Human impacts on headwater fluvial systems in the northern and central Andes

South America delivers more freshwater runoff to the ocean per km² land area than any other continent, and much of that water enters the fluvial system from headwaters in the Andes Mountains. This paper reviews ways in which human occupation of high mountain landscapes in the Andes have affected the delivery of water and sediment to headwater river channels at local to regional scales for millennia, and provides special focus on the vulnerability of páramo soils to human impact. People have intentionally altered the fluvial system by damming rivers at a few strategic locations, and more widely by withdrawing surface water, primarily for irrigation. Unintended changes brought about by human activities are even more widespread and include forest clearance, agriculture, grazing, road construction, and urbanization, which increase rates of rainfall runoff and accelerate processes of water erosion. Some excavations deliver more sediment to river channels by destabilizing slopes and triggering processes of mass-movement.The northern and central Andes are more affected by human activity than most high mountain regions. The wetter northern Andes are also unusual for the very high water retention characteristics of páramo (high elevation grass and shrub) soils, which cover most of the land above 3000 m. Páramo soils are important regulators of headwater hydrology, but human activities that promote vegetation loss and drying cause them to lose water storage capacity. New data from a case study in southern Ecuador show very low bulk densities (median 0.26 g cm^− 3), high organic matter contents (median 43%), and high water-holding capacities (12% to 86% volumetrically). These data document wetter soils under grass than under tree cover. Effects of human activity on the fluvial system are evident at local scales, but difficult to discern at broader scales in the regional context of geomorphic adjustment to tectonic and volcanic processes.     

Influence of rock strength on the valley morphometry of Big Creek, central Idaho, USA

Analysis of valley morphometry and bedrock strength along Big Creek, central Idaho, shows that valley floor width is strongly controlled by bedrock. We performed statistical analysis of Schmidt hammer rock strength as a function of lithology and aspect and of valley morphometry as a function of rock strength. Rock strength is significantly greater on the south side of the valley and in Eocene granodiorites. Rock strength is weakest in Eocene volcanic tuffs. Valley floor width depends negatively on weakest valley-side rock strength, and hillslope gradient on the north side of the valley depends positively on rock strength. Stream gradient does not depend on rock strength. Valley floor width appears to be controlled by bedrock strength on the weaker side of the valley, which was generally the north (south-facing) side. We speculate that a higher degree of weathering via freeze–thaw cycles contributes to lower strength on the north side. The positive dependence of hillslope gradient on rock strength on the north side provides evidence that differential weathering across lithologies determines the gradient that can be maintained as lateral migration of the stream erodes valley walls. These results suggest that in situ rock strength exerts strong influences on some measures of valley morphometry by modulating hillslope mass wasting processes and limiting lateral erosion.     

The fluvial cycle at cold–warm–cold transitions in lowland regions: A refinement of theory

A previously established non-linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm (temperate) to cold (periglacial) and from relatively cold to warm periods. Such instability typically starts with vertical erosion, successively followed by sedimentary fill of the erosive scar. In spite of frequent confirmation of this theory by geomorphological reconstructions, a few problems arise. First, there are fewer incision phases than climatic transitions. Secondly, remnants of erosion at ‘cold–warm’ transitions are scarce, in contrast to obvious erosion relics at ‘warm–cold’ transitions. Furthermore, it appears that the incision style is strikingly different at both kinds of climatic transitions. Similarly, the long stable phases are also expressed in terms of different floodplain development in cold and warm periods. These arguments require a modification of the general non-linear theory.At the transition from relatively temperate to colder conditions, rivers transformed gradually from a regular, low-energy, single-channel course to a periodically high-energy, multi-channel type. The latter (braided) type is characterized by intense lateral movement, rather than by deep vertical erosion. This results in a well-expressed morphology of wide, extensive floodplains and terraces. In contrast, the linear and constrained, meandering channels incise with small width–depth ratio and build floodplains of limited lateral extent. Consequences are twofold: 1) the spatial limitation of the deeply incised, meandering valleys at the beginning of warm periods counts against their recognition; 2) relatively strong, lateral migration of the braided rivers removes most traces of previous (meandering) systems, which contrasts with the limited lateral activity of confined meandering channels. It means that in a ‘warm–cold–warm’ alternation generally only one phase of vertical erosion is preserved, the one that is caused by the high-energy, braided river at the start of the cold period.     

