A Global Warming-Generated USO—Unidentified Seismic Object—Reverberated Through the Planet for Nine Days

In September 2023, researchers around the world were baffled by a seismic event that sent unusual shockwaves bouncing back and forth through the planet for more than a week. The nature of the event was so unprecedented that it took scientists nearly a year to determine the source of the strange waves: the collapse of a mountain peak in Greenland triggered a landslide that caused a mega-tsunami that, in turn, generated the seismic waves—a series of events set in motion by the meting of a key glacier due to global warming.

The event took place on September 16, 2023, near the Dickson fjord on Greenland’s east coast; there, a 1,200-meter (4,000-foot) mountain peak collapsed when the ice of a melting glacier below it was no longer able to support the adjacent rock face. The resulting landside of 25 million cubic meters (883 million cubic feet) of rock and ice generated a 200-meter (656-foot) tsunami that sloshed back and forth through the 2.2-kilometer (1.37-mile) fjord, with the energy from each rebound of the wave triggering a seismic signal, an event that took a full nine days to finally settle back to normal.

But before the source of the anomalous seismic waves was identified, the signal, labeled a USO (unidentified seismic object), was something that seismologists hadn’t encountered before, “far longer and simpler than earthquake signals, which usually last minutes or hours,” according to study lead Dr. Kristian Svennevig from the Geological Survey of Denmark and Greenland.

“When I first saw the seismic signal, I was completely baffled,” remarked Dr. Stephen Hicks, one of the research team leaders at University College London. “Never before has such a long-lasting, globally travelling seismic wave, containing only a single frequency of oscillation, been recorded.” Ultimately, it took 68 scientists from 40 institutions in 15 countries to finally decode what the strange signal meant.

Fortunately, researchers had set up sensors to measure water depth in the remote fjord just two weeks before the landslide, so the actual height of the tsunami was available from the instruments once the cause of the event was determined.

“That was also pure luck,” Svennevig remarked. “They were sailing below this glacier and mountain that they didn’t know was about to collapse,” he added, referring to the members of the expedition.

Key to linking the Dickson landslide to the nine-day USO was detailed modeling of the event; using what was known of the event through its seismic signature, the researchers were able to build a model that precisely matched what had happened in the fjord.

“Our model predicted an oscillation with exactly the same period–90 seconds–which is an amazing result, as well as the height of the tsunami, and the waves decayed in exactly the same way as seismic signals. That was the eureka moment,” Svennevig explained.

The researchers warn that unusual events such as this will become more common as the effects of global warming intensify.

“Even more profoundly, for the first time, we can quite clearly see this event, triggered by climate change, caused a global vibration beneath all of our feet, everywhere around the world,” according to Professor Anne Mangeney, a landslide modeler at the Institut de Physique du Globe de Paris.

“Those vibrations travelled from Greenland to Antarctica in less than an hour. So we’ve seen an impact from climate change impacting the entire world within just an hour.”