Processes, rates, and time scales of fluvial response in an ancient postglacial landscape of the northwest Indian Himalaya

Both glacial and fluvial processes are key elements in molding landscapes in high mountain environments--glaciers are highly efficient erosional agents and producers of sediment but are restricted spatially, while rivers can transmit such signals through landscapes and flush this sediment out of mountain belts and into sedimentary basins. However, little research has focused on the manner in which these two agents of landscape change interact, especially on longer time scales. We analyze a suite of catchments that drain the previously glaciated Ladakh Batholith in the northwest Indian Himalaya; which preserve the oldest known moraine succession in this mountain chain. We describe and quantify the rates, processes, and time scales of postglacial recovery of the fluvial system across a previously unstudied time interval of [10.sup.5]-[10.sup.6] yr. We demonstrate that glacial modification of the upper reaches of a catchment can have profound first-order influence on the hydraulic scaling of the channel downstream, where increasing degree of glacial modification systematically and nonlinearly elevates the channel concavities of downstream reaches above the expected value range of 0.3-0.6. We also demonstrate that the response time of these systems as they recover must exceed 500 k.y., which is longer than any previously reported estimate for recovery times from glaciations, but is comparable with estimates from many tectonically perturbed landscapes. doi: 10.1130/B30048.1