Alluvial fan aggradation/incision history of the eastern Tibetan plateau margin and implications for debris flow/debris-charged flood hazard

摘要

This paper reconstructs the Quaternary aggradation and incision history of a debris flow/debris-charged flood-affected valley in order to detect the impact of climate on alluvial fan dynamics. We used optically stimulated luminescence (OSL) dating of quartz to determine the ages of alluvial fan terraces. Comparison between the aggradation and incision history and regional climatic records suggests that aggradation occurred in cold and/or dry climates, whereas incision is a feature of warm and wet climates. Cold climates lead to enhanced frost shattering, and dry climates cause deteriorated vegetation. Both effects caused surplus sediment, which was transported by infrequent flood discharges to form alluvial fan/terrace deposits. Incision during wet and warm climates is due to increased vegetation cover and an increase in the frequency of flood discharges. This relationship between climate and valley evolution is applied to assess future changes in the present active channel by considering recent climatic records. The results show that the valley channel is expected to experience net incision if the average temperature continues increasing while precipitation maintains at a constant level.