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1.
陈苗  胡小飞  王维 《地理学报》2018,73(9):1702-1713
河流水力侵蚀物理模型表明基岩河道纵剖面在均衡状态时表现为平滑上凹的形态,其特征反映了构造、基岩抗侵蚀能力和气候的作用;然而自然界河道纵剖面多呈现以裂点为特征的不均衡形态,不均衡的剖面形态以及裂点的研究同样可以对外力作用的变化起到很好的指示作用。位于北祁连的走廊南山高海拔河道纵剖面普遍呈现不均衡形式且发育海拔较高的裂点。通过对裂点成因分析发现,这些裂点并不主要受控于岩性、气候、构造等因素,而反映了冰川作用遗留地形与河流地形的分界。这一结果说明在对河道纵剖面高海拔裂点进行分析时要考虑到古冰川遗留地形也会对现代河道纵剖面产生重要影响,为进一步认识和理解造山带地貌演化以及控制因素提供了思路。  相似文献   

2.
庐山是位于江南造山带北缘的断块山,其抬升过程对于认识本区的构造演化至关重要。利用河流纵剖面的形态参数可以定量估算相对的构造抬升速率。基于5 m分辨率的DEM提取了庐山9条主要河流的纵剖面,依据坡度—面积图确定了裂点类型,结合地质图判别出裂点成因,并利用河流水力侵蚀模型计算了稳定态河段的陡峭指数以及凹曲度。结果显示,庐山的河流基本呈过渡态,以发育数量不等的裂点为标志;垂阶型裂点的形成主要与岩石强度不均一有关,而坡断型裂点是侵蚀基准面下降产生的。坡断型裂点以下的基岩河段具有较大的陡峭指数,表明庐山经历了从早期低抬升速率到晚期高抬升速率的转变。庐山受快速抬升影响的河段,陡峭指数具有南高北低的特点,主要是由于庐山整体抬升过程中南部、北部的抬升速率存在一定差异,亦可能是岩性不同造成的。  相似文献   

3.
Rivers respond to a drop in their base level by incising the topography. The upstream propagation of an incision, as usually depicted by a knickpoint migration, is thought to depend on several parameters such as the drainage area, lithology, and the amplitude of the base level drop. We first investigate the case of the Messinian Salinity Crisis that was characterized by the extreme base level fall (1500 m) of the Mediterranean Sea at the end of the Miocene. The response of drainage areas of three orders of magnitude (103 to 106 km2) highlights the dominant role of the drainage area (with a square root relationship) in controlling the knickpoint migration after a base level fall. A compilation of mean rates of knickpoint propagation for time durations ranging from 102 to 107 years displays a similar relationship indicating that successive wave trains of knickpoint can migrate in a river: first, wave trains linked to the release of the alluvial cover and then, wave trains related to the bedrock incision, which correspond to the real time response of rivers. Wave trains with very low retreat rates (long lived knickpoints > 1 My) rather correspond to the response time of regional landscape.  相似文献   

4.
Rifted continental margins generally display an interior, low-relief, highly weathered upland area and a deeply incised, high-relief coastal area. The boundary between the two zones is commonly demarcated by an abrupt, seaward-facing escarpment. We investigate the rate and pattern of escarpment erosion and landscape evolution along the passive margin of south-east Australia, in the region of the New England Tableland. The process of rifting is shown to initiate an escarpment across which rivers flow, resulting in an escarpment that takes the form of dramatic, elongated gorges. Using a mass balance approach, we estimate the volume/unit length of continental material eroded seaward of the escarpment to be between 41 and 68 km2, approximately an order of magnitude less than the 339 km2 of terrigenous sediments calculated to have been deposited offshore, but consistent with earlier denudation estimates based on apatite fission track data. On the bedrock rivers draining the New England Tableland region, the escarpment is manifested as a series of sharp knickpoints punctuating the river longitudinal profiles. The knickpoints are situated the same distance upstream along the different channels and uniform escarpment retreat rates on the order of 2 km Myr−1 are estimated, despite some differences in bedrock lithologies. Gorge head migration appears to be very important as a bedrock incision mechanism. Field observations indicate a coupling between escarpment retreat and knickpoint propagation, bedrock channel incision, and hillslope development.  相似文献   

