孙禹
, 杜会石
SUN Yu, DU Hui-shi
中图分类号: P931.3
文献标识码: A
文章编号: 1000-0690(2015)07-0898-07
通讯作者:
收稿日期: 2014-02-28
修回日期: 2014-05-4
网络出版日期: 2015-07-20
版权声明: 2015 《地理科学》编辑部 本文是开放获取期刊文献，在以下情况下可以自由使用：学术研究、学术交流、科研教学等，但不允许用于商业目的.
基金资助:
作者简介:
作者简介：孙 禹（1987-）,男,吉林省长春市人,博士研究生,主要从事干旱区地貌与环境研究。E-mail:sunyu0611208@126.com
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摘要
风蚀坑是沙质海岸、湖岸及干旱、半干旱区沙质草原地区受风蚀作用形成的洼地。受风蚀坑地形的影响,坑内气流的风速、风向发生了变化,通过输沙过程的局部差异改变了风蚀坑的蚀积格局,并对风蚀坑形态进行改造。而形态的变化又反作用于近地表气流,由此产生风蚀坑形态-动力学的响应与反馈。总结并扼要评述国内外近年来风蚀坑形态-动力学及其发育演化方面的研究进展,分析现有研究的不足,以期对今后此类研究提供借鉴。
关键词：
Abstract
Blowouts are depressions produced by wind erosion, which occur on sandy coasts or lake shores and sandy grasslands in arid and semi-arid rergions. Topographic steering changes the velocity and direction of airflow within the blowout. Then a local difference in sediment transport exists, which changes the pattern of erosion and accumulation and reforms the morphology of the blowout. Topographic changing reacts on the near-surface airflow and forms the feedback and response mechanism between morphology and dynamics. This article briefly reviews the processes of morphodynamic and evolvement of blowouts, and analyzes its study trends, hoping to provide some reference for similar researches in the future. Although lots of progresses have been made in study of dynamic and evolvement of blowout, there are still many aspects need to be improved. First of all, airflow patterns in blowout are complicated, because of the limited field data, we often get an unreal construction and a poor understanding of airflow patterns. In order to aquire more sufficient field data and precise analysis, more intense observation sites and continuous observations are needed. Secondly, temporal and spatial scales of previous researches in blowout are relatively small. Most of the research just focused on the dynamics and evolvement of individual blowout, but ignored the others’ in the same region; and limited observations to the current developmental situation, but ignored the processes or morphology in the past and future. In order to summarize a relatively complete evolutionary pattern of blowouts tentatively, the large-scale and long-term monitorings to the blowouts, which in variety of developmental phases are requisite. At last, compared with foreign researches which made certain achievements in coastal blowouts, domestic researches in evolutionary processes of inland blowouts which developed in different conditions and different genesises are deficient. Many blowouts which in various developmental phases occurred in arid and semi-arid regions in north China, evolutional laws could be summarized according to their conditions and morphological characteristics. Then make comparisons with relevant research results of coastal blowouts, and validate their applicability in terrestrial environments.
Keywords：
风蚀坑是广泛分布在沙质海岸和干旱、半干旱沙质草原地区的一种重要的风沙地貌类型[1], 发育在从赤道到高纬度的海岸和内陆环境中[2],在有植被的固定和半固定沙丘地区尤为普遍[3]。在中国主要分布于东部沙地[4~6]及临近的沙化草地[7~10]。在沙质草原地区,风蚀坑是导致草原景观破碎化,并且转变为沙地的临界阈现象,也是固定沙丘（或沙地） 开始活化的明显标志[11]。这样的结果是加剧了地表的起伏程度,导致草原景观稳定性降低和土地生产力下降[12],并对当地的生态系统产生变化[13],导致植被演替等其他过程向沙漠化方向发展[14~16]。
现有对于风沙地貌的研究主要集中于沙丘的形态与移动[17]、形成条件及过程[18]、流场与蚀积特征[19]、粒度与构造特征[20]等方面,而对风蚀坑的相关研究稍显不足。国外对风蚀坑的研究主要集中于美国、荷兰、加拿大等地海岸风蚀坑的气流[21~23]、形态[24]、蚀积速率[25]和演化过程[26,27];中国对风蚀坑的研究起始于形态及其土壤与植被变化的初步认识[28,29],近年来,中国学者对呼伦贝尔沙质草原风蚀坑的形成原因[30]、影响因素[31]、发育模式[32]、发育过程[33]、表面沉积物的粒度特征[34]以及表面气流特征[35,36]和气流形态相互作用[37]等方面作用做了比较系统的研究。
Melton于1940年描述沙面受风蚀凹陷而形成抛物线沙丘时,首次使用“风蚀坑”这个词[38]。多数学者所认同的定义：由风蚀作用在原有的沙质沉积物上形成的碟、杯、槽形的凹地,风蚀所搬运的风成沙堆积于临近地段,属于风蚀坑的一部分[2]。
