Lecture Outlines Natural Disasters, 5 th edition

1. Lecture OutlinesNatural Disasters, 5th edition Patrick L. Abbott

2. Volcano Case Histories: Killer Events Natural Disasters, 5th edition, Chapter 8 Christiane Stidham, Stonybrook University

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 and emitted 230 million m3 lava and 26 million km3 pyroclastic material, increasing size of island by 20% • Destroyed 370 buildings and began to fill in harbor • Icelanders bulldozed lava and ash into barriers to divert lava flow, and sprayed flows with seawater to cool and harden into walls that diverted further flows • Used heat from flows to heat town

5. 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)

6. 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

7. Cascade Range, Pacific Coast United States and Canada • Subduction under Pacific Northwest is responsible for Cascade Range volcanoes • 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

8. 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

9. 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) • 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 fall from eruption cloud • Building of lava dome continues today

10. Lassen Peak, California, 1914-1917 • 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 • 1914-1917: three years of eruptions in May (probably initiated by melting of snow) of ash clouds and collapse of overtopped lava dome, creating pyroclastic flows and lahars

11. Mount Shasta, California • Active volcano – erupted 11 times in last 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 once established settlements persist for centuries

12. Killer Events and Processes Historic Record of Volcano Fatalities • About 275,000 people killed during last 500 years by about 12 processes

13. Pyroclastic Flows • Superhot, high speed turbulent cloud of ash, gas and air – can kill thousands of people in one event 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

14. Pyroclastic Flows 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 in all directions • Overran nine villages, killed 2,000 people • Plinian column up to 20 km high • Two more pyroclastic surges and Plinian columns • Change in global climate

15. Pyroclastic Flows Mount Unzen, Japan, 1991: • Unique insteady magma supplyand topography  chunks of lava dome frequently break off creating pyroclastic flows • 7,000 pyroclastic flowsbetween 1991 and 1995 • 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 Kraffts

16. Pyroclastic Flows Mount Pelee, Martinique, 1902-1903, 1929-1932: • Most pyroclastic flows from hot ash and gas overspilling crater • Few deadliest pyroclastic flows generated by directed blasts • 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

17. Tsunami • Krakatau eruption and caldera collapse in 1883 killed more than 36,000 people • Less than 10% killed directly by volcanic eruptions • More than 90% killed by volcano-caused tsunami • Mt. Unzen, Japan, 1792: earthquake triggered collapse of lava dome, sending avalanche/pyroclastic flow to ocean, creating tsunami that killed 15,000 people

18. 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

19. Lahars Nevada Del Ruiz, Colombia, 1985: • Very high volcano is topped by large ice cap • Initial Plinian column eruption sent pyroclastic debris falling down on to ice cap, melting ice and creating lahars flowing down mountain and killing 1,800 • Later eruptions melted more ice, creating bigger and 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)

20. Lahars 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

21. 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

22. Indirect – Famine 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% by eruption • 90% from famine or disease, after pyroclastic fallout damaged crops

23. Death at Ashfall, Nebraska • 10 million years ago – waterholes in grassland savanna, migrating wildlife • Eruption at Yellowstone 1,300 km away blanketed Nebraska with 0.3 m thick layer of volcanic ash, reworked by wind and dumped 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

24. 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 • 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

25. Gas Killer Lakes of Cameroon, Africa • Lake water is stratified, with densest water at bottom absorbing leaked carbon dioxide and trapping it there • 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 and more is continually being added • 20 years for lake water to become oversaturated in CO2 again • Pump system could be installed to degas lake water

26. 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

27. VEIs of Some Killer Eruptions • Does energy of eruption correlate to number of fatalities? • VEI is semi-quantitative estimate of magnitude of volcanic eruption, usingvolume 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

28. 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 150-250 years ago

29. 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

30. 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”

31. 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 began

32. Volcano Monitoring and Warning Mount Pinatubo, Philippines, 1991 • June 7 • Degassed magma reached surface, formed lava dome • June 12 • 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) blew in and washed volcanic debris downslope as lahars

33. 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)

34. 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

35. Volcano Monitoring and Warning Ground Deformation • Ground surface rises and falls in response to magma movement • Measured with tiltmeters, strainmeters, 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 is killing trees, increasing worry about impending eruption • 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

36. End of Chapter 8