Environmental changes in the central Po Plain (northern Italy) due to fluvial modifications and anthropogenic activities

The fluvial environment of the central Po Plain, the largest plain in Italy, is discussed in this paper. Bounded by the mountain chains of the Alps and the Apennines, this plain is a link between the Mediterranean environment and the cultural and continental influences of both western and eastern Europe. In the past decades, economic development has been responsible for many changes in the fluvial environment of the area.This paper discusses the changes in fluvial dynamics that started from Late Pleistocene and Early Holocene due to distinct climatic changes. The discussion is based on geomorphological, pedological, and archaeological evidences and radiocarbon dating.In the northern foothills, Late Pleistocene palaeochannels indicate several cases of underfit streams among the northern tributaries of the River Po. On the other hand, on the southern side of the Po Plain, no geomorphological evidence of similar discharge reduction has been found. Here, stratigraphic sections, together with archaeological remains buried under the fluvial deposits, show a reduction in the size of fluvial sediments after the 10th millennium BC. During the Holocene, fluvial sedimentation became finer, and was characterised by minor fluctuations in the rate of deposition, probably related to short and less intense climatic fluctuations.Given the high rate of population growth and the development of human activities since the Neolithic Age, human influence on fluvial dynamics, especially since the Roman Age, prevailed over other factors (i.e., climate, tectonics, vegetation, etc.). During the Holocene, the most important changes in the Po Plain were not modifications in water discharge but in sediment. From the 1st to 3rd Century AD, land grants to war veterans caused almost complete deforestation, generalised soil erosion, and maximum progradation of the River Po delta. At present, land abandonment in the mountainous region has led to reafforestation. Artificial channel control in the mountain sector of the basins and in-channel gravel extraction (now illegal but very intense in the 1960s and 1970s) are causing erosion along the rivers and along large sectors of the Adriatic coast. These changes are comparable with those occurring in basins of other Mediterranean rivers.     

Historic fluvial development of the Alpine-foreland Tagliamento River, Italy, and consequences for floodplain management

The fluvial geomorphological development of the Tagliamento River and its flooding history is analysed using historical documents and maps, remote-sensed data and hydrological information. The river has been building a complex alluvial fan starting from the middle part of its alluvial course in the Venetia–Friuli alluvial plain. The riverbed is aggrading over its entire braided length. The transition from braiding to meandering near Madrisio has shifted downstream where the river width determined by the dikes becomes narrower, causing major problems. The flood hazard concentrates at those places and zones where flooding occurred during historical times. Prior to the agrarian and industrial revolution, land use was adjusted to the flooding regime of the river. Subsequent land-use pressure led to a confinement of the river by dikes to such an extent that the flood risk in the floodplain downstream of Madrisio has increased consistently, and represents nowadays a major territorial planning issue. The planned retention basins upstream of the middle Tagliamento will alleviate the problem, but not solve it in the medium and long term. Therefore, fluvial corridors in the lower-middle parts (from Pinzano to the sea) have been identified on the basis of the flooding history in relation to fluvial development during historical times. The result should be used for hydraulic simulation studies and land-use planning.     

The fluvial system — Research perspectives of its past and present dynamics and controls

During the conference “The fluvial system — past and present dynamics and controls" held at the Department of Geography of Bonn University from 16 to 22 of May 2005 the participants organised in 12 international organisations working in the fluvial environment were asked about their opinions about the main aspects to be considered for sustainable progress in future research projects. The individual comments can be grouped by the following headlines: integration and application of experiences, considering system analytical approaches, considering effects of climate and global change, interdisciplinary work, regarding extreme events and their frequencies and quantification of human impact. Detailed explanations and selected references of previous studies initially considering the mentioned aspects are given as a review.     

