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Dissolved organic carbon (DOC) fluxes between environmental compartments are an important component of the global carbon balance and pedoecological processes. Tropical forests are the world’s most productive ecosystems and the forest floor is the main DOC-source in these environments. This study aimed to compare DOC concentrations under the forest floor with different litter-decomposition rates. Four study plots were established along a hillslope profile where heterogeneity was observed in previous studies: drainage divide (DRD); upper-hillslope (UHS); lower-hillslope (LHS); and valley bottom (VLB). Inversely proportional to the decomposition rates, the litter storage in this profile was as follows: DRD > UHS ≅ LHS > VLB. The bulk precipitation was a DOC source statistically similar to canopy-washing, and DOC concentrations in throughfall were statistically similar among the hillslope positions. There was some dilution effect in the inter-event modulation, mainly in throughfall and associated with the rainfall maximum intensity. The DOC concentrations under the forest floor were related in a non-linear manner with the litter storage: thin stocks in VLB showed lower DOC concentrations, but the thicker stocks in DRD did not materialise in the highest concentrations; the litter storage in UHS and LHS showed higher DOC-concentrations as a result of a balance between maintaining the DOC-source and making new soluble byproducts available that favoured the DOC-release to water.

The Nepalese Himalaya is well known for ongoing collisional tectonics, witnessed by major historical and recent earthquakes. The Siwalik Hills in Midwestern Nepalese Himalaya are bounded by eastwest trending Main Frontal Thrust (MFT) to the south and the Main Boundary Thrust (MBT) to the north. The area is dissected by numerous southwest to south-flowing bedrock rivers. This study investigates geomorphic metrics of these rivers to unravel landscape evolution and active tectonics of the Siwalik Hills. Digital Elevation Model (DEM) analysis was conducted to extract structural lineaments and longitudinal river profile and their metrics (knickpoints, Normalized Steepness Index (ksn), concavity index, and chi integral) using steam power-law approaches. Most of the lineaments trend eastwest like MFT. River profiles exhibit convex to double-concave shapes with upstream-propagating tectonic knickpoints that separate upstream and downstream reaches, indicating different phases of river incision. The spatial distribution of ksn shows high values along with low concavity values at the eastern part of the study area, reflecting disequilibrium conditions that are likely responding to a high uplift rate. Chi integral distribution shows a variation in drainage divide migration between the eastern and western parts of the study area. This study suggests that the rivers in the Siwalik Hills are undergoing active incision likely related to the ongoing uplift and active deformation associated with the Himalayan tectonics. The above findings can bring fresh perspectives to comprehend the neotectonic deformation and lateral variability along the Siwalik Hills landscapes within the Himalaya.

River incision and drainage reorganization have an important impact on the site selection of many major projects including city, road and others, and are the key issues of Quaternary environmental changes. Studies of river incision and river-network adjustment have traditionally been based on extensive field evidence, such as sediment age and beheaded river system. The Buyuan River basin is a large sub-basin of the upper Lancang-Mekong, with high mountains and extremely active erosion. The latter affects the preservation of the Quaternary period sediments leading to difficulties in understanding the main evolution characteristics of the basin. This study investigates differences in the equilibrium state of the longitudinal profile, infers incision rates, and evaluates drainage divide migration timelines using the stream-power incision model, the latest morphological dating, and Chi-plots (χ-z) based on digital elevation models (DEMs) on the GIS software platform. The final results show that two significant erosion base-level decreases occurred in the Late Pleistocene at least. The incision rate of the mainstream might have been 0–2.99 mm/yr since 100 ka BP and 0–3.28 mm/yr since 46 ka BP. The Chi-values across the divides suggest that space limited (or constrained) river reorganization and that there is no severe reorganization in the basin; the imbalance of traceable erosion only exists in local areas. The main driving force for the geomorphologic evolution of the Buyuan River basin is likely climate fluctuations rather than strong tectonic uplift since the Late Pleistocene.

Detailed topographic maps provide much of the information needed to understand how drainage divides like the southeast Wyoming Medicine Bow River-Laramie River drainage divide originated. Topographic map evidence for each Medicine Bow-Laramie River drainage divide segment is here described and analyzed first using a commonly published interpretation (accepted paradigm) in which drainage routes developed on a surface of now mostly absent Oligocene and Miocene sediments that previous investigators have hypothesized to have once filled the Laramie Basin and to have also buried (or partially buried) the surrounding Laramie and Medicine Bow Mountains. Second, the same map evidence is analyzed using a recently proposed interpretation (new paradigm) in which massive and prolonged floods flowed across Wyoming as the Laramie and Medicine Bow Mountains began to be uplifted and as the southeast-oriented North Platte River valley eroded headward along the rising Laramie Mountains northeast flank. Low points along the drainage divide (referred to as divide crossings) are interpreted to be places where water once flowed across the drainage divide with the drainage divide being formed when capture events diverted the water in other directions. Valleys leading away from divide crossings are used to determine the nature of observed capture events, many of which are difficult or impossible to explain from the accepted paradigm perspective, but which are consistent with the mountain uplift, headward erosion of deeper valleys, and/or draining of floodwaters trapped in the Laramie Basin as the new paradigm predicts. However, the new paradigm requires a North American continental ice sheet heavy enough to raise entire regions and mountain ranges as massive and prolonged meltwater floods flowed across them, something the accepted paradigm does not recognize.

