Mass Balance and Volume of South Cascade Glacier, Washington 1958–1985

Abstract

The mass balance of South Cascade Glacier has been calculated by means of snow accumulation and ice ablation measurements since 1958. The summation of the net balance values for the 1958–85 period is −10.0 meters water equivalent. Topographic maps of the glacier were made from late summer vertical aerial photography in 1958, 1961, 1964, 1977, 1980 and 1985. In addition, the topography in the late summer of 1970 is well known from the theodolite survey of about 10 points on the glacier surface. The mass balance and photogrammetry are independent measurements of the cumulative volume change. The volume change between 1958 and 1985, measured from maps and adjusted for the density of ice, is −12.7 m, multiplied by the area of the glacier. This discrepancy can be reconciled by using the density of firn in the accumulation zone, rather than ice, to convert the volume change to water equivalent. Differences between the methods within the 27 year period are probably due to map errors, and indicate the need for caution in this type of comparison.

Surveying, rather than photogrammetric, methods for determining the volume change of glaciers is preferable, and density profiles are necessary if the glacier is not in equilibrium.