由于发育环境与影响因素不同,风蚀坑的形态存在区域性差异,形态参数的变率较大（表1）,对其类型的划分主要以几何形状为依据。Ritchie定义了包括雪茄形、V形、勺形洼地及锅形、廊道5种类型。张德平等[28]将风蚀坑分为卵圆形、串珠状、带状或槽状等简单类型,以及裸地型、肾形、花朵状、葫芦状、掌状、方形等复合型共9种。王帅等[12]将沙质草原风蚀坑分为平坦草地风蚀坑和沙丘风蚀坑。其中,平坦草地风蚀坑又可以根据发育阶段和形态将其分为沙斑、碟形坑和槽形坑等简单风蚀坑。Cooper将风蚀坑定义为两大类型,命名为槽形风蚀坑和碟形风蚀坑[21]。Hesp[39]及Smyth[40]认为,风蚀坑分为碗形、碟形和槽形三大类（图1）。尽管风蚀坑形态多样,但他们共同特点在于积沙区边缘和侵蚀侧壁边界十分清晰。
表1 不同地区风蚀坑形态的观测数据
Table 1 The morphological parameters of blowouts observed in different regions
| 研究区域 | 长度（m） | 宽度（m） | 深度（m） | 参考文献 |
|---|---|---|---|---|
| 美国海岸 | 25~30 | 15~20 | 3~5 | [41] |
| 澳大利亚海岸 | 80 | 20~30 | 8 | [21] |
| 新西兰海岸 | 40 | 20 | 7~8 | [42] |
| 加拿大内陆 | 21.5 | 14.6 | 3.5 | [43] |
| 爱尔兰海岸 | 100 | 60 | 13 | [13] |
| 浑善达克沙地 | 130 | 60 | 20 | [44] |
| 呼伦贝尔沙质草原 | 8.1~214.1 | 6~93.2 | 0.3~11.1 | [7] |
碟形风蚀坑呈椭圆形,坑底宽平,深度较浅,侵蚀内壁短而陡,积沙区平坦,迎风坡为短而陡的凹形坡面,背风坡长而缓[37];碗形风蚀坑由碟形风蚀坑演化而来,比碟形风蚀坑更深,呈圆形或椭圆形,通常只有一个积沙区,但在盛行风方向不唯一的情况下会发育两个或多个积沙区[39];典型的槽形风蚀坑为细长形,侵蚀坑底部要比碟形风蚀坑更深、更窄,侵蚀侧壁也要更长更陡,积沙区更长面积更大,滑落面的坡度更陡[45,46]。风蚀坑受到坑内地形及人类活动的影响,其走向不完全与盛行风的方向一致。Gares研究发现,徒步旅行是影响风蚀坑走向的主要因素;Tiley发现非洲南部的沙丘风蚀坑走向与盛行风关系微弱,南非的海岸风蚀坑不仅没有典型的侵蚀区和积沙区,而且走向与盛行风不一致,可能是前丘地表的粗糙引起了坑内气流方向及输沙模式的变化[47]。坑内高速气流的走向决定了合成输沙方向,并与积沙区方向一致[2]。
风蚀坑的形态参数之间也存在着一定的关系。Hesp[2]发现侵蚀区宽度与积沙区长度的增长比例普遍为1∶2,槽形风蚀坑为1∶4,碟形风蚀坑为1∶2~1∶3。王帅对锡林郭勒和呼伦贝尔两个典型草原中大量风蚀坑形态参数进行分析发现,风蚀坑的长度与宽度大约以5∶2的比例同步增加,风蚀坑长度与积沙区以1∶3的比例同步增长[48]。
图1 风蚀坑形态
a.碗形风蚀坑[
Fig.1 Schematic figure of blowout morphology
a.Bowl Blowout; b. Saucer Blowout; c. Trough Blowout
风蚀坑表面气流是区域气流与形态之间相互作用的产物,是输沙过程与形态演变的动力因子。早期的气流研究以推断性和定性化的结论为主。Landsberg和Riley早在1943年首次对风蚀坑内的气流进行观测,Olson进行后续研究,发现风蚀坑使气流在一定位置气流加速,出现急流,而在另外一些位置气流分离、减速,同时也观测到了当气流由不同方向进人时,会出现涡流的现象[48] 。
Hesp[21]在澳大利亚海岸地区对槽形风蚀坑内气流进行了首次定量研究,发现当气流平行于风蚀坑轴向进入坑体时,气流沿侵蚀坑底部和侧壁加速出现急流,风速廓线明显不符合对数分布。气流在积沙区背风坡分流并减速,在侧壁上方溢出形成漩涡流;在斜向入风条件下,气流在风蚀坑内发生明显偏转,气流极端紊乱,形成大的漩涡流（图2）。之后对海岸槽形风蚀坑的气流观测中也发现了相同的现象[42,46]。王帅等[35]对呼伦贝尔沙质草原槽形风蚀坑进行气流观测时,发现气流从侧壁的上方流入坑体,并对侧壁进行侵蚀。气流与风蚀坑轴向平行时,气流的凝聚使风蚀坑不断的加深并顺风向延伸;当气流斜向进入风蚀坑时,出现了上风向侧壁侵蚀,下风向侧壁堆积的现象。
在海岸碟形风蚀坑的气流观测中发现,入风方向与长轴方向垂直时,坑内形成大的反向流;入风方向与风蚀坑轴向斜交时,风向发生偏转,最高风速出现在侵蚀坑底部[25];随着入风方向与风蚀坑轴向趋于平行,各观测点的风速有所增加[43]。李双权[37]等在呼伦贝尔沙质草地碟形风蚀坑的研究中也发现了相同的结果,并观测到了垂直轴涡流的存在。所测得风速的最小值出现在入风坡中部,与海岸沙丘槽形风蚀坑观测结果一致[21],而与王帅等[35,36]在碟形风蚀坑中最小风速出现在坑底的观测结果不同。这可能是风蚀坑的尺寸及局部的地形特点、地表性质不同造成的。
气流进入在碟形风蚀坑和碗形风蚀坑时,都在入风口发生扩散并减速[49]。Hesp和Walker首先应用三维风速仪对碗形风蚀坑中的气流模式进行三维观测,发现强烈的离岸风使气流被吸入坑体,在侵蚀坑底部扩散并沿侧壁加速,并发生明显的转向、分离、翻转和更加复杂的三维运动,最高风速出现在前丘脊线及积沙区丘顶[39]。Hesp认为气流在侵蚀坑底部的扩散意味着所有的侧壁都会在单一方向风的作用下被掏蚀,造成风蚀坑的扩张[2]。
Smyth首次应用计算机流体力学（Computational Fluid Dynamics,CFD）软件对气流进行模拟[13],并实测及模拟了风蚀坑上方气流的异质图谱[49],实现了对大量低频率暴风事件的模拟和量化[40]。这些研究都表明地形-气流存在互馈作用。
风沙输移是气流[37]、植被盖度[41]、地形[50]和沉积物粒径等因素共同影响的结果。Hesp[2,42]认为,在碟形风蚀坑和槽形风蚀坑中,任何风向的风都对输沙有效;很多研究都以观测到的输沙结果为基础,建立了能够反映风能和侵蚀率之间关系的方程[51]。Hugenholtz[52]认为植被通过增加局部的表面粗糙度来增加起沙风速,限制输沙过程;野外观测表明,当植被盖度大于30%时,基本无风蚀发生[53]。Jungerius认为地表物理特性（例如结皮）影响着沙丘风蚀坑的输沙动力[54],并在对荷兰De Blink地区的6个浅碟形的风蚀坑研究时发现,虽然观测期间侵蚀坑底部的加深最明显,但是多变的风速风向和其他气候因素造成了复杂的侵蚀及堆积格局[55]。Lancaster[56]、Jungerius和van der Meulen[57]、Pluis[58]也观测到了类似的结果,此外还发现了碟形风蚀坑通常向盛行风的上风向延伸,并且侵蚀坑底部的侵蚀速率较低,而侵蚀量最大的区域位于侵蚀侧壁的脊线附近,这可能是碟形坑的深度和长度有限,在高速气流条件下极少或不能产生急流的缘故。与碟形风蚀坑相比,槽形风蚀坑通常可以达到最大侵蚀深度,并能向下风向发育（或积沙区顺风向移动）较长距离（图3）。
图3 碟形风蚀坑蚀积格局[
Fig.3 Spatial distribution pattern of erosion and deposition on saucer blowout[
另外,风蚀坑内的输沙量有随季节变化的特点。Jungerius[54]认为春季和秋季是风蚀坑发育最重要的季节。在冬季,由于空隙冰的升华,输沙可在冻结条件下发生[59]。Byrne[60]总结了加拿大海岸槽形风蚀坑的输沙模式为夏末堆积,冬季侵蚀。而Pluis[58]在他的研究中发现,夏季的侵蚀量要比风蚀坑表面高度的净变化要高,因为雨水对风蚀坑边缘的冲刷可以对侵蚀进行部分的补偿。风沙输移随季节变化的不同模式,可能是区域风况及风蚀坑表面水分条件造成的。
风蚀坑是人为和自然因素作用下,沙面植被减少和破坏,强风对裸沙表面进行侵蚀形成的[47]。初始的形状、尺寸和位置以及后续的发育取决于波蚀、气候变化、水蚀、植被类型和覆盖的程度[38]、区域风况[61]和人类活动等诸多因素。例如,Smith发现在宽广的前丘脊线上发育的风蚀坑通常是浅碟形的,而发育在陡峭迎风坡上的通常是槽形的。浑善达克沙地中发育的风蚀坑深度一般不超过5 m[62],荷兰海岸发育的风蚀坑长度一般小于30 m。Jungerius认为侵蚀坑的形成归因于侵蚀性阵风的累积作用 [27];也有研究发现坡向在风蚀坑形态的发育中也起重要作用,并影响沉积物沙源供应的空间变化[52],Du[45]等研究表明过渡放牧等人为活动要比自然因素更能影响风蚀坑的发育。
目前普遍认为,风蚀坑的演化是由输沙过程来控制的。当携沙气流进入风蚀坑,坑内地形会改变气流垂直结构和水平格局,形成独特的气流场,侧壁上方气流的掏蚀作用,使侧壁变陡并引起坍塌,导致了风蚀坑的侧向扩张;随后侵蚀坑底部的气流会将崩落物向下风向输送[50],同时使侵蚀坑加深。不同部位蚀积速率的差异[43],导致风蚀坑形态及尺寸的变化。也有研究发现,风蚀坑的演化与6.25~12.5 m/s的气流关联性最大,因为该风速是0.15~0.42 mm颗粒移动的临界风速[55]。王帅等[35]认为槽形风蚀坑是在碟形风蚀坑的基础上,沿强风方向延伸扩展,最终合并而形成的大型风蚀地貌形态。
