Terrain controls on the occurrence of coastal retrogressive thaw slumps along the Yukon Coast, Canada

Retrogressive thaw slumps (RTSs) are among the most active landforms in the Arctic; their number has increased significantly over the past decades. While processes initiating discrete RTSs are well identified, the major terrain controls on the development of coastal RTSs at a regional scale are not yet defined. Our research reveals the main geomorphic factors that determine the development of RTSs along a 238km segment of the Yukon Coast, Canada. We (1) show the current extent of RTSs, (2) ascertain the factors controlling their activity and initiation, and (3) explain the spatial differences in the density and areal coverage of RTSs. We mapped and classified 287 RTSs using high-resolution satellite images acquired in 2011. We highlighted the main terrain controls over their development using univariate regression trees model. Coastal geomorphology influenced both the activity and initiation of RTSs: active RTSs and RTSs initiated after 1972 occurred primarily on terrains with slope angles greater than 3.9 degrees and 5.9 degrees, respectively. The density and areal coverage of RTSs were constrained by the volume and thickness of massive ice bodies. Differences in rates of coastal change along the coast did not affect the model. We infer that rates of coastal change averaged over a 39year period are unable to reflect the complex relationship between RTSs and coastline dynamics. We emphasize the need for large-scale studies of RTSs to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget. Plain Language Summary Retrogressive thaw slumps, henceforth slumps are a type of landslides that occur when permafrost thaws. Slumps are active landforms: they develop quickly and extend over several hectares. Satellite imagery allows to map such slumps over large areas. Our research shows where slumps develop along a 238 km segment of the Yukon Coast in Canada and explains which environments are most suitable for slump occurrence. We found that active and newly developed slumps were triggered where coastal slopes were greater than 3.9 degrees and 5.9 degrees, respectively. We explain that coastal erosion influences the development of slumps by modifying coastal slopes. We found that the highest density of slumps as well as the largest slumps occurred on terrains with high amounts of ice bodies in the ground. This study provides tools to better identify areas in the Arctic that are prone to slump development.