Surface hoar characteristics derived from a snow micropenetrometer using moving window statistical operations

This study aims to improve analytical techniques for studying stratigraphic dimensions and hardness characteristics of thin weak layers in the mountain snowpack, with particular interest to buried surface hoar layers. By determining which structural characteristics of such weak layers are associated with shear strength, we may be better able to monitor and predict stability, which is relevant for avalanche forecasting and management. We utilize moving window statistical operations to analyze SnowMicroPen (SMP) penetrometer hardness profiles of a buried surface hoar layer. Results indicate that significant weak layer thinning and hardening of the interface between the weak layer and its substratum coincided with significant increases in shear strength, as measured using a size-corrected shear strength index derived from concurrent stability tests. With aging, variations in slab thickness appeared to positively affect the hardness and inversely affect the coefficient of variation (CoV) of hardness of weak layer boundaries. These findings support previous research that proposed the strengthening of buried surface hoar layers results from the gradual penetration of the surface hoar crystals into the substratum which allows stronger bonds to form at this critical interface. These analytical techniques allow stratigraphic dimensions and hardness characteristics to be quantified and analyzed, improving our ability to monitor stratigraphic characteristics associated with shear strength and stability of the mountain snowpack.