The people in south Asia had no warning of the next disaster rushing toward them the morning of December 26, 2004. One of the strongest earthquakes in the past 100 years had just destroyed villages on the island of Sumatra in the Indian Ocean, leaving many people injured. But the worst was yet to come--and very soon. For the earthquake had occurred beneath the ocean, thrusting the ocean floor upward nearly 60 feet. The sudden release of energy into the ocean created a tsunami (pronounced su-NAM-ee) event--a series of huge waves. The waves rushed outward from the center of the earthquake, traveling around 400 miles per hour. Anything in the path of these giant surges of water, such as islands or coastlines, would soon be under water.

The people had already felt the earthquake, so why didn't they know the water was coming?

Energy from earthquakes travels through the Earth very quickly, so scientists thousands of miles away knew there had been a severe earthquake in the Indian Ocean. Why didn't they know it would create a tsunami? Why didn't they warn people close to the coastlines to get to higher ground as quickly as possible?

In Sumatra, near the center of the earthquake, people would not have had time to get out of the way even if they had been warned. But the tsunami took over two hours to reach the island of Sri Lanka 1000 miles away, and still it killed 30,000 people!

In the Pacific Ocean, a tsunami warning system has been installed. Sensors on the ocean floor and buoys on the ocean surface detect an earthquake and a resulting tsunami. Transmitters on the buoys send warning signals to satellites orbiting overhead. The satellites relay the warning to ground stations, where scientists can quickly feed the data into a computer and calculate when and where a tsunami might hit and how high the waves might be when they reach the coastline where people live. Then a message or signal can be sent warning people to evacuate to high ground. This animation [courtesy of the U.S. National Oceanic and Atmospheric Administration (NOAA) and U.S. National Tsunami Hazard Mitigation Program] shows how it works, using one of the GOES satellites operated by NOAA.

It is important, though, to understand just how the tsunami will behave when it gets near the coastline. As the ocean floor rises near a landmass, it pushes the wave higher. But much depends on how sharply the ocean bottom changes and from which direction the wave approaches. Scientists would like to know more about how actual waves react.

MISR has nine cameras all pointed at different angles. So the exact same spot is photographed from nine different angles as the satellite passes overhead. The image at the top of this page was taken with the camera that points forward at 46º. The image caught the sunlight reflecting off the pattern of ripples as the waves bent around the southern tip of the island. These ripples are not seen in satellite images looking straight down at the surface. Scientists do not yet understand what causes this pattern of ripples. They will use computers to help them find out how the depth of the ocean floor affects the wave patterns on the surface of the ocean. Images such as this one from MISR will help.

Click on this image to see an animated series of MISR pictures taken over six minutes on December 26, 2004. It shows tsunami waves breaking on the southeast coastline of India.

Images such as these from MISR will help scientists understand how tsunamis interact with islands and coastlines. This information will help in developing the computer programs, called models, that will help predict where, when, and how severely a tsunami will hit. That way, scientists and government officials can warn people in time to save many lives.