The Study Of Soil Depth On Hillslope In The Qilian Mountains And Its Indication To Landscape Evolution

Surface process is a hot issue in the research of landscape evolution at present, and is also a basic research to understand the interaction among lithosphere, hydrosphere, biosphere and atmosphere. In order to explore and understand surface processes, systematic researches on rock weathering process, soil depth and material transport process on hillslope and interactions between them are urgently required. Among rock weathering process, soil growth and material transport process on hillslope, soil is an important link between rock weathering process and material transport process on hillslope. The rate of rock weathering and material transport rate would both change when soil depth has changed on hillslope. Research on soil depth on hillslope can tell us how hillslope processes, such as weathering process and material transport process, affecting hillslope form and landscape evolution.The process-based model for soil depth proposed by Dietrich is widely used for predicting soil depth in hillslopes. The model is based on the principle of conservation of mass, and is built by simplifying the actual physical process. This model is used in this study to simulate the soil depth and related factors influencing the soil depth. Through comparing the simulation results and field investigation data, we find that:1) the initial soil depth does not affect the final soil depth. With any values of initial soil depth, soil depth will reach equilibrium when the simulation time is long enough (10-15kyr).2) Soil depth is very sensitive to the value of diffusion coefficient K. Simulated results show that diffusion coefficient is approximately0.012m2/yr in the study area.3) Bedrock weathering rate has a great impact on soil depth. Similar to the diffusion coefficient, bedrock weathering rate not only affects the range of soil depth change, but also has impact on the time span for soil depth reach steady state.Secondly, we use the process-based model to research the evolution of hillslope in the Qilian Mountains. Simulation results show that the slope form is still change even after the soil depth reach steady state. Comparing the height, slope and curvature results after10kyr?100ky?1000 kyr, we find that the top of the hillslope is gradually lowering and the slope is gradually decreasing. The evolution process of hillslope agrees with the theoretical model of Davis. Soil depth and slope analysis show that the relationship between soil depth and slope is exponential. Comparing simulation results and field measurements, we find that soil depth is mainly depending on slope, and that erosion rate will decrease while soil depth increased on the hillslope.