ESTIMATING GLACIER EQUILIBRIUM LINE ALTITUDE ON MOUNT RAINIER, WASHINGTON USING SATELLITE IMAGERY ANALYSIS

Mount Rainier, located in the Cascade Volcanic Arc, holds the highest area and volume of glaciers among volcanoes in the northwest of the U.S., with 87.0 km2 total area of ice and perennial snow in 2008 (Sisson 2011). These glaciers are critical to local water supply, electric power generation, and ecosystem productivity in several regions in Washington state. The equilibrium line altitude (ELA) of glaciers represents the divide between accumulation and ablation areas. This altitude is likely to change and to respond to regional weather patterns, which may be of particular interest given recent increases in temperature and changes in seasonal precipitation on Mount Rainier (Ford 2011). Previous studies have found high correlation in alpine glacier environments between snowline altitude determined by satellite imagery analysis, and observed ELA at the end of the melt season (Rabatel 2005, Mathieu 2009). We investigate the ELA of several glaciers on Mount Rainier using satellite imagery captured in late summer between 2006 and 2012. Our ELA estimates from analysis of 2006 and 2009 imagery of Nisqually and Emmons glaciers are within 100 feet of ELAs determined from National Park Service field measurements. These methods are subject to uncertainty surrounding the influence of wind patterns on snow distribution, the timing of the end of the ablation season, and local variation in glacier surface mass balance. However, our results suggest an increase in ELA on Nisqually, Emmons, Tahoma, and Winthrop glaciers between 2006 and 2009. This technique may be applied to other glaciers on Mount Rainier and to other alpine glacier environments, particularly as more satellite imagery becomes available.