Theses and Dissertations at Montana State University (MSU)
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Item Application of a continuum theory of multiphase mixtures to snow on the ground(Montana State University - Bozeman, College of Engineering, 1987) Adams, Edward EaganItem Metamorphism of dry snow as a result of temperature gradient and excess vapor density(Montana State University - Bozeman, College of Engineering, 1982) Adams, Edward EaganA heat conduction equation to determine the temperature profile in a snowpack is developed. The magnitude of temperature gradient tends to increase as the snow surface is approached, with local minimums through high snow density layers and local maximums above and below these layers. Calculations are made which determine the excess vapor density over the ice grain surfaces which border the pore space. In the presence of a temperature gradient faceted crystals will develop near the top of the pore, as ice is sublimated off of the surfaces in the lower region. Necks will deteriorate most readily, causing an overall weakening of the snowpack. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is enhanced at warmer temperature and larger temperature gradients. Temperature and excess vapor density are known to determine the habit of ice crystals grown in air. The model predicts excess vapor densities in the snowpack which are similar to those which exist in the atmosphere. Comparison of crystal habits predicted by the model are in good agreement with experimental evidence, when the pore geometry and temperature conditions are specified.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.Item Analytical and experimental study of radiation-recrystallized near-surface facets in snow(Montana State University - Bozeman, College of Engineering, 2004) Morstad, Blake Walden; Chairperson, Graduate Committee: Edward E. AdamsA study on the formation of radiation recrystallized near-surface facets in snow was performed experimentally in an environmental chamber. This recrystallization occurs when surface snow metamorphoses into faceted crystals that result from absorbed solar radiation coupled with cooling effects from longwave and turbulent fluxes. The environmental chamber utilized a metal-halide lamp to mimic solar radiation, which penetrates the snow adding thermal energy at depth. In addition, the ceiling was cooled to simulate a cold sky, thus inducing a net longwave radiation loss at the snow surface. Turbulent flux parameters, including relative humidity and wind velocity were measured. Forty-centimeter thick snow samples with insulated sides were placed in the -10 C chamber on a constant temperature plate also at -10 C. The study focused on the significance of radiation balance and snow density on the recrystallization of snow near the surface. Imposed constant boundary conditions led to formation of facets of varying size at and near the snow surface. Faceting was observed when applied solar flux between 350 - 1100W/m2 was combined with longwave and turbulent exchange for snow with densities below 300 kg/m3. To better understand the governing processes and to extend the number of scenarios a thermodynamic model was used to extrapolate upon the experimental results. The model incorporated meteorological inputs and calculated a snowpack temperature profile based on relevant snow parameters. Conclusions from both experimental and model analysis show radiation and snow density to be significant factors in radiation recrystallized near-surface facets.Item Water movement in a stratified and inclined snowpack : implications for wet slab avalanches(Montana State University - Bozeman, College of Letters & Science, 2009) Peitzsch, Erich Hans; Chairperson, Graduate Committee: Katherine J. Hansen; Karl Birkeland (co-chair)Wet snow avalanches are dangerous and can be particularly difficult to predict. The rate of change from safe snow conditions to dangerous snow conditions occurs rapidly in a wet snowpack, often in response to water production and movement. This research focused on the relationship between snow stratigraphy and water movement in an inclined snowpack. Concentrating on transitions that impede water and flow finger formation within the snowpack, dye tracer was mixed with water and applied to a stratified snowpack to observe and measure the movement of water in various snow grain types, sizes, densities, and temperatures. There were two types of layer transitions that impeded water. Water was impeded at capillary boundaries caused by fine grains over coarse grains. It was also impeded at hydraulic conductivity boundaries, such as ice layers. In layer transitions that impeded water, the grain size of the layer above was significantly smaller than the layer below. The layer above a transition that impeded water was also significantly less dense than the layer below the transition. A qualitative analysis of grain type showed that there was no relationship between grain types in the layer above or below a transition and whether they will or will not impede water. A SnowMicroPen (SMP) was used to measure changes in structural element length to identify capillary boundaries. Results from SMP measurements indicate that microstructural analysis of the snowpack aids in characterizing capillary boundaries that impede water flow. The step change, rate of change, and percent increase were significantly larger in capillary boundaries than transitions that did not impede water for the entire dataset from all 8 sessions. When all transitions were ranked according to absolute change for each profile, capillary boundaries consistently ranked in the top two of all transitions evident within each SMP profile. The amount of water needed to produce flow fingers was highly variable. There was no significant relationship between the amount of water necessary to form flow fingers and snow density, snow grain size, snow temperature, or grain type. Layer transitions that impeded vertical water movement and flow finger formation may both play a large role in wet slab avalanche formation.