Abstract: To the south of Yumenkou, there are some fixed and semi fixed sand dunes dist ributed on terraces of the Yellow River in the Hejin and Wanrong counties of Shanxi Province. The Fen river divided the dunes into two parts. The dunes in the north part, about 400 meters above the sea level and 35 meters above the present table of the Yellow River, are on the second terrace. They are composed of two sand ridges trending N-S and parabolic dunes between ridges. The parabolic dune s are 7~8 meters high and have convex downwind, their stoss slopes are 15°~20°, downwind slopes are around 40°. The alluvial sediments of the second terrac e was dated to be 26.40±0.8 ka BP by the ¹⁴C method, which indicate that the dunes were formed since 26 ka BP. The dunes in the south part, about 500 m above the sea level and around 150 m above the water surface, are on the third terrace of the Yellow River. A natural profile shows t hat the third terrace is composed of interbedded yellow coarse medium sand and siltclay grey green layers in the lower part, grey yellow loess (silts) in the middle part, and aeolian sands on the top. In the loess, the S₁ paleosol and a weaker paleosol, properly the L₁SS₁ and just below the aeolian sands, can be distinguished. It suggested that the aeolian sands were formed since 30 ka BP. The dunes on the terraces of the Yellow River are formed under strong wind, ri ch sand supply, and arid climate in this special area and during the special period. Though the aeolian sands are existed in forms of fixed or semi fixed dune s, the desertification is still a problem in this area. Some fixed dunes in the north part reactived because vegetation at inter dunes' low lands were replace d by apple trees 3~4 years ago. New parabolic dunes over 1 m high formed on the top of the older dunes. Exposed tree roots indicate that the surface soil and sand have been eroded about 0.3 m. The wind erosion is also very strong in the south part. For example, roots of persimmon trees to the north of Xifan village in Wanrong County have been uncovered about 1.2 m.

Key words: Dunes, Local environments, Climatic change, Human activity, The Yellow River