塔克拉玛干沙漠腹地高大复杂纵向沙垄区简单横向沙丘形态特征的空间变异

为了探讨小尺度风沙地貌形态的空间变异过程,对塔克拉玛干沙漠腹地高大复杂纵向沙垄横断面上简单横向沙丘形态特征进行了研究。沙丘形态野外测量采用RTK(real-tim e k inem atic)技术,并通过南方测绘软件(South Survey)量算形态特征参数。结果表明:简单横向沙丘形态特征参数及其相互关系具有空间变异性。在8个地貌部位之间,沙丘形态特征参数(不包括迎风坡度)存在显著性差异,主要体现在:垄顶、沙垄背风坡、其他地貌部位(包括垄间地和沙垄迎风坡)三者之间的差异。地貌部位、输沙风强度以及沙丘活动强度是驱动沙丘形态空间变异的因素。沙丘高度与翼展度余弦有负对数关系,发育指数与高度、迎风坡度成负线性相关,这些相关性的显著程度在垄顶、背风坡较高,在垄间和迎风坡较低。     

新疆策勒沙漠与砾质戈壁新月形沙丘表面沉积物粒度特征及其沉积环境

不同下垫面对同种类型的沙丘的表面风沙沉积物特征产生重要影响,通过数理统计法对新疆策勒沙漠与砾质戈壁新月形沙丘表面不同地貌部位表面沙物质的粒度进行分析,探讨不同下垫面形成的相同的沙丘类型而导致沙丘的粒度特征存在的空间差异及其原因。结果表明:沙漠新月形沙丘比砾质戈壁新月形沙丘表面沙物质的平均粒径更细,分选性较好,偏度更趋于粗偏,峰态更趋于宽峰态。沙漠新月形沙丘表面沙物质主要由极细沙、细沙、极粗粉沙组成,百分含量分别为58.67%、20.23%、16.83%,其侧翼表面沙物质平均粒径最粗,约为118.99μm,砾质戈壁新月形沙丘表面沙物质主要由中沙、细沙、极细沙、极粗粉沙、粗沙组成,百分含量分别为26.53%、26.43%、26.36%、9.58%、9.14%,其顶部表面沙物质平均粒径最粗,约为291.48μm。沙漠新月形沙丘表面沙物质分选系数介于1.45-1.73之间,属于中等-较好分选性,偏度值介于-0.03-0.07之间,主要表现为对称,峰态值介于0.96-1.01之间,属于常峰态,砾质戈壁新月形沙丘表面沙物质分选系数介于1.99-2.44之间,主要属于较差分选性,偏度值介于-0.32...     

内蒙古高原小叶锦鸡儿灌丛沙堆对气流结构与风蚀的影响

小叶锦鸡儿(Caragana microphylla)灌丛沙堆是内蒙古高原东南部农牧交错区的主要风沙堆积类型。通过对该区典型灌丛沙堆周围风沙气流的野外观测,结果表明,气流方向与强度和输沙率,随沙堆不同位置而发生变化。绕过沙堆两侧的气流和越过沙堆上部的气流在背风侧汇集,并在同等沙堆高度的范围内和1.5倍沙堆高度的水平范围内出现涡流。从灌丛沙堆迎风坡脚经南北两侧至背风坡脚以及背风侧5倍沙堆高度的水平距离间,风速依次出现逐渐增大—最大—逐渐减小—最小—回増至旷野风速的变化过程。在不同风向条件下,灌丛沙堆背风侧气流的风速廓线,并不完全遵循对数变化规律,沙堆南侧气流在0.3~0.6 m高度处出现变异。另外,沙堆周围输沙率在迎风侧和南北两侧与风速变化基本一致,但在背风侧因气流方向紊乱而出现变异。输沙率随高度增加,在沙堆迎风侧至两侧各部位呈有规律递减,但在背风侧无规律。     

乌海市沿黄河两岸沙丘风沙流结构差异与冰面风沙特征

为了研究乌海市沿黄河两岸沙丘风沙流结构差异与冰面风沙特征,开展以黄河西岸-黄河冰面-黄河东岸为路径的风沙观测实验,通过对比分析黄河两岸沙丘风沙流结构、沙尘粒度特征,为黄河沙尘防控问题提供理论依据。研究表明:两岸沙丘总输沙率均随着高度增加而减小,东岸输沙率垂直拟合优度较西岸差,风沙流比西岸更容易达到非饱和状态。黄河冰面裂缝滞留沙尘粒径大于0. 19 mm,较小颗粒则输移到东岸,东岸沙丘受矿采区粉尘影响,极细砂粒(0. 05～0. 1 mm)含量增加,极细砂平均含量东岸西岸,沙尘平均粒径东岸西岸。沿黄河两岸沙丘与冰面沙尘的粒度参数峰度均为宽峰态,沙物质来源相似。     

