Powerpoint Presentation Physical Geology, 10e

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TsunamiNatural Disasters, 6th edition, Chapter 5
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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

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Indian Ocean Tsunami, 26 December 2004
Figure 5.1
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Indian Ocean Tsunami, 26 December 2004
Figure 5.3
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Tsunami

• 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
  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

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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 20th
  century
• Single tsunami on 26 December 2004 killed about
  245,000 people in 13 countries

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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

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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

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Tsunami vs. Wind-Caused Waves
Figure 5.4
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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

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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 5.6
Figure 5.5
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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

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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

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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

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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
  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 Fools Day)

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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

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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

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Earthquake-Caused Tsunami
Alaska, 27 March 1964
Figure 5.10
Figure 5.11
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Earthquake-Caused Tsunami
British Columbia, Washington, and Oregon
upcoming

• 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
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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

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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

• 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
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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
  America
• Models simulate 10 to 20 m tsunami across
  Atlantic Ocean
• Flank collapses occur globally about every 10,000
  years

Figure 5.17
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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

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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

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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
  frequency)
• Would drop lake bottom about 4 m, generate 10 m
  waves across lake

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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

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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

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Tsunami and You