Abstract
Abstract. Snow slope stability evaluation requires considering weak layer as well as slab properties – and in particular their interaction. We developed a stability index from snow micro-penetrometer (SMP) measurements and compared it to 129 concurrent point observations with the compression test (CT). The index considers the SMP-derived micro-structural strength and the additional load, which depends on the hardness of the surface layers. The new quantitative measure of stability discriminated well between point observations rated as either "poor" or "fair" (CT < 19) and those rated as "good" (CT ≥ 19). However, discrimination power within the intermediate range was low. We then applied the index to gridded snow micro-penetrometer measurements from 11 snow slopes to explore the spatial structure and possibly relate it to slope stability. Stability index distributions on the 11 slopes reflected various possible strength and load (stress) distributions that can naturally occur. Their relation to slope stability was poor, possibly because the index does not consider crack propagation. Hence, the relation between spatial patterns of point stability and slope stability remains elusive. Whereas this is the first attempt of a truly quantitative measure of stability, future developments should consider a better reference of stability and incorporate a measure of crack propagation.
Highlights
Snow stability data are among the key ingredients when establishing avalanche forecasts
The newly developed stability index was calculated for data set (b) of the 129 cases with snow micro-penetrometer (SMP) profile and compression test (CT) score (Fig. 3)
The H test indicated that differences between all three classes, including between “poor” and “fair”, were statistically significant based on the Dwass–Steel–Critchlow–Fligner test statistic (p < 0.01)
Summary
Snow stability data are among the key ingredients when establishing avalanche forecasts. Snow stability can either be assessed from observations of instability such as recent avalanching (Jamieson et al, 2009), by stability tests performed in the field (e.g., Schweizer and Jamieson, 2010) or from stability indices derived from modeled snow stratigraphy (e.g., Durand et al, 1999; Schweizer et al, 2006). One way to overcome the limitation of point observations is to perform many measurements in a given area within a couple of hours. This approach is only possible with a quick probing method, for example, with the snow micropenetrometer (Schneebeli and Johnson, 1998) or potentially with remote sensing techniques
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