塔克拉玛干沙漠腹地垄间地上覆沙丘形态的空间变化特征及其成因

Spatial variation and formation mechanism of dune morphology in the dominant wind direction on interdune corridors of complex ridges in central Taklimakan Desert

垄间地是塔克拉玛干沙漠中的一种典型下垫面,发育有众多尺度小、形态简单的沙丘,而这些沙丘的分布及其形态的空间变化和成因,至今研究较少。基于Google Earth影像和实地观测,研究了塔克拉玛干沙漠腹地垄间地上覆沙丘在主导风向上的分布格局和形态特征,并分析了其成因。结果表明:(1)垄间地分布有沙片、新月形沙丘、新月形沙丘链和线性沙丘,但新月形沙丘分布最广泛、数量最多,沙丘数量次之,在整个垄间地都有分布,新月形沙丘链集中分布在沙垄背风坡脚,而线性沙丘则主要分布在沙垄迎风坡脚;(2)垄间地上覆沙丘具有明显的空间分布格局,沿主风向,沙丘密度和覆盖度呈上风向>下风向>中部,而新月形沙丘的长度、宽度、底面积、两翼开展度等形态示量参数,从沙垄落沙坡脚到垄间地中部偏迎风坡各参数呈现不同程度下降,沙丘呈逆向演变,随着靠近沙垄迎风坡脚各参数逐渐增大,沙丘又转为正向发育;(3)沙丘的空间分布和形态差异源于地表风动力和沙源供给的空间分异。沙垄背风坡脚风动力相对较弱,沙源丰富,沙丘密度高,新月形沙丘形态发育成熟度高;沙垄背风坡脚到垄间地近迎风坡脚,气流摆脱沙垄风影影响,风速逐渐增大,地表粗沙覆盖,沙源供给相对减少,沙丘物质收支失衡,形态趋于逆向演变;从垄间到沙垄迎风坡脚,受沙垄阻挡,风速降低,地表沙物质相对较细,地表沙源供给相对较充足,沙丘物质收支状况改善,沙丘形态有所恢复。

There exist a large number of dunes in small size and simple shape on interdune corridors in the Takli- makan Desert, while the distribution and the spatial variation and cause of which are poorly studied so far. Based on Google Earth images and field surveys, this paper mainly discusses the cause of the distribution pattern and morpho- logical characteristics of the dunes on interdune corridors in the Taklimakan Desert. The results are as follows： （1） There exist ple-shaped dunes, barchans, barchan chains and linear dunes on interdune corridors in the central of Taklimakan Desert. The density and coverage of barchans are the highest among the four types, while the pie-shaped dunes, widely distributed on all interdune corridors, rank only second to barchans. Barchan chains are mainly dis- tributed in the leeward slope toe, but linear ones in the windward slope toe of complex sand ridges. （2） There is a dis- tinct pattern of spatial distribution of the dunes in this area. The density and coverage of barchans in the dominant wind direction ranks in order of windward, leeward, central, whereas the length, width, basal area, coverage and wingspan decrease from the leeward slope toe of sand ridges to the middle of interdune corridors, but gradually in- crease from the middle of interdune corridors to the windward slope toe of sand ridges under similar conditions. It in- dicates that barchans first degrade and then recover on interdune corridors. （3） The spatial distribution and morpho- logical differences of dunes are determined by the spatial variation of sand supply and wind force. In the leeward slope toe of sand ridges, the wind force is relatively slight and the sand source is rich, moreover, the dunes are dis- tributed in high density and barchans maturely developed to great extent. From the leeward slope toe of sand ridges to the near windward slope toe, the airflow is hardly influenced by wind shadow of complex sand ridges, thus the wind speed rises gradually and the sand supply decreases accordingly due to the coarse sand covered surface. Then there tend to be an imbalance of the sand flux, so barchans have a reverse evolution trend. From the middle of inter- dune corridors to the windward slope toe of sand ridges, the wind speed reduces due to the blocking of sand ridges. Besides, the sand is fine and the supply is relatively sufficient. In that case, the dune compounds are improved and dunes recovered.