USING FLUME EXPERIMENTS TO TEST THE INFLUENCE OF DISCONTINUITY ORIENTATION ON FLUVIAL BEDROCK ERODIBILITY

The erodibility of bedrock within fluvial settings exerts a fundamental control on landscape evolution processes by impacting the rate and pattern of fluvial incision, ultimately modulating linkages between climate, tectonics, and topography. However, erodibility remains enigmatic – it is difficult to estimate in the field, and is often oversimplified in numerical landscape evolution models. These challenges stem from an incomplete understanding of the fundamental controls on erodibility within fluvial settings, e.g., which lithologic properties are responsible for determining erodibility, and to what extent? Recent work has demonstrated that discontinuity spacing plays a key role in impacting bedrock erodibility by setting the size of pluckable bedrock blocks. However, the impact of discontinuity orientation on susceptibility to fluvial plucking is likely also important, but has not yet been examined. Here, we use flume experiments to investigate the influence of discontinuity orientation on bedrock erodibility in plucking-dominated regimes.

Our experiments use stacked ceramic tiles to simulate fractured sedimentary bedrock. Within each experiment, tiles are held at a different dip orientation relative to flow (including upstream-dipping, downstream-dipping, horizontal, and vertically-bedded cases) using 3-D printed support trays placed in the flume. Using high-resolution photo- and video-recording, we document individual plucking events, erosion rates, and channel morphology. Early results demonstrate that small variations in bed orientation (e.g., from horizontal bedding to a shallow upstream dip) produce significant variations in bedrock erodibility. These results contribute to a more complete characterization of the relationships between lithologic properties and fluvial bedrock erodibility, and have important implications for landscape evolution in the layered, structurally complex landscapes which are common at Earth’s surface.