Landslide triggered tsunami: Cause of mysterious seismic signal clarified
On September 16, 2023, seismographs detected a mysterious 10.88 millihertz signal. The earth vibrated for nine days. Researchers have now solved the mystery.
On September 16, 2023, a landslide (situation before on the left, after on the right) triggered a tsunami in the Dickson Fjord in East Greenland, which sloshed back and forth for nine days.
(Image: UCL)
An international team of researchers led by Kristian Svennevig from the Geological Survey of Denmark and Greenland (GEUS) has uncovered the cause of a mysterious seismic signal that reverberated for nine days last year and puzzled seismologists worldwide. Their research results were recently published in the journal Science.
On September 16, 2023, seismographs around the world registered an unusual signal with a frequency of 10.88 millihertz (equivalent to the very long period of 92 seconds), which amazingly caused the earth to vibrate slightly for nine days. Because of its similarity to the ringing of a bell, it was initially dubbed an "unidentified seismic object" (USO). The researchers used a combination of different scientific methods to get to the bottom of the phenomenon.
Tsunami triggered by landslide
By analyzing seismic data, the research team was able to locate the origin of the signal in Dickson Fjord in East Greenland. Satellite images showed a conspicuous dust cloud in a gorge of the fjord. A comparison of photos taken by the Danish navy before and after the event revealed a massive landslide in which a 1.2-kilometer-high mountain peak broke off and parts of a glacier fell into the water. The scientists calculated that around 25 million cubic meters of rock fell into the water. This would correspond to the volume of 10,000 swimming pools.
Using detailed computer models of the water movements in the fjord, the researchers were subsequently able to prove that the landslide triggered a wave around 200 meters high. Even 75 kilometers from the starting point, the waves were still four meters high. What was unique about this event, however, was that the waves, which were around seven meters high, sloshed back and forth between the steep slopes of the narrow fjord for nine days – a phenomenon known as seiche. According to the research team's analysis, this effect is responsible for the unusual seismic signal.
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Supporting glacier caused mountain to collapse
The scientists identified climate change as the cause of the landslide: rising temperatures in Greenland caused the supporting glacier at the foot of the mountain to melt, which ultimately led to the collapse. In an article for Nature, geologist Göran Ekström from Columbia University described the study as a successful explanation for an "extremely strange and unusual" seismological event. Study leader Svennevig warns that such "crazy events" could occur more frequently in the future due to advancing climate change.
Dr. Stephen Hicks from London University College (UCL), one of the scientists involved, emphasized the uniqueness of the event: "We have never seen such a large-scale movement of water over such a long period of time." He added that this is "perhaps the first time that a climate event has affected the Earth's crust beneath our feet on a global scale".
(vza)
