The control of collisional tectonics over valley morphology: the case of the largest glacier in the European Alps

Abstract

Understanding how bedrock properties influence the valley-forming processes of Alpine landscapes is an outstanding challenge. A multi-methodological approach was used to uniformly quantify fault frequency, orientation, and rock hardness of crystalline basement rocks to evaluate their impact on the erosional processes that shaped the valley of the Aletsch Glacier, Switzerland. We show how variations in fault frequency and orientations, imposed by the inherited collisional framework of the area, controls the local erodibility of the valley, affecting both hillslopes and channel erosion processes. Our results highlight how tectonic preconditioning exerts a first-order control on the efficiency of erosion in the mountain chain, elucidating an integral link between deep-seated collisional dynamics and surface-based mountain shaping. Moreover, our results express the importance of a uniform, quantitative characterization of bedrock properties to comprehend the interaction and variability of erosional processes and hazards distributed within the valley systems.