5.
《Basin Research》2018,30(Z1):186-209
We present new data addressing the evolution, activity and geomorphic impact of three normal faults in the Southern Apennines: the Vallo di Diano, East Agri and Monti della Maddalena faults. We show that these faults have minimum total throws of ca. 1000–2000 m, and throw rates of ca. 0.7–1 mm year−1 for at least the last ca. 18 ka. We demonstrate that for the Vallo di Diano and East Agri faults, the landscape is effectively recording tectonics, with relief, channel and catchment slopes varying along fault strike in the same manner as normal fault activity does, with little apparent influence of lithology. We therefore use these data to reconstruct the time‐integrated history of fault interaction and growth. From the distribution of knickpoints on the footwall channels, we infer two episodes of base level change, which we attribute to fault interaction episodes. We reconstruct the amount of throw accumulated after each of these events, and the segments involved in each, from the fault throw profiles, and use fault interaction theory to estimate the magnitude of the perturbations and past throw rates. We estimate that fault linkage events took place 0.7 ± 0.2 Ma and 1.4 ± 0.3 Ma in the Vallo di Diano fault, and 1 ± 0.1 in the East Agri Fault, and that both faults likely started their activity between 3 and 3.5 Ma. These fault linkage scenarios are consistent with the observed knickpoint heights. This method for reconstructing fault evolution could potentially be applied for any normal faults for which there is information about throw and throw rates, and in which channels are transiently responding to tectonics.  相似文献   

6.
宛川河为黄河的一级支流,位于青藏高原东北部的兰州盆地东部.该区域历史时期曾发生多次6级以上地震.以DEM数据为基础,通过河流水系分析和地貌形态指数的计算,讨论了区域新构造活动特征.山前曲折度指数(SMF)在宛川河北为1.03~1.18,在兴隆山北前缘为1.83~2.88;河谷宽高比指数(VF)在宛川河北部为0.36~2.34,在南部的兴隆山为0.55~13.SMF与VF值的大小和分布特征表明研究区新构造活动活跃,且宛川河以北(前人推测有断层存在)新构造活动的活跃程度更高.流域盆地非对称性指数(AF)在宛川河北部东南端的异常揭示存在掀斜断块和褶皱运动;结合裂点分布和沟谷错断等地貌特征,发现宛川河北正断裂的东南端也存在西北--东南向走滑活动.  相似文献   

7.
The New River crosses three physiogeologic provinces of the ancient, tectonically quiescent Appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late Cenozoic. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. We used cosmogenic 10Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, to constrain the timing of events in this history. 10Be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield model cosmogenic exposure ages of 130, 600, and 600–950 ka, respectively, but uncertainties on these ages are not well constrained. These results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by New River terrace deposits. The exposure ages yield a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 100 m/my. Modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m/my, in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m/my rates of surface erosion from ancient terrace remnants. Fluctuations between aggradation and rapid incision operate on timescales of 104− 105 year, similar to those of late Cenozoic climate variations, though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events. These second-order fluctuations appear within a longer-term signal of dominant aggradation (until 2 Ma) followed by dominant incision. A similar signal is observed on other Appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late Cenozoic.  相似文献   

8.
《Geomorphology》2006,73(1-2):16-32
Well-constrained case studies of transient landscape response to external forcing are needed to improve our understanding of erosion processes in tectonically active mountain belts. The Peninsular Ranges portion of the San Jacinto fault zone (SJFZ) is an excellent location for such a study because it displays pronounced geomorphic disequilibrium resulting from initiation of a major strike-slip fault in the past 1.0 to 2.5 million years. We recognize two geomorphic domains in this region: (1) a relict low-relief upland domain consisting of broad flat valleys and low-gradient streams and (2) very steep, rough topography with deeply incised canyons and retreating erosional knickpoints. Pleistocene sediments exposed along and near the SJFZ include fluvial conglomerate, sandstone, and mudstone, with weak paleosols and west- to NW-directed paleocurrents. These sediments accumulated in a low-gradient stream system (represented by domain 1) during an early phase of slip in the SJFZ, prior to the modern phase of erosion and degradation (domain 2). Late Pliocene or early Pleistocene initiation of the SJFZ triggered a wave of headward erosion and stream capture that is still migrating NW along the fault zone. Using the total distance that capture points have migrated along the fault zone and a range of possible ages for fault initiation, the rate of knickpoint retreat is estimated at ∼ 12 to 44 km/my.To explore the signal of transient geomorphic response to fault initiation, we analyzed 23 tributaries along an ∼ 20-km portion of the main fault valley within domain 2. The analysis reveals three zones with distinctive morphologies: (1) strongly convex longitudinal profiles in the NW, (2) a large (ca. 5–6 km2) landslide in the central zone, and (3) concave tributaries in the SE with profile complexity decreasing and catchment area increasing from NW to SE. The distribution of these zones suggests close spatial and temporal association of active fault slip, bedrock incision, deep-seated landslides, and erosional modification. The fundamental driving force behind these processes is profound geomorphic disequilibrium resulting from initiation of the SJFZ. We suggest that landslides may have played a significant role in shaping the morphology of this fault zone, and that the influence of landslides may be underestimated in areas where characteristic landforms and deposits are obscured by later erosion and faulting.  相似文献   

