Modelling climate-induced instability of ice-rich permafrost slopes

Climate-induced slope failures in ice-rich permafrost environments typically manifest in surficial materials as active layer detachment failures (ALDF) and as newly initiated retrogressive thaw slumps (RTS). Instability is linked to high pore water pressures developed during thaw of ice-rich layers that reduce the factor of safety below unity. Here we develop a module within the CryoGrid community model that uses meteorological inputs and soil geotechnical characteristics to simulate ice segregation and thaw consolidation, and predicts potential instability at all levels within the soil column through time using an infinite slope analysis. The analysis is expanded spatially using clustering of slope gradients and aspect. The model was tested using a multi-decadal database of RTS initiation for an area of 2300 km 2 on Banks Island, Canada. We used RTS as a proxy for ALDF, since the majority of RTS in the field area were triggered in warm summers by exposure of massive ice following ALDF. Results showed that the Thawing Slope Stability Index (TSSI), based on the severity and duration of slope instability, was correlated with years in which tens to hundreds of RTS were initiated. These years were characterized by high summer air temperatures and high incoming short-wave radiation which led to a deepening of the active layer in the model, melting of ice-rich layers, and increased pore water pressures. Furthermore, the newly initiated RTS were concentrated on slopes with the highest TSSI values. The newly developed modelling scheme represents a significant step towards evaluating the stability of ice-rich permafrost slopes for different land use and climate change scenarios.