A massive landslide in a remote fjord in eastern Greenland triggered an extraordinary tsunami in September 2023 producing seismic vibrations that were detected by monitoring stations around the world. The unusual signal repeated approximately every 92 seconds for nine consecutive days, leaving scientists puzzled about its origin.
The event occurred on September 16, 2023, when a mountainside collapsed into Dickson Fjord, sending enormous quantities of rock and glacier ice crashing into the water. The impact generated a powerful tsunami that travelled across the narrow fjord, repeatedly pushing water against its steep surrounding cliffs.
Scientists later discovered that the unusual seismic signals recorded thousands of miles away were caused by the movement of water trapped inside the fjord.
Massive Landslide Created a Powerful Tsunami
The collapsing mountainside carried a mixture of rock and ice into the fjord, displacing a tremendous volume of water. The resulting tsunami surged more than 200 metres up nearby slopes.
According to research led by Kristian Svennevig and published in the journal Science in 2024, the average wave run-up reached approximately 60 metres along a 10 kilometre stretch of the fjord.
The incident demonstrated how unstable mountain slopes in glacial regions can generate extremely powerful waves, even in remote locations far from major population centres.
Another, smaller landslide struck the same location on October 11, 2023, indicating that the mountainside remained unstable after the initial collapse.
Why Did the Water Move for Nine Days?
Researchers discovered that the unusual shape of Dickson Fjord played a crucial role in prolonging the event.
According to research by Angela Carrillo Ponce and colleagues a sharp bend near the fjord’s outlet prevented the displaced water from escaping easily into the open ocean.
Instead the water became trapped and moved repeatedly from one side of the narrow fjord to the other. This phenomenon is known as a seiche a standing wave that oscillates within an enclosed or partially enclosed body of water.
As the enormous water mass repeatedly struck the surrounding rock walls it generated rhythmic vibrations that travelled through Earth’s crust.
Seismic monitoring stations around the world detected these low frequency vibrations at remarkably regular intervals of approximately 92 seconds.
Although scientists initially studied the phenomenon using seismic measurements, direct evidence of the water’s movement came later through satellite technology.
Researchers used observations from NASA and international partners’ Surface Water and Ocean Topography (SWOT) satellite mission to examine changes in the fjord’s water surface.
A study published in Nature Communications on June 3, 2025 by Thomas Monahan and colleagues revealed that the water surface tilted by as much as two metres across the fjord as the wave repeatedly changed direction.
By combining satellite radar observations with seismic measurements from Alert in Canada, researchers estimated that the standing wave had an amplitude of approximately 26 feet (eight metres).
Weather and tidal models also helped establish that ordinary winds and tides were not responsible for the unusual water movement.
Scientists have highlighted an important distinction between two measurements associated with the Greenland event.
The approximately 200 metre measurement describes the maximum run up meaning how high the tsunami water travelled up the steep surrounding slopes near the landslide.
In comparison, the approximately eight metre measurement represents the amplitude of the standing wave moving across the fjord.
These measurements describe different aspects of the same event and help scientists understand both the initial destructive impact and the prolonged movement of water.
Researchers believe that long term glacier thinning and the weakening of frozen ground contributed to the mountain collapse.
Glaciers often provide structural support to surrounding mountain slopes. As temperatures rise and ice retreats, previously supported sections of rock can become increasingly unstable.
Thawing permafrost can further weaken mountain structures, increasing the possibility of landslides and dangerous tsunamis.
Scientists have compared the risks with the 2017 Karrat Fjord landslide in Greenland, which triggered a tsunami that devastated the village of Nuugaatsiaq.
Despite advances in satellite monitoring, predicting exactly when an unstable mountainside will collapse remains a major challenge.
The Greenland incident has demonstrated how satellite radar technology can help scientists investigate dangerous water movements in remote regions where conventional monitoring instruments are limited.
The SWOT satellite mission provided valuable observations of the fjord’s changing water surface, helping researchers confirm the physical processes behind the mysterious seismic signals.
Scientists believe this approach could improve the monitoring of enclosed water bodies and remote coastal environments worldwide.
The extraordinary nine day event also highlights the potential consequences of a warming Arctic. As glaciers retreat and mountain slopes become increasingly unstable, understanding the relationship between climate change, landslides and tsunamis will become increasingly important for assessing future environmental hazards.