| Using a database created from aerial images taken in 1958 and 2006, areal changes were calculated for 742 North Cascade glaciers in a 175 km x 120 km study area. The 2006 glaciers have a combined area of 227.5 km2, an individual average area of 0.3 km2, with a range of 0.0008 km2 to 6.2 km2. The combined group showed a 49.9 km2 (18%) loss between 1958 and 2006. Intersecting the 2006 extents with a 10 m digital elevation model allowed us to calculate the average, minimum, and maximum elevations, the average aspect, the average slope, and the length of current extents. The frequency of glaciers by octant, clockwise from 0° (north), yields the following distribution: 222, 204, 86, 48, 21, 32, 46, and 83. These results indicate a strong concentration of glaciers on the north and northeast sides of peaks, an unexpected result given the dominant west-to-southwest regional precipitation patterns. Following regional temperature trends, average and minimum glacier elevations increase southward along the north-south transect extending 175 km from the Canadian border. Low correlations (<0.3) between percentage change and the average aspect, average slope, and average elevation suggest that none of these simple geometric data, as identified in the 2006 extents, explain changes in the size of these glaciers over the study period. Although the loss in glacier area over the 48 year period is similar to the response of other glacier systems to 20th century warming trends, this analysis suggests that the areal changes in North Cascade glaciers cannot be solely explained by a single climatic forcing. |
