PREDICTIONS OF THE PROPAGATION SAW TEST: COMPARISONS WITH OTHER INSTABILITY TESTS AT SKIER TESTED SLOPES Dave Gauthier* 1 and Bruce Jamieson 1,2 1 Department of Civil Engineering, 2 Department of Geoscience, University of Calgary, Alberta, Canada ABSTRACT: Several new fracture propagation field tests have been presented in recent years. These are designed to provide specific information about propagation propensity; however, each of the more common test methods are thought to be demonstrating at least part of the propagation process, and recent research has shown that the new propagation tests perform well at predicting skier-triggered avalanches. But which test performs best under which conditions? To address this question we compared the predictive success of the new Propagation Saw Test (PST) with that of the Compression test (CT), the Rutschblock test (RB), and the Yellow Flags structural instability index (YF) on skier-tested slopes that did and did not release avalanches in the Columbia Mountains of British Columbia, Canada. The results show that, for our dataset, the combined success rate of the PST in predicting stable and unstable conditions was the highest of the group, although it also had a much larger proportion of potentially dangerous ‘false stable’ results than the other tests. The CT, RB, and YF methods tended to overestimate instability, but often made correct predictions where the PST was incorrect. Overall, the tests usually performed better in combination than on their own, as each provided slightly different instability information. KEYWORDS: Propagation propensity, field test, instability assessment, snowpack properties, forecasting 1. INTRODUCTION In recent years, several completely new field tests or methods have been developed, and the interpretation of more common methods has been improved. Fracture Character (FC; van Herwijnen and Jamieson, 2007), shear quality (Johnson and Birkeland, 2002), and Release Type (RT; Schweizer, 2002) observations are becoming widely used and accepted additions to the standard Compression test (CT; Jamieson, 1999) and Rutschblock test (RB; Föhn, 1987) results, and the Yellow Flags (YF) structural stability index has improved snow profile interpretation (Schweizer and Jamieson, 2007). Each of these is thought to provide some information about both the ease of initiation and the propagation propensity of the tested slab and weak layer. In 2006, Simenhois and Birkeland presented their ‘Extended Column Test’ (ECT) and an excellent validation dataset, as a new method specifically designed to investigate propagation propensity in the field. The Propagation Saw Test (PST) was developed at around the same time, by both Swiss and Canadian researchers independently (Gauthier and Jamieson, 2006, 2008a; Sigrist and Schweizer, 2007). Each is well validated individually (e.g. Gauthier and Jamieson, 2008b), but direct comparisons between the refined and new test methods are lacking. However, many researchers are focusing on this very topic. For example, Birkeland and Simenhois (this volume), and Ross and Jamieson (this volume) present side-by-side comparisons of the PST and ECT. In this paper, we compare the predictive success of the PST with that of the Compression test, the Rutschblock test, and the Yellow Flags structural instability index on skier-tested slopes, some that released avalanches and some that did not, in order to assess the relative strengths and weaknesses of each. *Corresponding author address: Dave Gauthier, Dept. of Civil Engineering, University of Calgary, Calgary, AB, Canada T2N 1N4; tel: 403-220- 7479; e-mail: davidmgauthier@gmail.com