A new paper describes a rock avalanche in Greenland dating to about 10,900 years BP that had a volume of more than 1 billion cubic meters and traveled about 16 km.
An interesting paper (Pederson ET. 2026) has just been published in the journal Gemorphology It describes a newly discovered ancient rock avalanche in Greenland. This landslide, located in the Topasat Valley, is really massive. The authors estimate its volume to be more than 1 km3 (1 billion m3), with a distance of 15.8 km and a vertical elevation difference of 1,440 m.
The rear scar of the landslide is now located [60.4117, -44.2791]. It’s really hard to capture this landslide on Google Earth, but luckily this paper is published under a Creative Commons license. Here, then, is the landslide map by Pedersen ET. (2026):-
b) Map showing bathymetry data and landslide outline. The bathymetry data is obtained from the Danish Geodata Agency and is not suitable for navigation. The slopes of the region are presented below.
Pedersen’s photos ET. (2026)
I quickly interpreted a Google Earth image of the site, showing the source and the track of the landslide. Note that the pier extends into the fjord, and is thus underwater, which is a couple of kilometers away:-
Landslides on this scale are difficult to predict. If this volume of rock stood on a standard American football field (110 m x 49 m), it would create a column 185.5 km long.
Pedersen ET. (2026) dated the time of occurrence of this landslide. They conclude that this happened about 10,900 years ago. This coincides remarkably well with the history of aggradation (retreat of ice sheets) in this area. Thus, the authors suggest that the instability was probably related to the initiation of the glacier (i.e., the removal of adjacent ice from the slope. They cannot rule out the possibility that the earthquake may have triggered the final failure.
Another interesting question is whether the event triggered the tsunami in the fjord. The distance traveled by the landslide shows that it was very energetic. Given that it extended into the water (and some of the deposits are now within the lake) it is very likely that a displacement wave was triggered.
The latter point is very pertinent as there is growing concern about the risks of giant rock slope failures producing damaging tsunami events in fjords. For example, CNN published an article this week in the wake of the Tracy Arm landslide and tsunami that highlighted the danger to cruise ships. It notes that:
Alaska’s foremost expert on these landslides knows why deadly landslide-turned-catastrophic disasters haven’t happened, yet: sheer luck.
“It’s not because it’s not a threat,” said geologist Brett Wood Hageman, co-founder and executive director of the nonprofit GroundTrue Alaska. “That’s because it didn’t happen in front of someone’s house or a cruise ship.”
An additional piece of context is the notable flooding that occurred in Alaska last weekend as Typhoon Halong tracked through parts of the state. It seems to have gotten less attention than expected, at least outside of the US.
It is surely only a matter of time before we see a truly massive disaster resulting in a tsunami triggered by rock slope failure. A serious scenario is that a large cruise ship is overwhelmed and sinks. The loss of life can be very high.
Reference
LL Pedersen ET. 2026. A massive early Holocene tsunamigenic rock iceberg in southern Greenland predated by glacial sedimentation. Gemorphologyfor , for , for , . 492110057,
https://doi.org/10.1016/j.geomorph.2025.110057.
