EVOLUTION OF DEBRIS COVER ON EMMONS GLACIER, MOUNT RAINIER, WASHINGTON

Mount Rainier in Washington State is home to 29 glaciers, 19 of which have significant debris cover. The majority of these glaciers have experienced thinning at the terminus due to increased melting; however, thick debris cover on Emmons Glacier led to thickening at the terminus from 1970 to 2008 as the debris insulated the underlying ice. To better understand how Emmons Glacier is changing, the areal extent of the debris cover and the areal extent of the glacier ice were manually mapped on National Agriculture Imagery Program satellite imagery from 2006 to 2019. Debris cover extent averaged 2.90 km², and covered approximately a quarter of the total area of Emmons Glacier. Between 2006 and 2019 the debris covered area increased by 0.13 ±0.1 km², although the total area of Emmons Glacier decreased, and the debris covered area decreased at the terminus due to glacier retreat. Increasing debris covered area during a period of decreasing glacier area and terminus retreat indicates that debris cover is expanding up-glacier. This additional debris results from melt out as ice is lost, as well as redistribution of the existing debris cover as the surface evolves. In addition, the amount of annual snow cover and ice melt play a role in determining the extent of debris cover. It is expected that debris covered area will continue to increase and expand up-glacier in the future, especially if the amount and seasonal duration of snow cover continues to decrease and the amount of surface melting continues to increase.