A regional characterization of landslides in the Alaska Highway corridor, Yukon

The following report describes the settings, causes and geological controls of landslides in the Alaska Highway corridor. Although diverse geologic, geomorphic and climatic environments exist in the region, most landslides are related to the presence of shallow bedrock or permafrost, unconsolidated sediment on steep slopes, weak bedrock, groundwater hydrology, river erosion or the degradation of ice-rich permafrost. Where geologic controls provide appropriate settings, intense rainfall, rapid snow melt and seismic events play important roles in triggering failures. Rainstorms that reach thresholds of combined intensity and duration have triggered abundant shallow landslides within the corridor. Debris flows have historically posed the highest risk to lowlying regions and are capable of damaging settlements and transportation routes. The Shakwak Valley has the highest concentration of landslides within the corridor due to the abundance of steep slopes, high relief and widespread discontinuous permafrost. In Wellesley Depression, shallow permafrost and its subsidence has an important influence on slope instabilities. Landslides in the Yukon Plateau primarily relate to the presence of silt- and ice-rich tills on steep valley sides as well as the incision of fine-grained lacustrine terraces in valley bottoms. Debris flows after intense rainfall events are the most common form of landslide in the Kaska Mountains. Finally, in Liard Lowland, failures associated with glacial meltwater and modern stream incision are the most common landslide events. Permafrost plays an important role in landslide processes in the corridor due to its influence on soil moisture, drainage and strength. Slopes composed of icy sediment that have been burned by forest fires are particularly vulnerable to rapid mass movements due to permafrost degradation. The consequences of the dramatic increase in landslide potential after fire should be considered in local fire management plans. The climate?s local and regional influence on hydrology, fire frequency and permafrost distribution greatly affects landslide processes. Current climate change projections call for warmer temperatures and increased precipitation for the Yukon in the next half century. Among the anticipated effects of global warming in southern Yukon, increased incidents of intense snowmelt and/or precipitation events, river migration, permafrost degradation or forest fires may lead to an increase in landslide frequency and/or magnitude within the settings described in this report. The most significant impact of increased landslide activity may not be a direct impact. Rather, increased sediment input from landslides will likely increase stream channel instability and flooding. This would be particularly acute in the vicinity of alluvial and colluvial fan complexes along Kluane Lake where highway maintenance is already a challenge.