新月形沙丘对湖积平原风蚀荒漠化的影响

新月形沙丘是风蚀荒漠化过程中伴随的重要风积地貌类型,在以往的研究中主要侧重于沙丘体表面动力学过程,而关于沙丘在风蚀荒漠化过程中的作用鲜有报道。本文在台特玛湖的干涸湖盆区(曾经的塔里木河尾闾湖),采用测钎法,实地测定了新月形沙丘周围地表的蚀积变化,同时采用室内风洞模拟了典型新月形沙丘地表的气流分布模式,系统分析了新月形沙丘对地表蚀积影响的作用机理。结果表明:在新月形沙丘影响下,沙丘周围地表风蚀强度不均一,在沙丘迎风坡前区和沙丘左右翼,风蚀深度略大于不受沙丘影响区(CK),但单位面积平均净蚀积量接近平衡状态;在沙丘背风坡前区以风积为主,而在背风侧尾流区,地表以风蚀为主,且随着沙丘体积增加,单位面积平均净风蚀量也略有增大。在内陆干旱区干涸湖盆风蚀荒漠化过程中,新月形沙丘通过改变地表流场结构,使风沙流饱和度发生空间分异,从而影响了下伏地表蚀积的空间分布,尤其加剧了背风侧尾流区的风蚀,使新的风蚀面裸露,破坏沉积层结构,促进了河湖相沉积平原风蚀荒漠化的发展。     

敦煌月牙泉景区沙丘表面沙物质的粒度特征

结合风况和蚀积监测数据,系统分析月牙泉南侧线性沙丘、北侧金字塔沙丘表面沙物质粒度特征及其环境指示意义。结果表明:(1)线性沙丘SW坡面以风蚀为主,NE坡面以风积为主,由此导致NE坡面表面沙物质较SW坡面细、分选性好。(2)月牙泉北侧金字塔沙丘SW坡面以风蚀作用为主,沙物质粒径最粗,分选最差。NW坡面也是主要的风蚀面,但由于靠近绿洲防护林,底部以风积为主。E坡面以风积作用为主,沙物质粒径最细、分选最好。(3)从风场、粒度和蚀积变化监测结果来看,对月牙泉危害最大的是南侧线性沙丘NE坡面的积沙。金字塔沙丘SW坡面中部的持续积沙也会对月牙泉构成潜在的威胁。因此,为了更好的保护月牙泉这一自然奇观,应该加强景区周边环境监测与管理。     

河岸沙丘粒度分布特征

沙丘沉积物粒度特征分析是研究风沙地貌过程的主要内容之一。通过野外实地考察与测量,并沿盛行风向对西辽河平原西部响水河两岸的河岸沙丘进行样品采集,经室内激光粒度仪测试,研究河岸沙丘的粒度分布规律。结果表明:1响水河东岸沙丘粒径粗于西岸沙丘。东岸沙丘由迎风坡脚到背风坡中下部粒径总体变细,从两侧坡脚到丘顶分选性逐渐变好。西岸沙丘由两侧坡脚到丘顶粒径变细,偏度趋于正偏,分选均较好。河流砂最细,其平均粒径总体细于东、西岸沙丘砂,分选性好于东岸沙丘,差于西岸沙丘。2东岸沙丘受河流与风力作用可以从较深地层获取沙源,西岸沙丘主要受风力作用从较浅地层获得沙源。     

策勒流沙前沿柽柳灌丛沙堆地表蚀积变化特征

为了研究柽柳灌丛沙堆表面蚀积变化特征及其风沙环境演变方向,采用插钎法对策勒流沙地半球形柽柳灌丛沙堆进行地表蚀积变化观测,结合同步气象数据,采用数理统计和函数拟合方法分析,结果表明:柽柳灌丛沙堆迎风坡和顶部为风积区,沙堆外围西北区、北翼区、南翼区均为年蚀积动态平衡区,在一年内既不风蚀也不风积。灌丛沙堆外围的西南区为严重的沙丘前移风蚀区,受多风向变化影响,沙堆外围的东侧背风区为轻微-中等程度的风蚀区。沙堆表面年净风积量为0.47 m3,风蚀量为0.004 8 m3,风蚀主要发生在背风坡坡底和裸露的坡脚上。沙堆表面风积量与每个阶段起沙风时间呈一定相关性,除了北翼区表面风积量与大于起沙风平均风速中等相关外,其余几个观测小区风蚀量、风积量与对应的大于起沙风的平均风速之间相关性较差,沙堆西区、北翼区、背风区表面风蚀量与起沙风时间为中等程度相关性,背风区的相关性最好,灌丛沙堆表面和外围南翼区风积量与每个阶段起沙风时间呈中等程度相关性。     

