In a groundbreaking study, researchers pinpointed the cause of a seismic signal detected globally in September 2023 to a massive rockslide in Greenland’s Dickson Fjord.
In September 2023, seismometers worldwide captured a unique seismic signal that persisted for up to nine days in certain areas. This phenomenon was triggered by a massive rockslide in Greenland’s Dickson Fjord. What triggered this signal, and why did it last that long? An international team of scientistsincluding researchers from the Karlsruhe Institute of Technology (KIT) delved into this question. Their investigation revealed that the source of the vibrations was the continuous movement of water sloshing back and forth in the narrow fjord. Additionally, the researchers linked the rockslide to the thinning of a glacier, a change attributed to climate change.
Multinational Research Effort
Sensitive scientific instruments known as seismometers are used to record vibrations that resonate through the Earth. These instruments typically measure seismic waves generated during earthquakes, but they can also capture movements of large masses of water or earth on the planet’s surface.
“In September 2023, we discovered a signal that could be detected all around the globe,” says Dr. Thomas Forbriger from KIT’s Geophysical Institute. “The signal was totally different from those we know from earthquakes. It was an oscillation with a single dominant frequency, like a monotonous hum that decayed very slowly.”
In order to find the underlying cause of the phenomenon, 68 researchers from 40 institutions in 15 countries and various disciplines joined forces. They combined seismometer and infrasound data, field measurements, ground and satellite images, simulations of tsunami waves, and photos provided by the Danish Army. “Thanks to this cooperation across disciplines and the unique combination of local field observations and global data, we were able to retrace the extraordinary sequence of events,” explains Forbriger. “High-quality data as those recorded by KIT and the University of Stuttgart at the geoscientific Black Forest Observatory essentially contributed to this achievement.”
Model Reconstruction of the Seismic Event
Going beyond the results published on this topic before and using on-site observations and measurement data acquired directly at the remote Dickson Fjord in Greenland, the researchers were able to create a realistic high-resolution numerical model to reconstruct the event and unequivocally establish the origin of the signal. The model showed that a “seiche” (standing wave of water in a basin) caused vibrations that could be measured all across the globe. This phenomenon is similar to water sloshing back and forth in a bathtub when you step in on one side and thereby displace the water.
The Impact of a Massive Rockslide
The seiche was caused by a massive rockslide in the fjord, triggered by the collapse of a mountain peak that had previously risen 1,200 meters above the fjord. “ The volume of the falling material was enormous – more than 25 million cubic meters. That is enough to fill 10,000 Olympic swimming pools,” states Kristian Svennevig from the Geological Survey of Denmark and Greenland (GEUS), who coordinated the research. The falling masses displaced a huge amount of water, which was pushed out of the fjord as a mega-tsunami with an initial height of 200 meters. The waves generated by the event, which lasted only a few minutes, then sloshed back and forth in the narrow fjord for days.
Prolonged Seismic Oscillations
The researchers’ calculations revealed that the water had sloshed back and forth across the fjord with a period of around 90 seconds, which matches the oscillation period of the observed seismic waves. “It seems to be a special property of the Dickson Fjord that it is capable of such an oscillation. Seiche oscillations of such a frequency, which decay so slowly, have never been reported in scientific literature before. “Our findings are unique in this respect as well,” emphasizes Rudolf Widmer-Schnidrig from the University of Stuttgart.
The movements of these huge masses of water generated seismic waves that could still be measured nine days later at the nearest measuring stations. The waves circled the Earth and they could even be detected in Antarctica, which is almost 20,000 kilometers away. According to the study, the tsunami was one of the highest in recent history. Outside the fjord, waves as high as four meters damaged a research base on Ella Island, 70 kilometers away, and destroyed cultural and archaeological heritage sites across the fjord system.
