An international research team has solved the mystery surrounding the long seismic signal recorded a year ago across the planet: it was a huge landslide that affected the Dickson Fjord, in the Arctic, generating a gigantic tsunami wave that made the waters oscillate for days
A huge landslide caused by the collapse of a mountaintop in remote Dickson Fjord, in Greenland north-eastern, has in turn generated a 200 meter high mega-tsunami that continued to oscillate in the fjord for 9 days, causing a seismic signal never previously observed to be recorded throughout the world. This is what emerges from the study “A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days” just published in the scientific journal 'Science', in which 68 scientists from 40 institutions in 15 countries collaborated. “When we started this scientific adventure we were all quite perplexed and none of us had the faintest idea of what had caused that particular seismic signal: we only knew that it was somehow associated with the landslide”, he says Christian Svennevig, from the Geological Survey of Denmark and Greenland (GEUS), first author of the article. “This was the first landslide and tsunami due to melting ice observed in eastern Greenland, demonstrating that climate change is already having a strong impact there too.”. For Italy, the following took part in the research:National Institute of Geophysics and Volcanology (INGV),University of Catania andUniversity of Padua. “Our research began in September 2023, when a mysterious seismic signal lasting 9 days It has been discovered in recordings from seismic stations installed around the world, from the Arctic to the Antarctic”, explains Flavio Cannavò, researcher at INGV and co-author of the study. “We immediately noticed, however, that the signal appeared completely different from the seismic signals that are recorded in the event of an earthquake: in fact, it contained a single vibration frequency, similar to a monotonous-sounding buzz”. The simultaneous news of a huge tsunami in Dickson Fjord prompted researchers from numerous research institutions and universities around the world to join forces to try to understand if the two events were somehow connected. The multidisciplinary team then analyzed seismic and infrasound data, field measurements, data from the local network of oceanographic sensors, live and satellite images, and numerical simulations of tsunami waves, managing to reconstruct the extraordinary cascade of events triggered in September last year. “It is extraordinary how, nowadays, it is possible to easily assemble an international team with heterogeneous skills to solve complex problems and be able to explain phenomena never documented before in a short time”, explains Andrea Cannatta, researcher at the University of Catania and co-author of the study. “In particular, it was discovered that the landslide that started it all was caused by the collapse of over 25 million cubic meters of rock and ice into the fjord, enough to fill 10.000 Olympic-sized swimming pools. The collapse, in turn, was caused by the thinning, over the decades, of the ice at the base of the mountain overlooking the fjord, a clear expression of the effects of climate change”. “Multidisciplinary data analyses confirmed that the mega tsunami derived from the landslide was one of the highest ever recorded in recent history, reaching 200-meter waves inside the fjord. About 70 kilometers away, tsunami waves reached 4 meters high, damaging a research base on the island of Ella Ø”, he adds Piero Poli, researcher at the University of Padua and co-author of the study. “The movement of such a mass of water was able to generate vibrations through the Earth, with seismic waves radiating from the Arctic to the Antarctic, generating an anomalous global seismic signal. This event underlines the importance of creating special systems for monitoring seismic data on a global scale, which allow the rapid identification and characterization of new and increasingly frequent signals associated with surface processes, such as landslides and rapid movements of ice or fluids, associated with climate change”. The team's simulations showed that the water in the fjord swayed back and forth every 90 seconds, exactly the same period of oscillation as seismic waves. This correspondence indicates that the force of the moving water mass was able to generate seismic energy that propagated through the Earth's crust. Before losing strength, the oscillatory movement lasted 9 days. Never before had a seismic wave of such a long duration, traveling globally and containing a single vibration frequency, been recorded. “It is astonishing that what started as a routine check of a Belgian gravity sensor has turned into a global, multidisciplinary collaboration, with virtual exchanges online 24/24, spanning many time zones. In total, more than 7 messages were exchanged. In summary, this amounts to more than 7 million typed characters: the length of a 8.000-page detective novel.”, gloss Thomas Lecocq, from the Royal Observatory of Belgium (ROB) and co-author of the research. “As is known, the melting of the polar ice caps, which we have identified as the 'latent' cause of the incredible sequence of events recorded in Dickson Fjord last year, is due to the climate change. The rapid acceleration of this phenomenon in recent years requires us to pay ever greater attention to the characterization and monitoring of those regions considered 'stable' until a few years ago, as well as to the development of systems capable of providing early warning in the event of landslides and tsunamis"he concludes Flavio Cannavò.
Cover: Photos of the summit and glacier, taken from the fjord before the landslide (credits: Søren Rysgaard, Danish Army)
Fig.1: Comparison photo with labeling of the main features of the summit and the glacier, taken from the fjord before and after the landslide (credits: Søren Rysgaard, Danish Army) Fig.2: Planet Labs satellite images compared: 30 minutes before and 7 minutes after the landslide Fig.3: Graph of the seismic signals recorded as a function of the distance from the landslide (1 degree = 110 km; 180 degrees = antipodal to Greenland). The propagation of the wave front is noted