Transient landscape dynamics across the Southeastern Australian Escarpment

Abstract Passive margin escarpmentsprovide some of the best examples for large-scale transient landscape evolution. Despite the relative simplicity of their geological setting, when compared with active orogenic systems, many open questions exist concerning their modes and ratesof evolution. We use catchment wide denudationrates calculated from cosmogenic nuclidesconcentrations and high resolution topographic analysis to constrain landscape dynamics across the South Eastern Australian Escarpment. We determined denudationrates of ∼15 mm/ka in the lowlands at the foot of the escarpmentand of ∼10 mm/ka in the highlands, while catchment draining the escarpmentface display rates in the 20–60 mm/ka range. These denudationrates along a passive margin escarpmentare among the highest in the world and show greater sensitivity to topographic gradients when compared to other passive marginsettings. We interpret this situation as resulting from the intermediate precipitation regime of our study area, as opposed to drier or wetter settings, where hillslope processes can be inhibited due to water availability or deep weathering profiles and vegetation feedbacks, respectively. Combined with the extraction of topographic metrics across the escarpment, these rates allow us to constrain efficiency coefficients for fluvial incision and hillslope diffusion that are similar to other independent estimates in this region. These coefficients are used to calculate an escarpmentretreat rate of 40 to 80 mm/ka over the last 100s of ka. Our analysis of high resolution hillslope morphological properties suggests widespread small-scale disequilibrium across this landscape, illustrating the pervasiveness of transience across all spatial scales in this geomorphological setting.