One year ago, a seismic wave was registered that lasted for nine days. The signal, a vibration in the earth, was unusual in two ways: it lasted for so long and maintained the same frequency, like a long, monotonous humming.
Seismologists around the world were perplexed.
It was a seismic signal we had never seen before. It was very exciting and gave rise to all sorts of wild suggestions about what it could be, says Björn Lund, seismologist at Uppsala University.
Tsunami
Soon, suspicions were directed towards a tsunami in a Greenland fjord on September 16, roughly at the same time as the mysterious signal was discovered.
This led 68 researchers from institutions in 15 countries to initiate a collaboration to get to the bottom of the mystery using various data, field measurements, satellite images, and simulations. And now the mystery is solved, according to the study published in the journal Science.
It was a mountain top that collapsed into Dickson Fjord on eastern Greenland, triggering an enormous tsunami. The wave swelled back and forth in the narrow fjord and gave rise to the vibrations registered by meters around the world, according to the researchers.
A standing wave was formed in the fjord that oscillated back and forth for nine days and didn't dissipate much during that time, says Lund, who participated in the study.
It made the earth ring like a church bell for nine days, in a single tone.
Climate Effect
The triggering factor was most likely climate change, the researchers believe – since the melting glacier tongue no longer helps to stabilize the mountain side, which eventually collapsed into the sea.
We have previously seen seismic waves that could last for hours, but not for such a long time. Global warming may also lead to phenomena we have never seen before, says Lund.
No people were in the vicinity, but a cruise ship route passes by the fjord mouth. The researchers believe that it may require more monitoring in areas previously thought to be relatively safe.
This is the first time a major tsunami has been seen on eastern Greenland, says Lund.
It shows the dangers of global warming in ice-covered areas, that it's not just about the ice calving and disappearing, but also that the mountain sides are destabilized. We will likely get more landslides and tsunamis in the fjords of Greenland.
