Study: 30-Foot-Tall Tsunami Waves Hit Hawaii 500 Years Ago

Researchers have uncovered evidence of a devastating earthquake that brought a tsunami on the Hawaiian island of Kauai around 500 years ago, hinting that a similar event could damage Hawaii's shores in the near future.

Estimated to be a magnitude 9.0 quake, the powerful earthquake happened in Alaska and sent 30-foot-tall waves to Hawaii between 1425 and 1665, Live Science reported. For comparison, the resulting tsunami was at least three times the size of a tsunami that caused damage in Hawaii in 1946.

Publishing their findings in the journal Geophysical Research Letters, the scientists examined a sinkhole 328 feet from shore with walls 23 feet high. David Burney, a paleoecologist at the National Tropical Botanical Garden in Kalaheo, discovered the site back in the late 1990s, but his theory that a massive tsunami left the ocean debris found in the sinkhole was not verified until now.

Thanks to the new research, Honolulu officials have modified their tsunami evacuation maps in case a devastating tsunami hits the county that is home to around a million residents. Evacuation areas will be more than double in some locations on the new maps, according to an American Geophysical Union press release.

A tsunami the size of the one in the study is projected to occur once every thousand years, making the odds that it will happen in any given year quite small at 1 percent.

"People have to at least appreciate that the possibility is there," lead researcher Rhett Butler, a geophysicist at the University of Hawaii at Manoa, said in a statement.

The sinkhole left by the tsunami that struck 500 years ago holds a layer of sediment with distinct traces of the ocean: coral fragments, mollusk shells and beach sand. The sediment remained a mystery until the 2011 Tohoku earthquake hit Japan and pulled tall, damaging waves inland to flood the island nation.

"[The Japan earthquake] was bigger than almost any seismologist thought possible," said 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?"

For future research, scientists plan to hunt for tsunami evidence elsewhere in the Hawaiian islands.