An ancient tsunami wrecked Hawaii; it could happen again

"You’re going to have great earthquakes on planet Earth, and you’re going to have great tsunamis," said Rhett Butler.
By Brooks Hays  |  Oct. 21, 2014 at 2:41 PM
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HONOLULU, Oct. 21 (UPI) -- The most destructive tsunami in modern Hawaiian history occurred in 1946. That year, a swelling wall of water, rising ten feet in height, swept across Hawaii's beaches after a magnitude 8.1 earthquake registered near the Aleutian Islands. More than 170 people perished in the disaster, and the island was left reeling from tens of millions of dollars in damage.

As frightening as it sounds, researchers say new evidence suggests a tsunami three times as big devastated the islands some 500 years ago -- what researchers are calling a mammoth tsunami. And now, a new study posits that another mammoth tsunami isn't out of the question.

Evidence of the ancient tsunami was gathered in the 1990s when archaeologists found marine fossils and debris in an inland collapsed limestone cave. Researchers hypothesized a massive tsunami could have carried mollusk shells 328 feet in from the shore. But scientists didn't have enough evidence to confirm their suspicions. That changed in the wake of Japan's 2011 tsunami disaster.

Scientists say the probability of 30-foot wave hitting The Aloha State is only one-tenth of one percent in any given year, as it's believed such an event only happens about once every 1,000 years.

But a small chance is still a chance. Historical and geologic evidence suggested the chance of a 9.0-magnitude earthquake triggering a tsunami off the coast of Japan was also just 0.1 percent. That probability became irrelevant in 2011, when the Tohoku earthquake and tsunami killed nearly 16,000 along Japan's coasts.

"You're going to have great earthquakes on planet Earth, and you're going to have great tsunamis," study author Rhett Butler, a geophysicist at the University of Hawaii at Manoa, said in a press release. "People have to at least appreciate that the possibility is there."

"[The Japan earthquake] was bigger than almost any seismologist thought possible," explained Butler. "Seeing [on live TV] the devastation it caused, I began to wonder, did we get it right in Hawaii? Are our evacuation zones the correct size?"

Japan's tsunami enabled scientists like Butler to build a more accurate model of what might happen should a 9.0-magnitude earthquake register in the Aleutian Islands. The math predicted a scenario that would explain the fossil-filled sinkhole.

"[The researchers] stitched together geological evidence, anthropological information as well as geophysical modeling to put together this story that is tantalizing for a geologist, but it's frightening for people in Hawaii," said Robert Witter, a geologist at the U.S. Geological Survey who wasn't involved in the research.

The study, which was published earlier this month in the journal Geophysical Research Letters, has inspired Hawaii officials to begin redrafting their evacuation plans.

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