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 adjustment downstream. Today and in the past, north-facing slopes in the Qilian Shan have accumulated more ice because they receive less solar insolation and more precipitation than south-facing slopes. The larger glaciers that form on north-facing slopes may enhance erosion and drive southward migration of drainage divides, particularly during glacial periods. We combine numerical simulations with topographic analyses to examine the influence of glacial erosion on divide mobility and postglacial landscape response to drainage reorganization. Our analyses suggest that asymmetric glaciation in the Qilian Shan has caused southward migration of the main drainage divide, prompting river channels below the extents of ice on north-facing slopes to become oversteepened relative to their drainage area. This oversteepening should accelerate postglacial fluvial incision, even in this region where topography has not been directly modified by glacial erosion. Numerical modeling suggests this enhanced incision persists for millions of years – much longer than the duration of recent glacial-interglacial cycles – implying a widespread and enduring influence of intermittent glaciations on landscape evolution in mid-latitude mountain ranges during the Quaternary.