Gares[26]认为风蚀坑在形状,尺寸和植被模式上的不同可能是处于不同发育阶段的原因,并将发育在海岸前丘上的风蚀坑演化过程总结为4个阶段：① 初期吹蚀。由于前丘脊线植被盖度下降[54,59],出现初期破口;② 早期发展。破口的扩宽和加深,初期的风蚀坑形成;③ 成熟。风蚀坑继续扩宽,产生几乎垂直的不对称斜坡;④ 完成演化序列。风蚀坑侧壁的典型侵蚀斜坡消失,坑内的持续堆积促进了风蚀坑发育的停止。该阶段中,坡度和缓的侧壁不会有沉积物的堆积,植被和向岸的盛行风阻止了沙物质向海输出[50]。这个循环过程会被一些因素干扰而缩短,包括：① 地形、风况和植被盖度之间的反馈作用;② 波候的变化;③ 人类活动。
史培军根据风蚀坑的不同发育阶段,将科尔沁南部大青沟地区的风蚀坑分为风蚀破口,风蚀窝,风蚀碟形地,以及风蚀盘[63]。阎旭等[7]发现不同发展阶段的风蚀坑各形态参数之间具有较好的幂函数关系。对于侵蚀坑而言,坑长增长速度最快,其后依次是坑宽和坑深,坑后积沙体具有类似规律;并将发育在呼伦贝尔沙质草原上的风蚀坑分为裸地沙斑、活跃发展、固定和活化4个演化阶段,利用地貌异速生长原理,分析风蚀坑发育模式,探讨风蚀坑形态演变规律及控制因素。张德平等[33]将沙质草原风蚀坑的发育归纳为以下5个阶段：① 风蚀裸地;② 土层破口;③ 活跃发展风蚀坑;④ 风蚀坑固定;⑤ 风蚀坑消亡。地貌发育相应经历典型草原景观→沙漠-草原景观→沙地-草原景观的总体演变过程。坑后积沙逐步形成迎风坡短而较陡、背风坡长而较缓的抛物线沙丘。胡尔查等根据遥感解译和野外测量结果,发现随着风蚀坑面积的增加,风蚀坑形状变化模式可总结为：碟形→椭圆形→槽形→不规则形[62]。
风蚀坑不会无限扩张,当其面积达到一定程度后受底土层和周边植被的阻力以及坑内局部气流影响,将进入固定或稳定阶段[62]。荷兰的海岸风蚀坑发育到一定的规模会自行固定[27],Hugenholtz[52]在对两个不同尺寸的风蚀坑进行输沙观测时发现,当较大的风蚀坑达到了临界尺寸时,侵蚀坑底部不再发生侵蚀;而较小风蚀坑则继续向底部侵蚀。若继续向下侵蚀达到水位,或不易侵蚀的土层,也能阻止侵蚀坑向下侵蚀。因此,地下水位或不易侵蚀的土层,就成为限制风蚀加深的局部基准面[64]。Fraser[22] 、Carter、 Byrne[60]等认为风蚀坑中的崩塌块体,碎屑坡和扇体,残墩,植被残枝和出露的古土壤,都能增加气流的复杂程度,并作用于输沙过程,影响风蚀坑的演化。笔者认为,在外界条件相同的情况下,植被对风蚀坑的形成及演化过程起到决定性作用。植被能够覆盖地表、分解气流、截留沙物质、改善局部的水分条件,在改变近地表的流场、保护其下沙面不被侵蚀,防风固沙方面起到重要作用。
很多研究表明槽形风蚀坑会继续发育成抛物线沙丘[46]。Pye[65]从一些大陆和海岸环境沙丘的研究发现,风蚀坑发育的最后阶段可能转变成抛物线沙丘,并以风蚀坑发育为基础,提出了澳大利亚海岸地区抛物线沙丘形成的多阶段模型。Cooper[66]发现,在上风向海岸,风蚀坑会发育成大的移动抛物线沙丘;在下风向海岸,海岸沙丘风蚀坑呈现出类似抛物线的形状,但是没有明显的移动。
目前国内外学者主要通过野外观测与数值分析来监测形态变化,总结演化规律。对于风蚀坑形态数据的获取,普遍运用侵蚀钎法[50,52,60]和航空相片[47,67],地形三维变化主要通过全站仪和GPS来测量。计算机模拟技术逐渐在风蚀坑的演化方面发挥了重要作用,Jungerius[27] 在野外观测的基础之上,建立了一种二维计算机模型来模拟风蚀坑的发育过程,模拟结果与风蚀坑的实际纵剖面非常相似。杜会石等[68]以呼伦贝尔草地风蚀坑分布区1959、2002、2004、2009 年4期影像解译数据为基础,利用CA-Markov模型预测了该区未来土地覆被变化情景。结果显示,近5 a来风蚀坑的扩展速度得到了一定的控制,在目前自然和人为影响因素不变的情况下,草地优势景观将得以恢复。
目前风蚀坑动力学及演化过程的研究已经取得了一定的进展,但还需要进一步的完善。
1） 风蚀坑中的气流模式较为复杂,由于野外观测数据的有限性,不能完全的反应出气流的真实结构,使得对于气流模式的理解较为粗糙。在野外工作中架设更加密集的观测点位,并进行持续观测,以提供更加充足的实测数据,对气流模式做出细致分析。
2） 之前对于风蚀坑的研究空间和时间尺度都较小。大多研究只关注一个风蚀坑的动力学特征及演化状态,而忽略了同一区域风蚀坑群体的发育状况;只局限于当前的发育状况,而忽略了之前和之后的过程和形态。为了尝试总结出风蚀坑较为完整的演化模式,需要对处于各个发育阶段的风蚀坑进行大范围的长期监测。
3） 国外海岸环境下发育的风蚀坑的研究取得了一定的成果,国内对于内陆不同发育环境、不同成因的风蚀坑演化过程的研究较少。中国北方干旱半干旱地区发育着众多处于不同发育阶段的风蚀坑,可依据其所处环境条件和形态特征来分析并总结内陆风蚀坑的演化规律。并与海岸风蚀坑的相关研究成果进行对比,检验其在内陆环境中是否适用。
The authors have declared that no competing interests exist.
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随着风沙活动对全球变化的响应研究不断深入,沙质海岸、湖岸和半干旱区草原环境中不同程度植被覆盖沙丘及其风蚀坑的动态得到了广泛的重视.本文对沙丘风蚀坑的形态及动力学特征的研究成果作了初步总结,着重阐述了沙丘风蚀坑内气流场、沙粒输移和蚀积变化.最后,提出了沙丘风蚀坑研究中存在的问题和主要研究趋势.
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This paper reviews the initiation, dynamics, geomorphology and evolution of incipient foredunes, established foredunes, and blowouts. Incipient foredunes may be initiated in a variety of ways leading to the formation of ramps, terraces or ridges depending on progradation rates, vegetation type and cover, sediment transport rates and scale of erosional processes. Vegetation cover, morphology, growth rates, and types combine with aerodynamic processes to determine dune and swale morphology. Established foredunes are classified into five morpho-ecological types, and the flow behaviour over two types is detailed. A new model of foredune evolutionary paths at various possible time scales is presented. Blowout initiation, dynamics and sediment transport, and evolution is examined. Throughout the review, the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided.
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呼伦贝尔草原是我国优良的天然牧场,由于其所处的特殊地理位置, 生态环境极其脆弱,在自然因素和人为因素的共同作用下,近一个世纪以来区内生态环境退化加剧,表现为土地沙漠化,草场退化和水土流失加剧等过程.在软硬件 系统支持下应用 GIS和遥感技术,结合前人研究成果和野外调查,通过基于知识的多重判据复合分类实现多源信息的集成,对呼伦贝尔草原沙漠化现状及沙地演变进行了系统研 究.结果表明,呼伦贝尔草原沙漠化面积已达20 893.57km2,占总土地面积的25%.沙漠化总体特征表现为局部地段逆转,而总体仍在发展.近一个世纪以来,区内沙漠化的强烈发展是由于毁林、滥垦 和过度放牧.
