Fracture propagation propensity in relation to snow slab avalanche release: Validating the Propagation Saw Test

Abstract

The ‘Propagation Saw Test’ (PST) was designed to assess the fracture propagation propensity of weak snowpack layers in relation to snow slab avalanche release. Its predictions were tested against independent field observations of weak layer fracture initiation and slope‐scale fracture propagation (e.g., avalanche release). A total of 170 tests were performed at 23 sites. Approximately 76% of tests correctly predicted the observed slope‐scale fracture propagation or lack thereof; however, 20% of tests predicted that propagation would not occur at sites that had recently propagated fractures. The predictive accuracy of the dataset improves if only test columns approximately 1.0 m long are selected. Critical fracture energy release rate calculations show that the lowest values are found in snowpacks where fractures initiated but did not propagate. This suggests that physical descriptions of propagation propensity in weak snowpack layers should include a sustainability term.