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, external, 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 the fjord. Comparing photographs before and after the event revealed that a mountain had collapsed and swept part of a glacier into the water.
The researchers eventually worked out that 25 million cubic metres of rock – a volume equivalent of 25 Empire State Buildings – slammed into the water, causing a 200m-high “mega-tsunami”.
In the “after” photographs of the location, a mark is visible on the glacier – left by the sediment that the giant wave hurled upwards.
