Sloshing water and thinning ice: the story behind the 2023 rockslide-generated tsunami in the Dickson fjord
- Chiara de Geeter
- 5 days ago
- 4 min read
On the 17th of September 2023, the Danish military’s Arctic Command unit received a concerning message from a previous member of the Sirius Dog Sled Patrol. While travelling along the northeastern Greenland coast on board a cruise ship, the former employee noticed that the Patrol’s home base, located on the small island Ella Ø at the mouth of the King Oscar Fjord, appeared to be in serious disarray. Indeed, an inspection vessel and aircraft subsequently sent out by the Arctic Command found the area completely dishevelled, with equipment and infrastructure, valued at nearly 200,000 USD (about 174,000 EUR), shattered across the beach or floating in the water. Coincidentally, a distinct seismic signal was recorded by stations all across the world and triangulated back to the same region. The culprit? A rockslide-generated tsunami that had originated a day earlier in the Dickson fjord, a more inland branch of the King Oscar fjord system. The incident not only resulted in severe damage to the Sirius Patrol Station but also to several Inuit cultural heritage sites and century-old trapper huts in the area. Luckily, the Sirius Patrol station was abandoned for the season, and no cruise ships were in the vicinity of the fjord when the rockslide occurred. But the disaster makes one wonder, how did the rockslide happen, and is it bound to happen again?
Ella Island station after the tsunami. Credit: SIRIUS/Arctic Command via Facebook
Based on data collected at nearby observation stations and model simulations, an international team of scientists reconstructed the chain of events leading up to the incident. They determined that the rockslide had been in the making for years. That is because the glacier resides in a gully with steep side walls, which are steadied by the glacier’s presence. Over the last decade, however, the gully faces’ support has been slowly withering away as the glacier gradually but significantly thinned. Hence, the rock became increasingly more unstable, and on the 16th of September, a large chunk finally detached from the mountainside. The rockslide tumbled down the glacier, picking up ice along the way, until the twenty-five million cubic metres of rubble impacted the fjord. The displaced water engulfed the fjord’s shores as a tsunami wave, and locally, the initial backsplash reached heights of up to 200 meters above the regular water level. The direct aftermath of the tsunami and rock-ice avalanche was silently witnessed by several satellites flying overhead: the Dove mini-satellite swarm from Planet Labs Inc. and ESA’s Sentinel-2 satellite observed coastal areas darkened by the tsunami wave’s inundation, a smear of rubble left on the glacier surface by the rockslide, and a fresh ‘scar’ on the mountain face where the culprit rock originated. The fjord’s waters were muddy and littered with ice fragments and floating debris.
After the impact, the water continued sloshing back and forth in the narrow fjord for days, and the pressure variations at the fjord floor caused seismic vibrations that travelled all across the globe. The ringing seismic signal caused by this ‘seiche’ was picked up at seismic stations for up to nine days after the incident. Serendipitously, multiple oceanographic instruments had been installed in the fjord the previous summer, survived the tsunami wave, and had unwaveringly continued their observations during the seiche. Their measurements show how the water suddenly became cloudy after the landslide impact, and how the water level fluctuated periodically as the water seesawed up and down in the fjord. The seiche was even detected by NASA’s new Surface Water Ocean Topography (SWOT) satellite, only about seven weeks after the initialization of its science phase.
It is the first time that an event of this kind in Northeast Greenland has been recorded and described in such detail. However, after careful review of satellite observational records, it was found that the incident was part of a series of similar rockslides in the same gully, some of which could also be associated with distinct seismic signals. As the Earth continues to warm and the Greenland glaciers continue to thin, similar events will inevitably happen again. It seems it will only be a matter of time before slope instability becomes an undeniable danger to property, infrastructure, and communities in Greenland and the Arctic region. However, the remarkable detail with which this event has been reconstructed also showcases how global observing networks and international, interdisciplinary collaborations can drive our understanding of the hazards of a changing climate. The incident can also serve as a reminder that even the remotest of glaciers can send ripples through the entire planet.
Written by Chiara de Geeter
Sources and further reading:
Svennevig, K., Hicks, S. P., Forbriger, T., Lecocq, T., Widmer-Schnidrig, R. et al. (2024). A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days. Science, 385(6714), 1196–1205. https://doi.org/10.1126/science.adm9247
Carrillo-Ponce, A., Heimann, S., Petersen, G. M., Walter, T. R., Cesca, S., & Dahm, T. (2024). The 16 September 2023 Greenland Megatsunami: Analysis and Modeling of the Source and a Week-Long, Monochromatic Seismic Signal. The Seismic Record, 4(3), 172–183. https://doi.org/10.1785/0320240013
Monahan, T., Tang, T., Roberts, S. & Adcock, T. A. A. Observations of the seiche that shook the world. Nat. Commun. 16, 4777 (2025). https://doi.org/10.1038/s41467-025-59851-7
Original post by the Joint Arctic Command unit on Facebook: here
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