Drainage divides along a southern Laramie Range crest area and in the nearby southeast Wyoming Gangplank area (as observed on detailed topographic maps) suggest present-day drainage routes in the Cheyenne Tablelands region originated as headward erosion of south-oriented valleys (now the downstream Lodgepole, Crow, and Lone Tree Creek valleys) from an actively eroding northeast-oriented South Platte River valley captured flood flow in the south half of a large east-oriented anastomosing channel complex while headward erosion of a north-oriented valley (now the downstream Horse Creek valley) from the southeast-oriented North Platte River valley captured the north half of the same large anastomosing channel complex. The Gangplank, which today serves as a low gradient ramp of Tertiary Ogallala Formation sediments leading from the Great Plains to the Laramie Range erosion surface, is located along the Crow Creek-Lone Tree Creek drainage divide and low points along that divide (referred to here as divide crossings) suggest, prior to headward erosion of what is now its south-oriented downstream Lone Tree Creek valley, upstream east-oriented Lone Tree Creek drainage routes were intertwined with east-oriented Crow Creek drainage routes, which today flow much further in an east direction (than east-oriented upstream Lone Tree Creek drainage routes) before also turning in a south direction to reach the South Platte River. The ability of the commonly accepted regional geomorphology paradigm to explain this topographic map evidence is then compared with a fundamentally different and new regional geomorphology paradigm’s ability to explain the same evidence. While both paradigms offer possible explanations the new paradigm, which requires headward erosion of the valleys to have occurred as massive continental ice sheet melt water floods crossed the region, explains much more of the drainage system evidence and also permits much more detailed explanations.

To assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system. A multi-proxy approach helps ensure rigour in how provenance data are interpreted. U–Pb geochronology of refractory zircon and relatively less stable apatite, and Pb isotopic analysis of labile K-feldspar are employed in this study to reassess the provenance of Triassic sandstones in the Slyne Basin, offshore western Ireland. This approach aims at reducing the potential bias in each method, producing a complementary dataset. U–Pb zircon and apatite geochronology yields Archean–Paleoproterozoic ages, Caledonian ages and previously unrecognized Permo-Triassic ages. Pb isotopic analysis of K-feldspar does not identify the Permo-Triassic as a source. The detection of Permo-Triassic-aged detritus may suggest that volcanism was more widespread than previously recognized. These results support the hypothesis of a Triassic drainage divide between the basins offshore western Ireland and those onshore Britain and in the Irish Sea. Sand supply was dominantly from the north, with significant input from the flanks of the basin, and previously unrecorded sources, such as Permian-aged rocks, playing an important role. The provenance signal is consistent and homogenized throughout the sampled sequence indicating that the drainage system was long-lived. Supplementary material: Details of laboratory and sample preparation, data tables and summary pie charts for each sample are available at https://doi.org/10.6084/m9.figshare.c.4571096

Detailed topographic map evidence is used to test the ability of two fundamentally different regional geomorphology paradigms to explain Bighorn-Wind River drainage divide evidence in the Copper and Lysite Mountain areas between Wind River Canyon and the Bighorn Mountains. Identified divide crossings were interpreted to be places where water had once flowed across what is now a major drainage divide. More than 20 such divide crossings were identified and ranged in elevation from 1924 to 2485 meters and could all be linked to north-oriented Bighorn River tributaries and also to south-oriented streams flowing to west-oriented Badwater Creek (a Wind River tributary). Lowest elevation divide crossings were located to the north of both Copper Mountain and Lysite Mountain. An attempt was first made to explain each identified divide crossing or group of divide crossings from the accepted paradigm's perspective, which requires drainage routes to have originated on the surface of a hypothesized Oligocene and Miocene sediment cover that buried the drainage divide area with the drainage routes eroding down through the sediment cover as the drainage divide was exhumed. Next the same evidence was interpreted from a recently proposed paradigm's perspective, which requires massive south- and southeast-oriented floods to have flowed across the Missouri River drainage basin as mountain ranges and plateau areas were being uplifted. The accepted paradigm could not easily explain the large number of observed divide crossings, many divide crossing details, and why geologic maps show few or no hypothesized sediment cover remnants. The new paradigm explained the large number of observed divide crossing and most observed divide crossing details and did not require an Oligocene and Miocene sedimentary cover.