火星Kaiser陨石坑新月形沙丘近表层风况特征

风沙地貌的形态和分布能够较好地反映区域风况,而沙波纹作为一种小尺度的风沙地貌类型,可以很好地指示现代风况下沙丘近表层的流场状况。文中利用HIRISE影像监测了火星南部Kaiser陨石坑内新月形沙丘表层沙波纹的形态特征,并以此探讨分析了沙丘近表层的气流场特征。结果表明:(1)沙波纹的脊线长度主要分布在100-300m之间,平均长度为190.3m;波长主要分布在2-5m之间,平均波长为3.1m,且基本符合正态分布。(2)三处样地沙波纹的主要走向分别为NE-SW、N-S和NW-SE,与沙丘脊线走向呈近似90°的夹角。(3)沙丘近表层气流的走向主要为NW-SE、W-E和SW-NE,并由此推断陨石坑内沙丘主要受到自西向东气流到控制,在遭遇地形影像后又向西发生了折返。上述研究表明沙丘形态及其分布的区域差异性是在复杂的风沙环境下形成的,沙波纹可用作沙丘近表层风况特征研究的代用指标。     

玛曲高寒草甸风沙环境与沙化类型研究

玛曲县高寒草甸沙化是青藏高原地区发生沙化的典型案例,其成因、趋势和治理一直受到极大关注。利用三维激光扫描仪,结合野外监测和室内分析等方法,揭示了区域风沙环境,结合区域沉积物粒度与形态特征,依据沙物质来源复杂程度将沙化类型划分为风蚀坑沙化类型和复杂沙化类型。结果表明:区域全年输沙势为164.34VU,合成输沙势为91.57 VU,合成输沙方向132.37°,风向变率0.56,属于中比率低风能环境。综合风蚀坑沙化类型周边风蚀坑与积沙区的长度比、体积比、长轴线、与区域主风向吻合程度及沉积物粒度特征,可知风蚀坑是该沙化类型区域积沙的主要贡献者。在现代沙化过程中,复杂沙化类型除周边风蚀区、活化沙丘以及沙化草地等为区域积沙贡献沙物质外,黄河河道也为区域积沙提供一定量的沙物质。     

Contribution of underlying terrain to sand dunes: evidence from the Qaidam Basin,Northwest China

Underlying terrain strongly influences dune formation. However, the impacts of underlying terrain on the dune formation are poorly studied. In the present research, we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin, Northwest China. We quantified the dunes' sediment characteristics on different types of underlying terrain and the terrain's effects on the surface quartz grains by analyzing grain-size distribution, soluble salt contents and grain surface micro-textures. Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution, whose peak corresponded to the saltation load. Linear dunes were mainly composed of fine sands with a bimodal frequency distribution, whose main peak represented the saltation load, and whose secondary peak represented the modified saltation or suspension load. Sand was transported from source area by running water (inland rivers) over short distances and by wind over relatively longer distances. Thus, quartz grains had poor roundness and were dominated by sub-angular and angular shapes. Surface micro-textures indicated that dune sands were successively transported by exogenic agents (glaciation, fluviation and wind). Soluble salt contents were low in dunes that developed in the alluvial fans, which represented a low-energy chemical environment, so the grain surface micro-textures mainly resulted from mechanical erosion, with weak micro-textures formed by SiO₂ solution and precipitation. However, soluble salt contents were much higher in dunes that developed in the dry salt flats, which indicated a high-energy chemical environment. Therefore, in addition to micro-structures caused by mechanical erosion, micro-textures formed by SiO₂ solution and precipitation also well developed. Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin, China.     

