Tsunamis do not have a season and do not occur regularly or frequently. Yet they pose a major threat to the coastal populations of the Pacific and other world oceans and seas. Nothing can be done to prevent them, but the adverse impact on the loss of life and property can be reduced with proper planning.
The National Oceanic and Atmospheric Administration oversees the U.S. Tsunami Program with its mission to provide a 24-hour detection and warning system and increase public awareness about the threat of tsunamis. The NOAA National Weather Service operates two tsunami warning centers that continuously monitor data from seismological and tidal stations, evaluate earthquakes that have the potential to generate tsunamis and disseminate tsunami information and warning bulletins to government authorities and the public. The West Coast/Alaska Tsunami Warning Center in Palmer, Alaska, and the Richard H. Hagemeyer Pacific Tsunami Warning Center in Ewa Beach, Hawaii, are the operational centers of a vigilant 24-hour U.S. tsunami warning system for the Pacific Rim.
The waves radiate outward in all directions from the disturbance and can propagate across entire ocean basins. For example, in 1960 an earthquake in Chile caused a tsunami that swept across the Pacific to Japan. Tsunami waves are distinguished from ordinary ocean waves by their great length between peaks, often exceeding 100 miles in the deep ocean, and by the long amount of time between these peaks, ranging from five minutes to an hour. The speed at which tsunamis travel depends on the ocean depth. A tsunami can exceed 500 mph in the deep ocean but slows to 20 or 30 mph in the shallow water near land. In less than 24 hours, a tsunami can cross the entire Pacific Ocean.
In the deep ocean, a tsunami is barely noticeable and will only cause a small and slow rising and falling of the sea surface as it passes. Only as it approaches land does a tsunami become a hazard. As the tsunami approaches land and shallow water, the waves slow down and become compressed, causing them to grow in height. In the best of cases, the tsunami comes onshore like a quickly rising tide and causes a gentle flooding of low-lying coastal areas.
In the worst of cases, a bore will form. A bore is a wall of turbulent water that can be several meters high and can rush onshore with great destructive power. Behind the bore is a deep and fast-moving flood that can pick up and sweep away almost anything in its path, such as what happened in Papua New Guinea in 1998 when more than 2,000 people were killed and villages destroyed. Minutes later, the water will drain away as the trough of the tsunami wave arrives, sometimes exposing great patches of the sea floor. But then the water will rush in again as before, causing additional damage.
This destructive cycle may repeat many times before the hazard finally passes. Persons caught in the path of a tsunami have little chance to survive. They can be easily crushed by debris or they may simply drown. Children and the elderly are particularly at risk, as they have less mobility, strength and endurance.
Tsunamis typically cause the most severe damage and casualties very near their source. There the waves are highest because they have not yet lost much energy to friction or spreading. In addition, the nearby coastal population, often disoriented from the violent earthquake shaking, has little time to react before the tsunami arrives. The largest tsunamis, however, can cause destruction and casualties over a wide area, sometimes as wide as the entire Pacific Basin. These types of Pacific-wide tsunamis may happen only a few times each century.
in the U.S. Tsunami Program
As with any natural hazard, the more informed the public is, the better are the chances for survival. A strong public education program is one of the components of the National Tsunami Hazard Mitigation Program, a cooperative federal-state program created to help reduce the impacts of potential tsunamis to U.S. coastal areas. Managed by the NOAA Pacific Marine Environmental Laboratory, the program coordinates the efforts of the states of Alaska, Washington, Oregon, California, Hawaii, FEMA, the U.S. Geological Survey and NOAA. As part of this program, PMEL operates six tsunami buoys located off the Aleutian Islands, the Washington/Oregon coast and South America, that send warning signals if they sense a change in sea level. Additional information is available at http://www.pmel.noaa.gov/tsunami-hazard/.
In 1946, a tsunami originating in the Aleutian Islands struck Hawaii and more than 150 people died. The tragedy prompted the development of a warning system for Hawaii and in 1949 the Pacific Tsunami Warning Center was established. Today the Richard H. Hagemeyer Pacific Tsunami Warning Center provides warnings for tsunamis to most countries in the Pacific Basin as well as Hawaii. The center is named for the late director of the National Weather Service Pacific Region who ran the U.S. Tsunami Program for 19 years. During his tenure, the Ewa Beach complex was modernized with many technological upgrades. Hagemeyer also was instrumental in advancing tsunami warning systems around the world. For additional information, visit http://www.prh.noaa.gov/ptwc/.
The West Coast/Alaska Tsunami Warning Center was established in 1967 as a direct result of the great Alaska earthquake that occurred March 27, 1964. Of 132 deaths, 122 were attributed to the Pacific-wide tsunami generated by the magnitude 9.2 earthquake. The Center's area of responsibility covers the West Coast from Alaska to the California-Mexico border. See http://wcatwc.arh.noaa.gov.
The Tsunami Ready Community program was created by the NOAA Weather Service to help communities become prepared for tsunamis through better planning, education and awareness. The program is voluntary and communities must meet certain criteria to receive the designation. Information on how to apply may be found at http://wcatwc.arh.noaa.gov.
The NOAA Weather Service hosts the International Tsunami Information Center in Honolulu, Hawaii, for the Intergovernmental Oceanographic Commission. Publications and other information may be downloaded from http://www.prh.noaa.gov/itic/.
The NOAA Ocean Service
operates an extensive network of tide gauges used by the warning centers
to determine if a tsunami has been generated. Additional information may
be obtained from http://tidesandcurrents.noaa.gov/.
Updated August 2007