Dip angle controls on plucking susceptibility and knickpoint evolution in bedrock rivers

Abstract

Bedrock river erosion drives landscape evolution across much of Earth’s surface. Plucking is a key mechanism of fluvial bedrock erosion, yet our understanding of the controls on plucking is limited. Discontinuity orientation (e.g., dip angle) may significantly influence plucking dynamics, but this remains untested. We present the first direct observations of the impact of dip angle on plucking processes and knickpoint morphodynamics. Using flume experiments, we modeled erosion through dipping bedrock using stacked tiles held at three orientations: upstream-dipping, horizontal, and downstream-dipping. We find that horizontal beds are the most erodible, followed by downstream-dipping then upstream-dipping beds. Dip angle also influences knickpoint slope, bed roughness, armoring dynamics, and flow structure, which all interact to govern knickpoint morphological evolution. These observations demonstrate the profound effects of dip angle on the evolution of plucking-dominated bedrock knickpoints, and inform our understanding of landscape evolution within the many discontinuity-defined landscapes at Earth’s surface.