Tsunami!

Tidal waves of destruction

CHAPTER 2, CRO #7

What is a tsunami?

• Means “harbor wave” in Japanese.

• A series of tidal waves with long wavelengths. May resemble a rapidly rising tide rather than a high wave, depending on geography.

• Water surges inland rather than breaking and pulling back out to sea.

What causes them?

• Most result from submarine (beneath sea) earthquakes. Can also result from landslides and glacial slides into the sea as well as meteor impacts or large explosions.

• Earthquakes occurring near trenches in subduction zones are most dangerous (see next slide). These produce reverse faults that may drive the sea floor upward.

• These are common in Japan due to the large number of trenches in the western Pacific ocean.

Warning signs

• Tsunami often sneak up to a shore with little warning since they are low and long in deep waters.

• Any strong, shallow earthquake near a trench is cause for concern.

• As the wave approaches shore, it will often pull water back, resulting in a rapid low tide before striking.

Waves are low in deep water but elevate as they move into shallow

water.

Recent Fatal Tsunami

• 1960 Valdivia (Chile) – also affected Hilo, Hawaii. {9.5 earthquake; Peru-Chile trench}

• 1964 Alaska – affected Hawaii and Japan. {9.2 earthquake; Aleutian trench}

• 2004 Indian Ocean- affected Sri Lanka, India, and Indonesia. {9.2 quake; Java trench}

• 2011 Tohuko (Japan) {9.0 quake ; Japan trench}

Video footage

• Japan (2011) – http://www.youtube.com/watch?

v=k4w27IczOTk

• Japan (2011)– http://www.youtube.com/watch?

v=NW7vENdDu1o

• Indian Ocean (2004)– http://www.youtube.com/watch?

v=RDOuwMj7Xzo

Review Questions

• What causes tsunami?• What types of locations are most at risk of

tsunami?• Why is it difficult to detect tsunami in open ocean

water?• How are tsunami different than typical large wind

generated waves?• What are some warning signs that can signal the

need to evacuate a coastal area?