Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item The influence of forest on the distribution and size of surface hoar in small meadows(Montana State University - Bozeman, College of Letters & Science, 2015) Wieland, Matthew Allen; Chairperson, Graduate Committee: Jordy HendrikxSnow avalanches pose a significant hazard to winter recreationalists travelling in the backcountry and are difficult to predict on individual slopes. Weak layers responsible for these avalanches may form at the surface multiple times during the winter season and are buried by subsequent snowfall. Understanding causes of slope-scale weak layer variations during formation and destruction periods is crucial for gaining an understanding of their distribution after burial. Persistent weak snow layers, such as surface hoar, can pose hazards for months after burial. This study examines surface hoar crystals on the surface, directly after formation, in two small meadow openings in southwest Montana. Data collection occurred during two winter seasons for three surface hoar formation events. Three environmental metrics associated with surface hoar growth processes in meadow openings are explored and their relationships with crystal size examined using spatial regression and regression tree analysis. The spatial structure for each event is described using multiple crystal sizing measures through semi-variograms. Surface hoar crystals tended to grow largest in areas that were both shaded and possessed large unobstructed views of the sky on north and south aspects. The range of spatial autocorrelation for surface hoar crystal sizes varied from 7 m to beyond 25 m and differed depending on event or crystal sizing measure. Results vary between events and suggest the drivers controlling surface hoar growth are unique to each area and not consistent between events. This research highlights the need for multiple slope-scale snow stability assessments for understanding the distribution of a buried weak layer of surface hoar in a meadow opening. Targeted areas for assessment should incorporate a basic understanding of a meadow's shading and canopy openness and how this varies over a winter season.Item Surface hoar observations at the scale of a helicopter skiing operation(Montana State University - Bozeman, College of Letters & Science, 2014) Borish, Matthew John; Chairperson, Graduate Committee: Stephan G. CusterUnderstanding what controls coarse scale snowpack properties, such as surface hoar distribution, is imperative for predicting snow avalanches. Due in part to the inherent difficulties of winter travel in mountainous terrain, most spatial variability investigations of snow properties have been limited to relatively fine scales. To quantify snow surface spatial variability at the basin, region, and mountain range scales, a team of heli-skiing guides recorded observations describing surface hoar presence or absence coordinates, crystal size, and elevation throughout four major surface hoar formation periods over two heli-skiing seasons in rugged alpine terrain near Haines, Alaska across an extent of nearly 60 km. Geostatistical analysis yielded spherical semivariogram autocorrelation ranges from approximately 3-25 km, which is similar in size to many of the basins and regions within the study area. Kriging models built from the semivariograms were produced to aid geographic visualization of coarse scale snowpack processes. Geographically Weighted Regression revealed a positive relationship between elevation and surface hoar crystal size with adjusted R 2 values averaging near 0.40. The results of this research suggest it may be possible to identify areas with greater surface hoar growth and persistence potentials as a consequence of synoptic onshore or offshore flow, and glacially influenced katabatic winds. Additionally, larger surface hoar crystals may be found in the higher elevation avalanche starting zones in the alpine glaciated terrain near Haines, Alaska. These results can help in future efforts to forecast snow stability patterns over large areas.Item The effects of slope aspect on the formation of surface hoar and diurnally recrystalized near-surface faceted crystals(Montana State University - Bozeman, College of Letters & Science, 2008) Cooperstein, Michael Stephen; Chairperson, Graduate Committee: Katherine J. Hansen; Karl W. Birkeland (co-chair)This research was conducted to determine if slope aspect played a role in the formation, size and shape of surface hoar and near-surface faceted crystals and on the meteorological variables that are known to result in the formation of these two weak layers. No studies have specifically studied the effects of slope aspect on the size and shape of these crystals nor the effects of slope aspect on the meteorological variables which are known to result in differences in temperature and vapor pressure gradients and ultimately result in the formation of two weak layers.