Tsunamis: Facts About Killer Waves

Updated January 14, 2005

The Indian Ocean tsunami generated by the most powerful earthquake in decades on December 26 is believed to have killed more than 150,000 people and made millions homeless, making it perhaps the most destructive tsunami in history.

The epicenter of the 9.0 magnitude quake was under the Indian Ocean near the west coast of the Indonesian island of Sumatra, according to the U.S. Geological Survey, which monitors earthquakes worldwide. A violent movement of the Earth's tectonic plates displaced an enormous amount of water, sending powerful shock waves in every direction.

Within hours killer waves radiating from the epicenter slammed into the coastline of 11 Indian Ocean countries, snatching people out to sea, drowning others in their homes or on beaches, and demolishing property from Africa to Thailand.

Tsunamis have been relatively rare in the Indian Ocean. They are most prevalent in the Pacific. But every ocean has generated the scourges. Many countries are at risk.

In the wake of the Christmas weekend tsunami in the Indian Ocean, one of the worst disasters in history, National Geographic News examines the killer waves' causes and warning signs—information that can be a lifesaver in a tsunami zone.

• A tsunami is a series of great sea waves caused by an underwater earthquake, landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean.

Scientists have found traces of an asteroid-collision event that they say would have created a giant tsunami that swept around the Earth several times, inundating everything except the mountains 3.5 billion years ago. The coastline of the continents was changed drastically and almost all life on land was exterminated. (Read the story)

• Tsunami (pronounced soo-NAH-mee) is a Japanese word. Tsunamis are fairly common in Japan and many thousands of Japanese have been killed by them in recent centuries.

• An earthquake generates a tsunami if it is of sufficient force and there is violent movement of the earth causing substantial and sudden displacement of a massive amount of water.

• A tsunami is not a single wave but a series of waves, also known as a wave train. The first wave in a tsunami is not necessarily the most destructive. Tsunamis are not tidal waves.

• Tsunami waves can be very long (as much as 60 miles, or 100 kilometers) and be as far as one hour apart. They are able to cross entire oceans without great loss of energy. The Indian Ocean tsunami traveled as much as 3,000 miles (nearly 5,000 kilometers) to Africa, arriving with sufficient force to kill people and destroy property.

Scientists say that a great earthquake of magnitude 9 struck the Pacific Northwest in 1700, and created a tsunami that caused flooding and damage on the Pacific coast of Japan. (Read the story)

Continued on Next Page >>


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