on September 16, 2023, seismologists registered a strange signal from the eastern Greenland worldwide. The frequency variations that normally go hand in hand with events such as earthquakes were missing: the signal was "monochromatic", similar to the sound of a bell, and lasted for nine days. It was quickly classified as UFO, um, Uso: a non -identified seismic object.

"It is the first time that we have found a seismic signal of this kind in global database: some people thought that their sensors were broken," says Kristian Svennevig, geologist at the Geological Institute of Denmark and Greenland in Copenhagen, which a study 1 led over the event that was published on September 12th in Science . Remote stations registered the signal, including one that is located at the other end of the world in Antarctic.

The event triggered reports on a tsunami at a research station in the Dickson-Fjord in Greenland, and scientists were able to identify the likely source: a 1.2 kilometer mountain peak had crashed into a depression in the fjord. So they had a culprit, but remained unclear how a landslide could create such a long -lasting sustainable. Svennevig and his colleagues formed an interdisciplinary team for the investigation.

There were already precedent examples of such seismological signals in the specialist literature that go back more than a decade. Handshole in closed water basins had created a back and forth wave movement, known as the shallow, which had a monochromatic seismic signature similar to that of 2023. The difference was that these events were only registered locally and took less than an hour.

wave movement

svennevig and his colleagues began to document the landslide and the resulting tsunami. They calculated that the collapse of the mountain summit produced a landslide of around 25 million cubic meters of material, which corresponds to around 10,000 Olympic swimming pools. The earth material crashed into a local glacier at the end of a depression and generated a glacier and ice avalanche that fell into the fjord.

The original splash was 200 meters high, while the following waves reached about half of this height, reports Svennevig. The tsunami was 75 kilometers of the original impact 4 meters high. However, what made the event unique was the obvious resistance of the wave movement - with waves of around 7 meters - which lasted between the mountainous sides of the tight fjord. With detailed military cards of the fjord floor, the team modeled the event and suggested that the landslide could have created the mysterious signal.

"It is a good study that explains an 'extremely strange and unusual' seismological event," says Göran Ekström, geophysicist at the Lamont-Doherty Earthsobervatory at Columbia University in Palisades, New York. He attributes this to teamwork and the exchange of data. "The speed at which the team was able to document, describe and explain the events shows how science can work today."

In the end, Svenvenn and his team suggests that the true culprit was the global warming, which diluted the glacier under the mountain and ultimately formed the basis for the landslide. "We will probably see more of these strange events in the future," he says.