Hillslope Morphology Drives Variability of Detrital ¹⁰Be Erosion Rates in Steep Landscapes

The connection between topography and erosion rate is central to understanding landscape evolution and sediment hazards. However, investigation of this relationship in steep landscapes has been limited due to expectations of: (a) decoupling between erosion rate and “threshold” hillslope morphology; and (b) bias in detrital cosmogenic nuclide erosion rates due to deep-seated landslides. Here we compile 120 new and published ¹⁰Be erosion rates from catchments in the San Gabriel Mountains, California, and show that hillslope morphology and erosion rate are coupled for slopes approaching 50° due to progressive exposure of bare bedrock with increasing erosion rate. We find no evidence for drainage area dependence in ¹⁰Be erosion rates in catchments as small as 0.09 km², and we show that landslide deposits influence erosion rate estimates mainly by adding scatter. Our results highlight the potential and importance of sampling small catchments to better understand steep hillslope processes.