1 Natural Disasters Tsunami – The Great Wave Aerial View of Japan Tsunami

2 Alaska Tsunami 1946 Aleutian Island, Alaska (1946) –7.3M; traveled 659 km/hr, slowed to 47 km/hr in Hilo –135’ wave destroyed lighthouse, killed 5 crew members; No warning sent to Hilo Scotch Cap Lighthouse

3 Alaska, 1946 Hilo, Hawaii –Arrived 4.5 hrs. later –150 deaths, 90 in Hilo

4 What is a Tsunami? Abnormally long wavelength wave produced by sudden displacement of water in response to sudden fault movement Also called “seismic sea waves”

5 Tsunami Characteristics Wavelength Wave Height Frequency or Period Velocity

6 Wavelength Distance between two identical points of two successive waves –Crest-to-crest or trough-to-trough Normal ocean waves have wavelength ~100m Tsunami is extremely long of ~500 km

7 Wave Height Distance between crest and trough Tsunami are merely 1 m height in the deep ocean and may go undetected by boats and ships As it approaches land (shallower water), the wave slows and wave height may increase up to 30 m Wave Height

8 Period Amount of time for one full wavelength to pass a stationary point A normal wave’s period is ~5-20 seconds A tsunami’s period is ~10 min. to 2 hours

9 Velocity Speed of wave measured in distance per unit time; V = wavelength/period Normal waves travel ~90 km/hr (55 mph) Tsunami waves travel up to ~890 km/hr (550 mph) –Faster than a jet

10 Tsunami Characteristics Summarized In the deep ocean, tsunami are almost imperceptible with 1-m height waves As wave approaches land (shallower water): –Velocity decreases –Wavelength decreases –Wave height increases –Energy stays the same

11 Crest or Trough If crest approaches shore first, a large wave If trough hits shore first, water recedes (drawdown)drawdown –Followed immediately by crest

12 What Causes a Tsunami? Anything that displaces a large volume of water suddenly Meteor Impacts Landslides Volcanoes Earthquakes

13 Asteroid-Generated Tsunami Probability of a 1 km asteroid colliding with Earth is 1 in every 1,000,000 years Chances are extremely small, but event would be catastrophic Responsible for dinosaur extinction 65 million years ago

14 Volcano-Generated Tsunami Explosions, pyroclastic flows, landslides and debris avalanches are produced by volcanic eruptions Large volume of water is rapidly displaced

15 Volcano-Generated Tsunami Krakatau (1883) –2/3 of island blown away –Generated 3 tsunami –>36,000 killed

16 Volcano-Generated Tsunami Canary Island (potential) –100,000-year recurrence interval –May reach east coast of N. American in 6-7 hours May not be enough time to evacuate large cities

17 Earthquake-Generated Tsunami Usually associated with normal or reverse fault movement –Water is displaced suddenly

18 Earthquake-Generated Tsunami Chile, South America (1960) –9.5M, largest EQ ever recorded –3 rd wave 11 m (30’) high; 1 hour period –909 died; 834 missing –Tsunami Warning System in place

19 Lessons from Chile Hawaii –61 died

20 Chile, 1960 Japan –181 deaths

21 Landslide-Generated Tsunami As large mass of land falls into ocean, a huge volume of water is displaced

22 Landslide-Generated Tsubnami Lituya Bay, Alaska (1958) –150-m high (1700’) wave –Stripped vegetation –Ancient tree trim shows previous occurrence

23 Indonesia Tsunami, 2004 Indonesia (2004) –9.0M EQ; 8 minute duration –15 m offset on thrust fault for 1,200 km length –>283,000 deaths; >10,000 still missing Before After Banda Aceh

24 Tsunami Dangers Drowning Severe abrasion by dragging Thrown against solid objects Carried out to sea in outgoing wave Hit by debris House, cars, trees, rocks

25 Tsunami Hazard Mitigation Land Use Zoning –Build to elevations above flood potential –Structures engineered to resist erosion and scour –Streets and buildings built perpendicular to shore –vegetation

26 The Pacific Tsunami Warning System Two Steps 1.Tsunami Watch –Issued when an earthquake > 7.0M is detected in the Pacific Ocean 2.Tsunami Warning –Significant Tsunami is identified

27 Tsunami Prediction Pressure sensor on ocean floor detects changes in wave height Transmit signal via satellite

28 Surviving a Tsunami 1.If you feel an EQ when near the coast, get to high ground 2.Do not return to shore after initial wave 3.Never go to the shore to watch a tsunami 4.An unexpected rise or fall of sea level may indicate an impending tsunami