Predicting retrogressive thaw slump expansion across northern Alaska

Retrogressive thaw slumps (RTS) are a prevalent form of thermokarst mass wasting that mobilizes substantial soil carbon and nutrients through the thaw and collapse of ice-rich permafrost across high-latitude landscapes. While mechanisms influencing RTS expansion are relatively well understood, their spatiotemporal drivers remain limited. Across 66 RTSs in northern Alaska, we use aerial and satellite imagery (1949–2021), LiDAR from terrestrial and uncrewed aerial systems, and soil nutrient surveys to model past and projected RTS areal and volumetric change, assessing implications for nutrient mobilization. Generalized linear mixed models distinguished historically active from inactive RTSs (60% sensitivity, 66% specificity), with active slumps associated with gentle, west-facing slopes and higher precipitation. Among active RTSs, headwall length was the strongest predictor of both areal expansion (R 2 = 0.61, RMSE = 0.64) and volumetric loss (R 2 = 0.74, RMSE = 0.67), with temperature and precipitation as secondary controls. First-order estimates suggest RTSs may be substantial sources of carbon and nutrients, though concentrations varied with slump age. Projections assuming continued RTS activity indicate future change will be greatest for large slumps (9,000–90,000 m 2 ), although projected expansion rates remain highly uncertain, ranging from approximately 1- to 34-fold greater than present-day rates by century’s end.