LANDSLIDE INVENTORY AND SUSCEPTIBILITY MODELING FOR THE YUKON ALASKA HIGHWAY CORRIDOR, CANADA

As part of a research project to develop landslide susceptibility models, a landslide inventory has been updated for the Alaska Highway Corridor in the southern Yukon. The study area extends a distance of 873 km from Alaska to British Columbia (BC). It consists of a 40 km wide corridor centred on the highway and covers approximately 22,000 km² (excluding portions extending into BC).

The first step in landslide hazard analysis is compiling an inventory. A total of 1600 landslides were documented using a combination of air-photos mainly captured between the mid-1970s to 1990s, high resolution satellite imagery (2010), and field verification. A variety of landslide types were identified, including debris flows (32%), debris slides (32%), rockfalls/rock slides (14%), earth flows/slides (5%), and landslides triggered in permafrost, such as active layer detachment slides (ALD; 16%) and retrogressive thaw slumps (RTS; 1%).

As with most inventories, this landslide inventory only represents a “snapshot” in time based on detectable geomorphological landslide signatures. The landslide inventory map was used to validate qualitative landslide susceptibility models for debris flows, rockfall/rockslides, and ALD. Some of the limits to validation were the signature, or lack thereof, of the deposit and/or its initiation zone. For example: ALD and RTS re-vegetate rapidly leading to a relatively short geological signature; changing permafrost conditions in recent decades may have altered the frequency of ALD and RTS; small landslides may not be visible on low resolution air photographs; and there are difficulties in resolving individual events where recurring debris flows have produced large fans which have aggraded throughout the Holocene.

Nevertheless, the landslide inventory has helped characterize landslide hazards and validate the susceptibility models for the highway corridor at a preliminary level. Success rate curves, landslide susceptibility models and areas with high densities of landslides should be assessed in detail when planning infrastructure development such as roads and pipelines.