction Zones
Cascade Range, Pacific Coast United States and Canada
Eruption frequency: Mt. St. Helens
Every century or so for last 2500 years
1975 study predicted eruption before 2000
1980 major eruption
Figure 9.10

12. Volcanism at Subduction Zones
Mount St. Helens, Washington, 1980
Dozens of magnitude 3 earthquakes as magma pushed to surface and expanded out northern side
Magnitude 5.1 earthquake occurred and triggered landslide of north side of mountain, traveling great distance as mudflows (lahars)
Figure 9.11

13. Volcanism at Subduction Zones
Mount St. Helens, Washington, 1980
Landslide released pressure on magma and blast followed  pyroclastic flows
Figure 9.13
Figure 9.11

14. Volcanism at Subduction Zones
Mount St. Helens, Washington, 1980
Blast opened throat of volcano for vertical column eruption (Plinian phase) lasting nine hours
Continued pyroclastic flows and ash falls from eruption cloud
Figure 9.11

15. Volcanism at Subduction Zones
Mount St. Helens, Washington, 1980
Building of lava dome continues today
Figure 9.11
Figure 9.14

16. Volcanism at Subduction Zones
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
Figure 9.17

17. Volcanism at Subduction Zones
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
Figure 9.19

18. Killer Events and Processes
Figure 9.22

19. Killer Events and Processes
Historic Record of Volcano Fatalities
About 275,000 people killed during last 500 years by about a dozen volcanic processes
Figure 9.23

20. Killer Events and Processes
Pyroclastic Flows
Superhot, high speed turbulent cloud of ash, gas and air – can kill thousands of people in one event
Figure 9.24

21. Killer Events and Processes
Mount Mayon, Philippines, 1968
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
Figure 9.25

22. Killer Events and Processes
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
Change in global climate
Figure 9.26

23. Killer Events and Processes
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 volcano photographers, Maurice and Katya Krafft

24. Killer Events and Processes
Mount Pelee, Martinique, 1902
Most pyroclastic flows from hot ash and gas overspilling crater
Few deadliest pyroclastic flows generated by directed blasts
Figure 9.27

25. Killer Events and Processes
Mount Pelee, Martinique, 1902
1902: 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 nuee ardente (glowing cloud) enveloped town and killed all but two residents
Area is fully settled again now
Figure 9.28

26. Killer Events and Processes
Krakatau, Indonesia, 1883
Blast on August 27 generated pyroclastic flow across sea surface of Sunda Straits to Katimbang on Sumatra
Killed more than 2,000 people on Sumatra

27. Killer Events and Processes
Tsunami
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
Mount Unzen, Japan, 1792
Earthquake triggered collapse of lava dome, sending avalanche/pyroclastic flow to ocean, creating tsunami that killed 15,000 people

28. Killer Events and Processes
Lahars – Kelut, Indonesia, 1586, 1919
Pyroclastic material on slopes of volcano quickly decomposes to fertile soil in tropical climate, bringing people to live on slopes of volcano
Water in summit crater lake is frequently forced out and downhill by intruding magma
Water flowing downhill mixes with old pyroclastic debris from previous eruptions to form huge mudflows  lahar (Indonesian term)
Lahars can flow at velocities of 65 km/hr, tens of kilometers from volcano

29. Killer Events and Processes
Nevada Del Ruiz, Colombia, 1985:
Very high volcano is topped by large ice cap
Initial Plinian eruption sent pyroclastic debris falling down onto ice cap, melting ice, creating lahars 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)
Figure 9.29

30. Killer Events and Processes
Mount Rainier, Washington –
On Alert:
Considered very dangerous by volcanologists because of:
Great height
Extensive glacial cap
Frequent earthquakes
Active hot-water spring systems
Figure 9.32
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

31. Killer Events and Processes
Indirect – Famine
Laki, Iceland Fissure Eruption of 1783
Greatest lava eruption of historic times
Fissure eruption with lava flow of 5,000 m3/sec (1/3 volume of Mississippi River) over 50 days
Accompanied by enormous volume of gases
Haze of SO2 and fluorine killed Iceland livestock  about 20% of population died of famine