Topographic map evidence from the Wyoming Wind River-Sweetwater River drainage divide area is used to test a recently proposed regional geomorphology paradigm defined by massive south- and southeast-oriented continental ice sheet melt water floods that flowed across the entire Missouri River drainage basin. The new paradigm forces recognition of an ice sheet created and occupied deep “hole” and is fundamentally different from the commonly accepted paradigm in which a pre-glacial north- and northeast-oriented slope would have prevented continental ice sheet melt water from reaching or crossing the Wind River-Sweetwater River drainage divide. Divide crossings (or low points) are identified as places where water once flowed across the drainage divide. Map evidence is interpreted first from the accepted paradigm perspective and second from the new paradigm perspective to determine the simplest explanation. Both paradigm perspectives suggest south-oriented water crossed the drainage divide, although accepted paradigm interpretations do not satisfactorily explain the large number of observed divide crossings and are complicated by the need to bury the Owl Creek and Bridger Mountains to explain why the Wind River now flows in a north direction through Wind River Canyon. New paradigm interpretations explain the large number of divide crossings as diverging and converging channel evidence (as in flood-formed anastomosing channel complexes), Owl Creek and Bridger Mountain uplift to have occurred as south-oriented floodwaters carved Wind River Canyon, and a major flood flow reversal (caused by ice sheet related crustal warping and the opening up of deep “hole” space by ice sheet melting) as being responsible for the Wind River abrupt turn to the north. While this test only addresses topographic map evidence, Occam’s Razor suggests the new paradigm offers what in science should be the preferred Wind River-Sweetwater River drainage divide origin interpretations.

A new and fundamentally different regional geomorphology paradigm in which massive south- and southeast-oriented meltwater floods flowed across the entire Missouri River drainage basin is tested by interpreting detailed topographic maps of the Montana upper Sun River drainage basin region by trying to explain origins of previously unexplained or poorly explained erosional landforms located upstream from Sun River Canyon (which cuts across Montana’s north-to-south oriented Sawtooth Range). Mountain passes, through valleys, and other drainage divide low points along what are today high mountain ridges, including the North American east-west continental divide, are interpreted to be evidence of drainage routes that once crossed the region. These drainage divide crossings suggest that prior to erosion of present-day upper Sun River drainage basin valleys, massive floods moved in south directions across what are today the north-oriented Middle and South Fork Flathead River drainage basins into today’s upper Sun River drainage basin area and carved a complex of diverging and converging channels into what was probably a low relief surface now represented by the crests of the region’s highest mountain ridges. Further, the map evidence shows how a diverging complex of south- and southeast-oriented upstream Sun River drainage basin flood flow channels changed flow direction to cross the Sawtooth Range in a northeast direction before converging on the Montana plains at a location downstream from Sun River Canyon. The observed upper Sun River drainage basin area topographic map evidence is consistent with the new geomorphology paradigm predictions, in which massive south-oriented meltwater floods flowing across the rising rim of a continental ice sheet created deep “hole” (created by deep ice sheet erosion and ice sheet weight caused crustal warping) are diverted to flow in northeast and north directions into and across deep “hole” space being opened up by ice sheet melting.

The Dinarides fold and thrust belt on the Balkan Peninsula is the result of the long-lasting convergence between the Adriatic and Eurasian plates since the Mid-Jurassic. Late Jurassic obduction of ophiolites, Early Cretaceous composite nappe stacking, and subsequent continent-continent collision in the latest Cretaceous resulted in folding and thrusting that in the most external part of the Dinarides took place during the Middle Eocene – Oligocene. This extensive last phase of substantial crustal shortening and thickening was associated with flexural foreland basin deposition, resulting in Eo- to early Oligocene syntectonic units. These rocks and older Mesozoic carbonate platform units now form the mountain chain of the external Dinarides. So far, the driving mechanism behind the rock uplift was unknown and it was not clear when the present-day topography formed. Here we show that horizontal marine terraces preserved at elevations of up to 600 m in the external Dinarides are crucial to answer these questions.We extracted horizontal surfaces, river incision profiles, and the Adriatic and Black Sea catchments from a digital elevation model (DEM). The extracted horizontal surfaces are interpreted as marine terraces because they are degradational, locally preserved in a staircase morphology, neither bedding- nor fault-related, and located close to the present-day Adriatic shoreline. The marine terraces stretch c. 600 km along-strike the entire Dinaric coastal region. Their spatial correlation agrees with the position of a reported positive P-wave tomography anomaly beneath the Dinarides. This up to 180 km deep anomaly correlates also with the thinnest part of the Adriatic lithosphere and the Adriatic-Black Sea drainage divide. The orogen-perpendicular river incisions profiles reveal a symmetric river incision pattern on both sides of the drainage divide. The mean amount of the river incision is equivalent to the mean elevation of the documented marine terraces. All results point to an orogen-wide surface uplift of the Dinarides.Based on the geological record this post-collisional uplift event can be relatively dated to Oligocene-Miocene (28-17 Ma) and seems to be broadly contemporaneous with the emplacement of igneous rocks with mantle affinity (33-22 Ma) in the internal Dinarides. Previously published geophysical and petrological, as well as the new geomorphological data presented here suggest that the post-collisional reorganization of the Dinarides is attributed to an Oligocene-Miocene mantle delamination event, which results in uplift event affecting the entire Dinarides. We also show that no significant, orogen-scale deformation affected the uplifted Dinarides after the Early Miocene.

