Mountain and glacier before the landslide at Dickson Fjord
Photo: Søren Rysgaard
It might be one of those world records you’d rather not have, but a Greenland landslide triggering a nine-day tidal wave would have that format. The huge landslide was recorded on September 16, 2023 by seismographic measuring stations in the northern hemisphere. The German Georesearch Center (GFZ) in Potsdam was the first to notice the unusual strength and, above all, the length of time of the wave triggered. A joint working group with experts from other European countries as well as from Chile and the USA analyzed the unusual event.
Die Analysis of the measurement data revealed that the slope of a glacier in East Greenland’s Dickson Fjord had slipped. In a narrow channel with an angle of 30 degrees, around 25 million cubic meters of stones and earth fell 300 meters downwards and, upon impact, triggered a tidal wave up to 200 meters high. This raced down the fjord, which is only about two to three kilometers wide at this point, and shaved its banks. The amount of rubble corresponds approximately to a cube with an edge length of 300 meters. The tidal wave reached the offshore island of Ella after 50 kilometers and was still 60 meters high. The island was flooded and the provision station of the Danish Sirius patrol there was completely destroyed. The station, made up of containers, was unmanned at the time of the tsunami and is only visited when the dog sled patrol passes by in late winter. The destroyed station was discovered by a former Sirius soldier on a passing cruise ship. Looking through binoculars, the soldier noticed that everything was not as it should be. A few days later the station was inspected and cleaned up by a patrol.
A wave over nine days
What was of interest to the scientists was the trigger of the tsunami and the subsequent events. Due to the narrowness of the fjord and the impact on Ella Island, some of the water was pushed back and a standing wave was formed that swayed back and forth for nine days and was picked up by the seismological stations based on the specific signal value. The wave was only one meter high at this point. Angela Carrillo Ponce, who works as a doctoral student in the Earthquake and Volcano Physics section of the GFZ and led the working group, explained that they were able to model this signal and its slow decay and the dominant oscillation period of the long-lasting resonance signals. This will allow future researchers to look backwards into their records to detect similar events that have previously gone unnoticed.
It was fortunate that Dickson Fjord is not inhabited, but it wasn’t always that way. The ancestors of today’s Inuit settled there several centuries ago and left traces of settlement behind. About 100 years ago, Danish and Norwegian fur trappers settled here and built huts that stood until the tsunami. Due to the force of the water masses and their height, it is assumed that all traces of settlement have been wiped out.
Thawing permafrost as the cause
The cause of the landslide is believed to be that the permafrost was exposed to large temperature fluctuations after the protective ice layer melted away. If this is the case, it must be expected that such events will occur more frequently in the future. When planning settlements and mines in Greenland, Alaska, Canada, Norway or Chile with similar topography, consideration must always be given to what geological dangers lurk in the fjords and on the narrow coastal sections in order to prevent potential disasters. Carrillo Ponce stated that “the effects of global warming and permafrost changes are likely to further reduce slope stability and increase the frequency of landslides and tsunamis.”
Not the first tsunami
Back in June 2017, the village of Nuugaatsiaq in the Karrat Fjord on the west coast of Greenland was flooded by a tsunami. Most of the houses in the settlement were destroyed and five people disappeared forever into the sea. The cause was also a landslide 28 kilometers north of the village. Because there is a risk of further landslides, the settlement had to be abandoned.
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