The human role in changing fluvial systems: Retrospect, inventory and prospect

Historical and modern scientific contexts are provided for the 2006 Binghamton Geomorphology Symposium on the Human Role in Changing Fluvial Systems. The 2006 symposium provides a synthesis of research concerned with human impacts on fluvial systems — including hydrologic and geomorphic changes to watersheds — while also commemorating the 50th anniversary of the 1955 Man's Role in Changing the Face of the Earth Symposium [Thomas, Jr., W. L. (Ed.), 1956a. Man's Role in Changing the Face of the Earth. Univ. Chicago Press, Chicago. 1193 pp]. This paper examines the 1955 symposium from the perspective of human impacts on rivers, reviews current inquiry on anthropogenic interactions in fluvial systems, and anticipates future directions in this field.Although the 1955 symposium did not have an explicit geomorphic focus, it set the stage for many subsequent anthropogeomorphic studies. The 1955 conference provided guidance to geomorphologists by recommending and practicing interdisciplinary scholarship, through the use of diverse methodologies applied at extensive temporal and geographical scales, and through its insistence on an integrated understanding of human interactions with nature. Since 1956, research on human impacts to fluvial systems has been influenced by fundamental changes in why the research is done, what is studied, how river studies are conducted, and who does the research. Rationales for river research are now driven to a greater degree by institutional needs, environmental regulations, and aquatic restoration. New techniques include a host of dating, spatial imaging, and ground measurement methods that can be coupled with analytical functions and digital models. These new methods have led to a greater understanding of channel change, variations across multiple temporal and spatial scales, and integrated watershed perspectives; all changes that are reflected by the papers in this volume. These new methods also bring a set of technical demands for the training of geomorphologists. The 2006 Binghamton Geomorphology Symposium complements the 1956 symposium by providing a more specific and updated view of river systems coupled with human interactions. The symposium focuses on linkages between human land use, structures, and channel modification with geomorphology, hydrology, and ecology. The emergence of sustainability as a central policy guideline in environmental management should generate greater interest in geomorphic perspectives, especially as they pertain to human activities. The lack of theories of anthropogeomorphic change, however, presents a challenge for the next generation of geomorphologists in this rapidly growing subfield.     

塔克拉玛干沙漠河湖相沉积平原风蚀地貌发育的外营力作用机制

 河湖相沉积是一种非固结沉积物,是风蚀地貌发育的一种重要地质基础。在塔克拉玛干沙漠中发育在这种沉积物上的风蚀地貌分布非常普遍,但相关研究较少,尚缺乏风蚀地貌发育过程方面的研究。基于野外调查信息和理论分析,结合相关文献,分析了塔克拉玛干沙漠河湖相平原风蚀地貌发育的外营力作用机制。研究结果表明：（1）风蚀地貌发育的外营力作用主要有：风化作用、流水作用、风蚀作用以及重力作用;（2）风蚀作用是风蚀地貌发育的主要外营力,但是风化作用、流水作用和重力作用也发挥着重要的作用,它们的关键作用是形成风蚀突破口,而重力作用和风化作用是促进风蚀地貌后期快速发展的重要作用;（3）各种外营力协同作用和互为条件,它们在风蚀地貌发育的各阶段的重要性不同;（4）沉积层特殊沉积构造和外营力作用共同造成了风蚀地貌形态特征。     

Fish persistence and fluvial geomorphology in central Australia

The purposes of this paper are to document the composition and distribution of fishes in the Alice Springs region of Australia, and discuss constraints on fish persistence in this arid region. Nine native and six exotic species were recorded; most exotics no longer exist. Except in Finke River, only one or no native species were found. Fish survival in the area is ameliorated by the exceptionally broad environmental tolerances and migratory abilities of many species, but ultimately depends upon the effects of geology, geomorphology, and the vagaries in pattern of sediment transport on water persistence.     

Human-induced changes in animal populations and distributions, and the subsequent effects on fluvial systems

Humans have profoundly altered hydrological pathways and fluvial systems through their near-extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment, and through the introduction of now-feral populations of animals that bring to bear a suite of different geomorphic effects on the fluvial system. In the category of effects of extirpation, examples are offered through an examination of the geomorphic effects and former spatial extent of beavers, bison, prairie dogs, and grizzly bears. Beavers entrapped hundreds of billions of cubic meters of sediment in North American stream systems prior to European contact. Individual bison wallows, that numbered in the range of 100 million wallows, each displaced up to 23 m³ of sediment. Burrowing by prairie dogs displaced more than 5000 kg and possibly up to 67,500 kg of sediment per hectare. In the category of feral populations, the roles of feral rabbits, burros and horses, and pigs are highlighted. Much work remains to adequately quantify the geomorphic effects animals have on fluvial systems, but the influence is undeniable.     

