Bedload-Bedrock Contrasts Form Enigmatic Low-Relief Surfaces of the Pyrenees

Low-relief, high-elevation surfaces in mountain belts highlight the dynamic nature of landscapes and have provided evidence for changes in tectonics and/or climate. Yet quantifying when changes occurred from topographic data is challenging and relationships between erosion rate, lithology and precipitation are complex. In the Pyrenees, low-relief, high elevation surfaces are found across both plutonic massifs and the surrounding softer rocks and channel steepness values are relatively uniform between these lithologies. This suggests a weak relationship between erosion rate and lithology despite a clear relationship between the drainage network configuration and the location of the plutonic rocks. We explore this conflicting evidence for strength of the relationship between lithology and erosion rate using a landscape evolution model which accounts for the contrast between bedrock and bedload erodibility. This contrast produces dispersed channel steepness values and predicts the in situ development of low-relief surfaces, under steady forcing conditions.