Wind-generated electricity has grown from a niche enterprise in the late 20th century to become a major energy source globally and nationally, and Kansas has played a significant role. Kansas wind power expanded more than six-fold between 2008 and 2018. Among states, Kansas now ranks fourth for total wind generating capacity (>6 GW) and second for combined wind and solar electricity production as a fraction of electricity consumption (47%). Kansas is virtually tied with Iowa for the highest amount of wind energy as part of the electric grid mix (>41%). From early development in the High Plains, wind farms and energy complexes have expanded into nearly all regions of the state. The drainage divide between the Missouri River and Arkansas River basins is a geographic focus for recent development of wind farms in eastern Kansas.Generation of electricity in Kansas mirrors overall energy trends in the United States during the past two decades. Coal, petroleum, and nuclear have declined, hydroelectric has been stable, natural gas has grown, and renewable (wind, solar) energy has expanded dramatically. These shifts in energy sources are reflected likewise in significant declines of carbon, sulfur, and nitrogen emissions. Kansas reflects the international character of the wind-energy industry. Installed wind turbines are mainly of Danish, German, and/or Spanish origin with some components manufactured in Kansas and other nearby states.

The topography of continents is a dynamic interface that evolves in response to several external (tectonics, mantle dynamics, climate) or internal factors to the geomorphic system. If these systems tend naturally toward a steady-state, they often show transient regimes as evidenced by retreating knickpoints, fluvial captures or migrating divides. These two last phenomena are indicative of drainage reorganization and imply the growth of a network at the expense of another. Yet, the rate of drainage network growth is very poorly known. To our knowledge for example, only one study (Craddock et al., 2010) has attempted to constrain the rate of growth of a natural drainage network, in the specific case of a growth by sequential captures of endorheic systems.Our aim here is to constrain the mechanism, timing and rates of network growth and drainage reorganization in a natural setting located in southwest France (Aude river catchment), in a current anorogenic setting in the northern foreland of the Pyrenees.Geomorphic evidence indicate that this catchment is enlarging with about 40 km of displacement of its main divide in the last few hundreds of thousand years (precise timing under investigation). The Aude river and main tributaries show flight of strath terraces that converge downward over ~150 km long distance. This specific fan-shape of paleo-longitudinal profiles implies an upward increase of fluvial incision that we interpret as the consequence of a long-term growth of the Aude drainage network. The dating of these terrace system using cosmogenic isotopes (in-situ 10Be depth-profiles and 10Be-26Al burial isochrones) and Electron Spin Resonance (ESR) is under progress and will allow us to quantify the longitudinal trend of differential incision through time, which we will use to estimate the rate of drainage network growth and divide migration. To support these results, an analysis of the catchment-wide erosion rates on both sides of the migrating divide is also performed. First preliminary results indicate catchment-wide erosion rates of 0.06-0.08 mm.yr-1 in the Aude river catchment.In complement to this natural case study, the main question of network growth dynamic is also addressed through laboratory-scale experiments performed at the Géosciences Environnement Toulouse (GET) laboratory. The first results show that the divide migration rate related to drainage network growth depends positively on the uplift/base level fall rate. In the detail, the divide migration rate is however non-linear, it evolves step by step with periods of acceleration when cyclic retreating knickpoints hit the divide.

