The influence of terrain parameters on the spatial variability of potential avalanche trigger locations in complex avalanche terrain
More winter recreationists are venturing into steep avalanche chutes and "extreme" terrain each year, and avalanche fatalities are increasing. The slope-scale spatial variability of weak layers and slabs and how it relates to this complex terrain is of critical importance but poorly understood. In this study, I use terrain parameters to model potential trigger locations (PTLs) of slab avalanches, which are defined based on slab thicknesses and presence of weak layers. In a sample couloirs and chutes in Montana and Wyoming, field teams tracked and mapped persistent weak layers and slabs with probe sampling. Terrain parameters derived from a one meter DEM were used to explore the relationships between PTLs and terrain. Exploratory analysis, multi-model classification trees, and logistic regression models support strong relationships between terrain and PTLs. Modeling of PTLs was highly successful for individual couloirs, with terrain-based model success rates frequently exceeding 70% for depth hoar PTLs and 85% for near-surface weak layers. However, models varied widely from couloir to couloir, with generally poor cross-validation results between couloirs, suggesting that the relationships between terrain and PTLs in each couloir are unique and highly complex. For these 21 couloirs in steep alpine terrain, parameters relating to wind deposition and scouring have the strongest association with PTLs.. Parameters with the greatest ability to discriminate PTLs are distance from the edge of a couloir, relative elevation, degree of wind exposure, and degree of terrain exposure. The influences of these and other terrain parameters vary, depending on broader-scale terrain characteristics, prior weather patterns, and seasonal trends. Practical implications from this study are numerous. With an understanding of the broader scale influences and physical processes involved, we can use terrain to optimize stability test locations, explosive placements, or route selection. The unique nature of each couloir means that simple rules relating terrain to PTLs will not apply, although couloirs in the same cirque generally share similarities. This work increases our understanding of how each parameter relates to the physical processes causing PTLs and how these relationships can vary. This information will help to improve practical decision-making ability as well as future modeling efforts.