Last September, seismologists around the world detected vibrations never before observed.

The monotony seemed to come from Greenland and continued for nine days.

“We saw some very strange signals at some stations in the north that we'd never seen before,” said Karl Ebeling, a seismologist at the Scripps Institution of Oceanography at the University of California, San Diego.

Shortly after the vibrations began, a cruise ship sailing near a Greenland fjord noticed that a key landmark on the remote island of Ella, a scientific research and Danish military dog ​​sled patrol base, had been destroyed.

The event drew an international group of seismologists, the Danish military and oceanographers into the mystery: what struck the island, and where did it come from?

On Thursday, the researchers They published their findings in the journal Science.The island was hit by one of the largest tsunamis on record, leaving a scar about 650 feet high.

It was the result of a rare series of cascading events caused by climate change.

The researchers traced the initial trigger to the collapse of a glacier tongue that had been thinned by rising temperatures. This destabilized the steep mountainside, sending an avalanche of rock and ice into Greenland's deep Dikson Fjord. Massive amounts of water were displaced, causing towering waves to move across the narrow fjord, about a mile and a half wide.

The tsunami, at least as high as the Statue of Liberty, surged up the steep rock faces along the fjord and, because the landslide struck the waterway at a nearly 90-degree angle, sent waves circling the channel for nine days — a phenomenon scientists call a seiche.

“No one has ever seen anything like this,” said Christian Svennevig, lead author of the study and a geologist and senior research scientist at the Geological Survey of Denmark and Greenland.

The findings are the result of a complex year-long investigation. The team determined that Ella Island, about 45 miles from the landslide site, was hit by a tsunami at least 13 feet high.

Tourists visit the island from time to time.

“The cruise ship had been docked off the coast just a few days before,” Svennevig said. “We were really lucky that no one was there when it happened.”

The seiche was the longest scientists had ever observed: Until now, tsunamis generated by landslides have typically produced waves that dissipate within a few hours.

“This is really a cascade of events that has never been observed before,” said Alice Gabriel, co-author of the study. “The Earth is a very dynamic system, and we're currently at a stage where this very delicate balance is being disrupted pretty dramatically by climate change.”

Tsunamis triggered by landslides occur more frequently than many people realize and are a danger to people living and working in some Arctic and sub-Arctic regions.

In 2017, a landslide triggered a tsunami that killed four people and destroyed 11 homes. Attacked the village of Ngaatsiaq in West GreenlandThe tsunami was estimated to be at least 300 feet high. Two villages were abandoned in the aftermath of the tsunami due to fears of further landslides, and Svennevig said hundreds of people remain evacuated.

Bretwood “Higg” Higman, an Alaska geologist who studies landslide tsunamis but was not involved in the new study, said evidence suggests landslide tsunamis are a growing problem, but more research is needed.

“I'm pretty confident that these events are becoming more and more frequent,” he said. “Exactly how frequent these events are and can we predict the future? We're not there yet.”

Higman said he thought the Greenland study's researchers were “spot on” and that the research was an important example of how dangerous landslide-induced tsunamis could be.

The Arctic and sub-Arctic regions are warming two to three times faster than the rest of the Earth. As the ice melts, the exposed, dark surface absorbs more sunlight. Warming is triggering three dynamics that could make landslides more frequent in glacial regions, Higman said.

First, rising temperatures are eroding the permafrost within rock formations, weakening slopes and making them more susceptible to collapse. Second, warming is thinning the glaciers that support the rock slopes. Without the ice, sudden collapses could occur. Third, climate change is increasing the likelihood of heavy rains, which are the biggest risk factor for landslides because saturated rocks and soils become more slippery.

Higman has compiled a list of Alaska's slopes that are at risk for landslides that could trigger tsunamis. He said there are dozens of sites of concern that need further study, some of which are near populated areas where a landslide could be catastrophic.

“We're in an awkward position: Scientists know something, but they don't know enough to provide certainty to take action,” Higman said.

Last month, the U.S. Geological Survey reported a 56-foot-high landslide tsunami in Alaska's Pedersen Lagoon. Higman visited the site and believes the tsunami was larger than initially predicted.

Globally, risks are growing due to expanding development in some polar regions and increased visitation by miners, shippers and tourists, Svennevig said.

“At the same time as the population increases, the risk of landslides, geological hazards also increases,” he said. “It's an unfortunate combination.”