Drainage systems, consisting mainly of river networks and drainage divides, evolved through geologic time as governed by erosion, tectonic uplift, and climatic processes. The present topographic features of these functional landforms provided footprints of their evolution. Divide migration and river reorganization were indicative of their dynamic state which has implications on the delivery and transport of water, sediments, and nutrients from the upstream areas to downstream areas, and influences biodiversity and speciation across divides in response to gain or loss of drainage areas. The utility of topographic metrics to predict this dynamic state on synthetic and natural landscapes has been tested in previous studies. Application of the topographic metrics in a tropical island was aimed at understanding natural land surface variability critical for disaster risk assessment and sustainable resource management. The present study conducted a topographic analysis to understand the dynamic state of river networks and drainage divides of a tropical island using divide stability tools. Four across divide contrasts were tested, namely: chi (χ), mean gradient, mean local relief and channel bed elevation to decipher the state of tropical island drainage systems. The TopoToolbox implemented in Matlab facilitated the routine analysis with a 10-m digital elevation model as input. Outputs from Matlab were further analyzed in a GIS platform. The four metrics showed that the divide between major drainage systems was stable, however, anomalies indicated by differences of χ-values were found at the headwaters where mountain areas marked the boundaries between the major and small drainage systems. On these areas, divide migration was predicted to move from the areas with lower χ values to the areas with higher χ values. The χ – inferiority map gave a more detailed potential divide movement. This divide migration entailed either an increase in the drainage areas of the aggressor catchment or a reduction in the drainage area of the victim catchment. Literature suggested that divide and river network reorganization will continue until equilibrium is attained within the landscape.

The Indo-Burma Range (IBR) is an accretionary complex associated with the oblique subduction zone between India and the Burma microplate. It remains an outstanding question whether the ongoing plate-boundary deformation involves active subduction of the Indian plate. To study the tectonics in this region, we investigate drainage divide stability and the topographic expression of active tectonics across the IBR. We extract elevation data from the 30 × 30 m SRTM digital elevation model and identify streams, drainage divides and basins. We select the divide segments to construct and evaluate divide stability using the Gilbert metrics and χ values of the channel heads located on both sides of the divide portions. We calculate several geomorphic indices, including basin-scale (hypsometry and relief) and stream-scale (normalized steepness index [ksn]) measures to reveal tectonic uplift patterns. We find that most of the divide segments are static, allowing us to study the morphometry of streams and drainage as indicators of spatial variation in tectonic uplift in the context of large-scale variations of precipitation and lithology. Our morphometric results support ongoing tectonic uplift distributed across the inner belt of the IBR, and they cannot be explained by variations in precipitation or lithology. The eastern region is characterized by higher relief, hypsometry and ksn compared to the western outer belt. While the active deformation front lies far to the west, the inferred higher uplift rates in the eastern range suggest active out-of-sequence thrusts in the inner belt of the IBR that splay off from the active megathrust.

Watersheds are the fundamental organizing units in landscapes and thus the controls on drainage divide location and mobility are an essential facet of landscape evolution. Additionally, many common topographic analyses fundamentally assume that river network topology and divide locations are largely static, allowing channel profile form to be interpreted in terms of spatio-temporal patterns of rock uplift rate relative to base level, climate, or rock properties. Recently however, it has been suggested that drainage divides are more mobile than previously thought and that divide mobility, and resulting changes in drainage area, could potentially confound interpretations of river profiles. Ultimately, reliable metrics are needed to diagnose the mobility of divides as part of routine landscape analyses. One such recently proposed metric is cross-divide contrasts in χ, a proxy for steady-state channel elevation, but cross-divide contrasts in a number of topographic metrics show promise. Here we use a series of landscape evolution simulations in which we induce divide mobility under different conditions to test the utility of a suite of topographic metrics of divide mobility and for comparison with natural examples in the eastern Greater Caucasus Mountains, the Kars Volcanic Plateau, and the western San Bernadino Mountains. Specifically, we test cross-divide contrasts in mean gradient, mean local relief, channel bed elevation, and χ all measured at, or averaged upstream of, a reference drainage area. Our results highlight that cross-divide contrasts in χ only faithfully reflect current divide mobility when uplift, rock erodibility, climate, and catchment outlet elevation are uniform across both river networks on either side of the divide, otherwise a χ-anomaly only indicates a possible future divide instability. The other metrics appear to be more reliable representations of current divide motion, but in natural landscapes, only cross-divide contrasts in mean gradient and local relief appear to consistently provide useful information. Multiple divide metrics should be considered simultaneously and across-divide values of all metrics examined quantitatively as visual assessment is not sufficiently reliable in many cases. We provide a series of Matlab tools built using TopoToolbox to facilitate routine analysis.

Topographic maps are used to determine erosional landform origins along the Little Missouri River-Powder River drainage divide in the Chalk Buttes areas of Carter County, Montana. Asymmetric drainage divides, drainage divide gaps, and isolated erosional remnants are used to determine a sequence of erosion events beginning with headward erosion of northeast-oriented Little Missouri River tributary valleys and ending with headward erosion of the deeper north-northeast and north-northwest oriented Powder River valley. Gaps notched into present day drainage divides and orientations of valley heads on either side of those gaps suggest many closely spaced southeast-oriented streams flowed across the region immediately prior to being captured by headward erosion of deeper north-oriented valleys. Buttes capped by horizontal Miocene Arikaree sandstones stand 500 feet (152 meters) or more above surrounding Little Missouri River tributary drainage basin elevations while the Powder River valley floor elevation is as much as 800 feet (244 meters) below those surrounding elevations. A water source could not be determined from the map evidence, however the study area is located to the south and west of a known continental ice sheet margin and large southeast-oriented ice-marginal melt water floods should have logically crossed the region.

