Entire Earth vibrated for nine days after climate-induced megatsunami | Climate crisis

Scientific research has shown that the Greenland landslide and megatsunami in September 2023, triggered by the climate crisis, caused the entire Earth to vibrate for nine days.

The seismic event was detected by earthquake sensors around the world, but it was so completely unprecedented that scientists initially had no idea what caused it. Having solved the mystery, the researchers said it showed that global warming was already having planetary-scale effects and that large landslides were possible in places previously thought to be stable as temperatures rose rapidly.

The collapse of the 1,200-meter-high mountain peak into the remote Dickson Fjord occurred on September 16, 2023, after the melting glacier below could no longer support the rock face. It caused an initial 200-meter-high wave, and the subsequent splashing of water back and forth in the winding fjord sent seismic waves across the planet for more than a week.

How a mountaintop in eastern Greenland collapsed into the sea and triggered a megatsunami

The landslide and mega-tsunami were the first recorded in East Greenland. Arctic regions are experiencing the fastest global warming, and similar, although seismically smaller events have been observed in West Greenland, Alaska, Canada, Norway and Chile.

Dr Kristian Svennevig of the Geological Survey of Denmark and Greenland, lead author of the report, said: “When we set out on this scientific adventure, everyone was bewildered and no one had the slightest idea what had caused the signal. It was much longer and simpler than earthquake signals, which usually last minutes or hours, and was designated a USO – unidentified seismic object.

“It was also an unusual event because it’s the first giant landslide and tsunami that we’ve recorded in East Greenland. It definitely shows that East Greenland is starting to act up when it comes to landslides. The waves destroyed an uninhabited Inuit site at sea level that was at least 200 years old, which indicates that nothing like this has happened for at least two centuries.”

A large number of huts were destroyed at a research station on Ella Island, 70 km (45 miles) from the landslide. The site was founded by hunters and explorers two centuries ago and is used by scientists and the Danish military, but was empty at the time of the tsunami.

before and after

The fjord is also on a route commonly used by cruise ships, and one carrying 200 people became stuck in mud in Alpefjord, near Dickson Fjord, last September. It was freed just two days before the tsunami hit, avoiding waves estimated at four to six metres.

“It was pure luck that nothing happened here,” Svennevig said. “We are in uncharted waters scientifically, because we don’t really know what a tsunami does to a cruise ship.”

Dr Stephen Hicks of University College London, one of the leaders of the research team, said: “When I first saw the seismic signal I was completely bewildered. Never before has such a long-lasting, globally travelling seismic wave with only one oscillation frequency been recorded.”

The signal looked very different from the multi-frequency rumbles and pings of earthquakes. It took 68 scientists from 40 institutions in 15 countries to solve the mystery, combining seismic data, field measurements, ground and satellite images, and high-resolution computer simulations of tsunami waves.

An analysis published in the journal Science estimated that 25 million cubic meters of rock and ice hit the fjord and traveled at least 2,200 meters. The direction of the slide, at a 90-degree angle to the length of the fjord, along with the steep parallel walls of the inlet and a 90-degree turn 10 kilometers down the line, helped keep most of the slide’s energy in the fjord and resonate for so long.

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The tsunami wave shrank to seven meters in a matter of minutes, researchers calculated, and would have fallen to a few centimeters in the days the Danish military visited and photographed the fjord. But the sloshing of the vast body of water still sent seismic waves around the world.

By chance, scientists had placed sensors measuring water depth in the fjord two weeks before the landslide. “That was also pure chance,” Svennevig said. “They were swimming under a glacier and a mountain that they didn’t know was about to collapse.”

A key part of figuring out the cause of the seismic event was modeling the tsunami and comparing it with measurements. “Our model predicted an oscillation of exactly the same period—90 seconds—which is amazing, as was the height of the tsunami, and the waves decayed in exactly the same way as the seismic signals. It was a moment of revelation.”

Prof Anne Mangeney, a landslide modeller at the Institut de Physique du Globe de Paris in France, who was part of the team, said: “This exceptional, long-duration tsunami challenged the classical models we had previously used to simulate just a few hours of tsunami propagation – we had to move to an unprecedentedly high numerical resolution. This opens up new possibilities for tsunami modelling.”

Such events will become more common as global temperatures continue to rise. “What’s more, for the first time we can clearly see that this event, driven by climate change, caused global tremors beneath our feet, everywhere in the world,” Mangeney said. “These tremors traveled from Greenland to Antarctica in less than an hour. So we saw the impact of climate change all over the world in just an hour.”

Human impact on the planet has recently been proven by research showing that the reshaping of the Earth by the massive melting of polar ice has lengthened each day and caused the North and South Poles to shift. Other work has shown that carbon dioxide emissions are causing the stratosphere to shrink.