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野外调查测量呼伦贝尔沙质草原风蚀坑分布和形态参数,根据不同发展阶段的风蚀坑形态特征的差 异、形态参数间相关关系和拟合结果分析了风蚀坑的形态演变和发育、成因、规律。发现不同发展阶段风蚀坑形态参数之间的控制关系和扩展模式不同,各形态参数 之间具有较好的幂函数关系。对于风蚀坑的侵蚀坑而言,坑长增长速度最快,其后依次是坑宽和坑深,坑后积沙体具有类似规律。风蚀坑坑后积沙的3个形态参数, 受侵蚀坑3个参数的联合控制,但受坑深的控制最为显著。风蚀坑出现的起始形态、地形特征、植被、气流场、气候条件、人类活动的扰动等对其形态和发育具有重 要影响,并且形态和发育反作用于植被、气流等,形成形态与气流、植被之间的响应与反馈。
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沙质草原风蚀坑的发育过程主要 有以下几个阶段:风蚀裸地→土层破口→活跃发展风蚀坑→固定风蚀坑→消亡风蚀坑。固定或消亡的风蚀坑可能活化,并重新进入活跃发展阶段。地貌发育则相应地 经历典型草原景观→沙漠-草原景观→沙地-草原景观的总体演变过程。风蚀坑的发展有极限控制。但是各类沙丘的固定非常困难,有向大规模典型沙漠景观发展的 高度危险。风蚀坑的形成发展和植被的演替将平坦单调缺水的典型草原改造成地形起伏多变,并有星散分布的风蚀坑湿地点缀其间、植被类型丰富多样的乔、灌、草 相结合的沙地疏林草原。因地制宜地保护和利用沙质草原,可以保持其生态系统不致恶化并促进其不断优化。
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<FONT face=Verdana>呼伦贝尔沙质草原风蚀坑发育于宽单峰中能风况环境，是该区主要风沙地貌类型。对碟形坑表面气流的观测结果显示，气流进入风蚀坑后，在入风口扩散，风速开始降低至坑底达到最低;在坑后缘出风口汇集形成急流，风速剧增至坑后积沙顶部风速达到最高值。风蚀坑后缘在风沙流的磨蚀作用下后退，风蚀坑顺风向扩展，同时此处较大的剪切风速和输沙率使大量来自坑内的沙物质沉积到坑后草地上呈扇状蔓延。呼伦贝尔沙质草原风蚀坑在来自西北、西和西南方向风的交替作用下，向东南、东和东北方向扩展而生成。随着风蚀坑深度和水平尺度的增加，最终可能沿强风能方向或合成输沙方向扩展成为大型的槽形坑。<BR></FONT>
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对呼伦贝尔海拉尔气象观测站风速风向观测记录 (1951-2003年)统计分析,发现呼伦贝尔地区以西北、西和西南风为主,西北风出现频率最高.年输沙势为279.1 VU,属于中风能环境,合成输沙方向是148.3°.冬季风向变率指数较高,夏季较低,近50 a来风向逐渐趋于稳定,与本区的风蚀坑走向高度一致.呼伦贝尔沙质草原的风蚀坑可以分为两类,即沙丘风蚀坑和平坦草地风蚀坑.其中平坦草地风蚀坑又可以根 据发育阶段和形态将其分为沙斑、碟形坑和槽形坑等简单风蚀坑.
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SMYTH, TAG., JACKSON, D.W.T., COOPER, JAG., 2011,. Computational Fluid Dynamic modeling of Three-Dimensional airflow over dune blowouts. Journal of Coastal Research, SI 57 (Proceedings of the 11th International Coastal Symposium), 314 - 318. Szczecin, Poland, ISBN Blowout enlargement is primarily driven by aeolian transport, where high velocity winds entrain and remove sediment from the landform. However patterns of deflation in blowouts are poorly understood as near surface airflow in a blowout is complex. In this study three-dimensional airflow during a light (3.93 m/s) and moderate (8.98 m/s) onshore wind event was calculated using the two-equation Renormalized Group k-epilson airflow turbulence model, by the Computational Fluid Dynamics software OpenFOAM. The saucer blowout located on the coastal foredune in the Belmullet Peninsula, Western Ireland, measures 100 metres long, 60 metres wide and 13 metres deep. Results show that during both wind events flow separates and reverses as it enters the blowout over the foredune crest, as it reattaches it is steered, diverging from the centre of the blowout and before topographically accelerating over the rim crest. Flow which enters the throat of the blowout accelerates and remains directionally unchanged before accelerating up the deposition lobe slope, where flow at the crest was simulated as being 100% faster at the crest than velocity simulated on the beach. In lee of the blowout at the depositional lobe airflow decelerated and a large zone of flow separation and reversal was created. Whilst relative change of velocity and direction at I metre above the surface of the blowout displayed similar behaviour during both wind events, flow in the lee during the light wind event did not appear to fully reattach and recover to velocity levels on the beach.
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采用野外调查和测量、航片判读、室内制图、统计分析等方法对呼伦贝尔沙质草原典型地带的风蚀坑及坑后风沙沉积进行了研究。发现：①风蚀坑是由一个沙坑和坑后沙丘共同组成，两者具有一一对应关系；②风蚀坑和坑后沙丘可以根据形态特征、发展阶段、诱发原因进行分类；③呼伦贝尔三大沙带均由风蚀坑洼地及其坑后沙丘和背景沙质草原组成；④沙质草原风蚀坑的发生与人类活动关系密切，为气候干旱化与人类大范围强度活动干扰土层相耦合的环境事件所造成。该研究对沙质草原沙漠发生学，沙质草原地貌演化和沙漠化监测研究具有科学意义，对草原合理利用和沙漠化防治具有现实意义。
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以陕北黄土丘陵沟壑区延河、清涧河、汾川河3条流域作为研究区域,针对该区9个水文站点的6-9月径流量、输沙量的数据,探讨了时空尺度变化对径流与输沙相关性的影响.结果表明二者在不同的时间尺度和空间尺度上其相关程度差异明显.基于径流因子与输沙因子的关系所拟合的曲线模型中,7,8月份的模型拟合优度在整体上高于6月、9月,汛期的模型拟合优度一般低于7,8月份的模型拟合优度.汛期清涧河流域的模型拟合优度高于延河和汾川河流域,区域的模型拟合优度高于延河和汾川河流域,但略低于清涧河流域.
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呼伦贝尔沙质草原风蚀坑积沙区的植被分带性 [J].https://doi.org/10.11849/zrzyxb.2008.02.008 Magsci [本文引用: 1] 摘要
呼伦贝尔沙质草原现代风蚀坑主要包括平缓草地的简单风蚀坑、复合风蚀坑和固定沙丘的简单风蚀坑3种类型。坑后积沙区植被出现明显的分带性,且随风蚀坑及其下风侧积沙体的形态、尺度而发生变化。在平缓草地简单风蚀坑下风侧积沙体平面形态呈顺风向的舌状,由坑口至原生草地,随积沙厚度顺风向减小,依次出现沙蓬、冰草和百里香3个植被带;平缓草地复合风蚀坑后缘形成具有滑落面的大型流动沙丘,在沙丘背风侧顺风向依次出现舌状裸沙带、舌状拂子茅带及两侧的冰草带;固定沙丘风蚀坑坑后积沙呈裸沙形式穿越沙丘原有的山刺玫和小叶锦鸡儿两个灌木带,并在裸沙带外围形成舌状拂子茅带。风蚀坑下风侧积沙区植被的分带性反映了草地植被对风沙活动的响应,即随着坑后积沙体的扩大,草地植被由原生向沙生逆向演替。
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新月形沙丘是最简单且研究较深入的风积地貌，对其研究已有较长的历史。总结和扼要评述国内外对新月形沙丘形态与移动特征、形成条件与过程、流场与蚀积特征、粒度与构造特征及分布与相互作用的研究成果；分析了对其未来的研究趋势。
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雅鲁藏布江米林宽谷段新月形沙丘粒度分异研究 [J].
雅鲁藏布江中游米林宽谷段阶地面上广泛发育带状延伸,由上段风蚀槽、中段过渡区和下段堆积区组成的风沙活动带。风沙活动带各段新月形沙丘表面沉积物粒度分析表明,沙丘表面沉积物总体为细沙、中等分选、极细偏、多峰,表面粒度分布模式多属丘顶最粗型。受沙源和分选距离的影响,沙丘沙粒度特征在风沙活动带内表现出一定的空间差异性,上段风蚀槽内发育的沙丘规模小,粒径细,分选差,极细偏,多峰;中段和下段沙丘表面沉积物粒径变粗,分选变好,正偏转向近对称,多峰转为单峰。
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新月形沙丘表面100 cm高度内风沙流输沙量垂直分布函数分段拟合 [J].
