Snow stability variation on small slopes

The spatial variability of snowpack mechanical properties strongly influences the fracture initiation and fracture propagation properties of the snowpack, thereby largely controlling the avalanche formation process. To investigate variations in stability on the slope scale, we measured stability with stuffblock and rammrutsch tests on eight small potential avalanche slopes above timberline near Davos, Switzerland. On each slope, 17–26 point stability tests arranged in predefined arrays were done. The median, the spread and the spatial structure of the stability was investigated for 16 weak layers. Significant slope scale trends in stability were found in six weak layers. The quartile coefficient of variation for the drop heights was around 40% overall, 20% if the slope scale linear trend was removed. Auto-correlation in drop height was found in eight layers. In none of these layers a range of spatial auto-correlation could be determined. Depth of the fracture layer partly explained variations in stability. A stability rating scheme based on the median, the spread and the spatial structure of stability test results predicted the layers that were most critical for slope stability.