On December 26, 2004, a powerful earthquake occurred on the seafloor just off the coast of northern Indonesia. The earthquake measured at a magnitude of 9.0 and led to the worst tsunami that occurred in the past 40 years. The tsunami raced across the ocean at speeds up to 500 mph and reached some shores in just a matter of minutes. Some locations, including those on the other side of the Indian Ocean, anticipated the arrival of the tsunami for over 8 hours. The huge wave crashed onto the coasts of Indonesia, Malaysia, Thailand, Myanmar, India, Sri Lanka and other Asian and African countries.

Total devastation occurred in just minutes as the enormous wave, measuring between 10 and 40 feet, crashed onto the shores. Beaches and coastlines were washed away and modified in shape due to the speed and force of the intense waves and retreating water. Towns were flattened completely, trees and other vegetation were ruined, and as of January 5, 2005, the tsunami led to over 155,000 deaths of those who were unprepared. Water and airborne diseases were responsible for even more deaths after the water receded.

• South Asia Tsunami

• Indonesia

• Sri Lanka

• Maldives

• Thailand

• India

• Supplementary Materials about Tsunamis

The coastline of Sumatra, near the fault boundary, received waves over 10 meters (33 feet) tall, while those farther away (Sri Lanka and Thailand) were caught by waves over 4 meters (13 feet). On the other side of the Indian Ocean, Somalia and the Seychelles were struck by waves approaching 4 meters in height (13 feet).

Although the epicenter of the earthquake that triggered the tsunami was near the northern tip of Sumatra, the sea floor shifted along an arc stretching about 1200 km to the north. This shifting pushes a mass of water across the Indian Ocean. Wave travel times ranged from minutes (Sumatra) to 8 hours (Somalia) or more.

The effects of coastline flooding and strong coastal erosion can be observed.

The 'before' image was taken by NASA's Terra satellite on December 17, 2004 and the 'after' image was taken on Dec. 29, 2004.

On December 17, the green vegetation along the west coast appears to reach all the way to the sea, with only an occasional thin stretch of white that is likely sand. After the earthquake and tsunamis, the entire western coast is lined with a noticeable purplish-brown border.

The brownish border could be deposited sand, or perhaps exposed soil that was stripped bare of vegetation when the large waves rushed ashore and then raced away. Another possibility is that parts of the coastline may have sunk as the sea floor near the plate boundary rose.

On a moderate-resolution image such as this, the affected area may seem small, but each pixel in the full resolution image is 250 by 250 meters (820 by 820 feet). In places the brown strip reaches inland roughly 13 pixels, equal to a distance of 3.25 kilometers, or about 2 miles.

On December 26, 2004, the Indonesian province of Aceh was hit the hardest by the earthquake and tsunamis that followed.  Sumatra, an island where Aceh is located, received the largest waves leading to the flattening of towns and devastating fatalities.

The town of Lhoknga, on the west coast of Sumatra near the capital of Aceh, Banda Aceh, was completely destroyed by the tsunami. The only building that was not destroyed was the mosque, the large white feature, in the center of the city.

Most of the vegetation was wiped out as the tsunami flattened buildings, trees, and everything else in its path.  Beaches and coastlines were washed away and modified in shape due to the speed and force of the intense waves and retreating water.  Lakes and streams were flooded and piers were submerged in water. 

The low-lying agricultural areas remained covered with water and debris several days after the tsunamis

The 'before' image was taken by Space Imaging's IKONOS satellite on Dec. 3, 2003 and the 'after' image was taken on Dec. 27, 2004.  The 'after' image is cloudy and hazy so the level of detail is not as good as in the 'before' image.

The imagery shows sand and debris on the runway, debris and damage to the coastline and damage to structures on the sand jetties. Other changes visible in the images may have been produced by human development along the coast (like the sand bar in the lagoon).