Theses and Dissertations at Montana State University (MSU)
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Item Atmospheric processes related to deep persistent slab avalanches in the western United States(Montana State University - Bozeman, College of Letters & Science, 2019) Schauer, Andrew Robert; Chairperson, Graduate Committee: Jordy HendrikxDeep persistent slab avalanches are a natural hazard that are particularly difficult to predict. These avalanches are capable of destroying infrastructure in mountain settings, and are generally unsurvivable by humans. Deep persistent slab avalanches are characterized by a thick (> 1 m) slab of cohesive snow overlaying a weak layer in the snowpack, which can fail due to overburden stress of the slab itself or to external triggers such as falling cornices, explosives, or a human. While formation of such snowpack structure is controlled by persistent weather patterns early in the winter, a snowpack exhibiting characteristics capable of producing a deep persistent slab avalanche may exist for weeks or months before a specific weather event such as a heavy precipitation or rapid warming pushes the weak layer to its breaking point. Mountain weather patterns are highly variable down to the local scale (1-10 m), but they are largely driven by atmospheric processes on the continental scale (1000 km). This work relates atmospheric circulation to deep persistent slab events at Mammoth, CA; Bridger Bowl, MT; and Jackson, WY. We classify 5,899 daily 500 millibar geopotential height maps into 20 synoptic types using Self-Organizing Maps. At each location, we examine the frequency of occurrence of each of the 20 types during November through January during major deep persistent slab seasons and compare those frequencies to seasons without deep persistent slab avalanches. We also consider the 72-hour time period preceding deep persistent slab avalanches at each location and identify synoptic types occurring frequently, as well as those rarely occurring prior to onset of activity. At each location, we find specific synoptic types that tend to occur at a higher rate during major deep persistent slab years, while minor years are characterized by different circulation patterns. We also find a small number of synoptic types dominating the 72-hour period prior to onset of deep slab activity. With this improved understanding of the atmospheric processes preceding deep persistent slab avalanches, we provide avalanche practitioners with an additional tool to better anticipate a difficult to predict natural hazard.Item Snow drift and avalanche activity in a high arctic maritime snow climate(Montana State University - Bozeman, College of Letters & Science, 2016) Hancock, Holt John; Chairperson, Graduate Committee: Jordy HendrikxSnow drift endangers human life and infrastructure in alpine and arctic environments by contributing to snow avalanche formation in steep terrain and impacting transportation through reduced visibilities and drift deposition on roadways. Understanding the local and synoptic scale meteorological conditions just prior to and during hazardous snow drift conditions is a crucial element in forecasting for -- and mitigating the hazards associated with -- snow drift processes. This is especially true in Svalbard, a High Arctic Norwegian archipelago, where snow drift processes have been linked to avalanche activity and hazardous travel conditions in the region's unique, direct-action maritime snow climate. This study uses a record of road closures due to drifting snow on a mountain road to further investigate Svalbard's snow climate and avalanche regime by characterizing meteorological conditions leading to regional snow drift events and exploring the relationship between these periods of snow drift and regional avalanche activity. A nine-year record of road closures is coupled with local meteorological observations and NCEP/NCAR synoptic composite maps to characterize the local and synoptic weather conditions leading to and occurring during periods of snow drift near Longyearbyen, Svalbard's primary settlement. This record of snow drift events is then compared with regional avalanche observations using a case study approach to illustrate the relationship between snow drift and avalanche activity in Svalbard. Results show snow drift events result from five distinct synoptic circulation types and are characterized by increased wind speeds, higher precipitation totals, and elevated air temperatures relative to average winter conditions. Four case studies qualitatively illustrate the interactions between local and synoptic weather patterns, snow drift processes, and regional avalanche activity. In addition to the suggested mitigation strategies provided, these results will help advance avalanche forecasting efforts throughout the region.