Tsunamis

Often incorrectly called “Tidal Waves”, Tsunamis are usually caused by underwater earthquakes. They can also be caused by underwater land slides or volcanoes or even, rarely, by large meteoric strikes on the ocean. The waves are sent out in all directions.

These disturbances are a series of ocean waves that send surges of water, sometimes reaching heights of over 100 feet, onto land. These walls of water can cause widespread destruction when they crash ashore. Most of these storms, about 80 percent, happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where many volcanoes and earthquakes are common.In deep ocean, these waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than the bottoms of the waves. This difference in speed causes the waves to rise precipitously.

The most infamous tsunami of modern times hit Indian Ocean shorelines on the day after Christmas 2004. That one is believed to have packed the energy of 23,000 Hiroshima-type atomic bombs, and it killed about 228,000 people in a single day.

A slightly earlier disturbance was caused by a giant earthquake (magnitude 9.5), the largest ever measured, on the coast of Chile, May 12,1960. This disturbance killed more than 2000 people and caused damage estimated at $550 million (1960 dollars). From Chile, where most of the 2000 were killed, the tsunami radiated outward in the Pacific Ocean toward Hawaii, killing 61 and Japan, killing 122.

More recently, an 8.3 magnitude earthquake struck At 1748 GMT on Tuesday 29 September, 2009 in the South Pacific, 200 km southwest of Tutuila in American Samoa. This quake triggered a disturbance with 10 foot waves and killed more than 100 people on several islands, Samoa, American Samoa and Tonga. The following graphic is from the USGS Earthquakes Hazards Program. The star shows the location of the quake and the purple line shows the approximate boundary of the underlying plates. The Pacific Oceanic Plate, moving westward at more than 80 mm per year is subducting under the Australian Continental Plate.

NOAA’s Tsunami Warning Efforts

Through NOAA, the United States has made a significant investment in tsunami detection and warning systems since the last catastrophic tsunami occurred in 2004. Although the earthquake that triggered that tsunami was detected, warning systems were not in place in the Indian Ocean region for governments to alert people to evacuate the coasts to safety. As a result, nearly 230,000 people died.

Today, NOAA manages an expanded network of tide and seismic stations, and 39 tsunami buoys positioned throughout the world’s oceans to detect tsunamis. If staff members at NOAA’s Tsunami Warning Centers detect a tsunami threat, they broadcast alerts over an advanced telecommunications infrastructure.

Image Courtesy of NOAA Photo Library

To Science is Exciting From Tsunamis