雅鲁藏布江米林宽谷段爬升沙丘粒度分异特征研究

雅鲁藏布江米林宽谷段爬升沙丘分布广泛。选择卧龙镇西侧雅鲁藏布江右岸典型爬升沙丘,根据沙丘爬升高度和叠置沙丘地貌部位对其表面沉积物进行了系统采样。作为河谷风沙地貌的重要组成部分,相应采集了河漫滩、阶地沙丘沙样品。粒度分析表明,爬升沙丘对河漫滩沙丘、阶地沙丘在物源和形成过程方面具有继承性,其表面沉积物以细沙和极细沙为主(2.07～3.71Φ),分选中等或较好(0.20～1.41Φ),细偏,多峰。由坡脚向丘顶的沉积物粒径变细,分选变好,偏度和峰度降低。爬升沙丘表面叠置沙丘的粒度向丘顶变粗、分选变好。细沙、极细沙等粒级组分与高度相关,反映颗粒爬升能力不同。叠置条带状沙丘脊部和槽部的粒度存在分异。     

科尔沁沙地流动沙丘与玉米地辐射特性比较分析

利用2001年夏季内蒙古科尔沁沙地地区大气边界层实验观测资料,对比分析了流动沙丘和临近流动沙丘的玉米地两种典型下垫面的辐射通量特征。结果表明：流动沙丘和玉米地地区的总辐射与大气逆辐射相近,差异不足2%。净辐射、地表反照率、有效辐射存在较大差异,流动沙丘的净辐射明显小于玉米地,其中反照率差异的贡献约为60%,长波辐射差异的贡献约为40%。流动沙丘的反照率、有效辐射明显大于玉米地,反照率高出中国西北HEIFE实验沙漠地区约10%,有效辐射则小于沙漠地区。     

流动沙丘干沙层厚度对土壤水分蒸发的影响

利用Micro-lysimeter对流动沙丘不同干沙层厚度下的土壤水分蒸发作了测定与分析,结果表明:当干沙层厚度发育达到5 cm以上时,流动沙丘干沙层厚度成为土壤水分蒸发的决定因素。随着干沙层厚度的增加,土壤蒸发量逐渐降低;各观测日的蒸发抑制率随着干沙层厚度的增大而增大;5 cm的干沙层对蒸发的抑制作用最大可达70.6%,30 cm的干沙层则最大可达92.38%;干沙层厚度与土壤蒸发量之间存在显著的线性关系。各气象因子以及湿沙层不同深度土壤体积含水率对土壤蒸发量的影响作用很小,相关分析均没有达到显著水平。     

火星风沙地貌研究进展

作为最活跃的地貌塑造外营力,风力作用在火星表面塑造了各种各样的地貌形态。对火星风沙活动及风沙地貌的认识是随着观测和探测技术的进步而逐渐明确的。火星沙丘在北极地区连绵成带状分布,在其他地区分布比较零散,且主要与撞击坑、河谷和山谷相伴分布。火星风沙地貌与地球上相应的地貌类型形态相似而规模更大,表明两个星球上塑造风沙地貌的动力系统具有一定的相似性。火星沙丘主要由玄武岩质（北极部分沙丘为石膏质）颗粒堆积而成,沉积物粒度比地球粗,主要是由中沙和粗纱组成。随着获取影像时空分辨率的提高和着陆器在火星近表面的观测,发现火星上部分区域的沙丘和沙波纹比较活跃。同地球一样,火星风沙地貌也可指示火星气候的变化。     

Aeolian dune‐field development in a water table‐controlled system: Skeiđarársandur,Southern Iceland

Aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on Skei?arársandur, Southern Iceland. The largest aeolian dune complex on the sandur covers an area of 80 km² and is characterized by four distinct landform types: (i) spatially isolated aeolian dunes; (ii) extensive areas of damp and wet (flooded) interdune flat with small fluvial channels; (iii) small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small, predominantly damp, interdune corridors; and (iv) larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain. The morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune, interdune and fluvial processes that operate coevally on the sandur surface. The geometry, scale, orientation and facies composition of sets of strata in the cores of the aeolian dunes, and their relationship to adjoining interdune strata, have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation, construction, pattern of migration, style of accumulation and nature of preservation. Seasonal and longer‐term flooding‐induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds. Most of the dunes are currently undergoing active construction and migration and, although sediment availability is limited because of the high water table, substantial aeolian transport must occur, especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture. Bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing. Despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century, sediment compaction‐induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long‐term preservation. Wet, dry and stabilizing aeolian system types all co‐exist on Skei?arársandur and the dunes are variously undergoing coeval construction, accumulation, bypass, stabilization and destruction as a result of interactions between localized factors.     

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s^?1 (equivalent to pure wind velocity of 6 to 8 m.s^?1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s^?1.     

新月形沙丘维持相对稳定的两种过程

新月形沙丘顶部稳定性是风沙地貌学尚未解决的科学问题。研究新月形沙丘的顶部稳定性,对于绿洲边缘风沙运动规律揭示、防沙工程建设和沙区生态环境保护等具有重要的现实意义。选择民勤沙区新月形沙丘,通过测定沙丘各部位风速、风蚀风积和粒度等,分析了新月形沙丘顶部稳定机理。主风向（NW）作用是新月形沙丘最高点与沙脊线重合、沙丘前移和高度降低的过程;反向风（SE）作用是沙丘最高点与沙脊线分离、沙丘背风坡风蚀与沙丘增高的过程。由于研究区以NW风为主,新月形沙丘沿NW-SE方向前移,SE风只能风蚀减缓沙丘背风坡的坡度。人为干预将会阻止或减少从迎风坡向沙丘顶部输送沙量,使得新月形沙丘背风坡尤其是背风坡上部风蚀过程增强,新月形沙丘逐渐过渡为抛物线形沙丘。     

