2023 CSDMS meeting-008


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Evaluating the Impact of Talus Piles on the Evolution of Wide Bedrock River Valleys

Clay Robertson, Kansas State University Manhattan Kansas, United States. clayr22@ksu.edu

Preserved in the morphology of bedrock river valleys is a recorded history of geologic and climactic conditions experienced by that river over time. A deep, narrow valley suggests that conditions favored vertical incision over lateral erosion, and the presence of a wide bedrock valley indicates that lateral erosion and valley widening outpaced vertical incision. While vertical incision and the rates and mechanisms by which it operates are relatively well understood, the processes of lateral erosion and valley widening remain more enigmatic. Utilizing bedrock valley morphology as an interpretive tool is impossible without first improving our knowledge of the valley widening process. For a bedrock valley to widen the river must first laterally erode the bedrock wall until the overlying stresses cause the wall to collapse into a talus pile on the valley bottom. Once the material has collapsed, it then must be transported away from the bedrock wall so that the river can regain access to the wall and lateral erosion can continue. In this two-step conceptual model of valley widening, the size of the individual talus blocks and the volume of the pile itself plays a large role in the rate of valley widening over time. In this study, I use numerical modeling to estimate the long-term breakdown and removal of talus material in a river through chemical and physical weathering. Inputs for the model include measured talus pile characteristics from a bedrock river with wide and narrow bedrock valleys (Buffalo River) and long-term flood simulations generated by the LandLab tool, Random Precipitation Distribution Generator. Model results may offer some insight into the potential role of talus in the bedrock valley widening process and improve our understanding of the conditions favorable for the development of wide bedrock river valleys.