The hazards presented by tsunamis have brought many countries in the Pacific basin to establish tsunami warning systems. The government of Japan became the first to establish a national system, named the Tsunami Warning System (TWS), in 1941. The first elements of a similar structure in the United States were created in 1949, before its National Tsunami Warning Center (NTWC) became operational in 1967. Other national warning systems were developed in Russia, starting in 1954, and Chile, starting in 1960, followed by integrated multinational programs for the Pacific basin,
A warning may begin with an alert by a geological society that an earthquake large enough to disturb the ocean’s surface (for instance, magnitude 7.0 or higher) has occurred. Meteorological agencies may then report unusual changes in sea level, and then the warning centre may combine this information with data on the depth and features of the ocean floor in order to estimate the path, magnitude, and arrival time of the tsunami. Depending on the distance from the seismic disturbance, government authorities may have several hours’ notice to order the evacuation of coastal areas. The Pacific Tsunami Warning Center, located near Honolulu, Hawaii, was established in 1949, three years after a tsunami generated by a submarine earthquake near the Aleutian Islands struck the island of Hawaii around Hilo, killing more than 170 people. It serves as one of two regional warning centers for the United States—the other is located in Palmer, Alaska—and since 1965 it has also served as the warning center for 26 countries organized by UNESCO’s Intergovernmental Oceanographic Commission into the International Coordination Group for the Tsunami Warning System in the Pacific. Following the disaster of December 2004, UNESCO set a goal of establishing similar systems for the Indian Ocean, which became operational in 2006, and eventually the entire globe.
Meteotsunamis
A meteotsunami is a sea wave with a height of roughly 2 metres (about 6 feet) or more. In general, they are smaller than seismic tsunamis and are produced by sudden changes in atmospheric pressure, such as during the passing of squalls or storm fronts. The pressure change creates a buckle in the surface of the ocean or a lake, which pushes out in all directions. Like their seismic counterparts, the waves produced by meteotsunamis become larger as they move into shallower water and approach the shoreline, where they often produce storm surges and rip currents. The strongest meteotsunami on record occurred in 1978 at Vela Luka, Croatia, and had waves that reached a height of 5.9 metres (19.5 feet).
Extraterrestrial tsunamis
Tsunami waves are not limited to Earth’s surface. An analysis of the Martian surface conducted in 2016, which examined the desert planet’s northern plains by using photographs and thermal imagery, revealed evidence of two separate tsunami events that occurred long ago. These events are thought to have been caused by comet or asteroid impacts.