Assessing climatic controls of millennial erosion in the eastern end of Himalaya

Existing studies analyzing basin-averaged erosion rates from ¹⁰Be concentrations show a dominant tectonic control on erosion rates in the Himalaya. However, due to the co-varying nature of topography and climate in the Himalaya, it is difficult to isolate climatic controls from tectonics or topography. The eastern end of Himalaya exhibits one of the largest strike-perpendicular gradients in precipitation rates (a factor of ~35 times over 100 km), while hillslopes and channels are consistently steep across the region. This provides an ideal setting to examine the potential control of precipitation on erosion rates and surface processes. To do this, we determine basin-averaged erosion rates from ¹⁰Be concentrations (hereafter ¹⁰Be-derived erosion rates) from nine basins and compare them with potential climatic controls. Our results indicate that ¹⁰Be-derived erosion rates have a positive correlation with the basin-averaged number of extreme precipitation events (R² = 0.68; p = 0.006), while showing no correlations with topographic controls such as slope and channel steepness. Furthermore, our ¹⁰Be-derived erosion rates show a strong positive correlation with basin-averaged landslide density (R² = 0.94; p = 1.84*10^-5) that is calculated from 780 mapped landslides over a 20-year interval. ¹⁰Be-derived erosion rates over millennial timescale display a near one-to-one relationship with decadal erosion rates inferred from these landslides (R² = 0.74; p = 0.003). These results indicate that ¹⁰Be-derived erosion rates in the eastern end of Himalaya are largely controlled by precipitation rate and variability through landslide occurrences, implying a potential positive feedback between tectonic activity, climate, and erosion in this area.