The Influence of Fluvial Incision on the Lithospheric Stress Field: A Numerical Approach

Erosion along large fluvial valleys transports important sedimentary volumes across continents over geological time, modifying the loads imposed on the lithosphere and inducing isostasy‐related subsurface stresses. This work presents numerical experiments with a visco‐plastic lithosphere aimed at understanding the distribution and evolution of stresses and uplift arising from differential erosion in wide, tectonically quiescent valleys over 30 million years (Myr). We simulate valleys 30–150 km wide and a few hundred meters deep, and observe that these give rise to deviatoric stresses with maximum magnitudes ranging from 5 to 25 MPa, the distribution of which is largely controlled by the mechanical coupling between upper crust and lithospheric mantle. The upper crust in simulations with a weakly coupled lithosphere is strongly compression‐dominated beneath the valley, whereas scenarios with higher lithospheric coupling are characterized by compression and extension in similar proportions over crustal depths. Moreover, our simulations suggest that part of these stresses persists for tens of Myr after erosion rates have decreased, gradually concentrating around the valley due to viscous relaxation in the lower crust and lithospheric mantle. The adequacy of an elastic plate model in representing the topographic and stress responses of the lithosphere to fluvial incision is assessed, and examples from the Paraná, Colorado, Orange and Lachlan Rivers are discussed in light of our models. We conclude that large rivers are a factor to consider when assessing stresses in stable continental settings, especially if the valley is being actively excavated.