Hawaii, a state relatively benign place regarded by many as “paradise,” reveals a dark past: About 500 years ago, it was struck by a massive tsunami as much as 30 feet tall according to a buried debris pile uncovered by researchers, reports the American Geophysical Union.

According to researchers the wave, which deposited nine shipping containers worth of sediment on the island of Kauai, could happen again.

“You’re going to have great earthquakes on planet Earth, and you’re going to have great tsunamis,” said Rhett Butler, a geophysicist at the University of Hawaii at Manoa and lead author of the new study published online in Geophysical Research Letters, a journal of the American Geophysical Union. “People have to at least appreciate that the possibility is there.”

The most destructive tsunami in recent Hawaiian history occurred in  1946, a wave just one third the size of the monster of 500 years ago. Computer modeling suggests that there’s a 0.1% chance of such an event occurring in a given year, the same odds of the massive earthquake that struck Japan in 2011.

The find has lead many to question the tsunami evacuation protocols currently in place in Hawaii.

“[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?”

Radiocarbon dating alone isn’t enough to confirm that the debris from the sinkhole came from a tsunami, so the researchers also modeled the effects of various earthquakes around the Aleutian islands, where the quake that triggered the massive tsunami is believed to have originated. They found that anything over a reading of 9.0 would be enough to trigger a wave eight to nine meters high. Carbon dating also demonstrated that some of the sediment found in the sinkhole cold have come from the Aleutian islands around the same time.

“I’ve seen the deposit,” said Gerald Fryer, a geophysicist at the Pacific Tsunami Warning Center who was not involved in the study. “I’m absolutely convinced it’s a tsunami, and it had to be a monster tsunami.”