Validation of the Propagation Saw Test near Whumpfs and Avalanches

The Propagation Saw Test (PST) is a recently developed field test method for evaluating the fracture propagation propensity of slab and weak layer combinations. The PST is intended to replicate the fracture propagation behaviour found on nearby slopes. By following a simple interpretation guideline, PST results can indicate the propensity of a given snowpack to propagate weak layer fractures to an extent that would lead to avalanche release. We review a recent PST validation study in which fracture propagation was observed (or not) on nearby slopes for cases of confirmed fracture initiation. In addition, we present new PST results from 17 whumpf and avalanche sites in the Columbia Mountains of British Columbia, Canada. At these sites, the PST correctly predicted the high propagation propensity 71% of the time. However, as in the previous validation study, a relatively high proportion of tests (29%) incorrectly predicted low propagation propensity adjacent to whumpfs and avalanches. We review and discuss conditions associated with the false predictions, and we present suggestions for refining the test method and interpretation guidelines to reduce the occurrence of misleading results.