Two large unstable slopes in West Greenland illustrates an emerging Arctic tsunami hazard

Landslides entering fjords or lakes can generate tsunamis that threaten communities far beyond the source area. Here we document the active deformation of two newly identified unstable slopes within the Uummannaq Fjord system in central West Greenland: a large slope in Karrat Fjord ( ~ 400 million m³) and a smaller yet more imminent, slope in Kangerluarsuk Fjord ( ~ 30 million m³). Both were discovered following the catastrophic 2017 Karrat landslide and tsunami, which prompted closer investigations of the region. Numerical tsunami simulations indicate that a potential collapse of the Karrat unstable slope would produce a tsunami affecting the entire fjord system. The scale, location, and evolving nature of these slopes highlight the vulnerability of remote Arctic regions to landslide-induced tsunamis. Likely driven by permafrost degradation, these slopes represent an emerging hazard expected to worsen with continued Arctic warming. Our findings underscore the importance of the monitoring and risk mitigation efforts by local authorities in these rapidly changing high-latitude environments. Newly identified unstable slopes in central West Greenland highlight the emerging Arctic hazard from landslide-generated tsunamis, potentially linked to ongoing permafrost thaw, according to field observations, remote sensing and numerical modelling analysis.