THE USE OF PLANIMETRIC SURFACE-AREA IN GLACIER MASS-BALANCE CALCULATIONS - A POTENTIAL SOURCE OF ERRORS

Large errors in the estimation of glacier ablation and accumulation ma y arise from the uncritical use of planimetric surface areas in volume calculations based on specific point values. Three-dimensional digita l terrain models of glacier surfaces show that the actual surface area is likely to be substantially larger than the planimetric area; with high-resolution digital terrain models, approximations of the true sur face area may be as much as 20% larger. The errors are sufficient for questions to be raised about some calculations of water storage in gla ciers, because incorrect surface-area values may result in ablation be ing underestimated substantially. Errors may also be introduced into c alculations of radiation-energy inputs to a crevassed glacier surface.