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1.
Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation,iron precipitation,and rindlet exfoliation 
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下载免费PDF全文 Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well‐developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro‐cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high‐angle columnar and low‐angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro‐cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P‐wave velocity in the brown band, while micro‐crack formation decreases the tensile strength of the rock. Where the brown band has thickened to ~6 cm, the micro‐cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro‐crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
2.
Determining occurrence age is key to chronology analysis of huge landslides. However, in carbonated bedrock areas, it is difficult to carry out geochronological surveys of landslide evolution due to lack of suitable dating materials and methods. In carbonated bedrock areas, the cosmic nuclides 36Cl and 14C dating methods have been used for obtaining the exposed age of bedrock. But intense weathering, erosion and dissolution make it difficult to obtain an accurate total amount of cosmogenic nuclide accumulation, resulting in the dating results being affected greatly by weathering, erosion and dissolution of carbonate rock. Therefore, it is necessary to find new dating materials or methods for determining the occurrence age of landslide in carbonate bedrock areas with little quaternary sediments. In this study, a huge landslide developed in the carbonate bedrock area of south eastern Tibet is introduced briefly, which is named the Qiaojia landslide and blocked the Jinsha River. A thin layer including three obvious recrystallized carbonate sub-layers was formed in the sliding zone, indicating different sliding events. Three recrystallized carbonate samples were then collected for ESR dating research to obtain the age information of the Qiaojia landslide: one occurred 79 ± 8 ka years ago, and the other occurred 60 ± 10 ka years ago, and the third occurred 25 ± 2 ka years ago, which are in general agreement with other studies in the surrounding of the study area. It suggests that recrystallized carbonate on sliding face is suitable for chronologically identifying landslide activity by using ESR method in the carbonate area, especially in the areas with little or no quaternary sediments. 相似文献
3.
Fan Zhang Xiong Xiao Lijie Wang Chen Zeng Zhengliang Yu Guanxing Wang Xiaonan Shi 《水文研究》2021,35(8):e14330
Climate factors play critical roles in controlling chemical weathering, while chemically weathered surface material can regulate climate change. To estimate global chemical weathering fluxes and CO2 balance, it is important to identify the characteristics and driving factors of chemical weathering and CO2 consumption on the Tibetan Plateau, especially in glaciated catchments. The analysis of the hydro-geochemical data indicated that silicate weathering in this area was inhibited by low temperatures, while carbonate weathering was promoted by the abundant clastic rocks with fresh surfaces produced by glacial action. Carbonate weathering dominated the riverine solute generation (with a contribution of 58%, 51%, and 43% at the QiangYong Glacier (QYG), the WengGuo Hydrological Station (WGHS), and the lake estuary (LE), respectively). The oxidation of pyrite contributed to 35%, 42%, and 30% of the riverine solutes, while silicate weathering contributed to 5%, 6%, and 26% of the riverine solutes at the QYG, WGHS, and LE, respectively. The alluvial deposit of easily weathering fine silicate minerals, the higher air temperature, plant density, and soil thickness at the downstream LE in comparison to upstream and midstream may lead to longer contact time between pore water and mineral materials, thus enhancing the silicate weathering. Because of the involvement of sulfuric acid produced by the oxidation of pyrite, carbonate weathering in the upstream and midstream did not consume atmospheric CO2, resulting in the high rate of carbonate weathering (73.9 and 75.6 t km−2 yr−1, respectively, in maximum) and potential net release of CO2 (with an upper constraint of 35.6 and 35.2 t km−2 yr−1, respectively) at the QYG and WGHS. The above results indicate the potential of the glaciated area of the Tibetan Plateau with pyrite deposits being a substantial natural carbon source, which deserves further investigation. 相似文献
4.