The history of the Yangtze River is constituted by numerous river piracies that enabled the river to extend its drainage system. Two river captures are well recognized: the piracy of the Jinsha River (Jinshajiang) formerly tributary of the Red River at Shigu in Yunnan Province and the Three Gorges area that linked the upper and the middle Yangtze river reaches in Hubei province. The first one is well documented, while the second, because of difficulties to retrieve datable materials and the complexity of the area geomorphology, is still quite unknown. Numerous conflicting hypotheses have been formulated to explain the pattern of river piracy, no agreement exists on the location of the drainage divide and of the point of capture; chronologies extending from the Eocene to the late Quaternary are given. Geomorphic indices can be used to examine the geomorphological and tectonic processes responsible for the development of the drainage basins. In this paper, we analyzed drainage pattern, basin shape, basin asymmetry, stream junction angle to infer the drainage of the paleorivers that were pirated, and to propose a model of the pattern of river capture based on the importance of structure, tectonic and lithological controls in the area. We showed that the Three Gorges area has been very important to the history of the Yangtze river as the piracy of the upper and middle reaches enabled the river to reach its current extend.

The eastern margin of the Tibetan Plateau represents one of the morphologically most active regions on Earth, where the interplay of recent crustal deformation and subsequent fluvial landscape adjustment has affected the course of continental-scale rivers by river piracy events. Based solely on field observations, such an event has been hypothesised for two of the largest tributaries of the Yangtze River: the Jialing and Hanjiang Rivers. To test this hypothesis, we employ a novel combination of independent methods including a provenance study based on age distributions of detrital zircons from both modern riverbeds and river terraces and a morphometric analysis of river channels and drainage divides. We supported the morphometric analysis with a time-dependent numerical model describing the evolution of river channel long profiles and drainage divides in a succession of river capture events. Analysed zircon ages show clearly distinguishable distributions for the modern Jialing and Hanjiang Rivers, but similar distributions for the recent Hanjiang River up to its topmost terraces. This suggests that the capture of the Hanjiang headwaters by the Jialing River is unlikely to have taken place during the last 1.2 million years. However, several knickpoints in the main stem and the tributaries of the Jialing River cluster at an elevation of about 900 m and separate steeper (downstream) from less steep channel segments (upstream), which is consistent with the morphological expression of a major capture event. χ mapping indicates drainage divide asymmetry at catchment scale with on average steeper rivers on the Jialing side, whereas Gilbert metrics show a symmetric divide at hillslope scale. This numerical model explains this apparent contradiction by the travel time of capture-related knickpoints from the capture point towards the watershed, where χ mapping indicates divide asymmetry immediately after the river capture, while Gilbert metrics are only affected as soon as the knickpoints reach the channel heads and the divide effectively starts moving. Based on knickpoint travel distances and constraints on regional incision / uplift rates, we estimate the possible date of river capture to be the Pliocene. This is earlier than the formation of the terraces investigated in the provenance study but recent enough that most of the drainage divides are still unaffected and currently almost stable. Only the wind gap located in the almost dry valley connecting the two competing drainage systems is likely to have shifted towards the Hanjiang side. We suggest that this resulted in the capture of another important tributary of the Hanjiang River (the Heishui River) by the Jialing drainage system. Our results illustrate the complex evolution of drainage networks along the eastern margin of the Tibetan Plateau, and highlight the importance for combining provenance and morphometric analyses in regions of active landscape rejuvenation where river captures are likely to occur.

Mountain asymmetry is defined by the ratio of the lengths of two river systems across a drainage divide and is determined by the normalized location of the drainage divide. Understanding how asymmetric uplift influences the drainage divide, and therefore mountain asymmetry, is one of the preconditions for extracting tectonic information from topography. However, there is no consensus on this fundamental problem. Here we combined analytical solutions and numerical landscape evolution modeling to examine the impact of two key parameters (uplift gradient, and ratio of uplift rates at two edges) on mountain asymmetry. We followed the convention by assuming uniform gradient of uplift rate and erosion coefficient across the drainage divide. Our analytical approach and numerical simulations show that mountain asymmetry is not always controlled by the uplift gradient as previously suggested; instead, it is governed by the ratio of uplift rates at two edges across the divide. We quantified the relationship between the normalized divide location and the ratio of uplift rates. We applied the new formula to two natural examples to reconstruct the tectonics from the locations of the drainage divides. Moreover, we compared the influences of vertical and horizontal movements on the mountain asymmetry in different situations. The result suggests that in mountain belt with weak tectonic activity or high erosion coefficient, the mountain asymmetry is mainly controlled by the ratio of uplift rates.

