Theses and Dissertations at Montana State University (MSU)
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Item Meteorological controls on wind slab properties(Montana State University - Bozeman, College of Letters & Science, 2023) de Leeuw, Nathalie Marika; Chairperson, Graduate Committee: Jordy HendrikxSnow avalanches are dangerous phenomena, which can be made increasingly consequential through wind transport of snow. Wind-deposited snow has a broad range of possible physical and mechanical properties which can vary greatly over short distances, creating inconsistent and thus difficult avalanche conditions. This variability causes particular challenges for avalanche workers in data-sparse regions where important snowpack information at desired scales may be unavailable. Instead, snowpack properties are commonly inferred from available meteorological data. Though wind slab properties vary in space and time as meteorological conditions change, previous work has not explicitly studied these relationships at the slope-scale. In this research I aim to better understand how changes in meteorological variables relate to changes in wind slab physical properties. During two winters I recorded temperature, humidity, and wind speed at study sites in Montana's Madison Range (45.237, -111.424) and collected snowpack data during or immediately following blowing snow events. I found that average wind speeds at 0.5m and 1.5m above the snow surface were significantly higher during hard wind slab formation than soft wind slab formation, while unobstructed wind speed, maximum gust, and the length of time of wind transport were not associated with wind slab hardness. Temperature was higher during hard than soft wind slab formation, while humidity was not different between the two hardness categories. Although wind speed at 1.5m had a significant positive linear relationship with both wind slab density and blade hardness gauge force, it was a poor predictor of actual values for both of these parameters. Our findings help improve the understanding of the impact of near surface winds on wind slabs, which will aid avalanche forecasting and mitigation planning particularly in windy climates.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.Item Patterns of natural avalanche activity associated with new snow water equivalance and upper atmospheric wind direction and speed in the mountains surrounding Gothic, Colorado(Montana State University - Bozeman, College of Letters & Science, 2010) Chesley-Preston, Tara Lea; Chairperson, Graduate Committee: Stephan G. Custer; Karl Birkeland (co-chair)Snowfall, temperature and wind are three factors that quickly change avalanche conditions. Ridge-top winds have been used to assess avalanche conditions with mixed success due to high variability. Few analyses have tested the effect upper atmospheric winds have on avalanche conditions. This study attempts to quantify the effect upper atmospheric wind direction and speed have on the spatial pattern of natural avalanching in the mountains near Gothic, Colorado. The Gothic dataset consists of over 3,300 natural avalanches spanning a time period of 33 years. These data are associated with daily new snow water equivalence (SWE) collected at Gothic, as well as 500mb wind direction and speed from the National Centers for Environmental Protection/National Center for Atmospheric Research (NCEP/NCAR) gridded reanalysis project. I hypothesize that prevailing 500mb winds are more likely to be associated with natural avalanches in avalanche paths with a starting zone aspect lee to the prevailing free air winds. In addition, I hypothesize that the odds of a natural avalanche occurring increases with increasing new SWE, increasing 500mb wind speeds, and 500mb wind direction. These hypotheses are tested using simple probability analysis as well as a two-component hurdle model. As expected, avalanche paths lee to the 500mb wind direction have an increased probability of avalanching in relation to paths facing in other directions. However, exceptions do occur, some of which can be explained by cross-loading. The hurdle model results indicate that after accounting for new SWE, 500mb wind speed is significant in determining whether or not a day will be considered an avalanche day. Once a day is determined to be an avalanche day, 500mb wind direction is an important determinant for the daily avalanche hazard after accounting for new SWE. These results have practical significance. They give avalanche forecasters confidence that upper air wind direction is a useful predictor of the pattern of avalanche activity at the valley or mountain range scale, and the exceptions observed show that such predictions cannot be applied at the path scale. These scale issues demonstrate the general nature of backcountry advisories and why they cannot be applied at the scale of individual slopes.