Abstract Reaction zones of 0.5–10.0 m thick are commonly observed between serpentinite and pelitic schist in the Nishisonogi metamorphic rocks, Kyushu, Japan. Each reaction zone consists of almost monomineralic or bimineralic layers of talc + carbonates, actinolite (or carbonates + quartz), chlorite, muscovite and albite from serpentinite to pelitic schist. Magnesite + quartz veins extend into the serpentinite from the talc + carbonates layer, while dolomite veins extend into the pelitic schist from the muscovite layer. These veins are filled by subhedral minerals with oriented growth features. Primary fluid inclusions yield the same homogenization temperatures (145–150°C) both in the reaction zone and in the veins, suggesting their simultaneous formation. Mass-balance calculations using the isocon method indicate that SiO2 , MgO, H2 O and K2 O are depleted in the reaction zone relative to the protoliths. These components were probably extracted from the reaction zone as fluids during the formation of the reaction zone. 相似文献
5.
The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile. 相似文献
6.
CHARACTERISTICS AND FORMATION MECHANISM OF LARGE ROCK AVALANCHES TRIGGERED BY THE LUDIAN MS6.5 EARTHQUAKE AT HONGSHIYAN AND GANJIAZHAI 下载免费PDF全文
下载免费PDF全文 The 3 August 2014 Ludian, Yunnan MS6.5 earthquake has spawned more than 1, 000 landslides which are from several tens to several millions and over ten millions of cubic meters in volumes. Among them, the Hongshiya and Ganjiazai landslides are the biggest two with volumes over 1 000×104m3. The Hongshiya and Ganjiazai landslides are two typical landslides, the former belongs to tremendous rock avalanche, and the latter belongs to unconsolidated werthering deposit landslide developed in concave mountain slope. Based on field investigations, causes and formation mechanism of the two landslides are discussed in this study. The neotectonic movement in the area maintains sustainable uplifting violently all the time since Cenozoic. The landform process accompanied with the regional tectonic uplifting is the violent downward erosion along the Jinshajiang River and its tributary, forming landforms of high mountains and canyons, deeply cut valleys, with great height difference. The regional seismo-tectonics situation suggests that:Ludian earthquake region is situated on the southern frontier boundary of Daliangshan secondary active block, and is seismically the strongest active area with one earthquake of magnitude greater than M5.0 occurring every 6 years. Frequent and strong seismicity produces accumulated effects on the ground rock to gradually lower the mechanical strength of slopes and their stability, which is the basis condition to generate large-scale collapse and landslide at Hongshiyan and Ganjiazhai. The occurring of Hongshiyan special large rock avalanche is associated with the large terrain height difference, steep slope, soft interlayer structure and unloading fissures and high-angle joints. The formation mechanism of Hongshiyan rock avalanche may have three stages as follows:Stage 1, when P wave arriving, under the situation of free surface, rocks shake violently, the pre-existent joints(in red)parallel to and normal to the river and unloading cracks are opened and connected. Stage 2, on the basis of the first stage, when S wave arriving, the ground movement aggravates. Joints(in green)along beds develop further, resulting in rock masses intersecting each other. Stage 3, rock masses lose stability, sliding downward, collapsing, and moving over a short distance along the sliding surface to the inside of the valley, blocking the river to form the dammed lake. The special large landslide at Ganjiazhai is a weathering layer landslide occurring in the middle-lower of a large concave slope. Its formation process may have two stages as follows:Firstly, under strong ground shaking and gravity, the ground rock-soil body around moves and assembles to the lower of the central axis of the large concave slope, which suffers the largest earthquake inertia force and firstly yields plastic damage to generate compression-expansion deformation, because of the largest water content and volume-weight within the loose soil of it. Secondly, in view of the steep slope, along with the compression, the plastic deformation area enlarges further in the lower of slope, giving rise to a tensional stress area along the middle of the slope. As soon as the tensional stress exceeds the tensile strength of the weathering layer, a tensional fracture will occur and the landslide rolls away immediately making use of momentum. This two large landslides are the basic typical ones triggered by the MS6.5 Ludian earthquake, and their causes and mechanism have a certain popular implication for the landslides occurring in this earthquake region. 相似文献
7.
Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern
Guizhou. Two stages can be recognized during the process ofin situ weathering of dolomitite: the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical
weathering evolution of sedentary soil. Ni, Cr, Mo, W and Ti are the least mobile elements with reference to Al. The geochemical
behavior of REE is similar to that observed in weathering of other types of rocks. Fractionation of REE is noticed during
weathering, and the two layers of REE enrichments are thought to result from downward movement of the weathering front in
response to changes in the environment. It is considered that the chemistry of the upper part of the profile, which was more
intensively weathered, is representative of the mobile components of the upper curst at the time the dolomitite was formed,
while the less weathered lower profile is chemically representative of the immobile constitution. Like glacial till and loess,
the “insoluble” materials in carbonate rocks originating from chemical sedimentation may also provide valuable information
about the average chemical composition of the upper continental crust. 相似文献
8.
《地震研究进展（英文）》2021,1(3):100059
At present, substantial scientific research achievements have been made in the research on landslide occurrence, movement mechanism, mitigation measures, and structural stability during tunnel excavation. However, the interaction mechanism of a tunnel under-traversing a slope body with potential landslides is still not well understood. Based on the field data provided by previous investigations in the study area, six sets of 1:100 laboratory experiment model tests were conducted to study the stability of the landslide-prone zone of the slope body with an under-traversing tunnel. The selected distances between the tunnel and the sliding surface are 1.5, 3, and 5 times of the tunnel diameter, respectively. The experiment results show the interaction between the landslide-prone zone and the tunnel, elucidating the effect of potential landslides during the tunnel excavation process and the reaction of the landslide slip on the tunnel structure. Several conclusions are obtained: ① During the process of tunnel excavation, the vertical displacement of the tunnel vault decreases with the increase of the buried depth. ② The vertical displacement of the sliding surface increases with the increase of the buried depth of the tunnel. The horizontal displacement of sliding surface decreases with the increase of the buried depth. ③ After the occurrence of a rainfall-induced landslide, the vertical displacement of the tunnel vault in the 1.5-diameter-distance case is 57.29% greater than that in the 3.0-dismeter-distance case.④ For a two-cave tunnel, it is suggested that the cave farther from the landslide toe should be firstly excavated since it may generate less structural deformation. 相似文献
9.
We have established a monitoring record of phosphate (PO43−) migration in the Long Point, ON campground septic system plume that now spans 26 years. Previously, at year 16 (2006), a P plume 16 m in length was documented and provided a good fit with an analytical advection dispersion model when a P migration velocity of 0.8 m/yr was used (retardation factor of 37) and when P behaved in an otherwise conservative manner (sorption only). However, between years 16 and 26 (2016), the P plume length expanded by only 2 m (0.2 m/yr) and increased in depth by only 0.5 m. The zone of abrupt P depletion at depth occurs close to the zone where SO42− concentrations increase in response to NO3− oxidation of pyrite. Scanning electron microscope images of sand grains from the nose of the P plume reveal abundant authigenic mineral coatings of considerable thickness (∼5 to 20 μm), with Fe as the dominant cation and containing 1 to 3 wt % P. This evidence suggests that P is now being attenuated along a reaction front that coincides with the zone where pyrite oxidation is occurring. P migration may now be controlled by the rate of migration of the pyrite oxidation front and this is several times slower than the previously indicated rate in the shallower, sorption-controlled portion of the plume. Monitoring at Long Point has demonstrated the danger of embracing an overly simplistic conceptual model when attempting to predict wastewater P migration in groundwater and also highlights the unique insight provided by a long-term monitoring record. 相似文献
10.
青藏高原边缘地带堆积体滑坡的发生与地质构造、强降雨、地震等作用密切相关,其中多数属于大型高位堆积体滑坡。为研究其发生机理与稳定性,以舟曲县江顶崖大型高位堆积体滑坡为研究对象,首先,从滑坡所处的地理位置、地质条件等出发,分析滑坡的概况与成因;其次,基于传统传递系数法划分滑坡计算模型,提出滑坡稳定性分析的变坡法;最后,采用Midas GTS NX软件对江顶崖滑坡自然工况下稳定性进行数值模拟分析,并与传统及改进算法结果进行对比。研究结果表明：(1)研究区的地形坡度、地层岩性条件以及活动断裂、历史强震作用是滑坡发生的内因,外因是连续强降雨作用使岩土体力学强度降低以及暴雨导致滑坡前缘的白龙江水位上涨、流速加快,冲刷坡脚导致前缘失稳,滑坡中后缘发生牵引式滑动;(2)运用传递系数法计算折线形滑坡稳定性时,滑面倾角变化值大于10°会导致结果出现较大误差,应用改进的“等分均匀变坡法”可以减小误差,以江顶崖滑坡为计算实例并结合数值模拟验证该方法的有效性;(3)自然工况下模拟发现,滑体的前缘主要表现为水平滑移,滑体的中后部局部主要表现为垂直下沉,而滑坡前缘则主要表现为隆起,因此,滑坡部分区域出现了较大的位移... 相似文献
11.