The bulk of the crustal shortening across the Himalayas is accommodated across the Main Frontal Thrust (MFT), forming the topographic ridges of the Siwalik Hills. Here, we quantify topographic metrics to document the geomorphic response to progressive shortening. We use the integral method of channel profile analysis to assess the topographic response to the development of thrust anticline ridges in the eastern and western Churia, Dundwa, and Mohand Ranges. River channel steepness (ksn), the distribution of knickpoints, and channel concavity (θ) in the Siwalik Hills indicate geomorphic evolution during ongoing shortening across the deformation front. Mean channel steepness indices increase with increasing shortening over the Quaternary amongst the eastern Churia (~3.8 km shortening), Mohand (~6.9 km shortening), and Dundwa Ranges (~9 km shortening). Higher channel steepness at the western tip of the Churia Range (~0.4 km shortening) than in the eastern Churia and Mohand Ranges may indicate that the topography is still responding to the initial stages of shortening and relative uplift. Balanced cross sections reveal that there is spatial variability in the growth of these ranges, and as shortening increases, the drainage divide migrates southward (away from the mountains) relative to the flat-ramp transition of the underlying thrust; this results in steepening of the southward-draining catchments (basinward facing), and elongation of the northward flowing catchments. Basinward facing channels also have more prominent knickpoints and greater channel concavities caused by ongoing shortening between their fluvial base level and the drainage divide; this contrasts with the mountain facing channels where there is net growth of the distance between the drainage divide and the base level. Despite the asymmetry of erosional processes, the southward displacement of the drainage divide over the underlying thrust ramp drives topographic advection into the foreland succession which eventually leads to the propagation of new thrust-cored ridges.

The accepted Cenozoic geologic and glacial history paradigm (accepted paradigm) considers the southcentral Montana Musselshell-Yellowstone River drainage divide to have originated during Tertiary (or preglacial) time while a new and different Cenozoic geologic and glacial history paradigm (new paradigm) describes how headward erosion of a northeast-oriented Musselshell River valley segment captured huge southeast-oriented meltwater floods to create the drainage divide late during a continental ice sheet’s melt history. Northwest to southeast oriented divide crossings (low points observed on detailed topographic maps where water once flowed across the drainage divide), southeast-oriented Yellowstone and Musselshell River segments immediately upstream from northeast-oriented Yellowstone and Musselshell River segments, and southeast- and northwest-oriented tributaries to northeast-oriented Yellowstone and Musselshell River segments indicate a major southeast-oriented drainage system predated the northeast-oriented Yellowstone and Musselshell River segments. Closeness of the divide crossings, divide crossing floor elevations, large escarpment-surrounded erosional amphitheater-shaped basins, and unusual flat-floored internally drained basin areas (straddling the drainage divide), all suggest the previous southeast-oriented drainage system moved large quantities of water which deeply eroded the region. In the mid-20th century geomorphologists working from the accepted paradigm perspective determined trying to explain such erosional landform evidence from the accepted paradigm perspective was a nonproductive research activity and now rarely investigate erosional landform origins. On the other hand, the new paradigm appears to explain most, if not all observed erosional landform features, although the two paradigms lead to significantly different regional Cenozoic geologic and glacial histories that cannot be easily compared.&nbsp

Drainage divide migration is of wide interest because it drives changes in topography, aquatic species habitat, and fluxes of water and nutrients across Earth's surface. To date, divide migration rates have been measured in relatively few places, partly because of the rarity of denudation rate measurements on opposing sides of drainage divides. Here we report 54 basin-averaged denudation rates across the Qilian Shan, China, inferred from 10Be concentrations in stream-borne quartz. We combine these with 18 previously published basin-averaged denudation rates and new measurements of the topographic metric χ in the river networks. These data reveal divide migration rates of ∼3–1385 mm kyr−1 and area loss in the headwater reach of the Hei River basin. Cross-divide differences in denudation rate (ΔE) and channel-head χ values (Δχ) follow an exponential relationship Δ E = Δ E 0 e − b Δ χ , providing empirical support for the hypothesis that Δχ values can reflect ΔE. Here, b has the same value within uncertainty as in ΔE-Δχ data in the southern Appalachians and the Ozark Dome in previous studies, consistent with a common set of processes controlling divide migration in all three regions. The value of Δ E 0 is 1-2 orders of magnitude higher at Qilian Shan than at the two other sites, implying higher values of ΔE at a given Δχ. Our numerical simulations show that near-exponential ΔE-Δχ relationships can arise as topographic divides approach equilibrium under spatially uniform uplift rate, consistent with divide migration toward steady state in each of these regions. Further, they show that the magnitude of ΔE at a given Δχ increases linearly with rock uplift rate. Together, these results suggest that ln(ΔE) exhibits the same sensitivity to Δχ across mountain ranges, and that the magnitude of ΔE may be strongly sensitive to rock uplift rate.

