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The landslide that shook the Earth for 9 days

2024-09-13 19:24:00, Kuriozitete CNA

In September 2023, a giant landslide in eastern Greenland triggered a tsunami that spread for 9 days in the confined waters of a fjord, vibrating the Earth's crust and generating a seismic phenomenon detected by seismometers around the world.

A study just published in Science has reconstructed the event and linked it to climate change, which degrades permafrost and makes glaciers unstable, increasing the risk of landslides in Arctic regions.

In September 2023, an unidentified seismic signal lasting 9 days was picked up by seismographs all over the planet, from the Arctic to the Antarctic. The strange 10.88 millihertz (mHz) noise was dubbed "USO" (unidentified seismic object), similar to a long rumble, it sounded very different from the frequency-rich noises of ordinary earthquakes.

On the same day, Greenland authorities received news of a massive tsunami inside a fjord in a remote region of the island's northeast coast. An international, multidisciplinary team of 68 scientists has since reconnected the two events, using seismograms, infrasound analysis, satellite images and field expeditions, in which the Danish military also took part.

Part of a 1,200-meter-high mountain facing Dickson Fjord collapsed: 25 million cubic meters of rock and ice, enough to fill 10,000 Olympic swimming pools, poured into the water, lifting a surface 200 meters into the air and triggering a tsunami. 110 meters high. The landslide was caused by the thinning of a glacier at the base of the mountain, which had become too brittle to support the overlying rock. An effect, it is thought, of high temperatures and changes in rainfall due to the climate crisis.

The wave would then advance along 10 km of the fjord, gradually losing energy. Within a few minutes, it has decreased to 7 meters in height, becoming a few centimeters in the following days. Scientists used mathematical models to recreate the movement of water in the narrow space of the fjord. Thus they were able to demonstrate that seiche waves would originate from tsunamis, the periodic oscillations of water typical of closed basins (for example, those of alpine lakes). The mass of water would have continued to move back and forth every 90 seconds, generating exactly the same rhythmic vibrations of the Earth's crust recorded by seismometers.

"The study of this event strikingly highlights the complex interrelationships between climate change in the atmosphere, the destabilization of ice in the cryosphere, the movements of water bodies in the hydrosphere, and the Earth's solid crust in the lithosphere," says Stephen Hicks, Earth scientist from the University. College London and co-author of the work.

It is also the first time that a landslide and tsunami have been recorded in east Greenland, a testament to the widespread effect of climate change on degrading Arctic landscapes.

Landslides in confined bodies of water such as fjords can cause particularly destructive rogue waves. Considering that 70 km from Dickson Fjord, the tsunami reached a record height of 4 meters, if one of the many cruise ships passing along the coast had been present in the area at the time of the landslide, the consequences would have been dramatic. / CNA