The reality of rising sea levels caused by climate change means many coastal communities and island nations are vulnerable to tsunamis. The U.S. island state of Hawaii is vulnerable to tsunamis and is in the forefront of preparations for a tidal wave. But the devastating 2011 earthquake and tsunami in Japan led Hawaii officials to re-evaluate their plans.
Scientists and emergency managers are now preparing for an extreme tsunami, the kind that comes once in 500 or 1,000 years.
The 9.0 magnitude earthquake and resulting tsunami claimed nearly 19,000 lives when it struck the Tohoku region of northeastern Japan four years ago. Scientists say that Hawaii may be just as vulnerable.
University of Hawaii researcher Rhett Butler says a mysterious sinkhole on the island of Kauai shows signs that a massive tsunami swept through the islands 500 years ago.
“It’s geology. You’re looking for evidence that the ocean came onshore as a sand layer or a bunch of basalt cobbles. You’re looking for that kind of evidence," said Butler.
The evidence was uncovered by paleobiologist David Burney, who discovered old coral, shells and ocean sediment in a cave atop a slope 100 meters from the ocean.
Civil defense agencies keep the public prepared, frequently testing their tsunami warning system.
Scientists say a major tsunami could happen again. They say a theoretical 9.3 magnitude earthquake in the Aleutian Islands in the northern Pacific could create a super tsunami.
University of Hawaii researcher Kwok Fai Cheung devised a computer model to simulate the waves from a huge Aleutian earthquake.
“I used it as input to my tsunami model and simulated the propagation of the tsunami all the way across the Pacific Ocean from the Aleutian Islands to Hawaii," said Cheung.
The results were sobering. The computer model shows that tsunami waves could sweep inland, far beyond current safety zones.
The Hawaii Emergency Management Agency works with local governments to draw up disaster plans. Emergency planner Kevin Richards says the old strategy called for evacuation of 85,000 people on the island of Oahu.
“If this event took place, we’d have to move 340,000 or 350,000 people to safety, a much more daunting task. And safety is not in the same place anymore. It’s much farther away, it’s farther up the hill, it’s farther inland," said Richards.
Some residents could drive to higher ground. But driving is impractical in some parts of the islands, so residents there could walk to safety or take shelter on the fourth floor of a reinforced concrete building. New plans are being devised with an extended evacuation zone for an extreme tsunami.
The Japanese tragedy of 2011 is still fresh in the memory of Hawaii residents, and scientist Butler says they take the threat seriously.
“It doesn’t mean it’s going to happen in our time. It doesn’t mean it’s going to happen this year or next year. But it’s just the nature of the tectonic forces on our planet. They just keep marching along, and once you relieve all these stresses with these truly great earthquakes, the water responds," he said.
And water is part of life on these islands.