In September 2023, an apocalyptic event took place in the frozen, isolated wilderness of East Greenland’s Dickson Fjord. A mountain peak towering over a mile high gave way, sending a catastrophic rock and ice avalanche down into the deep, narrow waters below.

The impact triggered a mind-bending, 650-foot mega-tsunami, per the Economic Times.

To put that into perspective, the wall of water was high enough to swallow multiple high-rise buildings. While it didn’t quite eclipse the legendary 1,720-foot Lituya Bay tsunami that ripped through Alaska in 1958, this Arctic surge was undeniably huge. The driving force behind the disaster was a colossal collapse of roughly 880 million cubic feet of mountain rock and thinning glacial ice, accelerated by warming polar temperatures.

But the most bizarre part of the story happened after the initial impact. Instead of losing its energy and fading out into the open ocean, the massive wave became trapped inside the tight, twisting fjord. It stabilized into a seiche—a continuous sloshing wave that bounced back and forth from wall to wall for nine days straight.

For a visual analogy, think of sloshing back and forth in a bathtub…but with waves reaching nearly 30-feet, and for more than a week.

Related: 1,500ft Mega-Tsunami Hit Alaska, Second Largest Ever (Video)

This massive body of moving water acted like a giant planetary hammer, ringing the Earth like a bell. The relentless movement sent out a monotonous, ultra-low frequency hum that pinged seismic monitoring stations all over the globe every 92 seconds.

“We were like, ‘Oh wow, this signal is still coming in. This is completely different to an earthquake,’” recalled seismologist Stephen Hicks. “We called it an unidentified seismic object, or USO.”

Lead author Dr. Kristian Svennevig noted that the international team was initially entirely in the dark.

“When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal,” Svennevig stated.

It’s a sobering reminder that as the planet warms and glaciers retreat, the boundaries of our oceans are shifting in ways we’ve never witnessed before. And scientists warn that this won’t be the last time we see a (literal) earth-rattling event like this.

Related: The Biggest Tsunami Ever Recorded: Inside the 1,720-Foot Wave (Video)

This story was originally published by Surfer on Jun 24, 2026, where it first appeared in the News section. Add Surfer as a Preferred Source by clicking here.