This satellite image of the island of Sri Lanka and the Indian Ocean around it was taken on December 26, 2004. The camera, part of an instrument called MISR, points forward at an angle, so catches shadows and reflections that cameras looking straight down do not see.
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?
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.
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!
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.
The MISR (short for Multi-angle Imaging SpectroRadiometer) instrument on the Terra satellite happened to be orbiting and taking images over Sri Lanka just a few hours after the first tsunami wave hit. Huge waves continued to arrive for many hours afterward, so the ocean surface was still rocking and rolling.
On March 11, 2011, a magnitude 8.9 Earthquake under the ocean near Japan caused a huge tsunami to hit the coast. These two images from MISR show the coastline before (left) and after (right) the severe flooding from the tsunami. In these pictures, vegetation appears red and water appears blue.
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 46°. 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.
This series of MISR pictures was 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.
