A Mysterious Seismic Signal Lasted Nine Days Last Year. It Was a Mega-Tsunami Caused by Climate Change, Researchers Say

In September last year, scientists around the globe picked up an unusual oscillating seismic signal that peaked every 92 seconds—a pattern that’s atypical for an earthquake. But when the signal continued for nine whole days, they became even more baffled.

“We were like, ‘Oh wow, this signal is still coming in. This is completely different to an earthquake,’” Stephen Hicks, a seismologist and co-author of the study, tells New Scientist’s Michael Le Page. “We called it an unidentified seismic object, or USO.”

An international team of 68 scientists began brainstorming possible causes. After examining the data and running simulations, they concluded that the unusually long seismic signal was caused by a landslide in an East Greenland fjord that triggered a giant, sloshing tsunami called a seiche. Their findings were published in the journal Science last week.

The first clue was that the seismic signal corresponded with the location of the Dickson Fjord in Greenland. Photographs and satellite imagery revealed a mountain and part of a glacier in East Greenland had collapsed into the fjord at that time. But how such an event could unleash a lasting seismic signal remained unclear.

Using global seismic recordings, field measurements, satellite imagery and computer simulations, the team then tried to reveal what exactly took place, per a statement. They used a supercomputer to process the data and create a simulation of the events. Their work reconstructed the disaster, from the volume of falling ice and rock, to the trajectory of the avalanche. And ultimately, they mapped out the nightmare-worthy “mega-tsunami” at fault.

As climate change melted and thinned a glacier in the fjord, the structure became unable to support the mountain above it. So, on September 16, 2023, about 33 million cubic yards of rock and ice—equivalent to the volume of 25 Empire State Buildings—came crashing down, triggering a 650-foot-tall wave that had nowhere to go in the narrow fjord.

“This landslide happened about 200 kilometers inland from the open ocean,” Hicks explains to BBC News’ Victoria Gill. “And these fjord systems are really complex, so the wave couldn’t dissipate its energy.”

Imagery from the Danish Navy revealed that the fjord’s bottom was rounded, which would have decreased the resistance on the wave, preventing it from releasing its energy the way a wave normally would. Instead, water in the fjord oscillated back and forth for nine days, causing the seismic signal that scientists observed all over the planet.

“If we found no other explanation, we would have gone for sea monster or baby dragons,” Hicks jokes with Quanta Magazine’s Robin George Andrews.

Seismic & tsunami waves from the September 2023, Dickson Fjord, Greenland landslide & fjord seiche

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Even though the signal continued for more than a week, the size of the waves had diminished to the point of being unnoticeable within a few days. Three days after the landslide, a Danish naval boat passed through the fjord and did not notice anything unusual.

In August, a German team of researchers also studied the event—mostly through satellite imagery—and reached a similar conclusion, though with fewer details: “The methods chosen by the teams are different, but the results agree well,” Gesa Petersen, a seismologist and co-author of the August study who was not involved in this recent one, tells the Washington Post’s Kasha Patel.

While the landslide and tsunami led to $200,000 worth of damages at a nearby unoccupied research station, no one was hurt in the disaster. The site is close to a route followed by cruise ships, however, which researchers say is cause for concern as climate change drives more landslides in the Arctic.

“Climate change is shifting what is typical on Earth, and it can set unusual events into motion,” study co-author Alice Gabriel, a seismologist at the Scripps Institution of Oceanography, says in the statement.

Lead author Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland, tells BBC News that though the recent seiche event doesn’t necessarily confirm that megatsunamis are becoming more common, “its unprecedented scale underscores the need to carry out more research.”

Margherita Bassi | READ MORE

Margherita Bassi is a trilingual storyteller and freelance journalist with a particular interest in ancient history, astronomy and human interest stories.