汉江上游谷地与渭河谷地黄土化学风化程度比较

比较汉江上游谷地及渭河谷地典型黄土剖面的元素组成、化学风化强度及常量元素迁移特征,揭示秦岭南北两侧黄土-古土壤剖面的成壤强度及其所指示的环境演变特征,两者差异及共性如下：① 两剖面化学组成均以SiO₂、Al₂O₃和Fe₂O₃为主,元素组成均一且高度混合,与上部陆地壳（UCC） 的化学成分十分接近,该些证据均指示两区域黄土是来源广泛并经过充分混合的风尘堆积产物。② 据CIA 值可判定MTS 及YHC 剖面均经历了中等风化作用,比较两剖面CIW值、A-CN-K三角图投点特征及元素迁移率知,汉江上游谷地的黄土-古土壤序列经历的化学风化作用更强,Ca 及Na 元素的丢失率更高,Al、Na、Mg、Si 等常量元素的迁出率更大。③ 依据Fe、Na迁移率的全剖面变化曲线知,汉江上游谷地与渭河谷地自全新世以来经历了相同的气候演变阶段,均记录了6000-5000a BP的干冷气候事件。     

Relief-rejuvenation and topographic length scales in a fluvial drainage basin, Napf area, Central Switzerland

This paper explores how, and to what extent, a phase of relief-rejuvenation modifies the mode of surface erosion in an approximately 63 km² drainage basin located at the northern border of the Swiss Alps (Luzern area). In the study area, the retreat of the Alpine glaciers at the end of the Last Glacial Maximum (LGM) caused base level to lower by approximately 80 m. The fluvial system adapted to the lowered base level by headward erosion. This is indicated by knickzones in the longitudinal stream profiles and by the continuous upstream narrowing of the width of the valley floor towards these knickzones. In the headwaters above these knickzones, processes are still to a significant extent controlled by the higher base level of the LGM. There, frequent exposure of bedrock in channels and especially on hillslopes implies that sediment flux is to a large extent limited by weathering rates. In the knickzones, however, exposure of bedrock in channels implies that sediment flux is supply-limited, and that erosion rates are controlled by stream power.The morphometric analysis reveals the existence of length scales in the topography that result from distinct geomorphic processes. Along the tributaries where the upstream sizes of the drainage basins exceed 100,000–200,000 m², the mode of sediment transport and erosion changes from predominantly hillslope processes (i.e., landsliding, creep of regolith, rock avalanches and to some extent debris flows) to processes in channels (fluvial processes and debris flows). This length scale reflects the minimum size of the contributing area for channelized processes to take over in the geomorphic development (i.e., threshold size of drainage basin). This threshold size depends on the ratio between production rates of sediment on hillslopes, and export rates of sediment by processes in channels. Consequently, in the headwaters, erosion rates and sediment flux, and hence landscape evolution rates, are to a large extent limited by weathering processes. In contrast, in the lower portion of the drainage basin that adjusts to the lowered base-level, rates of channelized erosion and relief formation are controlled mainly by stream power. Hence, this paper shows that base-level lowering, headward erosion and establishment of knickzones separate drainage basins in two segments with different controls on rates of surface erosion, sediment flux and relief formation.     

Allometric development of glacial cirque form: Geological, relief and regional effects on the cirques of Wales

Headward and downward erosion near glacier sources, at rates exceeding fluvial erosion, is important in recent discussions of orogen development and the limits to relief. This relates to a long history of debate on how the form of glacial cirques develops, which can be advanced by relating shape to size in large data sets. For 260 cirques in Wales, this confirms different rates of enlargement in the three dimensions: faster in length than in width, and slower in vertical dimension whether expressed as overall height range, axial height range or wall height. Maximum gradient, plan closure and number of cols increase with overall size. This allometric development applies over different cirque types, regions and rock types. Headwall retreat, often by collapse following glacial erosion at the base, is faster than downward erosion. Welsh cirques form a scale-specific population and, as in other regions, size variables follow Gaussian distributions on a logarithmic scale. As in England, width commonly exceeds length. Vertical dimensions correlate with length more than with width. Cirque form varies with geology, but also with relief as both vary between mountain groups. The main contrast is between larger, better-developed cirques and higher relief on volcanic rocks in the north-west, and smaller, less-developed cirques and lower relief on sedimentary rocks in the south.     

