Numerical Simulation of the Influence of Tectonics and Precipitation on the Evolution of Alluvial Fans at the Northern Foot of Qilian Mountains

As achieves of regional environmental changes in the past, alluvial fans have received extensive attention from geoscience community. Tectonic activity and climate change are two of the main factors affecting the development of alluvial fans. The Qilian Mountains, which is located on the northeastern edge of the Tibetan Plateau, experienced severe uplift since the Cenozoic. With the huge relief from surrounding areas, a series of alluvial fans developed at the northern foot of the Qilian Mountains. That makes it become an ideal area to study the relationships between tectonic uplift, climate change, and alluvial fan development. In order to explore how climate and tectonic changes have effect on the formation and development of alluvial fans, based on stream power model and diffusion equations, a numerical model of the drainage basin-fan system was built. Xigou River and Dayekou River with their fans in Qilian Mountains were simulated by using the above-mentioned numerical model. The results show that both the change in precipitation and the uplift rate affect the fan slope. Either the increase in the uplift rate or the decrease in precipitation causes the increment of fan slope, and vice versa. Fan slope changes linearly with the uplift rate variation, while the effect of precipitation on fan slope is relatively small. The response of catchment to tectonic activity and precipitation disturbances, as the change of sedimentary flux, is also in different patterns. The research will provide a new perspective for understanding the influence of regional tectonic activities and climate change on the geomorphological process.