Tsunamis

GEOL 4093 Risk Assessment

Tsunamis

• Also known as “seismic sea waves”

• Generating force is not wind, but movement of the sea floor, volcano, landslide, etc.

• Travel rapidly over great distances

Tsunami Characteristics

• Extremely long wavelengths (100-200 km)

• Long periods (10-20 minutes)

• Low wave heights (1-2 meters)

• Shallow water waves

As the tsunami wave gets closer to shore, its speed decreases but its wave height greatly increases.

Tsunami in Hilo, Hawaii from 1946 Aleutian Islands Earthquake

1960 Chile Earthquake

• Magnitude 9.5

• Earthquake deaths in the thousands

• Tsunami deaths:– Hawaii—61– Japan—120– Phillipines—20

Tsunami damage from 1960 Chilean earthquake

Computer simulation of tsunami caused by 1960 Chilean Earthquake. Time: 0:00.

Time: 1:40 hrs

Time 3:20 hrs

Time 5:00 hrs

Time 10:00 hrs

Time 15:00 hrs

Time 20:00 hrs

Time 25:00 hrs

A wave front rushes up the Wailuku River in Hilo, Hawaii, during the tsunami of 1 April 1946.

Tsunami in Hilo Hawaii, on April 1, 1946

Tsunami in Hilo, Hawaii from Aleutian Islands earthquake

Scoth Cap Lighthouse was destroyed by tsunami from Aleutian Islands earthquake of April 1, 1946. The lighthouse stood 30 feet above sea level

The next three slides show the sequential arrival of a tsunami at Laie Point, Oahu Island, Hawaiian Islands.

The 8.3 magnitude 8.3 earthquake of March 9, 1957 in Alaska generated a tsunami that struck the beachfront of Hawaii, about 3,600 km from the generating area.

Japan, July 1993. The largest tsunami to strike Japan in recent times. Waves washed 29 meters (97 feet) above sea level; 120 people died.

In addition to the Pacific-wide early warning system (A) there are also regional warning systems (B-F), which warn residents about 10 minutes or 100-750 km from source. THRUST: A local

warning system to warn within 100 km from the source.

Not all tsunamis are caused by earthquakes. Here a landslide at the far end of this Alaska bay destroyed a forest in the foreground.

Krakatau, Indonesia, famous for its devastating 1883 eruption, one of the largest in history. Tsunamis reached heights of 40 m killed 36,000 people on the low shores of Java and Sumatra.

Tsunami inundation maps show areas of potential flooding.

Seiches

• Periodic standing-wave oscillation of water surface

• Occur in enclosed basins

• Travels back and forth at regular intervals

• Can be caused by winds, currents, pressure, earthquakes, landslides

Water sloshes up and down around a central node

The 1989 Loma Prieta earthquake was near enough to Monterey Bay to initiate seiche waves in the bay.