When rivers turn off but hillslopes and faults do not: oscillatory fluvial activity under strike-slip faulting

Rivers are primary agents of erosion, shaping valleys, drainage divides, and controlling the larger-scale landscape dynamics. Mass wasting and ‘diffusive’ processes on adjacent hillslopes also impact landscape form and dynamics, shaping hilltops, and hillsides, and adding sediment into channels. Extreme environments, such as hyper-arid deserts, offer a unique natural experiment to isolate landscape modification without continuous fluvial processes. Here, we explore numerical simulations of a landscape that experiences oscillatory fluvial activity, continuous vertical uplift, hillslope processes, and strike-slip faulting, inspired by a natural landscape in the Atacama Desert. Because strike-slip faults are structures known for diverting rivers and generating a dynamic response on hillslopes, we explore the landscape response to this perturbation when the climate is dry and the rivers are ephemeral. Our model simulates river incision, sediment deposition, hillslope diffusion, weathering, and faulting. The experiments bring light to three main findings: (1) under the absence of continuous fluvial incision, offset channels are less sinuous than offset channels that experience continuous fluvial erosion; (2) during long dry periods, hillslope sediment supply helps to decrease valley height and controls channel bed geometry; and (3) long river profiles in the oscillatory fluvial scenario preserve knickpoints for longer compared to those under continuous fluvial erosion that can readjust despite the cycle of strike-slip faulting. This work has implications for our understanding of sediment-dominated environments, strike-slip fault settings, and landscapes that continue evolving under the absence of steady fluvial erosion, and it highlights the importance of hillslope processes in dry climates, on Earth and other planets.