A massive landslide in a Greenland fjord triggered a wave that “shook the Earth” for nine days.
The seismic signal last September was picked up by sensors all over the world, leading scientists to investigate where it had come from.
The landslide – a mountainside of rock that collapsed and carried glacial ice with it – triggered a 200m wave.
That wave was then “trapped” in the narrow fjord – moving back and forth for nine days, generating the vibrations.
Landslides like this, scientists say, are happening more frequently with climate change – as the glaciers that support Greenland’s mountains melt.
The results of the investigation into this event, which are published in the journal Science, are the result of a detective mission involving an international team of scientists and the Danish Navy.
“When colleagues first spotted this signal last year, it looked nothing like an earthquake. We called it an ‘unidentified seismic object’,” recalled Dr Stephen Hicks from UCL, one of the scientists involved.
“It kept appearing – every 90 seconds for nine days.”
A group of curious scientists started to discuss the baffling signal on an online chat platform.
“At the same time, colleagues from Denmark, who do a lot of fieldwork in Greenland, received reports of a tsunami that happened in a remote fjord,” explained Dr Hicks. “So then we joined forces.”
The team used the seismic data to pin down the location of the signal’s source to Dickson Fjord in East Greenland. They then gathered other clues, including satellite imagery and photographs of the fjord that were taken by the Danish Navy just before the signal appeared.
A satellite image showed a cloud of dust in a gully in
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