乌兰布和沙漠流动沙丘风蚀空间分布规律及其影响因素

为科学治理黄河乌兰布和沙漠沿岸风沙入黄问题,以该河段风沙危害严重的刘拐沙头流动沙丘为研究对象,开展沿岸沙丘风蚀与沉积规律及其影响因素研究。结果表明：（1）沙丘不同部位风蚀与沉积存在差异,与风速在沙丘的空间分布相关。迎风坡坡脚、坡中以风蚀为主,风蚀速率分别为1.07、1.31 cm·d^-1;坡顶风蚀和沉积交替进行,风蚀速率2.16 cm·d^-1,沉积速率1.36 cm·d^-1;沙丘背风坡受反向气流影响以沉积为主,沉积速率2.19 cm·d^-1,风蚀主要出现夏秋季节反向风时期;丘间地受上风向沙丘阻挡的影响,一般以沉积为主,平均沉积速率0.12 cm·d^-1。丘间地净风蚀量与背风坡显著差异（P<0.05）,但与坡脚、坡中和坡顶差异不显著（P>0.1）;背风坡净风蚀量与坡脚、坡中和坡顶极显著差异（P<0.01）。从总风蚀速率来看,风沙活动活跃强度排序：坡顶 > 背风坡 > 坡中 > 坡脚 > 丘间地。（2）冬春季节风蚀与夏秋季节存在显著差异（P<0.05）,风力和降水的季节性差异是造成风蚀季节性差异的主要因素。研究结果可为沿岸流动沙丘风沙入黄防治和完善黄河沿岸风沙防护体系提供参考。     

石英光释光测年揭示的晚第四纪毛乌素沙地演化

本研究利用石英光释光测年的单片再生法(Single­aliquot Regenerative­dose Protocol,简称SAR)对毛乌素沙地内部西北－东南方向5个风成砂－砂质古土壤剖面进行了年代测定,结合年代框架和剖面沉积相、磁化率及粒度特征探讨了晚第四纪以来毛乌素沙地演化和气候变化。研究表明毛乌素沙地在晚第四纪以来经历了多次沙地固定与活化的交替演化： 距今91.0ka,71.0ka,48.0ka,22.0ka,11.6ka,5.0ka,1.1ka,1.0ka和0.4ka前后风成砂沉积,沙地活化,指示气候干旱,植被覆盖度低; 在距今65ka和全新世适宜期(8.5～5.0ka),沙地固定成壤,砂质古土壤发育,指示气候湿润。另外,剖面中风成砂层数变多、厚度增加、粒径变粗指示了晚第四纪以来毛乌素沙地干旱化趋势加强。     

BOOK REVIEWS

Book Reviewed in this article: Latin America: Case Studies . Richard G. Boehm and Sent Visser Locality and Rurality: Economy and Society in Rural Regions . Tony Bradley And Philip Lowe The City and the Grassroots . Manuel Castells Geopolitics and Conflict in South America. Quarrels among Neighbors . Jack Child Post-Industrial America: A Geographical Perspective . David Clark Coastal Research: UK Perspectives . Malcolm W. Clark A Rural Policy for the EEC? Hugh Clout Peasant Agriculture in Assam: A Structural Analysis . M. M. Das . Environmental Change and Tropical Geomorphology . I. Douglas and T. Spencer Advances in Abandoned Settlement Analysis: Application to Prehistoric Anthrosols in Colombia, South America . Robert C. Eidt Measuring Culture . Jonathan L. Gross and Steve Rayner North America: A Human Geography . Paul Guinness and Michael Bradshaw A Geographical Bibliography for American Libraries . Chauncy D. Harris et al. Geography and the Urban Environment: Progress in Research and Applications, Vol. VI . D. T. Herbert and R. J. Johnston Changes in Global Climate: A Study of the Effect of Radiation and Other Factors During the Present Century . K. Ya . Kondrat'ev . Rural Development and the State: Contradictions and Dilemmas in Developing Countries . David A. M. Lea and D. P. Chaudhri The Martial Metropolis: U.S. Cities in War and Peace . Roger W. Lotchin The Climate of the Earth . Paul E. Lydolph . Weather and Climate . Paul E. Lydolph . Spatial Divisions of Labor: Social Structures and the Geography of Production . Doreen Massey . Panorama of the Soviet Union . N. Mikhailov . Soviet Armenia . K. S. Demirchian . USSR: Geography of the Eleventh Five-Year Plan Period . K. Spidchenko . Planung und Verwirklichung der Wiener Ringstrassenzone (Planning and Materialization of the Ringstrasse-Zone of Vienna). Kurt Mollik , Hermann Reining , Rudolf Wurzer . The American West Transformed: The Impact of the Second World War Gerald D. Nash . An Overview of the Survey of Income and Program Participation . Dawn Nelson , David Mc Millen, and Daniel Kasprzyk . Phenomenology, Science and Geography: Spatiality and the Human Sciences . John Pickles . Biological Diversification in the Tropics . Ghillean T. Prance Die Wanderviehwirtschaft im gebirgigen Westen der U.S.A. und ihre Auswirkungen im Naturraum . Gisbert Rinschede . Social and Economic Aspects of Radioactive Waste Disposal: Considerations for Institutional Management . World-Wide Weather . K. Takahashi Coastal Geomorphology in Australia . B. G. Thom Settlement System in Rural India: A Case Study of the Lower Ganga-Yamuna Doab . Ram Chandra Tiwari . Computer Programming for Geographers . David J. Unwin and John A. Dawson . Late Quaternary Environments of the Soviet Union . A. A. Velichko, ed . H. E. Wright , Jr. and C. W. Barnosky Ethics in Planning . Martin Wachs