Life + Outdoors » Garlick's Notebook

Tsunami Terrors

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Understanding the nature of tsunamis could save your life. They are usually caused by large earthquakes, coastal or submarine. You could expect timely warning of a tsunami generated thousands of miles away, but if our local Cascadia Megathrust is the culprit, the violent shaking would be your cue to head for the highest ground reachable within a few minutes.

Tsunami waves have wavelengths of a few hundred kilometers and travel at almost 800 km per hour in deep water. The first image shows a simulation, by the USGS, of waves 4 hours after their creation by the Magnitude 9 Cascadia quake of Jan 26, 1700, dated by Japanese records. The map shows the propagation of such a tsunami at hourly intervals. It would reach Hawaii in five hours. One generated in Hawaii would reach us in five hours.

The plot of wave height verses water depth explains how a wave may be imperceptible at sea but damaging on the coast. Additionally, long-wavelength waves are more likely to surge than to break. A tide gage at Sitka, 1,000 km from the 1964 Alaskan epicenter, reveals the long duration of tsunami waves.

On March 26, at about 10:30 a.m., there will be a test of NOAA's Tsunami Warning System. Visit www.wrh.noaa.gov/eka/misc/tsunamitest.php for more information.

I thank Prof. Lori Dengler for her input.

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