In order to clarify the formation mechanism of linear dunes on the northern margin of Qarhan Salt Lake, northwestern China, we analyzed the grain-size and sorting parameters of the dune and interdune sands. The surfac...In order to clarify the formation mechanism of linear dunes on the northern margin of Qarhan Salt Lake, northwestern China, we analyzed the grain-size and sorting parameters of the dune and interdune sands. The surface sands （0-30 ram） from the dune base to the crest of both flanks and interdune corridors were sampled along transects from upwind to downwind through the dune field. The results indicated that the grain-size distribution differed at different positions between and within the dunes. The frequency curve for dune sands mainly showed a bimodal distribution, while the interdune sediments showed a trimodal distribution. The grain size distribution of the linear dunes showed a finer crest pattern, i.e. the crests were composed of sands that were generally finer, better sorted than those of base sands. In addition, at the dune field scale, the dune crest sands were tending to become much finer but sorting became worse along the downwind transects. However, the grain-size parameters of sediments in the interdune corridors showed no clear pattern. The results demonstrated that the grain size and sorting parameters exhibited a systematic change not only at the individual scale but also at the dune field scale. Our results quantitatively estimate the limited role of cohesive sediments on the formation of linear dune under unidirectional wind regime. More attention should be paid to a long-term wind regime observation, internal sedimentary structures and their formation ages.展开更多
In terms of formation mechanisms of linear dunes,there are open arguments for their widespread distribution and multi-morphological diversities.In order to clarify the formation mechanism of linear dunes of Qarhan Sal...In terms of formation mechanisms of linear dunes,there are open arguments for their widespread distribution and multi-morphological diversities.In order to clarify the formation mechanism of linear dunes of Qarhan Salt Lake,we used pattern analysis method to analyze the statistical characteristics and spatial variation of their pattern parameters.Except at the west-northwest margin,the pattern parameters showed regular spatial variation from the up-middle part towards the downwind end of the dune field.Based on the cumulative probability plots for inter-crest spacing and crest length,we divided the linear dunes into three groups,which corresponding to the three evolution stages of these dunes.The first group comprises erosional relics,with shorter crests,smaller inter-crest spacing and more random dune orientation.The second group comprises dunes whose sand supply is just sufficient to maintain stability and these dunes are approaching the net erosion stage.The crest length and inter-crest spacing of these dunes are much larger than those of the first group,and dune orientation is closer to the resultant drift direction （RDD） .The last group comprises linear dunes that are still undergoing vertical accretion and longitudinal elongation,which follows the RDD of the modern wind regime.The presence of regular spatial variation of pattern parameters and a similar geometry with the vegetated linear dunes suggest that deposition and erosion coexist in the development and evolution of linear dunes of Qarhan Salt Lake,i.e.deposition predominates at the downwind end of linear dunes in the vertical accretion and longitudinal elongation stage,whereas erosion mainly occurs at the upwind end of linear dunes in the degradation stage.Therefore,the formation mechanism of linear dunes in Qarhan Salt Lake can be reasonably explained by the combination of depositional and erosional theories.展开更多
The dynamical processes of a typical linear dune including morphological features, dune ridge swing range and crest height were investigated at different monitoring periods in the hinterland of Tengger Desert. The res...The dynamical processes of a typical linear dune including morphological features, dune ridge swing range and crest height were investigated at different monitoring periods in the hinterland of Tengger Desert. The results indicated that the development of linear dune depends on not only the northwesterly prevailing wind, but also the winds from northeast and southwest. The dune ridge swayed along its fundamental strike and took on an eastward movement gradually. The original dune strike was NW70° on August 3, 1994, and then changed to NE15° on April 21, 2001. The dune crest increased by 1.8 m longitudinally, which manifested strong wind-blown sand activities in this region. Wind erosion frequently occured at the bottom of sand dune, while sand accumulation appeared on its mid-upper section. The mean wind erosion depth was 25 cm on the bottom of linear dune and the height difference of the control points on the dune’s ridge was 1.13 m. Although the linear dune swayed laterally, the horizontal displacement of its ridge moved eastward 5.8 m averagely. The swing range of the dune crest line is very distinct, with a maximum value of 13.2 m. The highest site on the K-profile swayed on both sides of the dune ridge and the heights were 19.88 m at the control point K5, 19.61 m at K6 and 19.05 m at K7, respectively. The results indicated that the lateral swing of the linear dune was distinct under the northwesterly wind and it moved toward east gradually.展开更多
Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and ...Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand.Saline sand samples(mean particle size of 164.50–186.08μm and the total silt,clay and salt content of 0.80%–8.25%)were collected from three saline sand dunes(one barchan dune and two linear dunes)in the Qarhan Desert,Qaidam Basin of China.Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation,respectively.Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment.The motion of sand particles was determined by the observers with a solid laser.The laser sheet(0.80 cm thick),which was emitted by the solid laser,horizontally covered the sand surface and was bound to the sand.Results show that the cohesion of saline sand results from a combination of salt and water.The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes.There is a positive linear correlation between the original moisture content and relative threshold shear velocity.The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content.Our results will provide valuable information about the sand transport of highly saline soil in the desert.展开更多
基金funded by the National Natural Science Foundation of China (41171010, 41130533, 41301003)
文摘In order to clarify the formation mechanism of linear dunes on the northern margin of Qarhan Salt Lake, northwestern China, we analyzed the grain-size and sorting parameters of the dune and interdune sands. The surface sands （0-30 ram） from the dune base to the crest of both flanks and interdune corridors were sampled along transects from upwind to downwind through the dune field. The results indicated that the grain-size distribution differed at different positions between and within the dunes. The frequency curve for dune sands mainly showed a bimodal distribution, while the interdune sediments showed a trimodal distribution. The grain size distribution of the linear dunes showed a finer crest pattern, i.e. the crests were composed of sands that were generally finer, better sorted than those of base sands. In addition, at the dune field scale, the dune crest sands were tending to become much finer but sorting became worse along the downwind transects. However, the grain-size parameters of sediments in the interdune corridors showed no clear pattern. The results demonstrated that the grain size and sorting parameters exhibited a systematic change not only at the individual scale but also at the dune field scale. Our results quantitatively estimate the limited role of cohesive sediments on the formation of linear dune under unidirectional wind regime. More attention should be paid to a long-term wind regime observation, internal sedimentary structures and their formation ages.
