A huge tsunami caused a “standing wave” that flooded an entire fjord for a week and was recorded by seismographs from Alaska to Germany.
A huge landslide occurred on the east coast of Greenland, which caused a megatsunami with a height of 200 meters. But scientists were not shocked by the wave height – much more surprising and terrible were the consequences of the tsunami, which seismologists observed for seven days after the landslide.
IFLScience writes about this.
The event occurred in September 2023 and went virtually unnoticed, as the elements had nothing to destroy and no one to kill in this virtually deserted place with a harsh climate. And only a year later, scientists reported the amazing and frightening consequences – the appearance of a second type of wave, which caused the waters of the fjord to “rise up” and beat against the rocky shores for a week.
Most often, tsunamis are caused by volcanic eruptions or underwater earthquakes. But there is another reason – an avalanche or landslide falling into the water. And this type of tsunami is quite common, although often less destructive, as it occurs in northern sparsely populated areas.
One such tsunami in 1958 caused waves 524 meters high in Alaska – the highest in the history of observations. But at the same time, only five people and 4 square kilometers of forest were killed by the elements.
In September 2023, seismologists from the German Research Center for Geosciences GFZ detected a double signal off the east coast of Greenland. Its first “note” corresponded to the occurrence of a megatsunami more than 200 meters high, which rushed along a 20-kilometer fjord and quickly died down, finding itself in the open ocean.
But the second “note” turned out to be much more interesting. It was the so-called very long period (VLP) signal, which was created by a seiche – a “standing wave” that makes the entire thickness of the water resonate and literally “stand on end.”
“The fact that the signal of a standing wave caused by a landslide in a remote area of Greenland could be seen around the world for more than seven days is fascinating. It is this signal that attracted the attention of seismologists. Analyzing the seismic signal can lead to better monitoring of similar events in the future. If we had not studied this event seismically, we would not have known about the seiche that formed in the fjord system,” said Angela Carrillo-Ponce from GFZ.
In search of the source of the tsunami, scientists analyzed satellite images of Greenland and discovered a section of rocks near Dikson Fjord that “was here yesterday and gone today.” That is, a huge piece of rock broke off and caused a landslide that traveled almost 2 kilometers, capturing more ice and rocks along the way, until it reached the shore of the fjord and fell into the water from a height of 300-400 meters.
No one saw what happened to the waters of the fjord. Only the results of seismic observations allowed us to reconstruct the events. The seiche that formed after the main tsunami wave descended raised the waters of the fjord by more than 2.5 meters and beat between its side banks with a frequency of less than two minutes. It is worth noting that the width of the fjord is 2 km.
“What is impressive is that we were able to use quality data from stations as far away as Germany, Alaska and North America, and that these records were strong enough for at least one week,” said Carrillo Ponce.
The cause of the landslide is not reliably known. However, scientists believe that the rocks of Greenland are unstable and are held only by glaciers. Therefore, the probable cause of the landslides is the melting of glaciers caused by climate change. This hypothesis is also supported by the fact that most such events occur in late summer.
Recall that the Etna volcano has woken up again on the Italian island of Sicily. At night, an eruption began from one of the craters and continued all day. The lava fountain rose to a height of 10 kilometers.
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