Abstract:

Based on the analysis of the morphology， grain-size characteristics and wind regimes among three different dunes （barchan， parabolic dune and reversing dune） in Mu Us Sandy Land， we investigated the response of dune forms and their surface grain-size parameters to the change of external conditions （i.e.， wind regimes and vegetation cover）. The results show that the mean grain-size （M_{\mathrm{Z}}） of barchan decreases gradually from the bottom to the top of the stoss face， and the sorting becomes better， but the fine grain-size and poor sorting appear in the middle of the stoss face. With the increase of vegetation cover， barchan gradually transforms into the parabolic dune， and the near-surface sand transport and incoming sand supply are also limited. As a result， the mean grain size of the parabolic dune becomes coarser from the bottom to the top of the stoss face， and the sorting gradually becomes better. Seasonal wind regimes in Mu Us Sandy Land promoted the development of reversing dunes and reorganized sand grain-size characteristics. Under the influence of wind erosion in summer， eroded sand deposited on the upper of the stoss face and dune crestline flip. Thus， the mean grain-size and sorting are getting coarser and better in the dune crestal area， respectively.

Key words: dune morphology, grain-size characteristics, seasonal wind regimes, vegetation cover, decreasing wind strength