塔克拉玛干沙漠腹地纵向沙垄的粒度分布特征

塔克拉玛干沙漠东经８４°附近、北纬３９°－４０°之间垄间低地中纵向沙垄的粒度分布特征表现为：平均粒径３．１４５，以极细沙为主，其次为细沙和中沙，三者含量达８０％～９０％以上。两坡下部较细、丘顶较粗。标准高差平均值为０．５９，分选程度中等，两坡中部分选较好，丘顶分选较差。偏度平均值为０．２９，大部分沙样为正偏态，粗组分含量较高。上述粒度特征在沙垄两翼坡面上呈不完全对称分布，并随着不同方向起沙，风的作用呈现一定程度的周期性变化。     

Grain size distribution at four developmental stages of crescent dunes in the hinterland of the Taklimakan Desert,China

Although scientists have performed many studies on crescent (barchan) dunes in the Taklimakan Desert,few studies reported the changes in grain size at different development stages of crescent dunes.In order to evaluate the changing trends of surface sediment grain size with dune development,we investigated the grain size characteristics at four developmental stages (oval sand pile,shield dune,incipient crescent dune and mature crescent dune) of crescent dunes by measuring the morphology of sand dune and observing the near-surface wind regime.The dunes have developed in a wide inter-dune corridor between high compound longitudinal ridges in China's Taklimakan Desert.The surface sediments at four developmental stages of the crescent dunes were primarily composed of fine sands,followed by very fine and medium sands.Mean grain sizes ranged from 2.8 to 3.1 φ,with a unimodal distribution.The sands were moderately well-sorted,their distribution varied from platykurtic to very platykurtic,and symmetrical or skewed towards the fine particles.From oval sand piles through shield and incipient crescent dunes to mature crescent dunes,incipient grain size gradually increased,particles became finer,sorting became better,kurtosis and skewness increased.Grain sizes on the surface layer became coarser upwards from the toe of the windward slope and then became finer towards the bottom of the leeward slope.We found that the coarsest particles at different positions at the four developmental stages were different.The coarsest particles were distributed at the top of the oval sand piles and shield dunes,versus at the middle of the windward slope of the incipient and mature crescent dunes.Correlations between the mean grain size and other grain size parameters showed that as mean grain size became finer,sorting became better and kurtosis became wider,but skewness changed only slightly.In addition,grain size variation in the surface sediments correlated with the movement speed of the dunes in the study area.In the open ground among tall-complex longitudinal ridges in the hinterland of the Taklimakan Desert where aeolian environment is characterized by comparatively strong wind and unsaturated sand flow,faster dune movement corresponded to coarser grain size.     

Morphological characteristics and dynamic changes of seif dunes in the eastern margin of the Kumtagh Desert,China

The seif dune field over the gravel desert surface in the eastern margin of the Kumtagh Desert is a valuable experimental site for the observation of dune formation and dynamics. We used high-resolution remote sensing and station observation approaches, combined with wind and grain size data, to study the characteristics of the aeolian environment and the morphologies of and dynamic changes in seif dunes. We observed the ratio of the resultant drift potential (RDP) to the drift potential (DP), which was 0.37, associated with an obtuse bimodal wind regime. The drift potentials in the west-northwest (WNW) and east-northeast (ENE) directions were dominant, and the angle between the two primary DP directions was 135.00°. The dune orientations ranged from 168.75°-213.75°, which were parallel to the resultant drift direction (186.15°). The dune lengths ranged from 51.68 to 1932.11 m with a mean value of 344.91 m. The spacings of the dunes ranged from 32.34 to 319.77 m with a mean value of 93.39 m. The mean grain size of the sediments became finer, and the sorting became better from upwind tail to downwind tip, which indicated that the sediment of the seif dunes in the study region may be transported from northward to southward. The rate of increase in the length, the mean longitudinal migration rate of the dune tail, and the mean longitudinal extension rate of the dune tip (also called elongation rate) were 4.93, 4.63, and 9.55 m/a, respectively. The mean lateral migration vector of the seif dunes was approximately 0.11 m/a towards the west (-0.11 m/a), while the mean amplitude of lateral migration was 0.53 m/a, ignoring the direction of lateral migration. We found that the seif dune field formed first beside seasonal rivers, which can provide sediment, and then expanded downwind.     

