Snowpack stability information derived from the SnowMicroPen signal

Abstract

Snowpack measurements and stability tests are, next to recent avalanche activity and weather history, currently the basis for snowpack stability assessment in most avalanche warning operations. The SnowMicroPen (SMP), a high-resolution penetrometer for snow, measures penetration resistance force or snow hardness. In order to be useful for an avalanche warning service, stability information needs to be provided and must be derivable from the SMP signal. SMP profiles (25 on slopes, 14 on flat sites) were taken together with manual snow profiles and stability tests, such as Rutschblock and compression tests. The data are from three winter seasons of the years 2001–2002 to 2003–2004 in the Swiss Alps. According to their stability test score and failure interface properties the manual profiles were classified as stable or unstable. Based on the manual observations the failure interfaces were identified in the SMP profiles and possible indicators of instability were derived from the SMP signals at these interfaces. The distinct indicators of instability were the failure layer micro-structural length and hardness, the difference in structural length across the failure interface and the failure layer macro-elastic modulus. The cross-validated accuracy of classification into stable or unstable failure interfaces gained from SMP parameters was comparable to the classification accuracy from manual profile parameters (about 65%). It remains to be tested if stability information can be derived from a SMP measurement without knowing the location of the failure interface found by a stability test. If this can be done successfully and reliably, avalanche warning operations could definitely benefit from the instrument.