Warming‐induced destabilization of the polar coastal rock cliff of Forkastningsfjellet, Svalbard

Deep-seated landslides rockslides and related displacement waves threaten coastal settlements, infrastructure, and shipping routes in the Arctic. However, the occurrence, dynamics, and impact of such rockslides under a warming climate are poorly understood owing to scarce observational data. We have investigated two rockslides on the permafrost coastline of Forkastningsfjellet, Svalbard. Along this coastline, which was dormant for at least the last 80 years, a 175,000 m³ rockslide occurred in August 2016, followed by a second rockslide of 750,000 m³ in November 2022. Based on extensive field data collection starting in 2017, which includes the acquisition and differencing of drone-based DEMs, point-based displacement measurements (dGNSS), ground surface temperature logging, and field mapping, we documented accelerating surface deformation and the redirection of the drainage pathways from the surface into the ground that drove the dynamics of the 2022 rockslide. Our findings indicate that this rockslide was governed by rapid fluvial incision and accelerated thermo-erosion along colluvium-covered, pre-existing zones of weakness.

We attribute this localized permafrost degradation to climate warming, which increases the active layer thickness and water availability. Cliff instability is linked to cohesion loss and rising pore water/ice pressures from the refreezing cleft ice within the joint system of the bedrock.

Given continued Arctic warming with increasing permafrost temperatures, active layer depths, and changing precipitation patterns, thermal erosion might play a key role in permafrost degradation and future destabilization of rock slopes along the Arctic coastlines. In this context, the morpho-structural development of Forkastningsfjellet could serve as a model for the future development of other polar coastal landscapes.