The Characteristics and Distribution of the Source Area of Aeolian Sand in the Valley Lhasa River's Lower Reaches, Tibet, China

Based on IKONOS and Quickbird interpretation and field survey, the effects of human activities and characteristic of sand distribution, grain diameter of sand sources and vegetation in the valley of lower reaches of Lhasa River were discussed. The results indicate that valley sand sources distribute along river valley and its two sides, in patch and particle form from slope to bottom of valley, and have a close interrelation with large, medium and small scale of wind field in space; There are three categories of accumulation substances which are sources of sand in the lower reaches of Lhasa River valley: river alluvium, flood deposit and weathering substances of mountain rock. Among them, river alluvium is the most important sand source, grain diameter of sand source is mainly made of silver sand, extreme silver sand and sticky sand, over 90% of whose grain size is less than 0.15mm, and tends to produce wind erosion. Aeolian sand activity is the primary factor affecting sand-nurtured vegetation, especially on movable and semi-movable land is affected most seriously, the species and coverage of vegetation can well reflect the stability of sand sources. Vegetation succession is developing in the tendency in favor of aeolian sand activities, which is one of a main driving factor and outcome of worsening aeolian sand activities. Natural factors are the main cause of the aeolian sand activities in this region, and human activities will further strengthen aeolian sand activities.