土石混合滑坡体地表地形复杂，土、石混杂堆积，结构松散，探测难度大，目前尚缺乏有效的物探手段.本文首次尝试将小台阵二维微动剖面探测技术应用于衡阳市拜殿乡的土石混合滑坡体探测.探测结果揭示，该滑坡体上部为砂质黏性土层，含块石较多；下为全风化花岗岩层，岩性较为均匀，块石含量少，其顶部为该滑坡体潜在的滑动面.滑动面在滑坡体后缘较陡、中部较为平缓，从而后缘的重力失稳、滑动风险更大.滑坡体的滑床（中-强风化花岗岩、微-未风化花岗岩）埋深在10 m以下，起伏变化较大，但岩体相对致密、完整，稳定性好，不易滑动.探测结果与钻探资料较为吻合，为评价滑坡体稳定性、设计合理的治理方案提供了地球物理依据. 相似文献
12.
Quartz and quartzite are thought to be resistant as a mineral and a rock respectively; however, we have shown that the presence of small amounts of pyrite in the quartzites makes them vulnerable to weathering. We observe that weathering of Proterozoic quartzite in the semi‐arid conditions around Delhi proceeded from fractures towards the inside and produced weathering rinds. The chemical index of alteration (CIA), which is actually a measure of weathering of aluminosilicate minerals, increases from the core outwards, through the rinds. Although aluminosilicate minerals occur only as minor phases (<2 per cent), their weathering indicates a movement of the weathering front from the periphery towards the core. We have suggested a coupled mechanism in which the dissolution of pyrites by moving water produced a sulphate‐bearing acidic solution and ferrous iron, which reacted with aluminosilicate minerals and quartz, respectively. This initially makes the Delhi quartzite porous and subsequently friable. The total disintegration of grain to grain contacts imparted friability to this quartzite to produce silica sand. Subsequent physical erosion of loose sand, produced during rind development in the outermost zones, has given rise to features like tors, spheroids, gullies, cavities and small‐scale caves on these quartzites. Thus, the terrain has acquired ruggedness in semi‐arid conditions. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou.Two stages can be recognized during the process of in situ weathering of dolomitite:the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil.Ni,Cr,Mo,W and Ti are the least mobile elements with reference to Al.The geochemical behavior of REE is similar to that observed in weathering of other types of rocks.Fractionation of REE is noticed during weathering,and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment.It is considered that the chemistry of the upper part of the profile,which was more intensively weathered,is representative of the mobile components of the upper curst at the time the dolomitite was formed,while the less weathered lower profile is chemically representative of the immobile constitution.Like glacial till and loess,the "insoluble" materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust. 相似文献
14.
Duplex of metamorphic units including ultramafic rocks in the central region of Tokunoshima,Southwest Japan 下载免费PDF全文
下载免费PDF全文 Geological observations in the central part of Tokunoshima in the Amami Islands, Southwest Japan, reveal that discrete layers of serpentinite, dioritic gneiss, and amphibolite are intercalated into pelitic schist and these rock bodies form a northwest‐dipping tectonic stack. A subhorizontal psammitic schist layer overlies them. These rocks underwent ductile deformation that is denoted by penetrative foliation and mineral lineation. Microstructures of the sheared metamorphic rocks and serpentinite indicate top‐to‐the‐east, ‐southeast or ‐south (hanging‐wall up) displacements. The en echelon array of rock bodies is interpreted as a duplex with the psammitic schist layer on its top and the pelitic schist layer on its bottom. It is inferred that the serpentinite‐bearing duplex was formed due to the tectonic erosion and the subsequent accretionary growth operated in a Cretaceous or older subduction zone. Tokunoshima has been considered to belong to the Shimanto Belt. However, regional low‐pressure and high‐temperature type amphibolite‐facies metamorphism and related ductile deformation have not been recognized in the other areas of the Shimanto Belt. There is no metamorphic rock occurrence comparable to that of Tokunoshima in the neighboring islands. The metamorphic rocks in Tokunoshima can be correlated to any of low‐pressure/temperature type metamorphic regions in Kyushu. 相似文献
15.
