Tectonic advection of contacts enhances landscape transience

AbstractContrasts in bedrock erodibility have been shown to drive landscape transience, but it is unclear whether horizontal tectonic displacements would enhance such effects. Furthermore, one might expect these factors to coexist, as tectonic convergence helps to create rock strength contrasts in settings like the Himalayas. How do landscapes respond when contacts separating units are raised vertically and shifted horizontally by tectonics? To evaluate such questions, we use landscape evolution models to simulate the exposure of a weak unit in a landscape equilibrated to a strong unit. We explore different simulations varying factors like weak unit erodibility, diffusivity, contact dip, and topographic advection rate. In these simulations, we assess the migration of the main drainage divide as well as changes in channel steepness and topographic relief within the strong unit. Our model results show that the horizontal movement of a contact does enhance drainage divide migration and increases in channel steepness, especially when the contact migrates along rivers with low drainage areas. Across all simulations, however, increases in topographic relief are minimal and temporary. Unexpected behaviors emerge in our simulations in which the mass balance of topography is influenced by horizontal tectonic displacements. For example, the exposure of the weak unit causes a gradual decline in the steepness of the strong unit. We interpret such behaviors to be artifacts related to the fixed boundaries of our domain and likely unrepresentative of natural landscapes. Instead, we focus on simulations where advection does not influence the mass balance of topography. These models show that the horizontal movement of contacts can enhance landscape transience, but this transience is marked by features one can use as diagnostic characteristics. Detecting such characteristics in natural landscapes featuring tectonic convergence would be difficult, however, due to the natural coincidence of factors such as faulting, folding, and landslides.