Relative Rates of Glacial and Nonglacial Erosion in Alpine Environments

It is commonly argued that erosion rates in valleys occupied by temperate glaciers are greater than in valleys where nonglacial processes dominate. However, a recent study by Hicks et al. (Arctic and Alpine Research, 1990, 22: 26-42), comparing sediment yields from glacierized and unglacierized basins in New Zealand, casts doubt on this idea. Given the difficulty of estimating sediment yields, and procedural differences between studies, we suggest it is not yet possible to define a consistent relationship between glacierization and sediment yield. Further, the value of such a relationship is questionable because percent glacial cover is not an adequate surrogate measure of glacial erosional intensity, and because present day comparisons of sediment yields from different basins do not permit accurate estimation of relative rates of glacial and nonglacial processes. Relationships based on the narrow range of present-day spatial variations are not reliable indicators of the temporal changes in erosion that would occur during glacial/interglacial cycles, which include paraglacial effects with response times that vary with basin size. The evaluation of relative rates of glacial and nonglacial processes requires a sediment-budget approach in which the role of storage and paraglacial sedimentation in modulating sediment yields is explicitly recognized.