9.
Experiments with marked pebbles were carried out on different sized rivers of the Belgian Ardenne (catchment areas varying from less than 1 km2 to 2700 km2). Specific stream power required to cause bedload movement was evaluated and critical values were obtained. Three types of relationship between critical specific stream power (ω0) and grain size (D) were established. The values for ω0 in the largest river (the Ourthe) were the lowest and were close to the values obtained for mountainous rivers carrying large boulders. In medium sized rivers (catchment area between 40 and 500 km2), the critical unit stream power was higher. It is likely that it is due to the bedform's greater resistance. This resistance would use up some of the energy that can cause movement and transport of bedload. The amount of resistance of the bedform can be expressed as bedform shear stress (τ″), determined by the relationship between grain shear stress (τ′—that determines movement and transport of the bedload) and the total shear stress (τ). This ratio varies between 0.4 and 0.5 in the medium sized rivers, compared to 0.7 in the Ourthe. In headwater streams (less than 20 km2), there is greater loss of energy due to bedform resistance (τ′/τ<0.3). Critical specific stream power is higher in this third type of river than in the other two.  相似文献   

10.
Investigating topographic and climatic controls on erosion at variable spatial and temporal scales is essential to our understanding of the topographic evolution of the orogen.In this work,we quantified millennial-scale erosion rates deduced from cosmogenic 10Be and 26Al concentrations in 15 fluvial sediments from the mainstream and major tributaries of the Yarlung Zangbo River draining the southern Tibetan Plateau (TP).The measured ratios of 26Al/10Be range from 6.33 ± 0.29 to 8.96 ± 0.37,suggesting steady-state erosion processes.The resulted erosion rates vary from 20.60 ± 1.79 to 154.00 ± 13.60 m Myr-1,being spatially low in the upstream areas of the Gyaca knickpoint and high in the downstream areas.By examining the relationships between the erosion rate and topographic or climatic indices,we found that both topography and climate play significant roles in the erosion process for basins in the upstream areas of the Gyaca knickpoint.However,topography dominantly controls the erosion processes in the downstream areas of the Gyaca knickpoint,whereas variations in precipitation have only a second-order control.The marginal Himalayas and the Yarlung Zangbo River Basin (YZRB) yielded significantly higher erosion rates than the central plateau,which indicated that the landscape of the central plateau surface is remarkably stable and is being intensively consumed at its boundaries through river headward erosion.In addition,our 10Be erosion rates are comparable to present-day hydrologic erosion rates in most cases,suggesting either weak human activities or long-term steady-state erosion in this area.  相似文献   

11.
On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.  相似文献   

12.
黄河中游小流域坡沟侵蚀关系研究   总被引：35，自引：5，他引：30  
陈浩  王开章 《地理研究》1999,18(4):363-372
根据坡面水下沟时在沟坡（道）上“净产沙增量”的概念,探讨了沿程含沙水流侵蚀特性的变化和坡沟侵蚀关系及产沙机理,并采用成因分析法定量确定了典型小流域的泥沙来源。  相似文献   

13.
We examine quantitatively the ranges of applicability of the equation Ω= A+B [1− t/t f ] m for predicting 'system-sized' failure times t f in the Earth. In applications Ω is a proxy measure for strain or crack length, and A , B and the index m are model parameters determined by curve fitting. We consider constitutive rules derived from (a) Charles' law for subcritical crack growth; (b) Voight's equation; and (c) a simple percolation model, and show in each case that this equation holds only when m < 0. When m > 0, the general solution takes the form Ω = A + B [1 + t / T  ] m , where T   is a positive time constant, and no failure time can be defined. Reported values for volcanic precursors based on rate data are found to be within the range of applicability of time-to-failure analysis ( m < 0). The same applies to seismic moment release before earthquakes, at the expense of poor retrospective predictability of the time of the a posteriori -defined main shock. In contrast, reported values based on increasing cumulative Benioff strain occur in the region where a system-sized failure time cannot be defined ( m > 0; commonly m ≈ 0.3). We conclude on physical grounds that cumulative seismic moment is preferred as the most direct measure of seismic strain. If cumulative Benioff strain is to be retained on empirical grounds, then it is important that these data either be re-examined with the independent constraint m < 0, or that for the case 0 < m + 1 < 1, a specific correction for the time-integration of cumulative data be applied, of the form ΣΩ = At + B '{1 − [1 − t/t f ] m+1 }.  相似文献   

