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People flee as a destructive tsunami comes ashore in
downtown Hilo, Hawaii in 1946.
Tsunamis are large ocean waves generated by major earthquakes beneath the ocean floor. Tsunamis caused by nearby earthquakes may reach the coast within minutes. When the waves enter shallow water, they may rise to devastating force. People on the beach or in low coastal areas need to be aware that a tsunami could arrive within minutes after a severe earthquake.
Tsunamis also may be generated by very large earthquakes far away in other areas of the Pacific Ocean. Waves caused by these earthquakes travel at hundreds of miles per hour, reaching the Pacific Northwest several hours after the earthquake. The International Tsunami Warning System monitors ocean waves after any Pacific earthquake with a magnitude larger than 6.5. If waves are detected, warnings are issued to local authorities, who can order evacuation of low lying areas if necessary.
HISTORIC TSUNAMIS IN THE UNITED STATES
Twenty-four tsunamis have caused damage in the United States and its territories during the last 204 years. Just since 1946, six tsunamis have killed more than 350 people and damaged a half billion dollars of property on Hawaii, Alaska and the West Coast.
Tsunamis have historically been rare in Oregon. Since 1812, Oregon has experienced about a dozen tsunamis with wave heights greater than 3 feet; some of these were destructive. Ten of these were generated by distant earthquakes near Alaska, Chile or Japan. The worst damage and loss of life resulted from the 1964 Alaskan earthquake.
Oregon Department of Geology and Mineral Industries
800 NE Oregon Street #28, Suite 965, Portland, OR 97232-2162
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