The earthquake that generated the great Indian Ocean tsunami of 2004 is estimated to have released the energy of 23,000 Hiroshima-type atomic bombs, according to the U.S. Geological Survey (USGS).
Giant forces that had been building up deep in the Earth for hundreds of years were released suddenly on December 26, shaking the ground violently and unleashing a series of killer waves that sped across the Indian Ocean at the speed of a jet airliner.
By the end of the day more than 150,000 people were dead or missing and millions more were homeless in 11 countries, 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 USGS, which monitors earthquakes worldwide. The violent movement of sections of the Earth's crust, known as tectonic plates, displaced an enormous amount of water, sending powerful shock waves in every direction.
The earthquake was the result of the sliding of the portion of the Earth's crust known as the India plate under the section called the Burma plate. The process has been going on for millennia, one plate pushing against the other until something has to give. The result on December 26 was a rupture the USGS estimates was more than 600 miles (1,000 kilometers) long, displacing the seafloor above the rupture by perhaps 10 yards (about 10 meters) horizontally and several yards vertically. That doesn't sound like much, but the trillions of tons of rock that were moved along hundreds of miles caused the planet to shudder with the largest magnitude earthquake in 40 years.
Above the disturbed seafloor the great volume of the ocean was displaced along the line of the rupture, creating one of nature's most deadly phenomena: a tsunami. Within hours killer waves radiating from the earthquake zone 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, at least in human memory. They are most prevalent in the Pacific. But every ocean has generated the scourges. Many countries are at risk. (Read "Tsunami: Facts About Killer Waves" for more about killer waves' causes and warning signsinformation that can be a lifesaver in a tsunami zone.)
For more about the Indian Ocean tsunami of 2004 scroll down the page.
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.
A tsunami may be less than a foot (30 centimeters) in height on the surface of the open ocean, which is why they are not noticed by sailors. But the powerful pulse of energy travels rapidly through the ocean at hundreds of miles per hour. Once a tsunami reaches shallow water near the coast it is slowed down. The top of the wave moves faster than the bottom, causing the sea to rise dramatically.
The Indian Ocean tsunami caused waves as high as 50 feet (15 meters) in some places, according to news reports. But in many other places witnesses described a rapid surging of the ocean, more like an extremely powerful river or a flood than the advance and retreat of giant waves.
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