Abstract
AbstractIn this study, we present direct field measurements of modern lateral and vertical bedrock erosion during a 2‐year study period, and optically stimulated luminescence (OSL) ages of fluvial material capping a flat bedrock surface at Kings Creek located in northeast Kansas, USA. These data provide insight into rates and mechanisms of bedrock erosion and valley‐widening in a heterogeneously layered limestone‐shale landscape. Lateral bedrock erosion outpaced vertical incision during our 2‐year study period. Modern erosion rates, measured at erosion pins in limestone and shale bedrock reveal that shale erosion rate is a function of wetting and drying cycles, while limestone erosion rate is controlled by discharge and fracture spacing. Variability in fracture spacing amongst field sites controls the size of limestone block collapse into the stream, which either allowed continued lateral erosion following rapid detachment and transport of limestone blocks, or inhibited lateral erosion due to limestone blocks that protected the valley wall from further erosion. The OSL ages of fluvial material sourced from the strath terrace were older than any material previously dated at our study site and indicate that Kings Creek was actively aggrading and incising throughout the late Pleistocene. Coupling field measurements and observations with ages of fluvial terraces can be useful to investigate the timing and processes linked to how bedrock rivers erode laterally over time to form wide bedrock valleys.
Highlights
Bedrock rivers play a central role in landscape evolution by communicating signals of climate shifts, base level changes, and tectonics through landscapes (e.g., Hancock et al, 1998; Lavé & Avouac, 2000; Whipple, 2004; Whipple & Tucker, 1999)
Modern erosion rates from this study demonstrate that lateral bedrock erosion can proceed rapidly, suggesting that when the stream is in contact with bedrock walls, it can readily erode them
This study presents results of modern erosion rates and optically stimulated luminescence (OSL) ages of fluvial deposits sourced from a strath terrace in a small bedrock stream in northeast Kansas
Summary
Bedrock rivers play a central role in landscape evolution by communicating signals of climate shifts, base level changes, and tectonics through landscapes (e.g., Hancock et al, 1998; Lavé & Avouac, 2000; Whipple, 2004; Whipple & Tucker, 1999). Despite the substantial advances on processes of vertical incision, comparatively few studies have attempted to resolve controls on the processes and rates of lateral bedrock erosion (Beer et al, 2017; Bufe et al, 2017; Collins et al, 2016; Fuller et al, 2016; Langston & Tucker, 2018; Li et al, 2020; Turowski, 2018) This presents a fundamental knowledge gap in understanding how bedrock rivers respond to climatic and tectonic changes by widening their valleys, and how channel geometry is maintained and changed over time. Considerable research is needed to achieve the same level of understanding of processes and mechanisms of lateral bedrock erosion compared to vertical incision
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