The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
There has been quite a stir over the last week regarding a remarkable paper (Svennevig et al. 2024) that was published in the journal Science, describing a series of events that occurred on 16 September 2023 around and on Dickson Fjord in Greenland. The media interest has been on an anomalous seismic signal that was emitted from this area over a nine day period. The research demonstrates that this was caused by a seiche – a series of standing waves set up after a tsunami swept through the fjord. That tsunami was triggered by a rock-ice avalanche.
Whilst this seiche and tsunami signal was remarkable event, the landslide itself is very interesting.
Svenning et al. (2024) have reconstructed the failure event. It started at [72.81, 26.95] on at Hvide Støvhorn, located 1,200 metres above Dickson fjord at 12:35 UTC on 16 September 2023. The initial failure was 150 m thick, 480 m wide and 600 m long, consisting of a large block of metamorphic rock. The Planet Labs image below shows the site:-
This image was collected at 13:42 on the day of the landslide – one hour and seven minutes after the failure. This is incredible in itself. In the centre left of the image, the remains of the landslide mass can be seen as a dark area in one of the valleys. The landslide started on the eastern flank of this valley, descended onto the glacier (which was then entrained), turned right to flow to the north into the fjord. Note the huge pall of dust, lit by the sun, to the north of this area, with the cloud extending to the east along the southern flank of Dickson Fjord.
Svennevig et al. (2024) estimate that the initial failure had a volume of 25 million cubic metres, and that it entrained a further 2.2 million cubic metres of glacial ice and debris. The landslide removed a debris cone at the termination of the valley, possibly suggesting that it also triggered a submarine landslide.
The landslide runout distance was 2.2 km.
Svennevig et al. (2024) have used the seismic data of the landslide itself to determine the dynamics of the landslide. They estimate that it achieved a peak velocity of 42 metres per second (about 150 km per hour or 94 miles per hour). The seismic data shows two distinct drops in velocity – the first occurred when it struck the wall of the valley to the west of the failure, the second when it struck the water.
On striking the fjord, the landslide generated a tsunami with “an initial backsplash with a runup height of ~200 m and subsequent waves up to 110 m high“. The tsunami had a runup height of 4 metres at Nanok station, 72 km from the landslide event. The tsunami caused substantial damage. Thereafter, Dickson Fjord suffered the seiche that has been well-reported elsewhere.
This is both a remarkable event and a fabulous piece of science, involving a very large, multidisciplinary team of experts. My congratulations go to all of them, and in particular to the first author, Kristian Svennevig of the Geological Survey of Denmark and Greenland.
Whilst the interest in this event has mostly been in the seiche, it is worth noting the following from the conclusion of the paper:
“The large tsunamigenic rock-ice avalanche is an extraordinary event itself, the first ever recorded in East Greenland.”
Svennevig et al. (2024) hypothesise that the cause of the landslide was debuttressing of the toe of the slope associated with retreat of the glacier – i.e. the origin is in our changing climate. There is no doubt that we are seeing more of these events in high mountain areas, so understanding them is critical for the management of risk.
References
Svennevig et al. 2024. A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days. Science, 85 [6714], 1196-1205.
Planet Team 2024. Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
