Tsunami risk for U.S. mainland?

Monday, January 24, 2005
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Recently, tsunamis ravaged areas of Southeast Asia, destroying entire coastlines and taking thousands of lives. In contrast to what many people believe, tsunamis are not just relegated to foreign islands. The western coasts of the United States and Canada are vulnerable to tsunamis, and have experienced many in the past. Harry Williams a UNT associate professor of geography, spent time researching the often misunderstood phenomenon and the impact it has left in Washington State.

Williams: "A lot of the American public doesn't realize that the U.S. is at risk from these tsunamis as well. It's not just something that happens in Southeast Asia. The Pacific Northwest coastline, where I did my research, certainly has a long record of fairly frequent tsunami impact. Some of the Tsunamis that have struck that coastline have been just as big as the ones that occurred in Southeast Asia." .wav file (25 seconds)

Sometimes confused with tidal waves, tsunamis are actually seismic events that stem from fault lines.

Williams: "A tsunami is a large wave caused by an earthquake on the ocean floor that displaces a large amount of water, and that's what sets up the wave. The wave itself travels very quickly and can cover very long distances."  .wav file (15 seconds) 

Tsunamis generate in areas of the ocean that have fault lines. Certain areas on the Pacific and Indian coasts are more prone to tsunami impact.

Williams: "Well the areas that are prone are those that are exposed to plate boundaries that tend to generate the kind of earthquakes that cause tsunamis. So that would include Southeast Asia, off the coast of Washington and Oregon and British Columbia, and then there's another plate boundary near Alaska that is known to cause the same kind of earthquakes and did cause a large tsunami back in 1964." .wav file (26 seconds)

While there is no way to prevent a tsunami, there are precautions that governments can take to minimize the damage that can occur.

Williams: "What you need to have is a very good system for detecting the earthquake and then getting the warning out to the exposed coastline. The other thing is that you can determine areas that are at risk from a tsunami and then develop evacuation plans. You can strengthen bridges and roadways that are found near sea level." .wav file (23 seconds)

Dr. Williams studied the history of tsunami impacts on the coast of Washington state using a natural record found in local marshes.

Williams: "A tidal marsh has the ability to capture a record of the tsunami. These marshes are made of dead and decaying organic material. When a tsunami comes along, a large wave tends to scoop up sand and then dump it over the top of the marsh so you get a sand layer, which is then buried as plants grow over the years. So if you dig down into these tidal marshes you find these anomalous sand layers, and they potentially are a record of a large tsunami. And that's just what I did in Washington State; I found nine of these sand layers that potentially form a record of nine different tsunamis that have impacted that bay, and the oldest one was around 2500 years old." .wav file (41 seconds)

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