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And I'm Shirley Griffith. Our subject this week is tsunamis -- the sea waves often caused by earthquakes.

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Our broadcast today begins a few years ago on a beautiful day in Thailand.

A British schoolgirl, Tilly Smith, was spending the day at Maikhao Beach in Phuket. Then Tilly saw that the water seemed to have disappeared from the beach. When she looked out to sea, the surface of the water looked strange.

The ten-year-old girl warned her parents. They warned others. People moved away from the water, saving themselves from almost sure drowning. Tilly had recognized the signs of a tsunami. She had studied tsunamis at school.

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The incident produced a major effect on many countries. It has also led to actions to protect against future tsunamis.

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Some people say tsunamis are tidal waves. But tides are the ebb and flow of saltwater against the coast. Tsunamis are not normal tides. Instead, extreme events cause unnatural actions to form tsunamis. Scientists blame strong earthquakes for eighty to ninety percent of tsunamis. Other causes are landslides and underwater or nuclear explosions at sea. Still another is the crash of large asteroids, minor planets that fall to earth.

A tsunami is not just one wave, but a series of waves. Some of the waves can be huge.

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Some scientists say the earthquake that caused the great tsunami of two thousand four measured nine points in intensity. Others say it was nine point three. Whatever the force, it was among the strongest earthquakes many people could remember. The earthquake created a tsunami that killed people in eleven countries.

The earthquake of December twenty-sixth took place just east of the Sunda Trench. The trench is an extremely deep hole on the floor of the Indian Ocean. It stretches about two thousand six hundred kilometers along the island of Sumatra. A tsunami formed near the place where the earthquake began and traveled outward in all directions.

The water reached the northern edge of Sumatra about twenty minutes after the earthquake. In Aceh Province alone, up to one hundred seventy thousand unsuspecting people died in a short time. Pictures taken from the air after the tsunami also showed a shocking loss of land. 

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People all over the world reacted to the killer tsunami. They gave large amounts of money to help the victims. But they also made plans to protect against other terrible waves.

They built or improved existing walls and floodgates to block the waves. And they worked to create or improve tsunami warning systems. Such a system contains sensing equipment that notes danger. The system also operates the processes for spreading warnings to threatened areas.

Some countries, like Japan, already had good warning systems. Earthquakes often strike Japan. Some earthquakes cause tsunamis. Japan has suffered hundreds of tsunami waves over the years. For example, the Great Tsunami in nineteen thirty three killed more than three thousand people. But some tsunami waves were small, and looked just like normal waves.

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The United Nations agency UNESCO created the Intergovernmental Oceanic Commission, or I.O.C., in nineteen sixty. This organization has tsunami warning systems in many places. It supervised creation of a system for nations on the edges of the Indian Ocean after the great earthquake and tsunami of two thousand four.

Twenty-five stations watch for possible earthquake activity. The stations provide information to many national tsunami information centers and several deep ocean sensors. The I.O.C. says its efforts are the beginning of a worldwide tsunami-warning program.

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Continuing disasters in the Indian Ocean made Indonesia decide it must have a warning system of its own. In two thousand five, almost one thousand people were killed in an earthquake near the island of Nias. But the earthquake did not create a tsunami. Still another tsunami took place after an earthquake near Java in two thousand six. That tsunami was not nearly as severe as the one in two thousand four. But it still killed hundreds of people.

Last year, a tsunami warning system began operating especially for Indonesia. The system probably will be completed by two thousand ten.

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The new system is called the German-Indonesian Tsunami Early Warning System, or GITEWS. It has been busy recording earthquakes that could produce huge waves. On February eleventh, GITEWS reported a seven point three earthquake in Indonesia's Talaud Islands near Sulawesi. But no tsunami followed.

GITEWS is a joint project of Indonesia and the German government. Germany's national research center for geosciences organized the project. Germany, Indonesia and other partners helped make it financially possible.

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The Helmholtz Association of German Research Centres described new methods and technologies in the new warning system. The group says less time passes for an earthquake shock wave to reach a measuring instrument than in the past. But it is difficult to read and judge a wave when it is near.

To deal with that problem, the designers developed a special computer software program. They say the program can show the source, placement and size of several strong earthquakes within two minutes.

Another example of new methods in GITEWS involves how a tsunami behaves. A tsunami travels hundreds of kilometers per hour in deep water. But it slows down in water that is not deep. In coastal areas it can swell, or enlarge, to waves of up to thirty meters high.

To save lives, a tsunami must be recognized as such before it can reach land. GITEWS provides nine new measuring stations in the Indian Ocean. That means Indonesia is not the only nation to receive the information. The system also can help other countries.

Technical and mechanical systems are also responsible for getting the news of huge waves to threatened areas. Local officials are responsible for broadcasting warnings as fast as they can, by any method they can.

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The Indian Ocean tsunami of two thousand four was among the worst that ever happened. But the Pacific Ocean area has experienced more of the deadly waves. Experts estimate sixty percent of tsunamis take place there. The Pacific Tsunami Warning Center watches for earthquake activity that could cause tsunamis.

America's National Weather Service is an agency of the National Oceanic and Atmospheric Administration, or NOAA. Its experts serve as part of the Pacific Tsunami Warning System. They also keep watch on the American state of Hawaii from an operations center near Honolulu.

Hawaii suffered major tsunamis during the twentieth century. In nineteen sixty, the Great Chilean Earthquake caused waves that took many lives. That tsunami almost completely destroyed the city of Hilo.

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Last month, eighteen South Pacific countries sent representatives to a tsunami meeting in Samoa. Many expert observers also attended. Those taking part discussed the results of an exercise throughout the Pacific area last October. The exercise tested warning and emergency communications and national and local readiness.

NOAA's National Weather Service center in Palmer, Alaska supervises a warning station for the United States mainland and Canada.

In January of two thousand seven, Canada increased its protection. It opened the Canadian Atlantic Tsunami Warning System. The system was designed to especially protect the nation's Atlantic Ocean coast and the Gulf of Saint Lawrence. Canada's national government, five easternmost provinces and NOAA cooperated in the project.

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This SCIENCE IN THE NEWS was written by Jerilyn Watson. Brianna Blake was our producer. I'm Shirley Griffith.

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And I'm Bob Doughty. Join us again next week for more news about science in Special English on the Voice of America.