Assessing changes in the spatial variability of the snowpack fracture propagation propensity over time

Understanding the spatial variability in fracture initiation and fracture propagation is critical for avalanching as both are required for an avalanche to release. Most of the previous research looked at the spatial variability of fracture initiation. We focus on understanding the spatial variability of the fracture propagation potential using the Extended Column Test (ECT). This work uses a new overlapping grid methodology which allowed us to make repeat data collection on the same slope to collect data on two separate days at the slope scale from two environmentally different sites (windy and sheltered), thereby capturing temporal changes in the spatial variability of our results. In contrast to previous fracture propagation test research, our data demonstrates considerable spatial variability in fracture propagation potential. Interestingly, at both the windy and sheltered sites the first sampling day demonstrated a relatively random distribution of fracture propagation potential results, while the second sampling day for both sites showed evidence of increased resistance to propagation as well as increased spatial clustering at the scale of our observations. Since distinct clustering or pockets of propagation and non propagation exist on some slopes, the practical implication of our work is that it is often necessary to dig more than one snow pit on suspect slopes to assess stability, and those slopes might be more accurately assessed by widely (greater than 10 m) spaced measurements.Though our data are limited, these results represent the first statistically demonstrated temporal change in snowpack spatial variability at the slope scale. However, in order to definitively address the question of temporal changes in spatial patterns, much more work is needed on many slopes with varying weak layers and snowpack conditions.