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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Volcanism at Subduction Zones 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: 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

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

Killer Events and Processes Figure 9.22

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

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

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

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

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

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

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

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

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

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

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

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

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

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”

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

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

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

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

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

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

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

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

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

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”

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

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

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

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

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

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

End of Chapter 9