Climate aridity delays morphological response of Andean river valleys to tectonic uplift

In the south Central Andes, a complex relationship between climate, tectonics, erosion and topography is well documented. Building on recent advances in the mechanical modelling of subduction zones, we isolate the contribution of fault motion to topography and observe how rock uplift has been recorded in river valley morphology. Rivers on the wetter, western Chilean-side of the Andean cordillera have steep and narrow valleys, in stark contrast to those draining east across the arid Argentinian cordillera, whose valleys are variably wider and less steep. The Chilean rivers have responded to fault slip along the western mountain front by incising vertically and propagating a steepening zone upstream. In Argentina, there is little evidence of channel steepening despite predictions for higher vertical rock uplift rates. We hypothesise that the aridity of the Argentinian region has limited the transport capacity of the rivers to export their sediment fill and as a result, vertical incision has been inhibited and lateral incision and valley widening favoured. The long-term climate gradient appears to have been important in modulating the morphological response of these rivers to fault slip. These factors precondition future landscape sensitivity to both tectonic and climatic change.