Source-to-Sink Canyon-Fan Interaction in a Closed Basin

Closed basins are commonly found in desert environments. They delineate an excellent configuration with which to study source-to-sink processes. Here we use the Rainbow Canyon-Panamint Valley canyon-fan system, Death Valley, USA as an example for the development of a general numerical model. The upstream region of our study reach is incising into bedrock, with a retreating knickpoint. The downstream region of our study is alluviated, and ends with a closed boundary. In between is a normal fault. The upstream reach is in relative uplift, driving incision (e.g. Argus Range), and the downstream reach is in relative subsidence, driving deposition on an alluvial fan (e.g. Panamint Valley). The closure of the basin at the downstream end provides a simple model of a mountain range on the opposite side of the valley (Panamint Range). We use the model of Zhang et al. (2020) to study a range of conditions. At one end we study the conditions for the formation of a hanging valley, with a vertical waterfall at the fault. At another end we study the conditions for the partial or complete alluviation of the canyon reach. We place emphasis on conditions where the canyon and fan “talk” to each other, versus conditions where the fan becomes a passive recipient of sediment from the canyon. We also show the consequences of opening up the downstream end of the basin, so that sediment is removed at the base of the fan (e.g. Armagosa River). We offer a versatile tool to study source-to-sink morphodynamics in an arid environment.