In September, a strange nine-day signal shook our planet and confused scientists. They finally found the cause. Scientists have finally determined the cause of the mysterious seismic signal that shook the Earth for nine consecutive days last year. It turned out that our planet was hit by a megatsunami that remained in the fjord after the mountaintop collapsed.

A giant 200-foot wave bounced back and forth in East Greenland’s Dixon Fjord for nine days in September 2023, its motion causing seismic waves to reverberate through the planet’s crust.

At first, scientists were confused by the signal, but a study using satellite and ground-based imagery eventually found the cause of the seismic activity on the mountain, which was destabilized by climate change melting the glaciers at its base. The researchers published their findings today (September 12) in the journal Science.

“When we set out on this scientific adventure, everyone was confused and no one had the slightest idea what was causing this signal,” said Christian Svennevig, lead author of the study and a geologist at the Geological Survey of Denmark and Greenland (GEUS). “All we knew was that it was somehow connected to the landslide. We were only able to solve this mystery thanks to a huge interdisciplinary and international effort.”

Two aspects of the signal surprised scientists after it was recorded by seismic monitoring stations in September. First, it oscillated with a 92-second interval between peaks, unlike high-frequency earthquakes. Second, it did so for days in a row.

Scientists soon linked the probable cause to a landslide in the fjord, but to understand how this created the signal, scientists combined field measurements, satellite imagery and supercomputer models to reconstruct what happened.