为研究新月形沙丘表面不同层位风沙流输沙量的垂直分布函数,实测了塔克拉玛干沙漠腹地典型新月形沙丘表面100cm高度内(以1cm分隔)的输沙量。分段拟合分析表明新月形沙丘迎风坡脚输沙量垂直分布规律不完全服从指数函数,出现与戈壁风沙流结构特征相似的“象鼻效应”,在0~3cm区间内输沙量逐渐增大,3cm以上输沙量随高度呈指数函数衰减；沙丘顶部0~10cm区间输沙量随高度呈指数函数衰减,10cm以上呈二次函数衰减；沙丘左翼端输沙量随高度呈幂函数分布,沙丘右翼端0~20cm内以指数函数衰减,20cm以上呈三次函数衰减；沙丘背风坡脚风沙流输沙量在0~60cm和60cm以上分别呈不同形式的三次函数分布。
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Flow dynamics in a trough blowout [J].https://doi.org/10.1007/BF00123530 URL [本文引用: 4] 摘要
The dynamics and geomorphological development of a trough blowout located at Fiona Beach in the Myall Lakes National Park in NSW, Australia are examined. Wind velocities and flow structure were measured utilising an array of miniature Rimco cup anemometers, Gill bi-vane and UVW instruments, and wind vanes. Flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occur up the depositional lobe, jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe, and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls. Maximum erosion and transport occur up the deflation basin and onto the depositional lobe. Trough blowout morphologies are explained as a function of these flow patterns. When the wind approaches the blowout obliquely, the flow is steered considerably within the blowout. The degree and complexity of topographic steering is dependent on the blowout topography. The flow is usually extremely turbulent and large corkscrew vortices are common. The local topography of a blowout can be very important in determining flow patterns, overall sand transport and blowout evolutionary conditions and paths. Estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remote wind data are used.
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Olyphant,et al.Windflow circulation patterns in a coastal dune blowout [J]. |
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Wind velocity and algal crusts in dune blowouts [J].https://doi.org/10.1016/0341-8162(93)90018-K URL [本文引用: 1] 摘要
In two saucer-shaped blowouts wind velocity was measured at 0.18 m height and compared to the wind velocity data from the nearest standard meteorological station at Valkenburg about 3.5 km to the northeast. In blowout 1 relative velocities are highest when the wind blows from directions between E and SSE. In blowout 2 winds blowing from directions between S and WSW are relatively stronger. In general the wind speed increases as its moves along the surface inside the blowout, because the aerodynamic roughness of the blowout surface is less than that of the surrounding area. Less important are the influence of the configuration of the terrain surrounding the blowout and the influence of the slopes within the blowout.The frequency distribution of the general wind at Valkenburg is analysed and combined with the horizontal wind velocity pattern within blowouts. A simulation model, producing the spatial distribution of the wind power shows that the prevalence of algal crusts at the SW side of blowouts agrees well with the location which reaches the lowest wind power values. In other parts of the blowouts algal crusts are damaged by moving sand at times of high wind velocity.
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Geomorphic response to Late Holocene climate variation and anthropogenic pressure,northeastern Prince Edward Island,Canada [J].https://doi.org/10.1016/S1040-6182(01)00065-9 URL [本文引用: 1] 摘要
Not Available
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Wind and sediment movement in coastal dune areas.Proc.17th Internat [M]. |
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A cyclic model of foredune blowout evolution f or a leeward coast:Island Beach,NJ. [J]. |
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A simulation model of blowout development [J] .https://doi.org/10.1002/esp.3290090604 URL [本文引用: 4] 摘要
In four of the five experiments presented by Bargh and colleagues, achievement-related words to prime the goal of doing well subsequently led to better achievement. However, as the experiments used verbs for achievement words and nouns as neutral words, the results might be due to confounding conditions. To avoid this problem, we conducted an online experiment with a 2 (achievement-priming: achievement words, neutral words) x 2 (word class: verbs, nouns) factorial design. 89 men and 123 women whose mean age was 25.8 yr. (SD = 7.1), who were recruited via a student e-mail list of the university and former participants in other experiments, took part. Barge, et al.'s findings that the achievement content is responsible for the priming effect were confirmed. Moderator effects of task difficulty and achievement motivation are discussed.
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沙质草原风蚀坑形态及其土壤和植被变化[D] . |
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呼伦贝尔沙质草原风蚀坑研究(1) ——形态、分类、研究意义 [J].
<FONT face=Verdana>采用野外调查和测量、航片判读、室内制图、统计分析等方法对呼伦贝尔沙质草原典型地带的风蚀坑及坑后风沙沉积进行了研究。发现:①风蚀坑是由一个沙坑和坑后沙丘共同组成,两者具有一一对应关系;②风蚀坑和坑后沙丘可以根据形态特征、发展阶段、诱发原因进行分类;③呼伦贝尔三大沙带均由风蚀坑洼地及其坑后沙丘和背景沙质草原组成;④沙质草原风蚀坑的发生与人类活动关系密切,为气候干旱化与人类大范围强度活动干扰土层相耦合的环境事件所造成。该研究对沙质草原沙漠发生学,沙质草原地貌演化和沙漠化监测研究具有科学意义,对草原合理利用和沙漠化防治具有现实意义。</FONT>
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呼伦贝尔沙质草原风蚀坑的初步研究 [J].https://doi.org/10.3321/j.issn:1002-008X.2006.10.021 URL [本文引用: 1] 摘要
呼伦贝尔; 沙质草原; 风蚀坑; 形态及成因; 沙漠化
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呼伦贝尔沙质草原风蚀坑研究(Ⅳ) :人类活动的影响 [J].
<FONT face=Verdana>对呼伦贝尔沙质草原187个现代风蚀坑野外调查获得的形态指标、发展阶段、诱发原因、现代放牧压力进行了对比分析。发现87%的风蚀坑由人类活动引起。其中翻耕、道路、人类定居活动诱发的风蚀坑分别占35.8%、34.8%和16%。人类定居活动诱发的风蚀坑分布范围最广。翻耕诱发的风蚀坑有97%处于活动状态。翻耕造成的土壤损失对生态地质环境破坏严重且影响深远。放牧既能促使固定风蚀坑活化并助长风沙活动,也能促进风蚀坑加速消亡。合理确定放牧压力很重要。翻耕造成的面状土层破坏诱发大量风蚀裸地和规模巨大的短轴型风蚀坑。道路切割土层诱发受道路延伸方向控制串状分布的长轴型风蚀坑。呼伦贝尔沙质草原正面临新一轮沙漠化的严重威胁。保护沙质草原区植被和地表土层不受破坏是防止风蚀坑发生发展的关键。促进土层以及草原植被的形成与恢复是风蚀坑控制的根本途径。</FONT>
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呼伦贝尔沙质草原风蚀坑形态发育模式分析 [J].
野外调查测量呼伦贝尔沙质草原风蚀坑分布和形态参数,根据不同发展阶段的风蚀坑形态特征的差 异、形态参数间相关关系和拟合结果分析了风蚀坑的形态演变和发育、成因、规律。发现不同发展阶段风蚀坑形态参数之间的控制关系和扩展模式不同,各形态参数 之间具有较好的幂函数关系。对于风蚀坑的侵蚀坑而言,坑长增长速度最快,其后依次是坑宽和坑深,坑后积沙体具有类似规律。风蚀坑坑后积沙的3个形态参数, 受侵蚀坑3个参数的联合控制,但受坑深的控制最为显著。风蚀坑出现的起始形态、地形特征、植被、气流场、气候条件、人类活动的扰动等对其形态和发育具有重 要影响,并且形态和发育反作用于植被、气流等,形成形态与气流、植被之间的响应与反馈。
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呼伦贝尔沙质草原风蚀坑研究(Ⅱ) :发育过程 [J].
<FONT face=Verdana>沙质草原风蚀坑的发育过程主要有以下几个阶段:风蚀裸地→土层破口→活跃发展风蚀坑→固定风蚀坑→消亡风蚀坑。固定或消亡的风蚀坑可能活化,并重新进入活跃发展阶段。地貌发育则相应地经历典型草原景观→沙漠-草原景观→沙地-草原景观的总体演变过程。风蚀坑的发展有极限控制。但是各类沙丘的固定非常困难,有向大规模典型沙漠景观发展的高度危险。风蚀坑的形成发展和植被的演替将平坦单调缺水的典型草原改造成地形起伏多变,并有星散分布的风蚀坑湿地点缀其间、植被类型丰富多样的乔、灌、草相结合的沙地疏林草原。因地制宜地保护和利用沙质草原,可以保持其生态系统不致恶化并促进其不断优化。</FONT>
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| [34] |
沙质草原槽形风蚀坑表面沉积物粒度特征 [J].
