Methods for assessing and forecasting the survival of North Cascade, Washington glaciers

North Cascade glacier annual balance measured on 10 glaciers from 1984 to 2009 yielded mean annual balance (ba) of −0.51 m/y, and −13.26 m cumulatively. This is a significant loss for glaciers that average 30–60 m in thickness, 20–40% of their entire volume. This rapid volume loss has led to the complete loss of two glaciers, Spider and Lewis Glacier. This indicates the need for a method of forecasting glacier survival in the region. Temperate alpine glacier survival is dependent on the consistent presence of an accumulation zone. If a glacier does not have a persistent accumulation zone, all areas of the glacier will experience thinning, including the former accumulation zone. Examination of the accumulation zone can identify thinning from substantial marginal recession, emergence of new rock outcrops, and surface elevation declines in the accumulation zone. Nine of the 12 North Cascade glaciers examined exhibit these characteristics. Each glacier that exhibited accumulation zone thinning features also had frequent low annual accumulation area ratio values, below 0.30. This indicates the lack of a persistent accumulation zone.