Simulating the development of Martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing

On the highlands of Mars early in the history of the planet precipitation-driven fluvial erosion competed with ongoing impact cratering. This disruption, and the multiple enclosed basins produced by impacts, is partially responsible for a long debate concerning the processes and effectiveness of fluvial erosion. The role of fluvial erosion in sculpting the early Martian landscape is explored here using a simulation model that incorporates formation of impact craters, erosion by fluvial and slope processes, deposition in basins, and flow routing through depressions. Under assumed arid hydrologic conditions, enclosed basins created by cratering do not overflow, drainage networks are short, and fluvial bajadas infill crater basins with sediment supplied from erosion of interior crater slopes and, occasionally from adjacent steep slopes. Even under arid conditions adjacent crater basins can become integrated into larger basins through lateral erosion of crater rims or by rim burial by sediment infilling. Fluvial erosion on early Mars was sufficient to infill craters of 10 km or more in diameter with 500–1500 m of sediment. When the amount of runoff relative to evaporation is assumed to be larger, enclosed basins overflow and deeply incised valleys interconnect basins. Examples of such overflow and interconnection on the Martian highlands suggest an active hydrological cycle on early Mars, at least episodically. When fluvial erosion and cratering occur together, the drainage network is often disrupted and fragmented, but it reintegrates quickly from smaller impacts. Even when rates of impact are high, a subtle fluvial signature is retained on the landscape as broad, smooth intercrater plains that feature craters with variable amounts of infilling and rim erosion, including nearly buried “ghost” craters. The widespread occurrence of such intercrater plains on Mars suggests a strong fluvial imprint on the landscape despite the absence of deep, integrated valley networks. Indisputable deltas and alluvial fans are rare in the crater basins on Mars, in part because of subsequent destruction of surficial fluvial features by impact gardening and eolian processes. Simulations, however, suggest that temporally-varying lake levels and a high percentage of suspended to bedload supplied to the basins could also result in poor definition of fan–delta complexes.     

Effects of Stronach Dam removal on fluvial geomorphology in the Pine River, Michigan, United States

Although dam removal has been increasingly used as an option in dam management, and as a river restoration tool, few studies provide detailed quantitative assessment of the geomorphological response of rivers to dam removal. In this study, we document the response of the Pine River, Michigan, to the gradual removal of Stronach Dam. In 1996, prior to the initiation of removal, 31 permanent cross-sectional transects were established in the 10-km study area. These transects were surveyed annually during the course of the removal (1996–2003) and for the three years following removal (2004–2006). Dam removal resulted in progressive headcutting of sediments in the former impoundment, extending upstream 3.89 km of the dam. Over the course of the 10 years since dam removal was initiated, a net total of 92 000 m³ of sediment erosion occurred. The majority of sediments stored in the former reservoir remained in place, with only 12% of the estimated reservoir sediment fill being eroded. Approximately 14% of the net erosion was deposited within the stream channel 1 km downstream of the dam location, with the remainder being transported further downstream or deposited in the floodplain. Sediment fill incision resulted in a narrower and deeper channel upstream, with higher mean water velocity and somewhat coarser substrates. Downstream deposition resulted in a wider and shallower channel, with little change in substrate size composition. Counter-intuitively, water velocity also increased downstream because of the increased slope that developed. Prior to removal, bedforms in the former impoundment were dominated by runs but are showing signs of restoration toward reference conditions. Continuing changes in river geomorphology are evident even three years following removal and are likely to occur for years to come.     

