103

Simulation test on mechanisms of freezing-thawing induced wind erosion in Qinghai-Tibet Plateau, China

Yao Qian 1 ,2, Ping Yan1 ,2, Wei Wu1 ,2, Xiaonan Meng1 ,2, Miao Dong1 ,2
1State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing, China, 2Academy of Disaster Reduction and Emergency Management, Beijing Normal University, Beijing, China

Freezing-thawing induced wind erosion often occurs in the Qinghai-Tibet Plateau, China,, resulting in serious ecological and environmental problems locally and globally. In order to identify the mechanism of freezing-thawing induced wind erosion in the Qinghai-Tibet Plateau, wind tunnel experiments were conducted to compare wind erosion effects with two different frozen and thawed soil samples, loam soil (gray meadow soil) near the Yarlung Zangbo river valley, Nyingchi and sandy soil (aeolian soil) from Tingri, Xigaze in the plateau under various initial moisture (1%, 3%, 5%, 7%, 9%, 12% for loam soil and 1%, 3%, 5% for sandy soil), freezing-thawing cycles (0, 1, 3, 5, 10) and different freezing-thawing temperature differences (-10~10℃, -20~15℃, -30~20℃). Based on simulated experiments, we found that after repeated freezing-thawing cycles, the damages on soil structure of loam soil with low initial moisture (1%) and of sandy soil with high initial moisture (3、5%) were more serious, and their wind erosion rates changed more fierce due to their different particle size compositions and compactness. Erosion rates of two soil types decreased with the increase of initial moisture. Under low moisture content, wind erosion intensity increased with the frequency of the freezing-thawing cycles, and the temperature difference in the freezing-thawing process. While under high initial moisture, the wind erosion rate fluctuates at first, then increased suddenly, and finally stabled at a certain range. This was because during several freezing-thawing cycles, the soil structure became loosen in the beginning, after that loose soil particles rearranged and reached a new stable structure, so the wind erosion rate fluctuates, but after repeated freezing-thawing cycles, the extrusion force between soil particles due to frost heave effect was excessive, so soil particles cannot reach the new stable structure, so the wind erosion rate increased. It is concluded that, under low initial moisture, the damage of soil structure caused by the repeated, severe freezing-thawing behaviors was the main reason for accelerated wind erosion in the Qinghai-Tibet Plateau.