A mysterious seismic signal, observed on a global scale and lasting 9 days in September 2023, was caused by a huge landslide in Greenland. 25 million m³ of rock and ice collapsed into the isolated Dickson Fjord, causing a 200-meter-high mega-tsunami that continued to oscillate – a phenomenon known as seiche – in the narrow fjord for 9 days, triggering a never-before-observed global seismic signal. This is the conclusion of research published in the journal Science today.
The Epos-France RLBP stations, supplemented by those of the temporary network of the ANR Maciv project, constituting the densest network closest to Greenland, enabled the precise location of this event. Members of the French Solid Earth community then began studying the recorded signals to understand their origin. From Strasbourg, Grenoble and Paris, they joined the international mobilization of 68 scientists from 40 institutions in 15 countries.
Research conducted over almost a year points to climate change as the cause of this unprecedented event. Over the past few decades, it has caused glacial thinning at the base of the mountain, which used to rise 1.2 km above the fjord. On September 9, 2023, the top of the mountain collapsed, dumping the equivalent of 10,000 Olympic-sized swimming pools of material into the fjord and generating a gigantic tsunami. Detailed mathematical models have demonstrated that the direction of the landslide, combined with the particularly narrow and sinuous shape of the fjord, explains why the water oscillated back and forth every 90 seconds (the oscillation period observed in seismic waves). This movement of a large mass of water generated vibrations across the Earth, shaking the planet and emitting seismic waves observed worldwide.
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Seismic waves recorded by French stations from September 16 © Aurélien Mordret, Osug/ISTerre Grenoble. Watch the video on Youtube