The relative efficiency and influence of glacial and fluvial erosion on Tibetan Plateau landscapes

Abstract

Driven by climate change, periods of dominating glacial and fluvial erosion have both sculpted mountain ranges during the Quaternary. To understand the evolution of mountain landforms, there is considerable interest in knowing which erosion agent leads to more incision, how glacial thermal regime impacts erosion and landscape development, and whether glacial erosion can result in increased relief. To investigate the relative efficiency of glacial and fluvial erosion, and the influence of glacial thermal regime on topography, we compare two different mountain ranges–the Qionglai Shan (monsoonal temperate glaciation) and Lenglongling (subcontinental glaciation) in western China. We use a 1-D model to construct presumptive fluvial longitudinal profiles if glaciation had not occurred, and compare these with the actual glacial profiles to obtain relative incision rates of fluvial and glacial erosion. Results demonstrate that glacial incision is smaller than fluvial incision in Lenglongling and larger than fluvial incision in the Qionglai Shan, which may be influenced by different tectonics and glacier types. Topographic analysis of glacial and fluvial valleys with similar drainage areas show that glacial erosion results in valley widening, local valley relief increase induced by isostatic uplift, and slope gradient increase in Lenglongling. However, there is no local valley relief and slope increase observed in the Qionglai Shan, which may reflect slope process responses to threshold hillslope limiting the height above valley bottoms.