In a modern twist to the concept of “if a tree falls in the forest,” a global coalition of scientists collaborated to link unexplained seismic signals that were noticed worldwide last year to a major landslide and tsunami in a remote fjord in eastern Greenland.

The incident in Dickson Fjord, Greenland, registered on sensitive seismographs from the Arctic to Antarctica for nine consecutive days after a massive landslide unleashed over 32 million cubic yards of rock and ice into the water, resulting in a tsunami reaching heights of 650 feet. The tsunami’s movement generated vibrations that traveled through the Earth’s crust, leading seismologists to initially label this phenomenon as a USO, or unidentified seismic object.

The results of this research, featured in the journal Science, emerged from a collaboration of 68 scientists from 41 research institutions across 15 nations, who utilized satellite images, site photographs, and digital simulations to analyze the landslide’s effects.

What size was the landslide?

The landslide on September 16, 2023, resulted from the collapse of a mountain top that previously towered nearly 4,000 feet above the fjord. A glacier at the mountain’s base, which had been retreating for decades due to climate change, had eroded sufficiently to release 32.7 million cubic yards of rock and ice—equivalent to the volume of 10,000 Olympic-sized swimming pools—into the fjord.

Images of the glacier and the missing mountain peak were taken by the Danish military, who explored the fjord days after the incident to capture its effects. Photographs from September 2023 revealed the damage caused by the tsunami on the glacier.

The fjord stretches roughly the width of Manhattan, and for the nine days following the landslide, the water oscillated every 90 seconds. This movement corresponded with the seismic patterns recorded worldwide.

“When I first observed the seismic signal, I was utterly astonished,” said Stephen Hicks from University College London and co-author of the research. “We’ve never documented water movement over several days resulting from a single event lasting just minutes—like this landslide.”

A model by Hicks illustrated how seismic monitoring networks detected the ripples from the Greenland event within an hour of the landslide occurring.

“At the outset of this scientific investigation, we were all bewildered, and no one had the slightest clue what was causing these signals,” stated Kristian Svennevig from the Geological Survey of Denmark and Greenland and the study’s lead author. “What we could confirm was that it was somehow linked to the landslide. The puzzle was only pieced together through a vast interdisciplinary and international collaboration.”

Though there were no injuries from this event, the fjords are part of a route frequently used by cruise ships. The study pointed out that had there been ships present, the results could have been catastrophic.

The research emphasized that fast-changing climate conditions create instability in areas once considered safe, underscoring the urgency for monitoring these regions.