通过对呼伦贝尔沙质草原槽形风 蚀坑表面沉积物粒度的观测分析,发现活跃发展时期的槽形风蚀坑沙物质总体结构以中沙为主,其次是细砂,粗砂和粉沙含量很少,且不含砾石。由于沙源沉积物粒 度组成比较均一,风蚀坑各部位粒径频率曲线均呈单峰对称(或近对称)。响应于风力侵蚀和堆积,在粒度诸参数中,粗沙和细沙含量,频率曲线众数粒径,以及平 均粒径等发生了明显的变化。该研究结果作为表面气流的响应,支持了先前提出的槽形风蚀坑动力学过程。
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呼伦贝尔沙质草原槽形风蚀坑表面气流特征 [J].https://doi.org/10.3969/j.issn.1672-3007.2009.02.014 URL Magsci [本文引用: 6] 摘要
根据野外对呼伦贝尔沙质草原槽 形风蚀坑表面二次流的观测结果,利用相对风速(v/vR400)比较不同部位之间气流在水平方向上的变异情况。发现:槽形风蚀坑内气流结构紊乱,坑内前部 位置出现风速随高度降低的现象,形成反向回流;风蚀坑内在斜向气流的情况下有螺旋环流产生,由于气流聚集,在坑后部形成的高速气流容易将大量沙物质搬运到 坑后;在坑口积沙区坡脚遇阻减速后气流辐散溢出。认为槽形风蚀坑是在碟形坑的基础上,沿强风能方向延伸扩展,3个出风口最终合并而形成的大型风蚀地貌形 态。
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呼伦贝尔沙质草原槽形风蚀坑表面气流及其意义 [J].
<FONT face=Verdana>呼伦贝尔沙质草原风蚀坑发育于宽单峰中能风况环境，是该区主要风沙地貌类型。对碟形坑表面气流的观测结果显示，气流进入风蚀坑后，在入风口扩散，风速开始降低至坑底达到最低;在坑后缘出风口汇集形成急流，风速剧增至坑后积沙顶部风速达到最高值。风蚀坑后缘在风沙流的磨蚀作用下后退，风蚀坑顺风向扩展，同时此处较大的剪切风速和输沙率使大量来自坑内的沙物质沉积到坑后草地上呈扇状蔓延。呼伦贝尔沙质草原风蚀坑在来自西北、西和西南方向风的交替作用下，向东南、东和东北方向扩展而生成。随着风蚀坑深度和水平尺度的增加，最终可能沿强风能方向或合成输沙方向扩展成为大型的槽形坑。<BR></FONT>
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沙质草地碟形风蚀坑形态——气流相互作用 [J].
呼伦贝尔沙质草地碟形风蚀坑长轴走向呈WNW-ESE。野外观测结果表明,风向与碟形风蚀坑长轴走向关系决定了风蚀坑内部的气流模式,右斜交与垂直气流促使风蚀坑横向扩展与深挖,平行与左斜交气流有利于侵蚀区内部沙物质的向外输送并导致风蚀坑沿长轴向延伸。右斜交及垂向气流在碟形坑南缘产生顺时针向的垂直轴涡流,而平行与左斜交向气流在西北缘产生逆时针向的垂直轴涡流。沿长轴向,气流进入风蚀坑边缘发生分离减速,在风蚀坑底部重新附着,沿出风段坡面开始加速上升至坑后沙丘顶部,在坑后沙丘背风坡气流发生扩散减速。在横断面或弧形断面气流以单增或单减的形式存在。观测期间风蚀坑总体上以堆积作用为主,区域风能大小决定了蚀积作用强弱,而输沙方向与风蚀坑长轴向夹角决定蚀积空间分布格局。
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A tentative classification of sand dunes:Its application to dune history in the Southern High Plain [J]. |
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Three-dimensional æolian dynamics within a bowl blowout during offshore winds:Greenwich Dunes,Prince Edward Island,Canada [J].https://doi.org/10.1016/j.aeolia.2011.09.002 URL [本文引用: 3] 摘要
This paper examines the 忙olian dynamics of a deep bowl blowout within the foredune of the Greenwich Dunes, on the northeastern shore or Prince Edward Island, Canada. Masts of cup anemometers and sonic anemometers were utilized to measure flow velocities and directions during a strong regional ESE (offshore) wind event. The flow across the blowout immediately separated at the upwind rim crest, and within the blowout was strongly reversed. High, negative vertical flows occurred down the downwind (but seaward) vertical scarp which projected into the separation envelope and topographically forced flow back into the blowout. A pronounced, accelerated jet flow existed near the surface across the blowout basin, and the flow exhibited a complex, anti-clockwise structure with the near-surface flow following the contours around the blowout basin and lower slopes. Significant 忙olian sediment transport occurred across the whole bowl basin and sediment was delivered by saltation and suspension out the blowout to the east. This study demonstrates that strong offshore winds produce pronounced topographically forced flow steering, separation, reversal, and more complex three-dimensional motions within a bowl blowout, and that such winds within a bowl blowout play a notable role in transporting sediment within and beyond deep topographic hollows in the foredune.
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Three dimensional airflow patterns within a coastal trough-bowl blowout during fresh breeze to hurricane force winds [J].https://doi.org/10.1016/j.aeolia.2013.05.001 URL [本文引用: 2] 摘要
Wind flow within blowouts is extremely complex as streamline compression, expansion and reversal may occur over and around a single landform. As a result high resolution temporal and spatial measurements are required during a range of incident wind conditions to resolve near surface airflow patterns and turbulent structures. This study examined three-dimensional airflow within a coastal dune trough-bowl blowout using 15 ultrasonic anemometers (UAs) and a high resolution computational fluid dynamics model. Measured total wind speed and vertical wind speed behaved consistently through 5 Beaufort wind scales ranging from 'fresh breeze' to 'strong gale', increasing relative to incident wind speed, whilst wind direction at each UA did not alter. Due to the agreement of modelled and measured data, 'hurricane' (37 m s) incident winds were also simulated and were consistent with modelled and measured wind direction at lower wind speeds. Modelled wind turbulence data was not compared with measured as only average conditions were simulated. However, the standard deviation of measured wind direction remained constant at each anemometer throughout the range of incident wind speeds, whilst the standard deviation of wind speed and turbulent kinetic energy increased relative to incident wind speed. This paper demonstrates that wind flow behaviour within blowouts throughout this range of wind speeds is governed by topography and is relative to, but does not change structurally with incident wind speed. As a result the extent of streamline compression, expansion, steering and reversal remain constant.
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| [41] |
Lake Michigan dune development-2:Plants as agents and tools in geomorphology [J].https://doi.org/10.1086/626522 URL [本文引用: 1] 摘要
Not Available
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Flow behaviour in a trough blowout,Tangimoana,New Zealand [J]. |
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Form-flow interaction of an Aeolian saucer blowout [J].https://doi.org/10.1002/esp.1776 URL [本文引用: 2] 摘要
ABSTRACT Airflow patterns through a saucer blowout are examined from wind speed and direction measurements made during a chinook wind event. The blowout long-axis is oriented east-west with a broad depositional apron on the east side. Wind directions during the event rotated from south-westerly to westerly, permitting an assessment of oblique and axis-parallel flows. Results show that airflow passing over the windward rim of the saucer blowout expands and decelerates, leading to flow separation and a small re-circulation zone on sheltered lee slopes. Near the deflation basin, airflow re-attaches to the blowout surface and accelerates up to a small opening in the east rim, where it can be up to 50% faster than on the windward edge. Beyond the downwind rim the airflow expands and decelerates and sand is deposited onto a broad apron. Similar to coastal trough blowouts, the degree of airflow steering and acceleration along the deflation basin is determined by the angle of incidence between the approach wind and the long-axis of the blowout. As the angle of incidence increases wind speed accelerates at 0·3 m above the surface of the deflation basin and the degree of airflow steering increases. Overall, a two-fold process is identified, where south-westerly flows have greater potential for eroding the deflation basin, while westerly flows have greater potential for evacuating sand from within the blowout. Visual observations indicate that sand eroded from the deflation basin during south-westerly flows is re-distributed to adjacent zones of low wind speed until axis-parallel winds evacuate the sand through the opening in the east rim. Morphometric changes since 1994 indicate that the blowout morphology has remained relatively constant, suggesting a persistent interplay between oblique and axis-parallel wind erosion events. Collectively, these findings indicate that the angle of approach winds is an important control on saucer blowout morphodynamics.
