Tsunami of Christmas 2004

Christmas 2004 was a time people around the world were not soon to forget. By the time December 26th was over, a tsunami would pound the coasts of eight nations, destroying homes and businesses and killing 157,577 people. An additional 26,763 were missing. The human suffering from the tsunami was unbelievable. Four nations, Indonesia, Thailand, Sri Lanka, and India were affected the most while Malaysia, Maldives, Seychelles, and Somalia also posted deaths and damage. Thailand’s notable international tourist areas and the poorest rural areas of other countries were the most severely hit. Very few people knew that they were in the path of destruction until they saw the wall of water rush toward them. Many were washed out to sea.

The tsunami (a Japanese word that means “harbor wave”) began as many but not all tsunamis begin: as an earthquake under the ocean. This 9.1 magnitude earthquake was located under the Indian Ocean 18.6 miles deep in the ocean’s crust. The epicenter was 155 miles south-southeast of Banda Aceh, off Indonesia’s Northern Sumatra island. Of the four earthquakes in the area since 1900 which measured over 9.0 and triggered tsunamis, three were located in the Pacific Ocean. According to Jim Devine, the senior science advisor to the U.S. Geological Survey’s director, 9.0 magnitude earthquakes happen about every ten years but rarely with epicenters in the Indian Ocean. The Christmas earthquake of 2004 was the largest in 40 years.

The epicenter of the earthquake happened to be close to the point where the counterclockwise moving Australian, the Indian, and the Burmese plates meet. Ordinarily, the Indian plate slides past the Burmese plate without trouble in a northeasterly direction at about 6 centimeters per year. At about 00:58:53 UTC on December 26, the two plates collided, forcing the Indian plate to be subducted under the Burmese plate and creating seismic waves. The ruptured crustal patch was later estimated by the USGS to be over 600 miles long and about the size of the state of California. In that area the ocean floor moved horizontally about 10 yards and vertically several yards. According to the USGS, the energy emitted by this megathrust earthquake equaled the energy of 23,000 atomic bombs like those that destroyed Hiroshima. When several meters of the ocean’s floor raised with the force of the plate’s collision, several hundred cubic kilometers of seawater was displaced.

Think of the concentric circles which spread outward when a pebble is dropped into a basin of water. That is similar to the huge seismic and tsunami waves which had their origin at the earthquake epicenter. The tsunami waves would be hardly noticeable on the surface of the deep water, perhaps cresting to a maximum of three feet. Deep below the surface of the waters the energy of the wave travels at speeds of up to 435 miles per hour. The power and energy surges across thousands of miles of ocean floor with little resistance.

Then the first tsunami wave encounters the shallower coastal areas. Friction and turbulence rob the bottom of the wave of some of its speed and energy. The shoreline water recedes several hundred meters. Large areas of beach and ocean floor are left uncovered as if the water were suddenly sucked seaward. In about five minutes, the first tsunami wave hits, the top waters still traveling at the same speed as they had at the earthquake’s epicenter. From then on at five to forty minute intervals the successive tsunami waves surge ashore at about 45 miles per hour. In some places, the tsunami waves that came crashing onto land were about fifty feet high.

The tsunami waves reached Indonesia in about one hour from the time they were created by the earthquake. Thailand was hit at about the four hour mark, and Somalia, 3000 miles away from the epicenter, saw its first tsunami wave in about ten hours.

It took 32 hours and 34 minutes after the December 26, 2004, earthquake for the tsunami waves, now only about 13.4 inches high, to come ashore at Port Canaveral, Florida. By then, the whole world was aware of the devastation and death toll in the Indian Ocean perimeter.

http://www.pbs.org/newshour/bb/asia/july-dec04/tsunami_12-27.html interview of Jim Devine, senior science advisor to the director of the U.S. Geological Survey by Gwen Ifill of Online Newshour