Downstream patterns in bedrock valley morphology encode climatic and tectonic forcing

Claire C Masteller 

Fluvially-carved bedrock valleys are ubiquitous landscape features. Vertical incision into underlying bedrock generates valley relief, whereas lateral migration of the river channel widens the valley floor as the river erodes the valley walls. The relative efficacy of these processes, which can be modulated by precipitation and water discharge, sediment supply, lithology, and uplift rates is recorded by the relationship between valley width, channel width, and valley relief at a cross-section. Numerous studies have interpreted differences in bedrock valley morphology to be evidence for variability in tectonics, climate, or geology, or as evidence of landscape disequilibrium. However, expected downstream covariation of these parameters under steady-state conditions has not been yet thoroughly explored. This contribution develops a 1-D profile model to describe expected downstream coevolution of channel width, valley width, and valley relief, described holistically using a valley confinement index. Model predictions agree well with data from seven catchments in the King Range, CA spanning a gradient in tectonic uplift and precipitation. Systematic variations in valley morphology correspond with differences in the Erosion number between catchments, which summarizes the combined effect of multiple factors that influence fluvial bedrock incision. These results suggest that longitudinal patterns in bedrock valley morphology provide a promising, holistic metric to interpret the relative influence of tectonics, climate, and lithology on bedrock valley formation in detachment-limited landscapes.