After a climate-induced mega-tsunami, the entire earth vibrated for nine days | Climate crisis

A landslide and mega-tsunami in Greenland in September 2023, triggered by the climate crisis, caused the entire Earth to vibrate for nine days, a scientific study found.

The seismic event was recorded by earthquake sensors around the world, but was so unprecedented that researchers initially had no idea what had caused it. Solving the mystery, scientists say, shows that global warming is already having an impact on the entire planet and that as temperatures rise rapidly, large landslides are possible in places previously thought to be stable.

On September 16, 2023, a 1,200-meter-high mountain peak collapsed into the remote Dickson Fjord after the melting glacier beneath it could no longer hold the rock face up. This triggered a 200-meter-high wave, and the subsequent sloshing of water in the winding fjord sent seismic waves through the planet for over a week.

The landslide and mega-tsunami were the first to be recorded in East Greenland. The Arctic regions are affected by the fastest global warming, and similar, albeit 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, the lead author of the report, said: “When we embarked on this scientific adventure, everyone was confused and no one had the slightest idea what had caused this signal. It was much longer and simpler than earthquake signals, which usually last for minutes or hours, and was called a USO – an unidentified seismic object.

“It was also an extraordinary event because it was the first huge landslide and tsunami we have ever recorded in East Greenland. It clearly shows that East Greenland is on the rise when it comes to landslides. The waves destroyed an uninhabited Inuit site at sea level that was at least 200 years old, suggesting that something like this has not happened for at least two centuries.

Numerous huts were destroyed at a research station on the island of Ella, 70 kilometers from the landslide. The site was founded two centuries ago by fur trappers and researchers and is used by scientists and the Danish military, but was empty at the time of the tsunami.

The fjord is also on a route frequently used by cruise ships. Last September, a ship carrying 200 people became stranded in the mud of the Alpefjord, near the Dicksonfjord. It was freed just two days before the tsunami, avoiding waves estimated to be four to six metres high.

“It was pure luck that nothing happened to anyone here,” says Svennevig. “Scientifically, we are in uncharted territory 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 astonished. Never before has such a long-lasting, globally propagating seismic wave been recorded, containing only a single vibration frequency.”

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

The analysis, published in the journal Science, concludes that 25 million cubic meters of rock and ice fell into the fjord and were transported at least 2,200 meters. The direction of the landslide, which is at a 90-degree angle to the length of the fjord, the steep, parallel walls of the bay and a 90-degree bend 10 kilometers further on, contributed to much of the landslide's energy remaining in the fjord and reverberating for so long.

According to the researchers' calculations, the tsunami wave shrank to seven meters within a few minutes and sank to a few centimeters in the days that followed, when the Danish military visited and photographed the fjord. But this sloshing of a huge mass of water continued to send seismic waves around the world.

By chance, scientists had set up sensors to measure the water depth in the fjord two weeks before the landslide. “That 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 with measurements. “Our model predicted an oscillation with exactly the same period – 90 seconds – which is an astonishing result, as was 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 modeller 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 had previously used to simulate the spread of a tsunami over just a few hours – we had to achieve an unprecedentedly high numerical resolution. This opens up new possibilities for tsunami modelling.”

Such events will become more frequent as global temperatures continue to rise. “Even more profound is that we can see very clearly for the first time that this climate change-driven event has caused a global shaking beneath our feet all over the world,” Mangeney said. “These shakings spread from Greenland to Antarctica in less than an hour. So we've seen climate change affect the entire world in just one hour.”

Humans' impact on the planet has also been demonstrated recently by studies showing that reshaping the Earth through the mass melting of polar ice increased the length of each day and shifted the North and South Poles. Other work has shown that the stratosphere is shrinking due to carbon emissions.