Climate Change Connection to Geological Shifts
The researchers also investigated how this massive rockslide came about. Satellite images showed that the glacier at the foot of the mountain had thinned out considerably in recent decades. What is more, the rockslide and the tsunami were the first ones to be observed in the northeastern part of Greenland. The researchers trace the event back to climate change. It showed that its impact is already strong, even in this region. The investigations illustrate how climate change and processes in the atmosphere, the destabilization of the glacier ice (cryosphere), the movements of water masses (hydrosphere), and of the solid Earth’s crust (lithosphere) are interrelated.
The researchers are planning to install seismic instruments in Dickson Fjord to get an even better understanding of the area. “We were lucky that no one was injured in this event. But our study shows that, given the rapidly accelerating climate change, it will be more important than ever to characterize and monitor regions that were previously considered stable,” says Svennevig. “This is the only way we can warn in good time about such massive landslides and tsunamis in the future.”
Reference: “A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days” by Kristian Svennevig, Stephen P. Hicks, Thomas Forbriger, Thomas Lecocq, Rudolf Widmer-Schnidrig, Anne Mangeney, Clément Hibert, Niels J. Korsgaard, Antoine Lucas, Claudio Satriano, Robert E. Anthony, Aurélien Mordret, Sven Schippkus, Søren Rysgaard, Wieter Boone, Steven J. Gibbons, Kristen L. Cook, Sylfest Glimsdal, Finn Løvholt, Koen Van Noten, Jelle D. Assink, Alexis Marboeuf, Anthony Lomax, Kris Vanneste, Taka’aki Taira, Matteo Spagnolo, Raphael De Plaen, Paula Koelemeijer, Carl Ebeling, Andrea Cannata, William D. Harcourt, David G. Cornwell, Corentin Caudron, Piero Poli, Pascal Bernard, Eric Larose, Eleonore Stutzmann, Peter H. Voss, Bjorn Lund, Flavio Cannavo, Manuel J. Castro-Díaz, Esteban Chaves, Trine Dahl-Jensen, Nicolas De Pinho Dias, Aline Déprez, Roeland Develter, Douglas Dreger, Läslo G. Evers, Enrique D. Fernández-Nieto, Ana M. G. Ferreira, Gareth Funning, Alice-Agnes Gabriel, Marc Hendrickx, Alan L. Kafka, Marie Keiding, Jeffrey Kerby, Shfaqat A. Khan, Andreas Kjær Dideriksen, Oliver D. Lamb, Tine B. Larsen, Bradley Lipovsky, Ikha Magdalena, Jean-Philippe Malet, Mikkel Myrup, Luis Rivera, Eugenio Ruiz-Castillo, Selina Wetter and Bastien Wirtz, 12 September 2024, Science.
DOI: 10.1126/science.adm9247
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1 Comment
I “hear” tones prior to earthquakes; but of late the soft roar that has dominated my own head has puzzled me. Last night something triggered a higher frequency rush of sound that woke me with vivid dreams, as my own extra low frequency radio wave sounds have done; Now with this article I have another possible contributor to bothersome sounds and hardly anyone but one grandchild can “hear”. I quote the word because the sounds persist when I hold my ears. It’s an inner ear thing I’m told, because of a high mineral content in the fluid in my middle ear that turns it into a radio receiver. I have predicted several notable quakes; but this rushing thing lingers and interferes at highly active times with my regular hearing, just as trying to converse by a noisy ocean would do. Yes, mine is a strange life, but luckily I have many witnesses to the phenomenon. Now I have other reasons to evaluate. ELFRAD was a website devoted to the subject, not sure if it still exists. Many thought I was nuts. I gave up trying to inform authorities. as the science world has a strong NIH (not invented here) feature. I predicted the enormous California quake of 89 to CBS who years later denied my phone call, and never published it. After I made it; I learned from radiologist Anthony Frazier Smith at Stanford , who had placed a receiver on the fault, that we concurred as to the timing of the signal, date and time. That’s when I learned what I was receiving in my head. Today it’the rush is rather muted, but last night I got another type and I think we’re very due for a quake here, which is no secret to seismologists monitoring the San Andreas fault. here in Sunny Santa Cruz.