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Powerpoint Presentation Physical Geology, 10e


Tsunami swept through Indian Ocean, hitting Asian and African shorelines ... Eyewitness accounts of loud hissing sound, with advancing and retreating waves ... – PowerPoint PPT presentation

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Title: Powerpoint Presentation Physical Geology, 10e

TsunamiNatural Disasters, 6th 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
  • Japanese word tsuharbor, namiwaves
  • Tsunami reach greater height when they enter
    harbor or other narrow space
  • 8 m wave on open coastline ? 30 m wave in narrow
  • 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

  • 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 20th
  • 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
  • Tsunami
  • Huge mass of water with tremendous momentum
  • Velocity v (g x D) ½
  • g acceleration due to gravity D depth of
  • 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
  • Tsunami at the shoreline
  • Not a gigantic version of breaking wave
  • Very rapidly rising tide, rushing inland

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
  • Tsunami at Oahu, Hawaii, 9 March 1957
  • Advancing sheet of water

Figure 5.6
Figure 5.5
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,
  • 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

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

Earthquake-Caused Tsunami
Alaska, 27 March 1964
Figure 5.10
Figure 5.11
Earthquake-Caused Tsunami
British Columbia, Washington, and Oregon
  • Most killer tsunami generated at subduction zones
  • All oceans have at least some short subduction
    zones (Atlantic Oceans 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

Figure 5.12
Volcano-Caused Tsunami
  • Krakatau, Indonesia, 26-27 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

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
  • 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 5.14, 5.15
Landslide-Caused Tsunami
  • 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
  • Models simulate 10 to 20 m tsunami across
    Atlantic Ocean
  • Flank collapses occur globally about every 10,000

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
  • 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 (10th deepest lake
    in world)
  • 4 probability of magnitude 7 earthquake on
    lake-bounding lakes in next 50 years (low
  • Would drop lake bottom about 4 m, generate 10 m
    waves across lake

  • 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
  • Eyewitness accounts of water migrating from one
    end of lake to other, over 11.5 hours

Tsunami and You
  • 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
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