Simple Drivers of Snow Instability

Snow layers form during and after accumulation due to the interaction of meteorological and physical processes. It is known that the vertical structure and also the lateral continuity of layers de- pend on these processes and the boundaries set by the terrain. This study addresses the amount of vari- ation seen among vertical profiles on slopes and within a basin. In the past years a unique dataset was acquired with more than a thousand snow micro-penetration resistance measurements covering a variety of dry-snow conditions. With recent advances in signal processing all snow layer properties relevant to slab avalanche release are extracted from a SMP signal so that the propensity to failure initiation and crack propagation can be calculated. The modelled values correspond well with field test results obtained during the measurement campaigns and the verified, local danger. We then analyzed whether the spatial characteristics found were related to simple drivers such as slope aspect, snow depth and slope angle. In general, the older the slabs the more drivers were identified. Slope aspect was certainly a prominent driv- er, but also snow depth influenced the distribution of snow instability. However, the direction of influence depended on the size of the dataset, probably on whether the same or different slab-weak layer combina- tions were present. Our findings suggest that even though spatial variations of snow instability are hard to predict, simple drivers exist that may well help to reduce the uncertainty in avalanche hazard evaluation.