Scientists say rising temperatures on Earth's surface are to blame for rising sea levels. The reality of rising sea levels means many coastal and island communities are at risk when a tsunami strikes. The island state of Hawaii is taking steps to prepare for tsunami waves. Officials there want to be ready if such an event takes place.
In 2011, a strong earthquake struck northeastern Japan. The quake caused a tsunami. The huge waves damaged several nuclear reactors in the area. Those events led Hawaiian officials to reconsider their plan of action for dealing with a tsunami.
Scientists and emergency officials in the state are now preparing for an extreme tsunami -- the kind that comes every 500 to 1,000 years.
Almost 19,000 people died when the earthquake and tsunami struck Japan four years ago. Scientists say the Hawaiian Islands may be just as helpless if such a disaster were to take place there.
Rhett Butler is a researcher at the University of Hawaii. He says a mysterious hole on the island of Kauai has evidence that a huge tsunami hit Hawaii 500 years ago. David Burney discovered the evidence. He found remains of old shells, coral and other sea creatures in a cave about 100 meters from the ocean.
瑞德·巴特勒（Rhett Butler）是夏威夷大学的一名研究员。他说，考艾岛上的一个神秘洞穴存在证据可以证实500年前有一次巨大海啸袭击了夏威夷。大卫·伯尼（David Burney）发现了这些证据。他在距离海洋100米左右的一个山洞里发现了旧贝壳、珊瑚和其它海洋生物的遗骸。
Civil defense agencies keep people prepared by testing their tsunami warning system.
Scientists say a major tsunami could happen again. They warn that if a powerful earthquake struck the Aleutian Islands in the northern Pacific, a super tsunami could follow.
A researcher at the University of Hawaii created a computer model to show what would happen if an earthquake struck the Aleutians and produced a tsunami. The model showed the waves from a major quake could move further inland across Hawaii than officials thought, deep into areas considered safe.
The Hawaii Emergency Management Agency works with local governments to create disaster plans. Kevin Richards is an emergency planner with the agency. He says before the computer model, Hawaiian officials thought they would only have to evacuate 85,000 people from the island of Oahu.
"If this event took place, we'd have to move 340 and 350,000 people to safety -- a much more daunting task. And safety is not in the same place any more. It's much further away, it's further up the hill -- it's further inland."
Some Hawaiians could drive to higher ground. But driving is not possible in some parts of Hawaii. So people would have to walk to safety or go to the fourth floor or higher of a reinforced concrete building.
Officials are now developing a new plan of action, with an extended evacuation zone for an extreme tsunami. Scientist Rhett Butler says because of what happened in Japan in 2011, people take the threat seriously.
"It doesn't mean it's gonna happen in our time. It doesn't mean it's gonna happen this year or next year. But it's just the nature of the tectonic forces on our planet. They just keep marchin(g) along, and once you relieve all these stresses with these truly great earthquakes, the water responds."
I'm Christopher Cruise.