Glaciers are integral components of the region's hydrologic, ecologic, and geologic systems, and they are retreating rapidly. At NOCA, geologic mapping data and a 1998 inventory (Granshaw, 2001) indicate that glacier area has declined 44% in the last 150 years. Glacier changes are driven primarily by climate, and in special cases, debris cover from landslides, topographical factors, and tectonic drivers such as geothermal ablation.