Abstract: Desertification is a very obvious problem on the ecological environment,which has steadily deteriorated in the area of the Qinghai Lake.The dunes on the western shore of the Qinghai Lake are a newly evolving area of aeolian sand in recent ten years and are expanding the limits yearly,and the area is the second big depositional area of aeolian sand in the Qinghai Lake region.The dunes on the western shore of the Qinghai Lake distribute along the shoreline on the northwest of the Bird Island and in the northwestern margin of the Buhahe delta,and the dune-field forms a strip with 0.5~1.5 km width and more than 10 km length.The dominant dune types are crescent dunes and dune ranges.The former get mainly near the lake,its windward slope is convex to the lake and the two horn point to 215°~260°.The later get near the land,the main ranges distribute along the S-N direction and the vice ranges distribute in the NE-SW direction.These indicate that the dominant wind in the studied area is in the E-NE direction.Provenance analysis showed that the dunes are featured by the low mineral maturity index and high structural maturity index.The max grain size is lower than 0.5 mm,the grades from 0.25 mm to 0.063 mm are over 92 percent,and the average grain size of sand regularly change from windward slope(0.137 mm) to dune ridge(0.167 mm) and to lee slope(0.19),which indicates the formation process and the moving direction of the dune.The depositional place of the aeolian sand was more than 3 000 m apart from the shoreline of Qinghai Lake,when the Bird Island was 3 800 m apart from the shoreline and the deeph of water was five meters in 1956.The main stream channel of the Buhahe delta was situated on the North of the Bird Island and made that the north part of the delta developed faster than the south part before the 1980's.The delta-plain was linked with the Bird Island in 1979.After 1980,the main channel swayed to the south of the Bird Island because the main channel and the branch channels on the delta plain cut off and swayed to the south step by step.New delta deposit was built up to the south of the old delta,but the northeastern margin of the old delta stopped development without tributary channels and changed to normal lakeshore.So the large sediments of deltaic deposit is the material base of the aeolian dunes and the stopping development of the delta is the formation factor of the aeolian dunes.Accordingly climate continued arid,which led to soil desertification and the area of desert expanded continuously in recent ten years in the studied area.The onshore lake wind(E-NE) blows the well-sorted sand grains on sand bank along the shore-bar and the sands are transported landward,then built up coastal dunes.

Key words: western shore of the Qinghai Lake, coastal dune, provenance, grain size, formation