New study explains why tsunami signals last year in Greenland lasted for days

New research explains what exactly happened a year ago, when large seismic waves from Greenland caused the earth to tremble for nine days and the movement was detected at monitoring stations worldwide including in Yellowknife.

In a paper published last week in Science magazine, researchers describe how a tsunami became trapped insideDickson Fjord, Greenland, in September 2023 after a mountaintop collapsed. The resulting wave, which scientists measured up to 200 metres high, sloshed back and forth in the deep-water fjordin a phenomenon known as a seiche.

Lead researcher for the paper, Kristian Svennevig from the Geological Survey ofDenmark and Greenland (GEUS), says the occurrence was extremely unusual.

"I noted it down as a USO unidentified seismic object so, something that has never been seen before," she said.

The researchwork was happening alongside an expedition by the Danish army that went into the area three days after the first seismic signals came in. Svennevig says the results of that mission were confusing at first, given no gigantic waves were seen.

The tsunami wave got much smaller as the days went on but seismic signals continued to be picked up around the globe. Svennevig said this was due to the area being two-and-a-half kilometres wide and 500 metres deep.

"If you move that much watertencentimetres, that's enough to get a very powerful seismic signal," said Svennevig.

The researchers say the event highlights some of the effects of climate change andthe risk of large landslides in polar regions.

'Quite spectacular,' says seismologist

One of the monitoring stations picking up those seismic signals was the Yellowknife Seismological Array (YKA). The YKA, along with other stations in the North, transmits its reading to Ottawa.

Allison Bent, a seismologist with Natural Resources Canada, said she still remembers the widespread response from when the event happened a year ago.

"Somebody I know in Belgium sent an email out to a huge number of people saying, 'We see this really weird signal. It looks like it's coming from Greenland. Does anybody know what it is?' So I got curious," recalledBent.

She said she then looked at the data which was "quite spectacular."

Bent said initially,no one she spoke to knew what it was. It wasn't until a few months later at a conference that she heard of the discovery finally being figured out.

After looking into the study she brought up that researchers like Svennevig are taking note of the role climate change plays in landslides and events like this.

"The people working on it think it's likely to be more common as the ice caps in Greenland melt quicker than they usually would but whether they'll see a nine-days signal again, you don't know," she said.

YKA runsevery day, all day

While the seismic movementsfrom the event last year couldn't be felt in Yellowknife, the recording facility in the area picked them up.

Frederick Murphy, the officer in charge at the YKA, says theseismometers at the facilityrun constantly.

"They can pick up signals from almost all over the world. There's a few blind spots in the southern hemisphere, but most of the world," he said.

The main purpose of the seismometers is not todetect incidents like the Greenlandseiche, though. Murphy said originally they were used for detecting nuclear weapons tests and that is still their main purpose.

Murphy said he has seen his fair share of seismic readings in his time at the YKA.Signals are transmitted in real time for analysis in Ottawa.

"I've been here for 14 years. I've seen a lot of the squiggly lines.Sometimes if there's something big, we'll go and check out where it is."