Drivers of topography in fold-thrust belts: a perspective from central Nepal

The roles of climate and tectonics in the evolution of mountainous landscapes over geological time are often assessed via continuum models that balance the forces in mechanical wedges with the assumption of pervasive small-scale faulting accommodating deformation. In contrast, observations from mountain ranges indicate an evolution of large-offset faults and paleoclimate. Here we ask the question, can observed faulting and paleoclimate histories replicate the characteristics of Himalayan topography? We evaluate this question for the Nepal Himalaya through linked models of fault activity, precipitation, and surface processes over geological time. Our experiments confirm that motion along a few faults control topographic evolution in the Himalaya. Importantly, we identify two topography-generating mechanisms in the evolution of fast converging mountain ranges: one where uplifted topography is laterally translated when faults are active in the foreland, and one where hinterland fault activity coeval with temporary inactivity of faults in the foreland is required to facilitate river incision into the hinterland. Alternating between these two modes defines the physiography of present-day Himalayan-type mountain ranges and is consistent with the first-order regional catchment geometries.