GLACIAL MASS BALANCE 2003-2016 ON MOUNT RAINIER

Glaciers are sensitive indicators of climate change and important drivers of aquatic and terrestrial ecosystems. They are a defining feature of Mount Rainier; as of 2015 there were 29 major glaciers on Mount Rainier with a combined area of 78.8 km² and numerous unnamed permanent snow or ice patches. Since 2003, the National Park Service (NPS) has monitored the seasonal mass balance changes of Emmons Glacier (11.0 km²) and Nisqually glacier complex (6.6 km²) glaciers. Methods are standardized with other national parks in the region, the USGS Benchmark Glacier Program, and globally. Over the period of record, Nisqually and Emmons glaciers have negative cumulative mass balances of -11.69 (±10.81) and -13.20 (± 7.86) m water equivalent, respectively. Approximately 27 percent of these two glaciers are covered by debris, largely below the equilibrium line altitude. The insulative effect of the debris cover suppresses melt by approximately 30 percent when compared to debris-free locations at similar elevations.

Measurement uncertainty is greater at Mount Rainier compared to other glaciers monitored by the NPS. Measurement of mass balance at Mount Rainier is complicated by steep, often inaccessible ice falls, significant redistribution of snow by wind, debris cover, geothermal activity, and a 2900 m range in elevation. With the large vertical extent, glacial melt typically begins at the terminus in April and does not begin above 3000 m until July. New methodologies, including generation of elevational models from satellite imagery, are being applied to refine mass balance measurements.