断层带摩擦稳定性转换及其对应的微破裂特征对于地震成核条件和慢地震机理研究具有重要的意义.本文利用双轴实验装置研究了硬石膏断层带摩擦稳定性的转换及其对应的应变变化、微破裂特征,并分析了实验标本的微观结构.实验结果表明,σ2和加载点速度对断层滑动稳定性具有显著影响.在低σ2条件下,硬石膏断层带出现不稳定滑动,变形以局部化的脆性破裂和摩擦为主;随σ2的增加,断层由不稳定滑动向稳定滑动转换,断层带变形方式逐渐转变为分布式的破裂.在低σ2条件下,硬石膏断层带在较低加载点速度下表现为速度强化且滑动稳定,在中等加载点速度下表现为速度弱化并伴有准周期性的黏滑,在较高加载点速度下又有转向速度强化的趋势,σ2的提高使得速度弱化的范围逐渐减少,滑动趋于稳定.上述两次转换对应不同的微破裂特征,在较高速度下从速度弱化转换为速度强化时,断层滑动伴有能量较小但频度很高的微破裂活动,而在较低速度下从速度弱化转换为速度强化时,断层滑动伴有间歇性的微破裂,这与断层带的微观结构特征有较好的对应关系,表明其转换机制是不同的. 相似文献
16.
利用扫描电镜和能谱分析研究了长白山天池火山天文峰剖面全新世喷发物中长石表面风化溶蚀显微形貌和化学组成,结果显示: 天文峰剖面从顶部黑色浮岩向下到暗灰色浮岩中,长石表面发育风化溶蚀不同的显微形貌结构。其特征有,风化初期的溶蚀作用主要在双晶缝、解理缝等结构薄弱部位,形成规模较小的溶孔和溶缝等,随着风化溶蚀程度的增加,已经形成的溶蚀痕迹进一步扩大、合并、相互贯通而形成矩形溶孔或棱柱状溶孔。长石晶体上溶蚀痕迹的扩大受长石晶体各向异性的控制。天文峰剖面火山喷发物时代越早,长石颗粒表面风化溶蚀程度越强,结构越复杂; 火山喷发物时代越晚,长石颗粒表面风化溶蚀程度越弱,结构越简单。即长石表面风化溶蚀程度与火山喷发的时代具有一定的相关性。根据长石颗粒表面的显微形貌结构,认为漫江林场浮岩与天文峰剖面中灰色浮岩应是火山同一次喷发的产物。长石表面风化溶蚀度可以作为判定火山喷发精细序列的一个代用指标。能谱分析显示,较新鲜的长石表面与风化溶蚀的长石化学组成不同。长石风化溶蚀的显微形貌和化学组成反映了它是天然风化、溶解、淋滤,最后又有物质沉淀的自然成因。Fe元素则可能与微生物作用有关。详细研究长石表面的风化溶蚀特征,它将有可能成为从岩石微观方面探讨火山喷发后环境变化和火山喷发期次的一种新方法。 相似文献
17.
甘肃舟曲泄流坡滑坡地处活跃断层破裂带内,断层活动控制着该滑坡的发育和运动。为了研究该滑坡滑带土的动力特性,采用重塑滑带土样,在固结不排水条件下,利用分级循环加载法开展动三轴试验,重点探讨含水率的变化对滑带土动力特性的影响规律。试验结果表明:含水率一定时,泄流坡滑坡滑带土的动弹性模量随动应变的增大呈指数形式减小;动应变一定时,动弹性模量随含水率的增大而不断减小,且衰减速率随含水率的增大而增大;含水率并不影响动弹性模量-动应变关系曲线的形态,不同含水率下该关系曲线可以进行归一化。滑带土阻尼比随含水率的增大而增大,阻尼比-动应变关系曲线也具有归一化特征。不同含水率下泄流坡滑带土动应力-应变本构关系可以用双曲线模型进行描述。 相似文献
18.
