In September 2023, scientists worldwide were baffled by a mysterious nine-day seismic signal originating from East Greenland. However, what triggered this mysterious signal remains elusive.
An international team of scientists has finally identified the cause of a mysterious seismic signal. They found that this event started with glacial thinning.
On 16 September 2023, a mountaintop in an East Greenland fjord collapsed into the sea, triggering a mega-tsunami about 200 meters (650 feet) tall. The event was so energetic that it generated a global signal that reverberated through Earth’s crust for nine days.
Scientists call this phenomenon a seiche. Fortunately, there were no causalities, but the waves destroyed some $200,000 in infrastructure at an unoccupied research station on Ella Island.
It’s all because of climate change. The glacier at the mountain’s base melted and destabilized over 25 million cubic meters (33 million cubic yards) of rock and ice, which crashed into the sea. Climate change is increasingly predisposing polar regions to large landslides.
From left to right: before (August 2023) and after (September 2023) photos of the mountain peak and glacier, taken from the fjord. Credit: Søren Rysgaard / Danish Army.
Middle: Annotated versions labelling the key features. Credit: Søren Rysgaard, Danish Army.
The signal puzzled scientists for two reasons:
It did not look like signals generated by earthquakes on seismographs. Instead, it oscillated with a 92-second interval between its peaks, too slow for humans to perceive.
The signal stayed vital for days on end.
To identify the cause, scientists combined seismic recordings from around the world, field measurements, satellite imagery, and computer simulations to reconstruct the extraordinary events.
They also analyzed satellite and on-the-ground imagery to document the enormous volume of rock and ice in the landslide that triggered the tsunami. They studied the seismic waves better to understand the dynamics and trajectory of the rock-ice avalanche as it moved down the glacial gully and into the fjord.
The team used supercomputers to create high-resolution simulations of the events. Scientists found creating an accurate computer simulation of such a long-lasting, sloshing tsunami challenging.
Ultimately, these simulations could closely match the real-world tsunami’s height and the long-lasting seiche’s slow oscillations. Simulations show that the tsunami stabilized into a 7-meter-high long-duration seiche with a frequency (11.45 millihertz) and slow amplitude decay nearly identical to the seismic signal.
The authors found that the signal was generated by standing waves in the Dickson fjord due to the rockslide.
Robert Anthony, a geophysicist with the United States Geological Survey’s Earthquake Hazards program and co-author of the study, said, “The team, comprised of 68 scientists from 41 research institutions. It was exciting to be working on such a puzzling problem with an interdisciplinary and international team of scientists. Ultimately, it took a plethora of geophysical observations and numerical modeling from researchers across many countries to put the puzzle together and get a complete picture of what had occurred.”
Journal Reference:
Kristian Svennevig, Stephen Hicks, Thomas Forbriger at al. A rockslide-generated tsunami in a Greenland fjord rang Earth for nine days. Science. DOI: 10.1126/science.adm9247