In September 2023, around a hundred seismic stations around the world take turns recording a signal. Oscillation detected It is confusing. Seismometers measure a single-frequency wave, comparable to a monotonous hum, very different from the signals associated with earthquakes, which are usually multi-frequency. The phenomenon is recorded over an abnormally long period of nine days.
After several months of research, a group of scientists revealed in a study published on September 12 in the journal Science the causes of this mysterious earthquake. Using satellite data and aerial photographs, geophysicists reconstruct the sequence of events.
On 16 September 2023, in East Greenland, in the Dickson Fjord, a mountain peak collapsed, taking a glacier with it. Around 25 million cubic metres of rock and ice – the equivalent of 10,000 Olympic swimming pools – rolled down the slope at high speed and plunged into the fjord. This surge generated a colossal momentum, triggering a 200-metre-high mega tsunami in this desert region of the Arctic Circle. No casualties were recorded, only the scientific equipment at the Ella Ø station, 70 kilometres from the fjord, was damaged.
“Pendulum movement”
“ The closed topography of the fjord allowed the wave to bounce back and forth.explains Antoine Lucas, a researcher at the Institut de Physique Globo in Paris and co-author of the study, taking an image of a basin filled with water that would be carried with an outstretched arm. The energy generated was such that the wave maintained this pendulum motion and generated seismic waves that propagated under the fjord towards the different networks of stations. It was at that moment that the seismometers went crazy, recording a frequency never before observed for more than a week.
To reach these conclusions, more than 68 scientists from 40 institutions in 15 countries combined data from seismometry, infrasound, field measurements and images taken on the ground and by satellite. A long-term effort. “The location of the signal source was quickly identified and satellite data confirmed the landslide.explains the French researcher. A helicopter mission then enabled photographic studies to be carried out to reconstruct the course of events in high resolution. »
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