Asymmetric glaciation, divide migration, and postglacial fluvial response times in the Qilian Shan

Glacial-interglacial cycles have repeatedly perturbed climate and topography in many mid-latitude mountain ranges during the Quaternary. Glacial erosion can move drainage divides and induce fluvial adjustments downstream, yet the time scale over which these adjustments occur remains unclear. We examined landscape evolution in the northwest-southeast-trending Qilian Shan, where the contrast in solar insolation between north-and south-facing slopes has generated larger glaciers on the northern range crest. Our analyses suggest that this asymmetric glaciation has caused southward migration of the main drainage divide, prompting river channels below the extents of ice on north-facing slopes to become oversteepened for their drain-age area and channels on south-facing slopes to become analogously understeepened. These changes in steepness should accelerate or slow down postglacial fluvial incision, even in the regions where topography has not been directly modified by glacial erosion. Numerical modeling suggests these discrepancies persist for millions of years, much longer than the duration of recent glacial-interglacial cycles, implying a widespread and enduring influence of intermit-tent glaciations on landscape evolution in glaciated mountain ranges during the Quaternary.