Author(s):
Spencer Logan - Colorado Avalanche Information Center
Karl Birkeland - U. S. Forest Service National Avalanche Center
Kalle Kronholm - Dept. Earth Sciences, Montana State University
Kathy Hansen - Dept. Earth Sciences, Montana State University
Abstract:
Avalanche forecasting involves the prediction of current and future snow stability. Forecasters often extrapolate stability from a series of point measurements to the region of interest. Variability in those measurements leads to uncertainty in the extrapolation. The variations are often spatial, and an experienced forecaster successfully accounts for large-scale variations. However, at the smaller scale of a study plot, the spatial structure of the variability is not well understood. We examined the spatial structure of stability at the study plot scale, sampling three persistent weak layers in southwestern Montana, USA. We selected three homogeneous study sites, and assessed temporal changes in the spatial structure of shear strength and stability. Little spatial structure was detected using trend surface or variogram analysis. Shear strength in these plots could be spatially uniform, or the lack of detectable spatial structure could be due to the nature of the weak layers sampled, biases in the sampling array, or fundamental variability (error) in the stability test used. Our results suggest that, at the study plot scale, the location and placement of tests may not be important, while sampling a sufficient number of tests to characterize the distribution of test results is very important. The variability within results increased as the weak layers aged, so more tests would be required to characterize older layers.
