Hess Altitudes and Other Morphological Estimators of Glacier Equilibrium Lines

The Hess altitude h on a valley glacier is the altitude of that contour that is most nearly straight. The Kurowsky altitude k is the average of the glacier’s minimum and maximum elevations. The glaciation level g of a glacierized region is the average of the elevations of the lowest glacierized and the highest unglacierized summits. We study the relationships between these morphological variables in well-mapped areas in Axel Heiberg Island, Nunavut, and in northern British Columbia, and also in a set of more widely distributed glaciers with well-known equilibrium-line altitudes e. We confirm that the relationships are strong, although their dispersion is considerable both for single glaciers and at the regional scale. On average h is 130 m below the long-term mean equilibrium line, k is slightly below it, and g is 200 m above it. There is very little morphoclimatic information in h that is not also conveyed by k, and since the latter is faster to measure and is already tabulated for tens of thousands of glaciers, its use is preferable. The glaciation level is less concordant. We suggest that it records interactions between landscape and climate on a somewhat slower time scale. The linear dependences of h on k and g, and of e on each of the 3 morphological estimators, have slopes slightly but significantly less than 1. This result is not yet understood.