150Lec10 - Lecture #10: Tsunamis (Abbott, Chapter 5; pp....

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Lecture #10: Tsunamis (Abbott, Chapter 5; pp. 67-68) Introduction A tsunami ( plural: tsunami or tsunamis ) is a large and often destructive water wave that can strike a coast along an ocean, sea or even a large lake. Tsunamis are often mistakenly called "tidal waves." Actually, tsunamis have nothing to do with tides. Instead, they are catastrophic and may result from: 1) underwater earthquakes, 2) volcanic eruptions or landslides on the seafloor or near the coast or 3) from the impact of asteroids or large meteorites in oceans and seas (Table 5.1, p. 112; Figure 17.23, p. 482). Volcanoes can generate tsunamis by producing explosions, triggering landslides, or collapsing. For example, the infamous Krakatau volcanic eruption and collapse that occurred in Indonesia on August 26-27, 1883 produced tsunami waves that sometimes exceeded heights of 40 meters. The Krakatau tsunami killed about 36,000 people (Table 5-1, p. 112; Figure 5.13, p. 120; p. 111). Tsunamis can also be generated by underwater landslides or materials landsliding into coastal waters from islands or continents (for example, rockfalls into Lituya Bay, Alaska, on July 9, 1958; Figures 5.20, p. 124). Past tsunami-generated landslides have occurred in Hawaii (Figure 5.14, p. 121; Figure 5.15, p. 122; Figure 5.16, p .122), and future tsunami are expected to form in Hawaii (Figure 5.24, p. 127; Figure 7.28, p. 182), the Canary Islands off the northwest coast of Africa (Figure 5.17, p. 123), and from loose sediments on the underwater shelves of the continents. Both Hawaii and the Canary Islands are located on hot spots (Lecture #5). The underwater base of the volcanoes consists of relatively weak, water-quenched and fragmented basalts (Lecture #3) that cannot indefinitely support the overlying heavy lava flows that extend far above sea level. Over time the flanks of the volcanoes landslide into the oceans and produce devastating tsunamis. A landslide in the Canary Islands could devastate all of the east coast of North America (Figure 5.17, p. 123). Weak Base of Oceanic Hot Spot Volcanoes:
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Earthquake-generated tsunamis tend to occur along reverse, thrust or normal rather than strike-slip faults. In reverse, thrust and normal faults, the upward movement of hanging walls or footwalls occurs and extensive water displacements are possible. Formation of Tsunamis from Earthquakes from Faults: Tsunamis may travel across a deep and open ocean at speeds as high as 800 kilometers/hour (500 milers/hour or as fast as a jet airliner, p. 113). In deep water, tsunami tend to be very broad, perhaps no more than a meter high with very long periods and wavelengths (Table 5.2, p. 113), and often unnoticeable. As they approach a coastline, they come into contact with the ocean floor, which may cause them to build up to heights of 15 meters or more. Tsunami Formation on Shorelines:
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This note was uploaded on 07/14/2011 for the course GLY 150 taught by Professor Henke during the Spring '08 term at Kentucky.

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150Lec10 - Lecture #10: Tsunamis (Abbott, Chapter 5; pp....

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