32. Killer Events and Processes
Tambora, Indonesia, 1815
Most violent and explosive eruption of last 200 years
Two extremely violent Plinian eruptions tore open the volcano so that 50 km3 of magma erupted in pyroclastic flows over one week
Reduced elevation of mountain from 4,000 m to 2,650 m
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”

33. Side Note: 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
Figure 9.34

34. Killer Events and Processes
Gas
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
Figure 9.35

35. Killer Events and Processes
Gas
Killer Lakes of Cameroon, Africa
Four villages overwhelmed by cloud of gas
Residents lost consciousness – only four awoke
1,700 people killed, 3,000 cattle died, all local wildlife died
Gas was carbon dioxide
Dose determines the poison
Too much 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

36. Killer Events and Processes
Killer Lakes of Cameroon, Africa
Lake eventually became unstable (triggered by unknown disturbance, overturning of water layers), and CO2 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 CO2 again
Degassing pipes installed to allow high-pressure gas to escape before building up to explosive levels
Figure 9.36

37. Killer Events and Processes
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

38. 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

39. VEIs of Some Killer Eruptions
Toba
May have nearly driven human race to extinction due to climate change
Eruption equivalent to 560 Mount Pinatubo eruptions

40. Volcano Monitoring and Warning
Long Valley, California, 1982
Abundant crustal melting (no hot spot), including colossal eruption 760,000 years ago creating Long Valley caldera and erupting pyroclastic debris (Bishop Tuff) hundreds of meters thick
Giant continental caldera
Rare giant eruptions
Frequent small eruptions
Long Valley 600 years ago
Mono Lake ~200 years ago
Figure 9.38

41. Volcano Monitoring and Warning
Long Valley, California, 1982
1980 (few weeks after Mt. St. Helens eruption)
Numerous earthquakes, including four magnitude 6
1982
Resurgent dome rose 25 cm
U.S. Geological Survey issued Notice of Potential Volcanic Hazard, lowest level alert
House prices dropped 40%, tourism diminished
Residents extremely angry – volcano did not erupt
Figure 9.40

42. Volcano Monitoring and Warning
Long Valley, California, early 1990s
Trees began dying on Mammoth Mountain as CO2 leaked from underlying magma into soil
Small earthquakes resumed
Ground surface began rising
Volcanologists hesitant to release alert after ‘false alarm’ of 1982
“Prepare for the worst, but hope for the best”

43. Volcano Monitoring and Warning
Mount Pinatubo, Philippines, 1991
Volcano-warning success story
Largest eruption in 20th 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
Three small steam-blast craters and SO2 gas emissions
Intense monitoring program by U.S. and Philippine scientists began

44. Volcano Monitoring and Warning
Mount Pinatubo, Philippines, 1991
June 7
Degassed magma reached surface, formed lava dome
June 12 (Philippine Independence Day)
Large explosive eruptions began
Evacuation cleared everyone out and closed military base
June 15
Cataclysmic eruption
More than 5 km3 magma and rock, up to 35 km in atmosphere
Pyroclastic flows 200 m deep
Typhoon (hurricane) arrived and washed volcanic debris downslope as lahars

45. Volcano Monitoring and Warning
Mount Pinatubo, Philippines, 1991
Assessment:
300 people killed but millions moved out of harm’s way (20,000 estimated deaths without evacuation)
$500 million property saved (include military aircraft)
Figure 9.41

46. Volcano Monitoring and Warning
Signs of Impending Eruption
Several phenomena are being evaluated as signs of impending eruption
Determine if reliable to justify evacuation
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

47. Volcano Monitoring and Warning
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 m3 magma rose
Gas Measurements
Magma approaching surface loses gas as pressure drops
Mammoth Mountain, California
CO2 from magma killed trees
Declining CO2 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

48. Volcano Monitoring and Warning
Volcano Observatories
In 20th 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, Long Valley and Yellowstone
Each with own websites to report current activity

49. End of Chapter 9