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浑善达克沙地的土地沙漠化过程研究 [J].Magsci 摘要
<FONT face=Verdana>借助TM/ETM＋影像和GIS平台，采用实地考察与野外实验和室内分析整理相结合的办法，对浑善达克沙地土地沙漠化过程进行了初步研究。结果表明，过去50 a来，浑善达克沙地经历了强烈的沙漠化发展。位于沙地中部正蓝旗的沙漠化土地从1987年的5 593.8 km<SUP>2</SUP>发展到2000年的6 015.3 km<SUP>2</SUP>，发展速率为32.4 km<SUP>2</SUP>·a<SUP>-1</SUP>。2000年紧急启动的风沙源治理工程，一定程度改善了当地沙漠化发展态势，2005年正蓝旗共有沙漠化土地5 950.4 km<SUP>2</SUP>，有约330.7 km<SUP>2</SUP>的严重沙漠化土地得到了控制和逆转。其他大部分沙漠化土地虽有不同程度改善，但5 a的时间里尚未发生质的变化。沙漠化过程是原生植被逐步被沙生植被和沙生先锋植被取代的过程;同时也是土壤粗化、贫瘠化和空间重新分布过程。随着土地沙漠化程度的加剧，起沙风速降低，输沙强度增大，沙地近地表表现出相对高风能环境。沙漠化过程以固定沙丘活化为主，主要有发育“马蹄形”风蚀洼地、“鱼钩”型沙丘和“串珠状”风蚀槽三种沙丘活化形式，最终导致景观支离破碎、不少地区出现了流沙连片的现象。同时，农田开垦引起土壤风蚀的危险，也不容忽视。<BR><BR></FONT>
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Landscape pattern change and driving force of blowout distribution in the Hulun Buir Sandy Grassland [J].https://doi.org/10.3724/SP.J.1226.2012.00431 URL [本文引用: 4] 摘要
The land coverage pattern changes for the past 50 years in a typical region of the Hulun Buir Sandy Grassland were interpreted and analyzed based on a series of remote sensing images in 1959, 2002, 2004 and 2009. The temporal and spatial changes of landscape patterns were revealed and the driving forces were analyzed. The results show that all land coverage types had large variable amplitudes. The grassland area decreased, whereas other areas increased. Owing to implementation of artificial sand fixation from 2004 to 2009, the areas of flowing blowouts and depositional area decreased by 71,369 and 128,835 m2 , respectively. The average patch area reduced, but the number of blowouts increased, fractal dimension increased, and blowout structure became complex. The fragmentation index increased, whereas contagion index decreased. Driving force analysis shows that human factors such as overgrazing are slightly larger than natural factors of increased temperature and decreased precipitation.
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Flow dynamics and geomorphology of a trough blowout [J].https://doi.org/10.1046/j.1365-3091.1996.d01-22.x URL [本文引用: 3] 摘要
Not Available Not Available
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Blowouts in coastal foredunes [J].https://doi.org/10.1016/0169-2046(95)00218-9 URL [本文引用: 3] 摘要
ABSTRACT Foredune blowouts within many embayments along the south coast of South Africa are traditionally believed to be caused by human activities and the result of onshore winds reducing vegetation cover and developing landward migrating patches of bare sand. These bare areas are not blowouts sensu strictu, however, and are more likely the elongated horns of barchan dunes formed across the direction of the dominant winds. Blowouts of this type have been present on the foreshore of Algoa Bay for more than 100 years and long before present-day human pressures could be the possible causal factor. They are not likely to present major management problems provided buildings are not constructed within them or closely behind them. Where necessary, vegetation cover should be maintained either by keeping people out of the dunes or by implementing revegetation options. Some mechanical sand relocation may occasionally be a helpful short-term management solution.
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风蚀地貌形态与过程研究进展 [J].https://doi.org/10.3969/j.issn.1672-6561.2009.01.015 URL [本文引用: 2] 摘要
辨析了雅丹、风蚀坑等主要风蚀地貌的概念,雅丹是典型的风蚀正地貌形态,通过回顾雅丹地貌形 态与过程的研究历史与进展,发现目前对其发育过程的认识尚不清楚,并且只关注了对残存土墩的观测和分析,没有充分重视凹槽的形态动力学过程;风蚀坑是典型 的风蚀负地貌形态,特别是草原景观转变为沙地景观的临界阈现象,目前已经对独立风蚀坑的形态、气流特征、沉积物粒度以及植被演替过程等方面进行了初步研 究,但由于风蚀坑形态是多因素共同作用的结果,需要由单因素观测转向综合分析其形态动力学过程。认为对风蚀过程机理及其模拟的研究中,在利用风洞模拟实 验、野外观测等手段对风蚀过程微观尺度进行研究的同时,也需要加强通过遥感和GIS手段从景观尺度对风蚀地貌发展变化过程进行分析。
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High resolution measured and modelled three-dimensional airflow over a coastal bowl blowout [J].https://doi.org/10.1016/j.geomorph.2012.07.014 URL [本文引用: 2] 摘要
Blowouts are common landforms found within coastal dunes. Their dynamics are primarily driven by aeolian transport caused by surface wind stress, though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex. Three-dimensional wind flows around blowouts have yet to be properly quantified, especially within zones of separation, re-attachment and acceleration. This has been largely due to inadequate measurement of airflow and a lack of suitable airflow models. With this in mind, we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the Belmullet Peninsula, Ireland. Using ultrasonic three-dimensional anemometry (measuring at 50 Hz) and three-dimensional computational fluid dynamic (CFD) modelling, we measure and model for the first time in 3D a detailed picture of the heterogeneity of wind flow over this type of terrain.
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Topographic changes associated with coastal dune blowouts at island beach State Park,NJ [J]. |
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A field experiment on the role of small scale wind gustiness in aeolian sand transport [J].https://doi.org/10.1002/esp.3290120311 URL [本文引用: 1] 摘要
Not Available
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| [52] |
Morphodynamics and climate controls of two aeolian blowouts on the northern Great Plains,Canada [J].https://doi.org/10.1002/esp.1367 URL [本文引用: 4] 摘要
Abstract Blowouts are the most regionally pervasive active aeolian landform on the northern Great Plains of North America. This study reports a long-term investigation into the morphological development of two adjacent blowouts in a continental dune field. The blowouts were monitored for a decade in the Bigstick Sand Hills of southwestern Saskatchewan, Canada. Topographic changes were determined from dense arrays of erosion pins in each blowout (1 per 4 m 2 , n = 171; and 1 per 16 m 2 , n = 150). Pin measurements were made 16 times between May 1994 and May 2004. Over the decade both blowouts expanded and more than doubled in volume. Differences in form–flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin, and the smaller blowout to erode by more than a metre. A negative feedback effect was triggered when the larger blowout reached a critical size around 1994 (60 m × 36 m × 8·1 m, length × width × height) when sediment was no longer eroded from the deflation basin. A positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin. Monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability. Sediment is more readily available throughout the year on south-facing slopes, which receive greater insolation than north-facing slopes and are often drier and more frequently thawed in this cold-climate environment. Comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level. Nevertheless, the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station: (i) the amount of precipitation, (ii) the transport capacity of the wind and (iii) transporting winds from a directional wedge between 180 and 330°. Taken altogether, the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings. Copyright 08 2006 John Wiley & Sons, Ltd.
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| [53] |
Vegetation and sand mobility in the Australian desert dunefield [J].
ABSTRACT The desert dunes of Australia lie in a wide range of climates which are sufficiently benign to promote considerable vegetation. This cover of plants has been assumed to stabilize these 'relict' dunes, but most of the dunefield experiences few winds above the threshold for sand movement, with the exception of the southern winter rainfall zone. -from Authors
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Van Boxel J H.The effect of changing wind regimes on the development of blowouts in the coastal dunes of The Netherlands [J].https://doi.org/10.1007/BF00157743 URL [本文引用: 3] 摘要
Extreme aeolian events such as northwestern storms have little effect on blowout development compared to events which have a lower magnitude but occur with a higher frequency. An eventual shift towards higher effective wind velocities would probably result not in larger blowouts but in a break-down of the whole system, especially if this shift were accompanied by a change in wind direction. The accumulation of sand in the blowouts during storms should be seen as a first step of adaptation to a higher energy level.
