Preparing to sample a slope near Lionshead in
the southern Madison Range, MT
B.A., Geology, Whitman College
M.S. in Earth Sciences
Title of Research Project:
Examining the Slope Scale Spatial Variability of Snowpack Fracture Propagation
Project Outline:My research focusing on investigating differences in the spatial variability of fracture propagation propensity at the slope scale. I am testing slopes with a variety of weak layers (surface hoar, depth hoar, new snow, and near surface facets), a variety of slab characteristics (slab harness, slab depth), and varying levels of forecasted stability. I am then performing statistical analysis to examine both the amount of variability and the scale of any clustering that is found. Preliminary data shows that on many slopes there is considerable spatial variability in fracture propagation potential. There was often significant variability in fracture propagation even without substantial variation in snowpack structure. Weak layer type was found not to be a controlling factor in the level of spatial variability; for any given weak layer type some slopes had very variable fracture propagation while others had quite homogenous results. The regionally forecasted stability level also does not seem to be an indicate of the level of spatial variability on a slope.
The overarching goal of this research is to provide an improved understanding of this variability. This will give a better idea of what can be interpreted about the stability of a slope as a whole from a single snowpit. This is critical information to backcountry travelers and avalanche professionals trying to stay safe in avalanche terrain and gain an understanding of a snowpack as fully yet efficiently as possible.
Field Methods:To examine the spatial variability of fracture propagation this study will use a number of different study sites each with multiple snow pits on a single slope. These slopes will be below treeline, relatively uniform, wind sheltered clearings of at least 40m by 40m. This will minimize the terrain effects on our results as well as provide enough area to collect data. To minimize avalanche concerns while sampling these slopes will be less than 25º. In order to sample a variety of snowpacks within a single season, study sites will be located across southwest Montana. At least 30 sets of field data will be collected, to ensure a robust sample for statistical analysis.
One full snow pit profile will be conducted at each site in order to determine snowpack structure, weak layers of interest, and composition of those weak layers. At each site we will space 28 Extended Column Tests (ECTs) across the slope. The ECT is a snow stability test that measures fracture propagation propensity as well as ease of fracture initiation and it has been shown to be a reliable measure of slope stability (Simenhois and Birkeland, 2009). These tests will be on a fixed sampling layout, attempting to maximize extent, while still capturing small scale variability. By using a fixed layout and then offsetting it by five meters for a second field day, we will be able to sample a single slope more than once, capturing changes in spatial variability over time.
Grants:American Alpine Club Research Grant
Barry C. Bishop Scholarship for Mountain Research