14.
基于数字高程模型（DEM）及地理信息系统（GIS）技术,系统提取和分析了中条山北麓河流坡降指标、河道陡峭指数及面积高程积分等河流地貌参数。研究表明：河流坡降指标、河道陡峭指数及面积高程积分在永济至解州一带表现出较高的值;综合分析岩性、降水及构造等因素可知,新构造运动是控制中条山北麓河流地貌发育的主要因素,自北向南总体表现出增强的趋势,在永济南活动最强。前人研究表明,中条山北麓断裂晚第四纪以来构造活跃,全新世以来仍有多次活动,但不同部位活动强度各异,解州段晚更新世晚期以来滑动速率相比韩阳段及夏县段高,极高值在出现在永济南一带。可见,基于河流地貌参数获得的中条山北麓新构造运动强弱与断裂晚第四纪以来的活动强弱一致。  相似文献   

15.
合理的配置公共服务设施对城市的现代化建设至关重要。空间可达性是度量公共服务设施配置是否合理的方法之一。在诸多的研究方法中,高斯两步移动搜索法由于直观且运算简便,因而得到广泛应用。但该方法也有不足之处,本文运用格网GIS方法,以上海市的绿地空间可达性为例,对两步移动搜索法进行模型方法的改进研究,并对高斯两步移动搜索法和格网化的高斯两步移动搜索法进行对比分析,结果表明：后者可降低空间可达性的误差,提高可达性精度,对上海市绿地空间可达性反映更加真实、客观。如果选择合理的数据将其格网化,该方法也可以用于其他公共服务设施的空间可达性研究。  相似文献   

16.
巴江流域演变与路南石林发育耦合分析   总被引：1，自引：0，他引：1  
本文分析了巴江喀斯特流域的水系、地貌结构特征,通过多次野外调研,探讨了石林的形态及其在巴江流域内的空间分布特征。研究表明石林主要发育在二叠系的栖霞组、茅口组灰岩上,岩性和地层的差异对石林的形状有较大影响;石林的分布在地貌部位上并无明显的选择性,在洼地、斜坡及山顶均可发育,但石林的形态和高度在三种地貌部位间有明显的变化规律;以路南群为中心,往北、东方向距路南群越远,石林的高度有逐渐减小的趋势,同时石柱间的距离也越来越大,由簇状石林向分离程度很好的单个石柱变化;天生桥为一地貌裂点,石林的形态和分布特征在其上、下也表现出明显的差异。同时,根据石林发育的“三元剥蚀”机制,结合路南地区的水文、地质、地貌演化史,作者进一步分析了路南石林发育和巴江流域演变之间的内在联系,并把路南石林的发育划分为三个时期,即路南古湖期、石林遍生期和流域回春期。作者认为,石林的出现和大范围分布并非偶然,而是巴江流域演变到一定阶段的产物。  相似文献   

17.
The downstream distribution of stream power is derived and analysed for 11 different streams in the upper Hunter River catchment, Australia. Stream long profiles were produced in a GIS environment using DEM data and catchment area–discharge analysis. These profiles were analysed using three approaches, namely long profile smoothing, curve fitting and a theoretical model. The methodology for deriving stream power profiles using these three approaches is discussed. The long profile smoothing method provides a good approximation of the subcatchment variability in stream power trends. The curve fitting method shows that higher-order exponential curves provide a better fit for long profile data. For the streams of the upper Hunter River catchment, second-order exponential curves fit well with significantly less error. The curve fitting method predicts a bimodal (upstream and midstream) distribution of stream power, which is a deviation from our earlier understanding of a single midstream peak. The theoretical approach provides a mathematical expression of the observed bimodal stream power distribution. The bimodal distribution emphasises the erosion potential of headwater reaches. The resultant stream power distribution provides a catchment-scale characterisation of the distribution of available energy in any given system. Using these approaches, the variability of stream power in headwater reaches is explained by discharge variability, while variability in midstream and downstream reaches is related to high variability in channel gradient.  相似文献   