Morphological variation of star dune and implications for dune management: a case study at the Crescent Moon Spring scenic spot of Dunhuang,China

Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang, China, are used to investigate the changes in dune morphology on timescales from months to decades. The result revealed that relative-equilibrium airflow strength in three wind directions of northeast, west and south was an important condition for the stability of star dunes with limited migration. Transverse and longitudinal airflows exerted a crucial impact on variation processes of star dune morphology. Controlled by transverse airflows, the easterly winds, the east side was dominated by wind erosion; and strong deposition occurred on the south-south-east arm with a maximum deposition rate of 0.44 m/a in the 46-a monitoring period, causing the east side becoming steep and high. Controlled by longitudinal airflows, the westerly winds, the west-north-west side was mainly eroded and the north arm migrated from west to east with a rate of 0.30 m/a, causing the dune slope becoming gentle and elongate. The local air circulation(southerly winds) exerted a significant impact on the development process of the star dune. Due to the influence of human activities, the south side present surface processes from a concave profile to a convex profile in 46 a, which is a potential threat to the Crescent Moon Spring. The results indicate that rehabilitating the airflow field at most is a crucial strategy to the protection of Crescent Moon Spring from burial. Opening up the passage of easterly, westerly and southerly winds through intermediately cutting the protection forest, demolishing the enclosed wall and changing the pavilion into a porous pattern have been suggested to protect the Crescent Moon Spring from burial.     

塔克拉玛干沙漠腹地纵向沙垅表面沙物质粒度特征

本文对塔克拉玛干沙漠腹地纵向沙垅表面沙粒、丘间地沙粒进行了粒度分析。结果表明,沙垅以极细沙为主,平均粒径３．０６Φ,沙粒从沙垅迎风侧到背风侧逐渐变细。沙丘沙比丘间地沙分选好,沙垅背风侧比迎风侧分选好。沙粒属极负偏,偏度－０．２２,丘间地沙比沙丘沙更趋向负偏。峰度１．３８,属尖峰态。粒径与偏度和峰度成正相关,分选和偏度成良好负相关。沙丘沙以单峰态为主,累积频率曲线为２～３段式,丘间地以双峰态为主,累积频率曲线为３～４段。大尺度地形对沙粒段式没有影响,对各段组分含量相对大小有影响。     

Grain-size characteristics of linear dunes on the northern margin of Qarhan Salt Lake,northwestern China

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 mm) 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.     

Sand source and formation mechanism of riverine sand dunes: a case study in Xiangshui River,China

Riverine sand dunes develop as a result of fluvial-aeolian interactions. The primarily barchan dune chains along the Xiangshui River (a branch of the Xar Moron River in the western part of the Horqin Sandy Land of China) form a typical riverine dune field. We collected a series of samples from the riverine sand dunes parallel to the direction of the prevailing wind and investigated the sand sources and formation mechanisms of these dunes by determining the grain size, heavy mineral content and optically stimulated luminescence (OSL) of the samples. The sand of the near-river dunes was coarser than the sand of the dunes distant from the river, indicating that coarse sand of the valley mainly deposited on near-river dunes. The heavy mineral analysis suggested that wind-sand activity levels were intense on the upwind dunes, but relatively weak on the downwind dunes. This indicated that the sand sources for the near-river dunes were more abundant than those of the distant dunes. Our OSL analysis of samples suggested that the deposition rates on dunes near the river were greater than the deposition rates on dunes distant from the river. The development of dunes along the river indicated that the river played an important role in dune formation and development. In addition, airflow fluctuation and the formation of the waveform dunes had a type of feedback relationship. Grain size, heavy mineral and OSL analyses are widely used methods in wind-sand research. Sand dune grain size characteristics reflect the effects of airflow on the transport and separation of sand materials, as well as the physical characteristics of the sand sources. Heavy mineral characteristics are often used to investigate the relationships between sediments and sand sources. OSL indicates dune age, revealing formation of dunes. Therefore, it is useful to explore dune sand sources, as well as the mechanisms underlying dune formation, by determining grain size, heavy mineral content and OSL. This study investigated the sand sources of riverine dunes and provided new information about riverine dune formation and development.     

塔克拉玛干沙漠新月形沙丘不同部位的粒度特征

通过对塔克拉玛干沙漠东经84°沿线,北纬38°50′～40°50′之间复合型沙垄垄间平地新月形沙丘的粒度筛析资料分析表明:沙丘沙以极细沙和细沙为主,二者含量达80～90%以上。平均粒径3.34φ。落沙坡脚最细,往迎风坡脚越来越粗。分选程度以沙丘脊部最好,向两坡逐渐较差。沙丘上沙子搬运以跃移为主,该组分含量占90%左右。粗截点2～3φ、细截点4φ左右。地面滚动组分平均含量<6%,悬移组分平均含量<3%。丘间地平均粒径2.94φ,分选也较沙丘差。作为对照,文中还论述了纵向沙垄的粒度特征。