Ellen Phiddian
Cosmos science journalist
On 16 September 2023, a mega-tsunami ripped through eastern Greenland. The waters reached 200 metres high in some places and damaged an empty military base. The remote location meant that no-one was hurt, but nor was it easy to figure out the cause.
A team of German seismologists has found the source of the mysterious mega-tsunami.
They used seismological data and satellite imagery to spot a landslide that triggered the tsunami. They’ve also shown that waves from the event lingered in a fjord for a week afterwards.
The researchers have published their findings in The Seismic Record.
Landslides have been known to cause tsunamis in Greenland, and may be increasing as the climate warms. In 2017, a landslide triggered a wave on the northwestern coast that killed 4 people and forced inhabitants to permanently abandon the villages of Nuugaatsiaq and Illorsuit.
In September last year, seismometers around the world lit up with signals, indicating a disturbance in eastern Greenland.
The initial signal, caused by the landslide, was short – but it was followed by a very long-period (VLP) signal that persisted for more than a week. The VLP was spotted by stations as far as 5,000km away from the source, from Germany to Alaska.
The researchers used satellite imagery and seismic data to identify a missing patch of cliff on the southern shore of Dickson Fjord, in the centre of Greenland’s east coast. This was ground zero for the avalanche that caused the tsunami, say the researchers.
“While we were able to obtain information on the direction and magnitude of the force exerted by the landslide, we do not have data to investigate the original cause of the landslide,” says lead author Angela Carrillo-Ponce, a doctoral student at the German Research Centre for Geosciences.
The tsunami triggered a “seiche”, or a standing wave, in the fjord: water oscillated backwards and forwards for a week. It was this standing wave that caused the VLP signal.
“The fact that the signal of a rockslide-triggered sloshing wave in a remote area of Greenland can be observed worldwide and for over a week is exciting, and as seismologists this signal was what mostly caught our attention,” says Carrillo-Ponce.
“The analysis of the seismic signal can give us some answers regarding the processes involved and may even lead to improved monitoring of similar events in the future.”
The researchers say their monitoring method might also be useful for studying past events and gleaning more information from them.
“We have compared our results with remote sensing data to validate our solutions, and our study shows that the force produced by the signals is well resolved,” says Carrillo-Ponce.
“Therefore it becomes a useful analysis as seismic signals contain information on the type of source generating the signal and how the energy is radiated.”
