Snow avalanche release

Avalanche occurrence is closely related to the local meteorological conditions which may be quite variable in mountain topography. To investigate these conditions, and to provide information for avalanche forecasting, we designed and built a weather station which is currently relaying information to a base station from a remote site. Most field tests of snow do not adequately describe the engineering properties. In this study, we wanted to design some tests which would measure such properties and also provide an estimate of snow slope stability. Our tests of shear and tensile strength of snow were designed to simulate as closely as possible conditions expected in a naturally occurring snow slab, and were made in-situ using large samples. We describe several sets of measurements made across crownwalls after avalanche release. Such measurements typically showed considerable spatial variability and in 4 cases out of 5, a probabilistic approach combined with a simple force balance provided a satisfactory indication of the likelihood of failure. From the results or this analysis, we proposed a new field test to estimate stability. This test requires only a snow saw and is simple and quick to complete. It is well known that the strength of materials depends on strain-rate, and we made some measurements using a strain gauge in conjunction with the simple field tests. Although the rates applicable during snow avalanche release are uncertain, investigations or such properties provides an insight into release mechanisms. A device to measure air permeability of snow in the field was designed and built. Results from measurements showed that air permeability gave a good measure of snow structure which is related to strength. We think most of the variability of snow strength originates from air-flow patterns above the slope during storms, and further studies concerning these patterns could define the location of weak zones within a snow pack. Such information would enhance understanding of release mechanisms, and also improve avalanche forecasts