Drainage Divide Migration in Steady-State Landscapes Experiencing Horizontal Tectonic Advection

Any tectonic forcing acting on a mountain range consists of vertical uplift motion and horizontal advection motion. In landscapes with a high advective component, such as those affected by low angle normal faults, advection can form a substantial portion of the total tectonic forcing. Questions therefore remain relating to the role of advection in shaping mountain range topography, surface drainage patterns and erosion rate distributions. We ask, how does advection influence mountain range topography and drainage? How do drainage basins and divides respond to advection? And how does advection influence the spatial distribution of erosion rates? Through numerical modelling with the Channel-Hillslope Integrated Landscape Development (CHILD) model and comparison to a natural landscape, the Sierra de la Laguna (Mexico), we test the extent to which advection affects mountain range evolution. Advection is shown to alter surface drainage patterns by promoting catchment elongation and reducing outlet spacing at the mountain front. The mountain range’s Main Drainage Divide (MDD) exhibits faster erosion on the distal flank’s headwaters; relative to the proximal flank’s headwaters, leading to a migration of the MDD towards the fault. Steady-state is achieved when the MDD migrates towards the fault at a rate equal to the rate at which the footwall is advected away from the fault. This pattern of erosion rates is found across all spatially fixed geomorphic features. Cosmogenic radionuclide analysis for catchment-averaged erosion rates in the Sierra de la Laguna demonstrates a difference in erosion rates across the MDD that is also indicative of a migration of the MDD towards the fault. Topographic, drainage and erosion rate observations for the Sierra de la Laguna are consistent with the numerical modelling when advection is included, suggesting that advection induces continual drainage migration whilst maintaining mountain range flank widths. We suggest that highly elongate catchments are indicative of substantial advection, and we also identify a mechanism through which divide migration can occur without altering the size of adjacent drainage basins.