LANDSLIDE SUSCEPTIBILITY MAPPING IN PERMAFROST TERRAIN ALONG THE YUKON ALASKA HIGHWAY CORRIDOR, SOUTHWESTERN YUKON, CANADA

Slope stability in the permafrost terrain of northern Canada can greatly influence infrastructure design and performance. Several types of landslides and ground hazard features were identified for a proposed pipeline route along Yukon Alaska Highway Corridor (YAHC=950 km x 40 km). Some were directly related to permafrost conditions, such as, active layer detachment slides, retrogressive thaw flows, solifluction, thermo-karstic depressions, and rock glaciers. Landslide inventory and preliminary susceptibility maps of debris flows, rockfalls/rock slides, active layer detachment slides, and retrogressive thaw flows were produced. The inventory identified a total of 1743 landslides, or 1 landslide per 17 km². These were debris slides (31%), debris flows (28%), rock slides (11%), rockfalls (4%), solifluction (8%), earth slides/flows (5%), thermo-karstic depressions, retrogressive thaw flows and active layer detachments (1%) and rock glaciers (6%). Landslide susceptibility modeling was based on a qualitative heuristic approach, which was split into four different mapping exercises reflecting the different parameters that trigger these landslides. Validation of the debris flow susceptibility map indicates that 69% of the debris flow deposits occur downstream from a high susceptibility zone and 28% from moderate zone. The rockfall/rock slide susceptibility map indicated that 64% of failures occur in high susceptibility zones and 20% in moderate zones. Thus, there is a good correlation between the landslide susceptibility maps and landslide inventory. Validation of active layer detachment slide and retrogressive thaw flow susceptibility maps was more difficult as these types of landslides are considered temporary because they disappear from the geological record in a short period of time. These are usually small and are re-vegetated rapidly, which makes them less easily identifiable on air-photos. Nonetheless, there is good correlation with the available inventory and the susceptibility maps.