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

Tsunami Natural Disasters, 7 th edition, Chapter 5

Indian Ocean Tsunami, 26 December 2004 Tsunami swept through Indian Ocean, hitting Asian and African shorelines Estimated 245,000 deaths (probably higher) Seafloor west of Sumatra ruptured northward for 1,200 km over 7 minutes Caused by second largest earthquake (magnitude 9.2) of last 100 years, on subduction zone of Indian- Australian plate under Asian plate Movements on fault of up to 20 m Second earthquake 28 March 2005, magnitude 8.7, south of first rupture

Indian Ocean Tsunami, 26 December 2004 Figure 5.1

Indian Ocean Tsunami, 26 December 2004 Figure 5.3

Tsunami Japanese word: tsu=harbor, nami=waves Tsunami reach greater height when they enter harbor or other narrow space –8 m wave on open coastline  30 m wave in narrow harbor Japan, 1896 –Offshore earthquake shifted seafloor, causing tsunami to hit coastline 20 minutes later –Highest waves (29 m) in narrow inlets –27,000 killed ‘Tidal wave’ inappropriate as not related to tides

Tsunami Created most often by earthquakes –Vertical shift of ocean floor that offsets water mass, transmitted throughout ocean in tsunami –Usually vertical fault motions at subduction zones, mostly in Pacific Ocean 70,000 people killed by 141 tsunami in 20 th century Single tsunami on 26 December 2004 killed about 245,000 people in 13 countries

Tsunami vs. Wind-Caused Waves Wind waves –Single wave is entire water mass –Velocity depends on period of wave 17 mph for 5-second wave; 70 mph for 20-second wave Tsunami –Huge mass of water with tremendous momentum –Velocity: v = (g x D) ½ g – acceleration due to gravity; D – depth of water For average D = 5,500 m, v = 232 m/sec (518 mph) Actual observations of tsunami speed peak at 420 to 480 mph Wave will slow as approaches shore, but still fast

Tsunami vs. Wind-Caused Waves Tsunami –Height: ~1 m in open ocean, 6 to 15 m in shallow water, higher in narrow topography –Wave height is leading edge of sheet of water that flows on land for minutes –Usually series of waves separated by 10 to 60 minutes Tsunami at the shoreline –Not a gigantic version of breaking wave –Very rapidly rising tide, rushing inland –Sometimes water retreats first

Tsunami vs. Wind-Caused Waves Figure 5.4

Tsunami vs. Wind-Caused Waves Earthquake and Tsunami in Chile, 8 August 1868 Large earthquake shook Arica in Bolivia, where several ships were moored in harbor Eyewitness accounts of rising of sea, second earthquake followed by falling of sea, then massive second (phosphorescent) wave hours later which carried ship two miles inland

Tsunami vs. Wind-Caused Waves Tsunami at Hilo, Hawaii, 1 April 1946 Large earthquake in Aleutian Islands of Alaska created tsunami across Pacific Eyewitness accounts of loud hissing sound, with advancing and retreating waves for several minutes Tsunami at Oahu, Hawaii, 9 March 1957 Advancing sheet of water Figure 5.5 Figure 5.6

Wavelength and Period versus Height Destructive power of tsunami is not due to height, but due to momentum of large mass, with ultra- long wavelength and period Tsunami rushes inland for 30 minutes before water pulls back to form next wave Long wavelengths and periods mean waves can bend around islands and hit all shores – no protected shores, as with wind waves

Causes of Tsunami Water mass is hit with massive jolt of energy, such as earthquakes, volcanoes, mass movements, impacts Biggest tsunami caused by rarest events – impacts of asteroids and comets

Earthquake-Caused Tsunami Fault movements of sea floor – must be vertical movement, result in uplifting or downdropping seabed, earthquake of at least magnitude 7.5 Tsunami Warnings –Feel the earthquake –See sea level draw down significantly –Hear wave coming –Seek high ground immediately –Go upstairs in well-built building –Warning system First sensors activated in 2003 Tsunami warning center in Honolulu for Pacific Ocean

Alaska, 1 April 1946 Two large subduction earthquakes in Aleutian islands, shook Scotch Gap lighthouse (steel- reinforced concrete, 14 m above low-water level) Twenty minutes after second earthquake, 30 m tsunami swept lighthouse away (first wave was biggest) Tsunami traveled across Pacific at 485 mph, slowing to 30 mph near Hilo Rushed ashore and killed 159 people in Hilo, despite warnings (April Fool’s Day) Earthquake-Caused Tsunami

Chile, 22 May 1960 Magnitude 9.5 subduction event was most powerful earthquake ever recorded, created large tsunami Three waves, each successively larger, hit Chilean coast, killing 1,000 Chileans Adequate warning was given in Hawaii but 61 people killed Tsunami continued to Japan, killing 185 people Could continue to be measured in Pacific Ocean for a week Earthquake-Caused Tsunami

