In a remote part of Greenland, a massive landslide triggered a mega-tsunami that reverberated across a fjord for nine days, causing seismic vibrations around the world.
Researchers from UCL have published a study in the journal Science, linking this water movement to a global seismic signal that puzzled seismologists in September 2023. The initial event, unseen by human eyes, involved the collapse of a 1.2km-high mountain peak into the Dickson Fjord, resulting in a 200-meter water swell and a 110-meter high wave. This wave, spanning 10km of the fjord, dissipated to seven meters within minutes and gradually decreased to a few centimeters in the following days.
The research team utilized a sophisticated mathematical model to replicate the angle of the landslide and the unusually narrow and winding fjord. This allowed them to illustrate how the water would have continued to slosh for nine days, with minimal energy able to dissipate.
Annotated versions are labeling the key features.
According to the model, the water mass would have oscillated every 90 seconds, aligning with the seismic vibrations detected worldwide.
The experts concluded that the landslide resulted from the thinning of the glacier at the mountain’s base, which could no longer support the rock face above it. This was ultimately caused by climate change. The landslide and tsunami were unprecedented in eastern Greenland.
“When I first saw the seismic signal, I was completely baffled. Even though we know seismometers can record various sources happening on Earth’s surface, never before has such a long-lasting, globally traveling seismic wave, containing only a single oscillation frequency, been recorded. This inspired me to co-lead a large team of scientists to figure out the puzzle,” said Co-author Dr Stephen Hicks of UCL Earth Sciences.
The mountain after the landslide, on September 19, 2023
“Our study of this event amazingly highlights the intricate interconnections between climate change in the atmosphere, destabilization of glacier ice in the cryosphere, movements of water bodies in the hydrosphere, and Earth’s solid crust in the lithosphere.
“This is the first time that water sloshing has been recorded as vibrations through the Earth’s crust, traveling the world over and lasting several days.”
The mysterious seismic signal, detected by seismometers worldwide, was distinct from typical earthquake vibrations, featuring a single frequency, akin to a monotonous hum.
Upon discovering the signal, the researchers initially classified it as a “USO” – an unidentified seismic object.
Simultaneously, reports of a significant tsunami in a remote northeast Greenland fjord reached authorities and researchers in the region.
A group of 68 scientists from 40 institutions across 15 countries collaborated in a one-of-a-kind multidisciplinary effort, combining seismometer and infrasound data, field measurements, on-the-ground and satellite imagery, and simulations of tsunami waves.
The team also utilized Danish military imagery, acquired just days after the event, to assess the collapsed mountain-face and glacier front, as well as the striking marks left by the tsunami.
Lead author Dr Kristian Svennevig, from the Geological Survey of Denmark and Greenland (GEUS), said: “When we set out on this scientific adventure, everybody was puzzled, and no one had the faintest idea what caused this signal. All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort.”
He added: “As a landslide scientist, an additional interesting aspect of this study is that this is the first-ever landslide and tsunami observed from eastern Greenland, showing how climate change already has major impacts there.”
The catastrophic event involved the collapse of 25 million cubic meters of rock and ice into the fjord, equivalent to filling 10,000 Olympic-sized swimming pools. The ensuing tsunami, one of the largest in recent history, caused significant damage over a distance of 70 kilometers, affecting a research base, cultural sites, and archaeological heritage.
The potential impact on tourist cruise ships navigating the Greenland fjords underscores the need for vigilance in monitoring and providing early warning for such events, especially in the face of accelerating climate change.
“We wouldn’t have discovered or been able to analyze this amazing event without networks of high-fidelity broadband seismic stations around the world, which are the only sensors that can truly capture such a unique signal,” said Co-author Thomas Forbriger, from Karlsruhe Institute of Technology.
Journal reference:
Kristian Svennevig, et al. A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days. Science, 2024; DOI: 10.1126/science.adm9247