Research at a sinkhole on the island of Kauai has revealed fragments of coral, mollusk shells and coarse beach sand which provide evidence for a monster tsunami caused by an earthquake in Alaska. The earthquake would have occurred between 1425 and 1665, and measured around 9.0 on the Richter scale.
Scientists are worried that another large earthquake in Alaska could cause a similarly large and catastrophic tsunami.
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Tsunami in Hawaii: A troubling discovery
The evidence points to a tsunami that was three times the size of the 1946 tsunami which battered Hawaii, caused by an 8.6-magnitude earthquake off the Aleutian Islands.
Tsunamis as large as the one described in the study are incredibly rare, happening once every thousand years on average. According to experts there is a 0.1% chance of one happening in a year, equal to the probability of the 9.0-magnitude Tohoku earthquake and related tsunami in Japan, 2011.
“You’re going to have great earthquakes on planet Earth, and you’re going to have great tsunamis,” said Rhett Buler, geophysicist at the University of Hawaii and lead researcher on the study. “People have to at least appreciate that the possibility is there.”
Tsunami in Hawaii: Modeling and evacuation maps
The study has already made Honolulu officials revise their tsunami safety measures. New evacuation maps, which affect 1 million people and over twice the previous evacuation area in Honolulu County, have been released and will be distributed by the end of the year.
More research into the sinkhole was prompted by the 2011 Tohoku earthquake, which led to a rapid surge of water which reached 128 feet above sea level.
“[The Japan earthquake] was bigger than almost any seismologist thought possible,” Butler said. “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?”
By stitching together evidence from the region, researchers were able to model how powerful earthquakes in Alaska and the Aleutian Islands would cause tsunamis to hit Hawaii. More research is required to confirm whether the debris at Kauai was carried there by a mammoth tsunami, but the fact that officials are sufficiently worried to have revised the evacuation maps points to something more convincing than mere conjecture.