Alaska, 27 March 1964 Magnitude 9.2 subduction earthquake killed 122 people in sparsely populated Alaskan coast Tsunami hit Vancouver Island, then California Series of waves, with fifth one largest Which wave in series will be largest is not predictable Earthquake-Caused Tsunami

Alaska, 27 March 1964 Earthquake-Caused Tsunami Figure 5.10 Figure 5.11

British Columbia, Washington, and Oregon – upcoming Earthquake-Caused Tsunami Figure 5.12 Most killer tsunami generated at subduction zones All oceans have at least some short subduction zones (Atlantic Ocean’s Puerto Rico trench had magnitude 7.3 earthquake on 11 October 1918, causing submarine landslide and 6 m tsunami hitting Puerto Rico coast) British Columbia, Washington and Oregon coastlines slipped in magnitude 9 earthquake on 26 January 1700, generated massive tsunami recorded in Japan Next event will be deadly Insert revised Figure 5.12 here

Krakatau, Indonesia, August 1883 Volcanic eruptions and explosions increased in frequency and strength, with volcanic masses flowing into sea and creating tsunami Culmination of eruption sequence was collapse of mountain into partially emptied magma chamber, creating tsunami 40 m high More than 36,000 people killed Volcano-Caused Tsunami

Landslide-Caused Tsunami Volcano Collapses –Hawaii in the Pacific Ocean Deposits of slumps and flank-collapses cover more than five times land area of islands Huge tsunami when chunk of island collapses into ocean Figure 5.14 Coastal area southeast of Kilauea (active volcano on Big Island of Hawaii) slides at up to 25 cm/yr into ocean, would create tsunami up to 30 m high, directed to southeast Figure 5.15

Volcano Collapses –Canary Islands in the Atlantic Ocean Three of Canary Islands have had mega-collapses, last one 15,000 years ago Next mega-collapse could send powerful tsunami to coastlines of Africa, Europe, North and South America Models simulate 10 to 20 m tsunami across Atlantic Ocean Flank collapses occur globally about every 10,000 years Figure 5.17 Landslide-Caused Tsunami

Earthquake-Triggered Movements –Newfoundland, Canada, 18 November 1929 Magnitude 7.2 earthquake offshore, triggering submarine mass movement, which set off tsunami Waves arrived at coast of Newfoundland 2.5 hours later, in three pulses over 30 minutes –Papua New Guinea, 17 July 1998 Magnitude 7.1 earthquake 20 km offshore, triggered underwater landslide that caused tsunami Hit coastline of Papua New Guinea about 5 minutes later, washing four villages on barrier beaches into lagoons Rethinking tsunami threat – not caused just by large earthquakes, also by landslides from moderate earthquakes Landslide-Caused Tsunami

In Bays and Lakes –Lituya Bay, Alaska, 9 July 1958 Largest historic wave run-up Magnitude 8 earthquake on Fairweather fault, causing collapse of more than 900 m of rock and ice into Lituya Bay Three boats anchored in bay, hit by huge wall of water about 30 m high, faster than 100 mph Crews of two boats survived being lifted and dropped by wave Wave sent surge of water 525 m up side of bay Landslide-Caused Tsunami

In Bays and Lakes –Lake Tahoe, California and Nevada High in Sierra Nevada, created by active normal faults dropping land between (10 th deepest lake in world) 4% probability of magnitude 7 earthquake on lake-bounding lakes in next 50 years (low frequency) Would drop lake bottom about 4 m, generate 10 m waves across lake Landslide-Caused Tsunami

Seiches Oscillating waves in enclosed body of water – sea, bay, lake, swimming pool Energy from strong winds or earthquakes Hebgen Lake, Montana, 17 August 1959 –Two faults under lake shifted in 6.3 and 7.5 earthquakes –Eyewitness accounts of water migrating from one end of lake to other, over 11.5 hours

If You Feel the Earthquake –Mild shaking for more than 25 seconds: powerful, distant earthquake may have generated tsunami –Sea may withdraw significantly, or may rise, before first big wave –Water may change character, make unusual sounds Tsunami and You

Insert table 5.4

Simuele Island, Indonesia, 26 December 2004 –Closest inhabited land to epicenter of magnitude 9.2 earthquake –After shaking stopped, residents fled uphill immediately –Only 7 out of 75,000 inhabitants were killed –Oral history reminded people: when ground shakes, run to hills before giant waves arrive Nicaragua, 1 September 1992 –Subduction earthquake shifted ground very slowly, creating little ground shaking, but transmitting energy into water very efficiently, generating large tsunami Tsunami and You

Tsunami Warnings –Coastal Maps Tsunami-hazard map of Hawaii Big Island, based on local topography Coastline mapping of Indonesia, India and Sri Lanka after 2004 tsunami indicated where human activities increased damage and loss of life –Removal of vegetation, reefs increased impact of waves –Buoys and Pressure Sensors Before 2004, NOAO operated six-buoy warning system in northern Pacific Ocean Funding since provided for 32 buoys around world, transmitting information to scientists New tide-gauge stations and seismometers along coastlines

End of Chapter 5