Tsunami, Japanese word meaning “harbor wave,” used as the scientific term for a class of abnormal sea wave that can cause catastrophic damage when it hits a coastline. Tsunamis can be generated by an undersea earthquake, an undersea landslide, the eruption of an undersea volcano, or by the force of an asteroid crashing into the ocean. The most frequent cause of tsunamis is an undersea earthquake. When the ocean floor is uplifted or offset during an earthquake, a set of waves is created similar to the concentric waves generated by an object dropped into the water. Most tsunamis originate along the Ring of Fire, a zone of volcanoes and seismic activity, 32,500 km (24,000 mi) long, which encircles the Ocean Pacific. Since 1819, about 40 tsunamis have struck the Hawaiian Islands. A tsunami can have wavelengths, or widths (the distance between one wave crest to the next), of 100 to 200 km (60 to 120 mi), and may travel hundreds of kilomet...
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