新月形沙丘稳定性机理——以甘肃河西沙区为例

新月形沙丘是一种重要的沙丘类型,一般存在于绿洲边缘。研究新月形沙丘的稳定性,对于揭示绿洲缘的风沙运动规律有重要学术价值,而到目前新月形沙丘的稳定性还是沙漠生态学领域中一个的尚未解决的科学问题。以河西沙区新月形沙丘为例,通过调查其分布环境、测定沙丘各部位风速和风蚀积沙等,分析了新月形沙丘顶部稳定机理。结果表明:1)甘肃河西沙区的新月形沙丘分布在沙漠边缘的下风向,一般为斑块状分布。分布区域为平坦的沙粘质或沙砾质滩地,丘间地较为开阔且具有明显的主风向。2)主风向(NW)过程是新月形沙丘顶点与沙脊线重合的过程,也是新月形沙丘前移和高度降低的过程;反主风向(SE)过程是新月形沙丘顶点与沙脊线分离的过程,也是新月形沙丘背风坡上部风蚀与沙丘增高的过程。3)新月形沙丘越高大,两翼越长、夹角越小。4)较为开阔的前后滩地是新月形沙丘及新月形沙丘链存在所必须的环境条件,相对单一的主风向是新月形沙丘及新月形沙丘链维持其稳定性的关键因子,反向风及两翼的廊道效应是新月形沙丘增高增大的关键因子,主、反两个方向的风速及其分布频率是控制该区域新月形沙丘及新月形沙丘链高度的限制因子。

Stability mechanisms of barchan sand dunes:a case study in the Hexi Desert in Gansu

Barchan sand dunes, which are distributed at the oasis fringe, are an important type of dune. The study of the mechanism of stability of barchan sand dunes is of great importance to the determination of the regulation of aeolian-sand movement at the oasis fringe. However, the stability of barchan sand dunes remains an unresolved scientific issue. This study took the barchan dunes in the Hexi Desert as a case study. The stability mechanism of the top of barchan dunes was analyzed. The results showed that: (1) The barchan dunes in the Hexi Desert of Gansu Province were distributed as patches downwind from the desert fringe. The distribution area was flat sandy-clay or sandy-gravel soil. The lowlands among the dunes were wide, with prominent prevailing winds. (2) The prevailing northwestern winds caused the top of the dunes and the sand line to coincide, and the dunes to move forward and become lower. The southeastern winds (opposite to prevailing winds) caused the top of the dune to separate from the sand line, and the upper part of the leeward slope was wind-eroded and the dunes were heightened. (3) The higher the barchan dune was, the longer the two flanks were, and the smaller the angle was. (4) The wide flat area was vital to the formation of barchans and barchans chains. The largely prevailing wind was the key factor for the stability of the barchans and barchans chains. The opposite wind and the corridor effect between the two flanks were key factors enabling the barchans to grow in size and height. The wind speed and distribution frequency of the prevailing and opposite winds were factors restraining the height of the barchan dunes and barchan dune chains.