Production and Preservation of Elevated Low-Relief Surfaces in Mountainous Landscapes by Pliocene-Quaternary Glaciations

Abstract

Global cooling during the Late Cenozoic led to periodic glaciations in many mountain regions. The repeated waxing and waning of glaciers and ice sheets resulted in continuously changing erosion regimes that modified the underlying topography. While some studies have argued that relief increased due to glaciation, others have argued that glaciations limit relief. The (pre-glacial or glacial?) origin of elevated low-relief surfaces (ELRS) in mountain belts is similarly controversial. ELRS have been used to reconstruct pre-glacial landscapes, trace patterns of glacial incision, and infer tectonic uplift; it is thus important to test to what extent, and under which circumstances, glaciations may produce ELRS. We use a glacial landscape-evolution model to quantify the integrated effect of Pliocene-Quaternary glaciations on the topography of a mountain range. Our simulations show that glaciations can produce ELRS by shielding bedrock under slow-moving, non-erosive ice at intermediate elevations, with erosion focused on ice-free summits and at lower elevations. We term this mechanism for ELRS formation the glacial shelter effect. The final extent of ELRS strongly depends on the climatic history and the efficacy of local erosion, which affect both ELRS formation and preservation. Specifically, efficient fluvial erosion during warm interglacials may dissect previously formed ELRS. Modeled ELRS are distributed across elevations because their formation and preservation depend on ice extent rather than on the average equilibrium-line altitude. Our model results provide a comprehensive framework for the impact of glaciations on topography that explains both the presence and absence of ELRS in glaciated areas.