Tsunami is a Japanese word meaning "harbor wave," a rather benign term for such a disastrous natural event.
The Indian Ocean tsunami of 26 December 2004 riveted world attention on this phenomenon. Numerous tourist videos showed rising waters sweeping away people and structures. News reports showed the tragic human aftermath. Satellites captured the westward movement of wave trains across the Indian Ocean that took several hours to travel from Indonesia to the east coast of Africa.
A tsunami is a "packet" of energy radiating outward from its point of origin. It is triggered by a powerful underwater event that imparts a massive pulse of energy to the sea.
In the deep open ocean, the wave pulses will have such little height that ships will not notice them even though they could be moving at several hundred miles per hour. As the packet nears shore, it begins to "feel" the bottom. The wave begins to increase in height and slow down. The wave height at the y coastline is largely determined by the shape of the sea floor and the configuration of the coast. Heights over 100 feet have occurred when the tsunami's energy is focused on a narrow, steep coastline. There is evidence of this in an Alaskan fjord where waves destroyed trees hundreds of feet above sea level.
Tsunamis can be initiated four different ways. Most common is a sudden vertical sea floor displacement resulting from plate movement-an earthquake. Most of these tsunamis happen in the Pacific Ocean region. Earthquake detection and epicenter location provide the first indication of a possible tsunami.
Underwater landslides are a second source. This happens when large subsea "hillsides," mostly on the continental shelf, suddenly break away and tumble into deep ocean basins. Being close to shore, there is little time to warn nearby coastal communities. There are several places where conditions are right for these events. Two large sites have been found off the U.S. East Coast and another is underwater at the active Kilauea volcano on the island of Hawaii.
Tsunamis can also occur with the massive collapse of coastal land into the sea. Some researchers point to the Canary Islands, where an entire side of a mountain could break off into the sea. If it happened suddenly, with a large enough piece of mountain, a tsunami could be generated, threatening the U.S. East Coast.
The fourth, and possibly most damaging of all, is an object from space hitting the ocean. This happened in the past and will certainly happen in the future, however their frequency makes this an extremely rare event. The bestknown example occurred 65 million years ago when a large asteroid slammed into the edge of the Yucatan Peninsula, creating a massive tsunami that swamped the peninsula and surged into what is now the U.S. midwest.
Early warning is possible using a large network of sensitive tidal and pressure gauges. An earthquake is first detected by seismographs. If triangulation shows an undersea location, then the tsunami warning network is monitored. Wave trains radiating out from the epicenter will show sea level rise as they pass through the detection sites. An alert is transmitted, hopefully providing time for coastal area residents in the path of the waves to evacuate. However, inhabited areas close to the epicenter would not have enough time to react.
The only tsunami detection network in existence has monitored the Pacific Rim for several decades. The lack of a system in the Indian Ocean is being quickly remedied with the first elements of a $30 million system to be in place this year.
The Indian Ocean disaster was no surprise. Characteristics of the geologic plates on the east side of that ocean basin show that this has happened before and will happen again. When the Indonesian Island of Krakatau exploded in 1883, there was a massive loss of life from its tsunami, which reached as high as 120 feet. Lack of a detection system in this ocean is thus not due to an unexpected event, but rather to a lack of investment by the region's coastal nations.
The Atlantic region is not immune. In 1755, a massive tsunami leveled the lower part of Lisbon, Portugal. Newfoundland lost more than 29 people in a 1929 tsunami and, in the past 500 years, 88 tsunamis have been recorded in the Caribbean Sea. This year, the United States announced construction of an Atlantic-Carribean system that should be in place by 2007.