Massive Debris Pile Reveals Past Mammoth Tsunami in Hawaii

A massive debris pile discovered in a giant sinkhole in the Hawaiian Islands reveals that at least one mammoth tsunami has struck the islands in the past. The findings show that it's possible that a similar tsunami could strike Hawaii in the future.

"You're going to have great earthquakes on planet Earth, and you're going to have great tsunamis," said Rhett Butler, one of the researchers, in a news release. "People have to at least appreciate that the possibility is there."

About 500 years ago, a 9.0-magnitude earthquake off of the coast of the Aleutian islands triggered a massive wave about 30-feet high. This wave hit the island of Kauai and left behind up to nine shipping containers worth of ocean sediments in a sinkhole. In fact, the researchers estimate that the tsunami was at least three times the size of the 1946 tsunami, which was the most destructive in Hawaii's recent history.

The scientists used a wave model to predict how a tsunami would flood the Kauai coastline. In addition, they simulated earthquakes with magnitudes between 9.0 and 9.6 originating at different locations along the Aleutian-Alaska subduction zone. In the end, they found that the unique geometry of the eastern Aleutians would direct the largest post-earthquake tsunami energy directly toward the Hawaiian Islands.

These recent discoveries actually prompted Honolulu officials to revise their tsunami evacuation maps for the possibility of an extreme tsunami hitting Hawaii. The new maps more than double the area of evacuation in some locations.

"[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 Robert Witter at the U.S. Geological Survey in Achorage, who was not involved in the study. "An important next thing to do is to look for evidence for tsunamis elsewhere in the Hawaiian island chain."

The findings are published in the journal Geophysical Research Letters.