Glacial erosion promotes high mountains on thin crust

Abstract

Every mountain range on Earth is unique in its tectonic evolution, but Quaternary climate cooling resulted in alpine landscapes with globally similar landforms such as horn-shaped peaks, cirques and overdeepened valleys. On a global scale, the impact of glacial and periglacial processes on the geometry of mountain ranges and the relative efficiency of glacial and fluvial erosion are still discussed. To address these issues, we analyse a novel, worldwide dataset of more than 16,000 mountain peaks. We relate peak height and steepness to mean elevation and crustal thickness. We show that the geometry of mountain ranges systematically varies with latitude and thus with climate. For peaks of similar height, the steepness increases towards high latitudes, while mean elevation and thickness of the supporting crust decrease. Modelling flexural isostasy based on the topographic load of mountain ranges demonstrates that the crustal thickness required to support peaks of similar height dramatically declines with intensity of glacial erosion. In concert with latitudinal trends in peak steepness, mean elevation and crustal thickness, this shows that Quaternary climate cooling reduces the topographic load by transforming the geometry of mountain landscapes from fluvial to glacial conditions. We conclude that the prevalence of glacial erosion in cold climate reduces the topographic load of mountain ranges and enables the growth of high mountain peaks even on moderately over-thickened crust.