A landslide and mega-tsunami in Greenland in September 2023, caused by the climate crisis, caused the entire earth to vibrate for nine days, a scientific investigation found.
The seismic event was detected by earthquake sensors around the world, but was so completely unprecedented that the researchers initially had no idea what caused it. Having now solved the mystery, the scientists said it shows how global warming is already having impacts on a planetary scale and that large landslides are possible in places previously believed to be stable as temperatures have risen rapidly.
The collapse of a 1,200 meter high mountain peak in the remote Dickson Fjord happened on September 16, 2023 after the melting glacier below the rock face could no longer hold. It caused an initial wave 200 meters high and the subsequent sloshing of water back and forth in the winding fjord sent seismic waves across the planet for more than a week.
The landslide and mega-tsunami were the first recorded in East Greenland. Arctic regions are affected by the fastest global warming, and similar although smaller seismic events have been seen in western GreenlandAlaska, Canada, Norway and Chile.
Dr Kristian Svennevig of the Geological Survey of Denmark and Greenland, the lead author of the report, said: “When we set out on this scientific adventure, everyone was amazed and no one had the faintest idea what caused this signal. It was much longer and simpler than earthquake signals, which usually last minutes or hours, and was labeled a USO – an unidentified seismic object.
“This was also an extraordinary event because it is the first giant landslide and tsunami we have ever recorded in East Greenland. It certainly shows East Greenland is coming online when it comes to landslides. The waves destroyed an uninhabited Inuit site at sea level that was at least 200 years old, suggesting that nothing like it had happened for at least two centuries.
A large number of huts were destroyed at a research station on Ella Island, 70 km (45 mi) from the landslide. Established two centuries ago by fur trappers and explorers, the site is used by scientists and the Danish military, but was empty at the time of the tsunami.
The fjord is also on a route commonly used by tourist ships and one that carried 200 people stranded in mud in Alpefjordnear Dickson Fjord, last September. It was freed just two days before the tsunami hit, avoiding waves estimated at four to six meters.
“It was pure luck that nothing happened to any people here,” Svennevig said. “We are in uncharted waters scientifically because we don’t really know what a tsunami does to a vessel.”
Dr Stephen Hicks at University College London, one of the research team leaders, said: “When I first saw the seismic signal I was completely taken aback. Never before has such a long-lasting, globally moving seismic wave, containing only a single frequency of oscillation, been recorded.”
The signal seemed completely different from the multi-frequency rumble and ping of earthquakes. It took 68 scientists from 40 institutions in 15 countries to solve the mystery by combining seismic data, field measurements, on-the-ground and satellite images and high-resolution computer simulations of tsunami waves.
The analysis, published in the journal Scienceestimated that 25m cubic meters of rock and ice crashed into the fjord and traveled at least 2,200 meters along it. The direction of the landslide, at 90 degrees to the length of the fjord, together with the inlet’s steep parallel walls and a 90-degree bend 10 km along the line all helped to channel much of the landslide’s energy into the fjord to last and resonate for so long. .
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The tsunami wave reduced to seven meters within a few minutes, the researchers calculated, and would have dropped to a few centimeters in the following days, when the Danish military visited and photographed the fjord. But this flush of a large amount of water continued to send seismic waves around the world.
Coincidentally, sensors measuring water depth were set up by scientists in the fjord two weeks before the landslide. “It was also pure luck,” Svennevig said. “They sailed under this glacier and mountain that they didn’t know was about to collapse.”
An important part of determining the cause of the seismic event was modeling the tsunami and comparing it to the measurements. “Our model predicted an oscillation with exactly the same period – 90 seconds – which is an amazing result, as well as the height of the tsunami, and the waves decayed in exactly the same way as seismic signals. That was the eureka moment.”
Prof Anne Mangeney, a landslide modeler at the Institut de Physique du Globe de Paris in France, who was part of the team, said: “This unique long-lasting tsunami challenged the classical models we used before to only take a few hours of tsunami propagation – we had to go to an unprecedented high numerical resolution. This opens up new avenues for tsunami modelling.”
Such events will become more common as global temperatures continue to rise. “Even more profoundly, for the first time, we can see very clearly that this event, caused by climate change, has caused a global vibration under all of our feet, all over the world,” Mangeney said. “Those vibrations traveled from Greenland to Antarctica in less than an hour. So we have seen an impact of climate change that affects the whole world within an hour.”
Human impact on the planet has also recently been demonstrated by studies showing that the reshaping of the Earth by the mass melting of polar ice lengthen the length of each day and cause the north and south pole to move. Other work has shown that carbon emissions are the stratosphere is shrinking.
