Relating complex terrain to potential avalanche trigger locations

More winter recreationists are venturing into “extreme” terrain each year, and avalanche fatalities in that terrain are increasing. The slope-scale spatial variability of snow stability and how it relates to this complex terrain is critically important but poorly understood. In this study, we use terrain parameters to model potential trigger locations (PTLs) of slab avalanches, which are defined based on a minimum slab thickness overlying a persistent weak layer or the presence of a weak layer on the snow surface which could be subsequently buried. In a sample of seventeen couloirs from Lone Mountain, Montana, field teams tracked and mapped persistent weak layers and slabs with probe and pit sampling. We used terrain parameters derived from a one-meter digital elevation model to explore the relationships between PTLs and terrain, and our results show strong statistical relationships exist. However, results varied widely from couloir to couloir, suggesting that the relationships between terrain and PTLs in each couloir are unique and highly complex. For these steep alpine couloirs, parameters relating to wind deposition, wind scouring, and sluffing are most strongly associated with PTLs. The influences of these and other terrain parameters vary, depending on broader-scale terrain characteristics, prior weather patterns, and seasonal trends. 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 study will help to improve practical decision-making as well as future modeling efforts.