Distributed landscape response to localized uplift and the fragility of steady states

A primary goal of geomorphology is to infer from topographic form the processes that drive landscape evolution. Often implicit is the assumption that orogen-scale (
10 10m2 planform area) transient landscape changes on Earth are driven by equally large-scale transient tectonics, climate, or sea level. Here we argue that meso-scale (105–1010 m2) uplift perturbations may affect landscapes on scales that far exceed their size and duration. We study the consequences of transient variations in uniform surface uplift that are localized in space, such as may occur in volcanic landscapes or during landslide emplacement. These localized uplift perturbations define a class of landforms that are larger than typical hillslope lengths but smaller than orogens, and grow at rates that are rapid compared to fluvial bedrock erosion. We use 1D and 2D landscape evolution models to show that uplift perturbations drive transient lateral migration and vertical amplification of nearby ridges, sometimes generating a spatially distributed imbalance between uplift and erosion that causes plateau-like topography. Relaxation to steady-state conditions, in which erosion balances uplift everywhere, depends on the degree to which wave-like adjustment within channels or of ridges dominates subsequent landscape erosion. We find that the spatial structure and timescales of landscape response are predictable given uplift perturbation parameters. In 2D models, localized uplift generates a radial pattern of channel network and drainage divide reorganization that remains long after the perturbation is eroded. The spatial pattern of ridges and channels in a landscape thus may record both the scale and pace of perturbations to the uplift field.