Debris Mass in Huge Sinkhole Shows Hawaii’s Tsunami Risk: Study

A massive earthquake strikes Alaska’s Aleutian Chain, spawning a 30-foot-high tsunami that blasts onto Hawaii’s shore and fills a huge sinkhole with debris. Researchers sift through it 500 years later, find evidence of the catastrophe and urge authorities to redraw evacuation maps to prepare for such a disaster. That’s the thrust of a new study, reported in Geophysical Research Letters, that examined deposits in Kauai’s Makauwahi sinkhole.

The researchers, led by Rhett Butler, a geophysicist at the University of Hawaii at Manoa, found evidence that a 9.25 magnitude earthquake in the Aleutians between 350 and 575 years ago caused a tsunami that carried large amounts of marine debris — coral, shells, beach sand — 100 meters inland and into the sinkhole. The researchers said that Japan's 2011 earthquake and tsunami show the danger in relying on modern observations in disaster planning, and they said their model for what would occur in a similar Aleutian quake today far exceeded all tsunamis recorded in Hawaii in the past 200 years. They called for upgrading NOAA tsunami warning buoys to allow more time for evacuation orders. Gerald Fryer, a geophysicist at the Pacific Tsunami Warning Center in Hawaii who wasn't involved with the study, told the American Geophysical Union that he’s convinced it's correct and has worked with Honolulu authorities to update evacuation maps by the end of the year.

Image: Simulated earthquakes in the Aleutians and resulting tsunamis
The researchers simulated earthquakes with magnitudes between 9.0 and 9.6 originating at different locations along the Aleutian-Alaska subduction zone, and found that the unique geometry of the eastern Aleutians would direct the largest post-earthquake tsunami energy directly toward the Hawaiian Islands. The red circles are centered on Kauai and encircle the Big Island. Rhett Butler



— Gil Aegerter