Linked canyons and fans communicate through a migrating bedrock-alluvial transition

Li Zhang , Gary Parker , Jeffrey Nittrouer, Xudong Fu, Shanghong Zhang, Guangqian Wang

The evolution of net-erosional fluvial landscapes is often treated separately from net-depositional fluvial landscapes, using different methods and different data input. Yet these landscapes are often tightly linked by means of a moving-boundary bedrock-alluvial transition. We consider a linked canyon-fan system in the setting of a Basin and Range province, basing our work loosely on Rainbow Canyon and Panamint Valley, Death Valley National Park, USA. The canyon is mixed bedrock-alluvial, and is incising into a plateau undergoing relative uplift. The fan is purely alluvial, and is part of a bajada complex in an adjacent valley undergoing relative subsidence. It might be thought that uplift would push the bedrock-alluvial transition out to the fault line denoting the canyon-fan boundary. Yet this transition is observed to be well up the canyon itself. Here we show that this behavior can be explained in terms of canyon-fan interaction captured by a single dimensionally homogeneous morphodynamic model which folds in both alluvial and incisional processes. We find that all other things being equal, increasing uplift rate tends to push the location of the transition valleyward, but under appropriate constraints the elevation of the transition point can be insensitive to uplift rate.