基金funded by the National Basic Research Program of China (2013CB956000)the National Natural Science Foundation of China (41171010,41371102,41301003)
文摘In terms of formation mechanisms of linear dunes,there are open arguments for their widespread distribution and multi-morphological diversities.In order to clarify the formation mechanism of linear dunes of Qarhan Salt Lake,we used pattern analysis method to analyze the statistical characteristics and spatial variation of their pattern parameters.Except at the west-northwest margin,the pattern parameters showed regular spatial variation from the up-middle part towards the downwind end of the dune field.Based on the cumulative probability plots for inter-crest spacing and crest length,we divided the linear dunes into three groups,which corresponding to the three evolution stages of these dunes.The first group comprises erosional relics,with shorter crests,smaller inter-crest spacing and more random dune orientation.The second group comprises dunes whose sand supply is just sufficient to maintain stability and these dunes are approaching the net erosion stage.The crest length and inter-crest spacing of these dunes are much larger than those of the first group,and dune orientation is closer to the resultant drift direction （RDD） .The last group comprises linear dunes that are still undergoing vertical accretion and longitudinal elongation,which follows the RDD of the modern wind regime.The presence of regular spatial variation of pattern parameters and a similar geometry with the vegetated linear dunes suggest that deposition and erosion coexist in the development and evolution of linear dunes of Qarhan Salt Lake,i.e.deposition predominates at the downwind end of linear dunes in the vertical accretion and longitudinal elongation stage,whereas erosion mainly occurs at the upwind end of linear dunes in the degradation stage.Therefore,the formation mechanism of linear dunes in Qarhan Salt Lake can be reasonably explained by the combination of depositional and erosional theories.
基金supported by the National Key Basic Research Development Program of China (2009BAC54B01-1)National Natural Science Foundation of China (41071009 and 40701171)
文摘The dynamical processes of a typical linear dune including morphological features, dune ridge swing range and crest height were investigated at different monitoring periods in the hinterland of Tengger Desert. The results indicated that the development of linear dune depends on not only the northwesterly prevailing wind, but also the winds from northeast and southwest. The dune ridge swayed along its fundamental strike and took on an eastward movement gradually. The original dune strike was NW70° on August 3, 1994, and then changed to NE15° on April 21, 2001. The dune crest increased by 1.8 m longitudinally, which manifested strong wind-blown sand activities in this region. Wind erosion frequently occured at the bottom of sand dune, while sand accumulation appeared on its mid-upper section. The mean wind erosion depth was 25 cm on the bottom of linear dune and the height difference of the control points on the dune’s ridge was 1.13 m. Although the linear dune swayed laterally, the horizontal displacement of its ridge moved eastward 5.8 m averagely. The swing range of the dune crest line is very distinct, with a maximum value of 13.2 m. The highest site on the K-profile swayed on both sides of the dune ridge and the heights were 19.88 m at the control point K5, 19.61 m at K6 and 19.05 m at K7, respectively. The results indicated that the lateral swing of the linear dune was distinct under the northwesterly wind and it moved toward east gradually.
基金funded by the National Natural Science Foundation of China(41601002,41871008)
文摘Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand.Saline sand samples(mean particle size of 164.50–186.08μm and the total silt,clay and salt content of 0.80%–8.25%)were collected from three saline sand dunes(one barchan dune and two linear dunes)in the Qarhan Desert,Qaidam Basin of China.Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation,respectively.Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment.The motion of sand particles was determined by the observers with a solid laser.The laser sheet(0.80 cm thick),which was emitted by the solid laser,horizontally covered the sand surface and was bound to the sand.Results show that the cohesion of saline sand results from a combination of salt and water.The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes.There is a positive linear correlation between the original moisture content and relative threshold shear velocity.The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content.Our results will provide valuable information about the sand transport of highly saline soil in the desert.
