14 DAY TRIAL // Having analyzed debris found in a massive sinkhole at a considerable distance from the shoreline, researchers with the American Geophysical Union and colleagues concluded that, about 500 years ago, the Hawaiian Islands were hit by a mammoth tsunami.
Evidence at hand indicates that the freakishly big tsunami was birthed by a powerful earthquake that struck at a considerable distance from Hawaii. Specifically, the tsunami was caused by a shake off the coast of the Aleutian Islands in Alaska.
Studying marine debris to document past tsunamis
In a paper in the journal Geophysical Research Letters, the scientists behind this investigation detail that the sinkhole they focused on is located on the island of Kauai. Its mouth sits at a distance of 100 meters (328 feet) from the shoreline, and its walls measure 7 meters (23 feet) in height.
The marine debris that the American Geophysical Union found and analyzed comprised bits and pieces of corals, fragments of mollusk shells, and coarse beach sand. Hence, it was concluded that it could have only got there from the nearby ocean.
Since the chances that, 500 years ago, a bunch of people decided to have some fun carrying marine debris on land and dumping it in this massive sinkhole are slim to none, the only possible explanation is that the corals, mollusk shells, and sand were dragged ashore by a mammoth wave.
Judging by the makeup of the debris and how much of it was deposited inside the sinkhole, the scientists agreed on a tsunami standing as much as 9 meters (30 feet) tall as the most likely suspect. As mentioned, the tsunami is said to have been birthed by a 9.0-magnitude shake near the Aleutian Islands.
Just to put things into perspective, it need be said that this tsunami was about 3 times the size of one other massive wave that hit the Hawaiian Islands in 1946 and that is widely regarded as the most destructive thus far documented in the region's recent history.
Rethinking tsunami evacuation maps
Writing in the journal Geophysical Research Letters, the scientists behind this research project argue that Aleutian Islands earthquakes powerful enough to birth tsunamis like the one that hit Kauai half a century ago can happen once every thousand years.
Hence, they recommend that high officials in Hawaii take the time to review existing tsunami response plans and double the evacuation area in some of the Islands' regions. More so given the fact that Hawaii's population is now close to 1 million people.
“[The authors] 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 geologist Robert Witter.
“You’re going to have great earthquakes on planet Earth, and you’re going to have great tsunamis. People have to at least appreciate that the possibility is there,” added Rhett Butler, a geophysicist at the University of Hawaii at Manoa and study lead author.