Surficial geology, quaternary history and active layer detachment landslides of the Kluane Ranges, Southwest Yukon

Surficial geological mapping in the central Kluane Ranges was undertaken to better understand the distribution and character of surficial materials. Upland surficial materials in the area are dominated by near-source bedrock derivatives. Valley bottom settings, including Shakwak Trench and Duke River valley, are characterized by broad open valleys with thick deposits of Quaternary sediment. Mass wasting processes in the study area include rock fall and avalanches, debris flows and avalanches and active layer detachment slides. The stratigraphy of the southern Kluane Lake region was examined and a Quaternary history for the area was developed. The presence of a till containing relict permafrost features and organics dating back to 41-43 ka suggests MIS 4 deposition at Mines Creek with subaerial exposure during MIS 3 and glacial tectonism during MIS 2. The retreat of ice, marked by outwash gravels and evidence of a proglacial lake, delineates the post-glacial landscape. Notably, a post-glacial high stand of Kluane Lake, recorded at Lewis Creek North, indicates a higher elevation than previously thought, possibly influenced by cooling periods during the Younger Dryas causing a readvance of local valley glaciers from the St. Elias and Ruby ranges blocking northern outflow of Kluane Lake. This research also examines active layer detachment landslides (ALDs) in the northern Kluane Ranges from 1923 to 2021, revealing a substantial increase in ALD frequency. Analysis of ALD initiations per year demonstrates an overall upward trend, with more than twice as many ALDs recorded in the last three decades compared with the first three decades examined. Climatic factors, particularly rising mean temperatures and increased precipitation during thaw months, align with this trend, indicating a considerable influence of changing climate conditions on ALD occurrences. Aspect, slope class, bedrock lithology, and dominant surficial materials also play crucial roles in ALD initiation, with certain characteristics, such as east to southeast aspects and colluvium, exhibiting higher susceptibility. The study underscores the complex interplay of climatic, geological, and environmental factors in ALD dynamics and emphasizes the need for further research to understand and mitigate the increasing risk of ALDs in a changing climate.