AbstractsEarth & Environmental Science

This thesis presents the results of an investigation into the measured and modeled mass balance of the Collier Glacier, a small (0.70 km²), valley glacier located in the Oregon Cascade Range (44° 10' N, 121° 47' W). Here we present mass-balance measurements conducted for the 2009 and 2010 balance years on the Collier Glacier. The glacier has a unique photo record of retreat throughout the 20th century, thus making it one of the best-recorded glaciers in the Oregon Cascade Range. As part of the study, we installed and maintained automated weather stations (AWS) to collect data needed to apply and validate the OSU surface energy balance model (SEBM). The variations in the mass balance for the Collier Glacier continue previously determined variations where there are years with significant mass loss, and years of mass gain. The general form of the Collier Glacier's net balance did not change appreciably between 1989 and 2010, with high ablation gradients below the ELA and low gradients above the ELA. However, there was a slight increase in elevation of the location of maximum ablation as well as the terminus, coinciding with the decrease in surface area since completion of the last study in 1994. The net balance curve continues to translate back and forth along the x-axis from year to year depending on the timing and magnitude of winter snow accumulation and summer temperatures. These data suggest that potential negative balance years could result in an ELA that is above the icefall, exposing a significant amount of mass flux to the ablation area, enhancing ablation and subsequent retreat. Model results indicate that the OSU SEBM is capable of capturing the seasonal pattern of mass balance for the Collier Glacier. The model also shows good agreement both spatially and temporally with the mass-balance measurements conducted for the 2009 and 2010 balance years. Model experiments were conducted to compare model performance and investigate the superiority of more complex models with simpler approaches. Model comparisons between the OSU SEBM calculating the turbulent heat fluxes with the bulk method showed similar performances with the SEBM calculating the turbulent heat fluxes with a simpler transfer coefficient method. Furthermore, the OSU SEBM was also compared to a simple positive degree-day (PDD) model. Model simulations indicated that the PDD model explained approximately 82% of the variance in summer ablation, while the SEBM explained approximately 78% of the variance in summer ablation. These results indicate that simpler methods to model glacier mass balance may be just as effective as the more complex methods.