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The Development of Blowouts in 'de Blink' a Coastal Dune Area near Noordwijkerhout,The Netherlands [J].https://doi.org/10.1002/esp.3290060316 URL [本文引用: 2] 摘要
Not Available
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Dynamics of deflation hollows in the Elands Bay area,Cape Province,South Africa [J].https://doi.org/10.1016/S0341-8162(86)80009-1 URL [本文引用: 1] 摘要
ABSTRACT
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The development of dune blowouts, as measured with erosion pins and sequential air photos [J].https://doi.org/10.1016/0341-8162(89)90021-0 URL [本文引用: 1] 摘要
The development of blowouts in dune terrains where no stabilization measures are taken requires constant watch to detect unwanted developments at an early stage. Two methods for investigating blowout development are in use. Since 1983, blowouts in a 40 ha section of Meijendel, a coastal dune area near The Hague have been twice yearly measured with erosion pins. Most of the 32 to 35 blowouts grew in length against the prevailing SW wind. The total blowout deflation area increased from 2.8 to 3.3% of the terrain in 4 years time. Air photos of 1958, 1967, 1977, 1984 and 1986 were used to study blowouts in a nearby area, De Blink north of Noordwijk, one of the most severely eroded dune terrains along the Dutch mainland coast. Total deflation area here increased from 0.8% in 1958 to 3.7% in 1986. There is a definite modal length class but the size is site-specific: 25 to 30 m in Meijendel, 15 to 20 m in De Blink. Many blowouts disappear shortly after they are formed. From the results it appears that the processes involved in the formation of blowouts can best be investigated with erosion pins whereas aerial photographs are preferable when changes in the spatial and temporal pattern of blowouts and the contributing factors are of interest.
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| [58] |
Relationships between deflation and near surface wind velocity in a dune blowout [J]. |
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The rate of grain release by pore-ice sublimation in cold-aeolian environments [J].https://doi.org/10.1111/1468-0459.00192 URL [本文引用: 2] 摘要
Abstract Pore-ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore-ice sublimation. In 1996鈥1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park.
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| [60] |
Seasonal sand transport through a trough blowout at Pinery Provincial Park,Ontario [J].https://doi.org/10.1139/e17-118 URL [本文引用: 3] 摘要
Not Available
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Geographical Variation in Coastal Development [M]. |
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基于ALOS数据的浑善达克沙质草地风蚀坑空间格局及特征分析 [J].https://doi.org/10.7522/j.issn.1000-694x.2013.00095 URL Magsci [本文引用: 3] 摘要
以2008年的ALOS卫星多光谱波段（空间分辨率10m）和全色波段（空间分辨率 2.5m）融合后的影像数据及地面调查数据为数据源,借助ArcGIS和Fragstats3.3软件,采用景观格局指数方法,从类型和斑块水平上定量分 析了浑善达克沙质草地风蚀坑的空间格局和特征。结果表明,浑善达克沙质草地风蚀坑面积占景观面积的6.1%,密度为0.026个.hm-2,分布范围广且 呈局部聚集分布;根据不同发育阶段,风蚀坑形状分为碟形、椭圆形、槽形和不规则形;风蚀坑斑块面积与形状指数、分维数之间存在显著正相关关系,面积的增 加,可使风蚀坑形状复杂化趋势明显。复杂形状风蚀坑主要由若干个独立的风蚀坑扩大并联结形成;相对于宽度与深度,风蚀坑面积与长度间存在更显著正相关;浑 善达克沙质草地风力侵蚀基准面较高,风蚀坑深度一般不超过5m;风蚀坑长度与宽度之间、宽度与深度之间存在相互制约关系。
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| [63] |
试论科尔沁南部大青沟地区沙漠化土地的地表形态特征及其发育过程 [J].
正 科尔沁南部系指西拉木伦河以南、教来河以东、西辽河以西、养畜牧河以北的科尔沁沙地。大青沟地区则位于科尔沁南部科左后旗及库仑旗境内,面积334.1平 方公里。本区土地沙漠化的研究,前人做了不少工作,但对沙漠化土地地表形态的特征及其发育过程的专门研究还未见到。鉴于此,笔者撰写了此文。
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| [65] |
Morphological development of coastal dunes in a humid tropical environment,Cape Bedford and Cape Flattery, north Queensland [J].https://doi.org/10.2307/520647 URL [本文引用: 1] 摘要
ABSTRACT The dunefield consists of several generations of superimposed parabolic and elongate parabolic dunes, the older members of which are deeply weathered. The large scale of dune development in this area reflects an abundant sand supply from widespread outcrops of Mesozoic sandstones and older granites on the neighbouring part of Cape York Peninsula, and the exposed location of Cape Bedford and Cape Flattery in relation to the prevailing SE winds. Many of the dunes are stabilized at the present day, and the major periods of dune formation appear to have taken place earlier in the Holocene or Pleistocene.-from Author Dept Earth Sciences, Cambridge Univ, U.K.
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| [66] |
The Coastal Sand Dunes of Oregon and Washington [J].https://doi.org/10.1130/MEM72-p1 URL [本文引用: 1] 摘要
In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man hasbeen comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, andconclusions arrived at deductively are confirmed by slow-motion photography ofsmoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, developmentinvolves the following phases: trough blowout, merging of troughs, reduction todeflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are theprecipitation ridge and the parabola dune.In Regions II, III, and IV the existing features came into being mainly during thelast grand period of sea-level rise, and the seaward portions of massive parabolacomplexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River.South of Tillamook Head there is, in a number of well-distributed localities, evidenceof three episodes of advance. The first is represented by the strip of thoroughlystabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained itsmaximum of advance-attested by the slicing away of portions of completely stabilizedmasses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges fromcomplete stabilization to vigorous activity. The third episode is represented by activedunes with open access to the shore. In certain localities there are only an innerstrip of stabilized dunes and an outer zone of active dunes. It is assumed that in thesethe visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants wereformed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded bystability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene.
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| [67] |
Blowout dynamics on Lake Huron sand dunes:analysis of digital multispectral data from colour air photos [J].https://doi.org/10.1016/j.catena.2004.11.004 URL [本文引用: 1] 摘要
We adapted a digital image analysis procedure to extract multispectral data from sequential colour air photos of a Lake Huron sand dune system and then classify land cover into water, sand, and vegetation. We isolated portions containing individual blowouts from georeferenced land cover maps of the dune system in 1973 and 1998 and overlaid the sequential images using geographic information systems (GIS). This allowed us to quantify changes in blowouts over the 25-year period. Net change in land cover (m 2 ) within each blowout was expressed as the difference between retrogression (bare areas created by erosion or burial of existing vegetation) and colonization (vegetation patches created by plant establishment on bare areas). The analysis procedure produced maps with an overall accuracy of 鈮90% for land cover classification within blowouts. The individual blowouts fell along a continuum of activity, varying from significant retrogression (+748 m 2 ) to significant colonization (鈭1148 m 2 ). Overall, sand movement in all sampled blowouts produced 3991 m 2 (17.9% of the blowout area in 1998) of bare sand patches that replaced formerly existing patches of vegetation. Colonization of bare areas over the 25-year period was 4127 m 2 or 18.5% of the 1998 blowout area. Retrogression and colonization are natural cooccurring processes in coastal dune systems, and the technique described here represents a new tool for the study of temporal and spatial vegetation dynamics in blowouts.
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| [68] |
呼伦贝尔草地风蚀坑分布区土地覆被景观变化 [J].
以呼伦贝尔草地风蚀坑分布区 1959、2002、2004、2009年4期影像解译数据为基础,研究该区近50a土地覆被变化情况,揭示景观格局时空演化规律,模拟未来土地覆被变化 情景。结果表明:研究区各土地覆被类型变幅较大,除草地面积减少外,其它类型面积总体都呈增加趋势。其中,裸露风蚀坑、流沙区面积呈先增后减趋势,与近 5a加大人工固沙力度有关。斑块尺度上,风蚀坑景观数量增加,平均斑块面积先增后减,分维数增加,风蚀坑结构变得复杂;景观尺度上,多样性和破碎度指数增 加,蔓延度指数减少,草地遭到风蚀破坏。预测2012-2020年间,土地覆被格局继续保持目前发展态势,但发展速度减慢。若保持目前影响因素不变情况 下,风蚀坑的发展将得到有效控制。
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