Considerable debate revolves around the relative importance of rock type, tectonics, and climate in creating the architecture of the critical zone. We demonstrate the importance of climate and in particular the rate of water recharge to the subsurface, using numerical models that incorporate hydrologic flowpaths, chemical weathering, and geomorphic rules for soil production and transport. We track alterations in both solid phase (plagioclase to clay) and water chemistry along hydrologic flowpaths that include lateral flow beneath the water table. To isolate the role of recharge, we simulate dry and wet cases and prescribe identical landscape evolution rules. The weathering patterns that develop differ dramatically beneath the resulting parabolic interfluves. In the dry case, incomplete weathering is shallow and surface parallel, whereas in the wet case, intense weathering occurs to depths approximating the base of the bounding channels, well below the water table. Exploration of intermediate cases reveals that the weathering state of the subsurface is strongly governed by the ratio of the rate of advance of the weathering front itself controlled by the water input rate, and the rate of erosion of the landscape. The system transitions between these end‐member behaviours rather abruptly at a weathering front speed ‐ erosion rate ratio of approximately 1. Although there are undoubtedly direct roles for tectonics and rock type in critical zone architecture, and yet more likely feedbacks between these and climate, we show here that differences in hillslope‐scale weathering patterns can be strongly controlled by climate. 相似文献
19.
针对高速滑坡超前气浪灾害的动力学问题,建立了滑坡体沿坡面滑动的二维模型;采用动网格技术,数值仿真了高速滑坡超前冲击气浪的流场特征,分析了其形成的动力学机理。计算结果表明：随着滑坡体下滑速度增大,在滑坡体前缘上方和滑坡体后方出现的涡流逐渐加强,速度也逐渐变大;滑坡体下滑速度越大,在滑坡体正前方不同高度处的气浪速度越大,气浪所影响的距离越远,所造成的破坏也越大。在滑坡体正前方出现高压区,并且随着滑坡体下滑速度增大,滑坡体前方的压力变化也增大,压力的急剧增大也导致气浪速度变大。高速滑坡引发的,中击气浪在前方100m范围内产生12级以上的大风,破坏力极大。此研究将为超前气浪灾害的防治提供科学依据。 相似文献
20.
Susan L. Brantley Molly E. Holleran Lixin Jin Ekaterina Bazilevskaya 《地球表面变化过程与地形》2013,38(11):1280-1298
Weathering is both an acid‐base and a redox reaction in which rocks are titrated by meteoric carbon dioxide (CO2) and oxygen (O2). In general, the depths of these weathering reactions are unknown. To determine such depths, cuttings of Rose Hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the Susquehanna Shale Hills Observatory (SSHO). Pyrite concentrations are insignificant to depths of 23 m under the ridge and 8–9 m under the valley. Likewise, carbonate concentrations are insignificant to 22 and 2 m, respectively. In addition, a 5–6 m‐thick fractured layer directly beneath the land surface shows evidence for loss of illite, chlorite, and feldspar. Under the valley, secondary carbonates may have precipited. The limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale. However, carbonate depletion coincides with the winter water table observed at ~20 m (ridge) and ~2 m depth (valley). It would be fortuitous if carbonate‐containing strata are found under ridge and valley only beneath the water table. Furthermore, pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature. We propose that deep transport of O2 initiates weathering at SSHO and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity. According to this hypothesis, the mineral distributions at SSHO are nested reaction fronts that overprint protolith stratigraphy. The fronts are hypothesized to lie subparallel to the land surface because O2 diffuses to the water table and causes oxidative dissolution of pyrite. Pyrite‐derived sulfuric acid (H2SO4) plus CO2 also dissolve carbonates above the water table. To understand how reaction fronts record long‐term coupling between erosion and weathering will require intensive mapping of the subsurface. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献