Grain size variation response to the morphology and mobility of an inland parabolic dune during the incipient phase of stabilization in the Hobq Desert, China
Meiping Liu, Eerdun Hasi, YU Sun, Binbin Tao
College of Resources Science & Technology, Beijing Normal University, Beijng, China
The significant increase in rainfall in the summer of 2012 on the Southern Fringe of the Hobq Desert, Inner Mongolia resulted in currently vegetated and stable of much of this vast region. Our research focuses on a typical parabolic dune, which was active before 2011 and became stabilized after the vegetation colonization in 2012. Topographic surveys and surface sediments analysis in May 2011, September 2012, September 2013 and March 2014 of the parabolic dune indicate that the study dune expanded eastward with reducing dune volume and height and increasing dune area during the 2011-2012 interval and the slipface of the dune was replaced by a low-angle (12°) apron in 2012, while there were slight changes in dune morphology during the 2012-2014 interval. A pattern of decreasing mean grain size and sorting values (better sorted), increasing proportion of fine sand and silt and decreasing in coarse sand occurred over the dune surface during the incipient phase of stabilization. This study shows that the grain size and sorting characteristics is very sensitive to the change of dune morphology. The surface of the dune head in 2011 was generally characterized by coarser stoss slope and finer lee slope, the proportion of coarse sand decreased, whereas the fine sand increased from the stoss slope to the lee slope. While the surface in 2013 and 2014 were characterized by relatively fine stoss slope and coarse lee slope, the percentage of medium sand increased and the percentage of very fine sand decreased from the stoss slope to the lee slope. The trend in grain size distribution from the stoss slope to the lee slope on the dune head exhibited significant similarity between 2013 and 2014, and was quite different from that in 2011, the difference in the coarse and fine sand percentages between the stoss and lee slope in 2011 were relatively great, whereas in 2013 and 2014 the range of the difference was relatively small; however, the range in the medium and very fine sand conditions was quite the contrary. There was a strong relationship between the grain size and sorting characteristics and the dune mobility, once anchored (2013-2014), the overall morphology, and the grain size and sorting characteristics of the parabolic dune tented to be more constant and were quite different from those when the dune was active.