A glacial buzzsaw effect generated by efficient erosion of temperate glaciers in a steady state model

Abstract

Studies on relief and hypsometry in glaciated mountain ranges have recognized the equilibrium line altitude of glaciers as a major control on mountain height. This has led to the belief that, in contrast to fluvial topography, glacial topography is limited by climate, with tectonics playing a secondary role. This concept is known as the glacial buzzsaw. However, the understanding of controls on glacial relief has remained mainly qualitative, in part because a reference scenario for glacial landscape evolution — a glacial topographic steady state linked to the base level by a fluvial topographic steady-state downstream of the glacier terminus - and its dependencies have not yet been defined. Here we define such a reference and compare steady state longitudinal profiles in a coupled system of glacial and fluvial erosion that involves both tectonics and climate. Our model is based on the stream power law for fluvial erosion, the shallow ice approximation in combination with a glacial erosion rule, and an empirically determined drainage area-flow length relationship for both rivers and glaciers. Further, we introduce a new approach to incorporate dendritic glacier network structures into the one-dimensional model. Modeling of coupled glacial-fluvial steady-state profiles with empirical glacial and fluvial erosion parameters shows that the difference between glacial and fluvial relief depends on climate, tectonics and the applied erosion laws. Our results imply that glacial erosion can typically balance tectonic uplift rates at lower relief and topographic slopes than fluvial erosion. This steady state equivalent of the glacial buzzsaw effect suggests that glaciers may indeed be more efficient erosional agents than rivers increasing erosion in a cooling climate.