Role of fluvial and structural processes in the formation of the Wahiba Sands, Oman: A remote sensing perspective

The Wahiba Sands in northeastern Oman are bordered on the north, south and west by highlands. Remote sensing data are used to characterize the region between 19–23.5°N and 56.5–60°E by mapping surface and near-surface drainage, faults and fractures and aeolian features. It is suggested that the sands were originally deposited with surface runoff from the principal wadis and fluvially reworked fault zones, which define the northeastern and southwestern margins. These fluvial processes resulted in the accumulation of the vast groundwater resources now stored there. During dry climates, wind became the principal modification regime and it began to sort and shape the sediments into the dune forms that characterize today's Wahiba region. The thickness of the sands reflects the depth of the basin in which they lie. The center of the basin is filled with the thickest sand (the High Sands) and contains the highest groundwater concentrations. Presently, aeolian reworking dominates in the Wahiba region, although the Low and the Peripheral Sands continue to experience some fluvial action from occasional, seasonal rainfall. Even though dry conditions dominate today, it is clear that similar to the Sahara of North Africa, the surface sands of the Wahiba basin are indicators of groundwater occurrence.     

Surficial patterns of debris flow deposition on alluvial fans in Death Valley, CA using airborne laser swath mapping data

Debris flows are a common event in mountainous environments. They often possess the greatest potential for destruction of property and loss of lives in these regions. Delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones. Current research indicates debris flow fans have two distinct depositional zones. However, the two zones were derived from studies containing detailed analyses of only a few fans. High resolution airborne laser swath mapping (ALSM) data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of Death Valley. The relationship between these parameters is assessed to 1) identify if debris flow fans are accurately represented by two depositional zones, and 2) to assess how these terrain parameters relate to one another at the individual fan scale. The results show at least three zones of deposition exist within the sampled fans. These zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients. Fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature. Steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature. The surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features.     

Discrimination of fluvial, eolian and neotectonic features in a low hilly landscape: A DEM-based morphotectonic analysis in the Central Pannonian Basin, Hungary

The Gödöllő Hills, a low-relief terrain within the Central Pannonian Basin in Hungary, is characterised by moderate tectonic deformation rates. Although typical tectonic landforms are not clearly recognisable in the study area, this paper succeeded in discriminating between tectonically controlled landforms and features shaped by fluvial erosion or deflation with no tectonic control.DEM-based morphometric parameters including elevation, slope and surface roughness, enabled the delineation of two NW–SE trending spearhead-shaped ridges separated by a wide rectilinear valley of the same strike. Although directional statistics suggested possible tectonic control of NW–SE striking landforms, precise morphometry completed with an analysis of subsurface structures rejected their tectonic preformation. Deflation plays a significant role in shaping the area, and the presence of two large-scale yardangs separated by a wind channel is proposed. In temperate-continental areas of Europe, no deflational landforms of such scale have been described so far, suggesting that Pleistocene wind power in periglacial areas was more significant than it was previously thought.Characteristic drainage patterns and longitudinal valley profiles enabled the recognition of areas probably affected by neotectonic deformation. A good agreement was observed between locations of Quaternary warping predicted by the morphometric study and subsurface structures revealed by the tectonic analysis. Zones of surface uplift and subsidence corresponded to anticlinal and synclinal hinges of fault-related folds. In low-relief and slowly-deforming areas, where exogenous forces may override tectonic deformation, only the integrated application of morphometric and subsurface-structural indications could assure correct interpretation of the origin of various landforms, while a morphometric study alone could have led to misinterpretation of some morphometric indices apparently suggesting tectonic preformation. On the other hand, the described morphological expression of subsurface structures could verify Quaternary age of the deformation.     

Paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in Huangshui Valley, the northeastern Tibetan Plateau, China

Gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system. In this study, flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the Xining Region, northeastern Tibetan Plateau, China. These gravel deposits range in age from the modern Huangshui riverbed to Miocene-aged deposits overlain by eolian sediments. Our major objectives were not only to collect first-hand field data on the fluvial gravel sediments of the Xining Region, but also to the reconstruct the evolution of the fluvial system. These data may offer valuable information about uplift of the northeastern Tibetan Plateau during the late Cenozoic era. Reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130–180°. In addition, the lithological compositions in the higher gravel deposits differ significantly from the lower terraces, suggesting that the source areas changed at the same time. Eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1.55 Ma and 1.2 Ma. We suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period. Therefore, this study provides a new scenario of fluvial response to tectonic uplift: a reversal of flow direction. In addition, field observation and statistical analyses reveal a strong relationship between rock type, size and roundness of clasts.