Rates of basin-wide rockwall retreat in the K2 region of the Central Karakoram defined by terrestrial cosmogenic nuclide ¹⁰Be

Basin-wide rockwall retreat rates are estimated using cosmogenic ¹⁰Be concentrations in supraglacial debris from the Baltoro Glacier basin in K2 region of the Central Karakoram, Pakistan. Total cosmogenic ¹⁰Be concentrations of the supraglacial debris were measured using accelerator mass spectrometry to determine ¹⁰Be concentrations inherited from the rockwalls within the glaciated basin. Given that rockfall induced by periglacial weathering and snow and ice avalanches is the most important source of supraglacial debris production in the high mountain glaciated basin, the erosion rate of the bare bedrock can be considered to be the rate of rockwall retreat. The rate of the rockwall erosion, converted from the calculated inheritance of ¹⁰Be concentrations, using the maximum velocity of the active glacier, places an upper limit ranging from 0.65 mm/year to 2.48 mm/year. This rate of rockwall retreat is in the same order of magnitude reported in other high Himalayan mountains. The rate, however, is an order of magnitude higher than erosion rates inferred from sediment budget studies and half that of the fluvial incision rate and exhumation rate for the same region. The difference between rates of basin-wide rockwall retreat and fluvial incision rates over the Late Quaternary suggests that in this glaciated basin fluvial incision is likely enhanced by localized/differential tectonism and/or isostatic uplift.