18.
Knickzones, defined here as locally steep reaches including distinct knickpoints, in bedrock river morphology, have often been investigated in relation to local anomalies in lithology, tectonics, hydraulics, climate and associated base‐level change, and/or deformation of valley‐side slopes. However, exact formative causes of many knickzones in a humid, tectonically active island arc remain unclear. Using databases of geology, streams and knickzones, we examine knickzone distribution across the Japanese Archipelago to evaluate the effects of the stream network structure and rock type boundaries on knickzone formation. Knickzones are frequently found just upstream and downstream of major stream confluences along mainstreams, whereas knickzones are less frequent around major rock type boundaries. While the major confluences do not form hanging valleys due to similar catchment size, this observation suggests that many knickzones have been formed by the long‐term effect of flow turbulence scouring bedrock at the confluences. Such a hydraulic control on bedrock erosion in the steep Japanese mountains under humid climate conditions indicates that the formative cause of many knickzones therein can be autogenic by means of stream hydraulics.  相似文献   

19.
Spores of coprophilous fungi, especially Sporormiella, are often well preserved in lake sediment cores. It has been hypothesized that such spores can be used to quantify past livestock abundance. The quantitative relationship between fungal spore abundance and livestock populations, however, is not well established, nor are the mechanisms of spore transport and deposition in lacustrine systems. Multiple cores from Lake Allos, a large high-elevation lake in the French Alps, were used to map the modern abundance of Sordaria and Sporormiella spores throughout the lake. We observed high spatial heterogeneity with respect to spore numbers. No correlation with the distance from shoreline was found. There was, however, a relation with distance from the two main lake inlets. These results were used to select two fungi-rich sediment cores to investigate grazing pressure over the last two centuries. Comparisons were made between spore influx and historic data on livestock densities in the catchment. A sharp decrease in Sporormiella influx ca. 1894–1895 was associated with a reported reduction in sheep in the Allos catchment at that time. Mean influx of Sporormiella decreased by a factor of three between the nineteenth and twentieth centuries, reflecting a reduction in the reported number of animals in the Lake Allos catchment, from 6,000 to 2,000. This study confirmed that Sporormiella spore abundance in lake sediments can be used as a proxy for catchment herbivore numbers in paleoecological reconstructions. Nevertheless, our data indicate that before spore accumulation can be used to infer past domestic herbivore density, one must understand the processes of coprophilous spore transfer from the catchment to the lake and the influence of core location on spore numbers in the sediment.  相似文献   

20.
Longitudinal profiles of bedrock streams in central Kentucky, and of coastal plain streams in southeast Texas, were analyzed to determine the extent to which they exhibit smoothly concave profiles and to relate profile convexities to environmental controls. None of the Kentucky streams have smoothly concave profiles. Because all observed knickpoints are associated with vertical joints, if they are migrating it either occurs rapidly between vertical joints, or migrating knickpoints become stalled at structural features. These streams have been adjusting to downcutting of the Kentucky River for at least 1.3 Ma, suggesting that the time required to produce a concave profile is long compared to the typical timescale of environmental change. A graded concave longitudinal profile is not a reasonable prediction or benchmark condition for these streams. The characteristic profile forms of the Kentucky River gorge area are contingent on a particular combination of lithology, structure, hydrologic regime, and geomorphic history, and therefore do not represent any general type of equilibrium state. Few stream profiles in SE Texas conform to the ideal of the smoothly, strongly concave profile. Major convexities are caused by inherited topography, geologic controls, recent and contemporary geomorphic processes, and anthropic effects. Both the legacy of Quaternary environmental change and ongoing changes make it unlikely that consistent boundary conditions will exist for long. Further, the few exceptions within the study area–i.e., strongly and smoothly concave longitudinal profiles–suggest that ample time has occurred for strongly concave profiles to develop and that such profiles do not necessarily represent any mutual adjustments between slope, transport capacity, and sediment supply. The simplest explanation of any tendency toward concavity is related to basic constraints on channel steepness associated with geomechanical stability and minimum slopes necessary to convey flow. This constrained gradient concept (CGC) can explain the general tendency toward concavity in channels of sufficient size, with minimal lithological constraints and with sufficient time for adjustment. Unlike grade- or equilibrium-based theories, the CGC results in interpretations of convex or low-concavity profiles or reaches in terms of local environmental constraints and geomorphic histories rather than as “disequilibrium” features.  相似文献   

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