Weather Classroom: Tsunami
When you hear the word "tsunami" you might picture a big, towering wave, but that isn't always the case. NOAA defines a tsunami as a series of ocean waves generated by sudden displacements in the sea floor, landslides, or volcanic activity. In the deep ocean, the waves may only be a few inches high. They could come gently on shore, or they increase in height to become a fast moving wall of water.
Tsunami is a Japanese word: "tsu" means harbor and "nami" means wave. Major tsunamis are generated by earthquakes in marine and coastal regions. They frequently occur in the Pacific when oceanic plates slide under continental plates. A tsunami is hard to detect in the open ocean because the wavelength is hundreds of miles long, and the amplitude is only a few feet. When the waves get close to shore, they slow down and the amplitude (or wave height) increases. Water can race inland as far as 1000 ft. and cause catastrophic flooding.
NOAA monitors sea height through a network of buoys and tide gauges, but it is difficult due to the vast expanse of the ocean. They use the DART® system, and that stands for Deep-ocean Assessment and Reporting of Tsunami. It consists of an anchored seafloor bottom pressure recorder which transmits data to a surface buoy. When an event such as an earthquake is detected, the recorder sends data more frequently, and that helps the Pacific Tsunami Warning Center to issue watches and warnings.
The tsunami warning system began in 1946 in the Pacific basin. A warning is issued when a tsunami is imminent and coastal locations should prepare for flooding. A watch is issued to areas outside of the warning area based on the magnitude of an earthquake. Water levels will continue to be monitored, and the warning center will then decide to either cancel or continue the warning.
If a tsunami warning is issued, you should immediately move to higher ground and stay away from the beach until the warning is canceled. Several parts of the U.S. coastline are verified as Tsunami Ready by the National Weather Service, especially in Oregon and Washington.
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