Lecture #10: Tsunamis
(Abbott, Chapter 5; pp. 67-68)
) 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).
generate tsunamis by producing explosions, triggering landslides, or collapsing.
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).
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
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: