Glacial impact on short-wavelength topography and long-lasting effects on the denudation of a deglaciated mountain range

Abstract

Distinct alpine landforms in most high to mid-latitude mountain chains highlight the importance of glacial erosion in shaping mountain topography. The modifications to the initially, fluvially shaped landscape are associated with a massive and sustainable change in the distribution and magnitude of denudation following deglaciation. In this paper we focus on the glacially induced modifications to the short-wavelength topography of the deglaciated European Central Alps in an attempt to characterize the degree of glacial erosion on mountain topography and to explore the potential impact on millennial scale catchment denudation. We propose that short-wavelength topography is characteristically obliterated by glacial action and a measure of this process is provided by drainage density, which can be obtained by measuring the topographic curvature extracted from a DEM. Drainage density is well correlated with catchment-wide denudation rates from cosmogenic nuclides (10Be), but in two separate domains, identified by the degree of glacial conditioning. At lower elevations, where fluvial erosion processes dominate at present, drainage density tends to increase with denudation rate and mean slope. At higher elevations drainage density tends to decrease with increasing denudation rate but is not sensitive to mean slope. The transition between these domains is approximately coincident with the equilibrium line altitude of the last glacial maximum. Our results indicate that the decreasing drainage density in the higher domain reflects the cumulative impact of glacial erosion. We speculate that the commensurate lengthening of hillslopes increases slope instability and mass flux, thereby resulting in higher denudation rates. Rock mass strength seems to have a further significant effect on these relationships.