The topography of mountain ranges reflects the competition of constructive and destructive processes driven by tectonics and climate, respectively. There is a vital debate whether the topography of individual orogens reflects stages of growth, steady-state or decay that is fueled by the million-year time scales hampering direct observations on landscape evolution, the superposition of various process patterns and the complex interactions among different processes. Hence, there is a demand for sophisticated analysis tools to extract constraints on the long-term evolution of orogens from their topography. We review the field of orogen-scale landscape evolution from a numerical perspective, summarize the most prominent modelling concepts and their implications for the fluvially-driven development of mountain topography, and finally evaluate their applicability for understanding real-world orogens. Following the concept of equilibrium – a state where uplift rates are balanced by erosion rates and topography remains steady over time – the erosional long term response of rivers and hillslopes can be mathematically formalised by the stream power and mass diffusion equations, respectively. Based on a simple 1-dimensional model consisting of two rivers separated by a watershed we explain the influence of uplift rate and rock erodibility on steady-state channel profiles and show the time-dependent development of the channel - drainage divide system. Dynamic drainage network reorganisation adds additional complexity and its effect on topography is explored on a two-dimensional model. River capture events and drainage divide migrations as expression of the ongoing drainage network reorganisation cause changes in topography until a stable network topology, and hence full topographic steady-state is achieved. The long time spans needed for this drainage network optimization suggest that orogens on Earth may never reach full topographic steady-state. In real world orogens, we find evidence for premature, mature and decaying topography as well as relief rejuvenation by analysing slope-elevation distributions and trace the expression of crustal strain distorting drainage networks by applying the χ transform. We conclude that modern concepts of landscape evolution allow sophisticated analyses of real-world orogens, but emphasize that unambiguous results are mostly derived from regions dominated by a limited number of interacting processes such as mountain ranges with limited or no glacial imprint. This results in a high demand for techniques to disentangle the complex topography of real-world orogens into the signals resulting from the individual land-shaping processes.

In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for > 80% of valley network length and relief. While hillslope and fluvial process models have frequently been combined with digital topography to develop morphologic proxies for erosion rate and drainage divide migration, debris-flow-dominated networks, despite their ubiquity, have not been exploited for this purpose. Here, we applied an empirical function that describes how slope-area data systematically deviate from so-called fluvial power-law behavior at small drainage areas. Using airborne LiDAR data for 83 small (~ 1 km2) catchments in the western Oregon Coast Range, we quantified variation in model parameters and observed that the curvature of the power-law scaling deviation varies with catchment-averaged erosion rate estimated from cosmogenic nuclides in stream sediments. Given consistent climate and lithology across our study area and assuming steady erosion, we used this calibrated denudation-morphology relationship to map spatial patterns of long-term uplift for our study catchments. By combining our predicted pattern of long-term uplift rate with paleoseismic and geodetic (tide gauge, GPS, and leveling) data, we estimated the spatial distribution of coseismic subsidence experienced during megathrust earthquakes along the Cascadia Subduction Zone. Our estimates of coseismic subsidence near the coast (0.4 to 0.7 m for earthquake recurrence intervals of 300 to 500 years) agree with field measurements from numerous stratigraphic studies. Our results also demonstrate that coseismic subsidence decreases inland to negligible values > 25 km from the coast, reflecting the diminishing influence of the earthquake deformation cycle on vertical changes of the interior coastal ranges. More generally, our results demonstrate that debris flow valley networks serve as highly localized, yet broadly distributed indicators of erosion (and rock uplift), making them invaluable for mapping crustal deformation and landscape adjustment.

The topography of the eastern Southern Alps (ESA) reflects indenter tectonics causing crustal shortening, surface uplift, and erosional response. Fluvial drainages were perturbed by Pleistocene glaciations that locally excavated alpine valleys. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA-EA drainage divide have not been identified. We demonstrate the expected topographic effects of each mechanism in a one-dimensional model and compare them with observed channel metrics. We find that the normalized steepness index increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and amplitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease toward the east. Changes in slope of χ-transformed channel profiles coincide spatially with the Valsugana-Fella fault linking crustal stacking and uplift induced by indenter tectonics with topographic evolution. Gradients in χ across the ESA-EA drainage divide imply an ongoing, north directed shift of the Danube-ESA watershed that is most likely driven by a base level rise in the northern Molasse basin. We conclude that the regional uplift pattern controls the geometry of ESA-EA channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration.

The proclivity of river networks to progressively carve mountain surfaces and preserve markers of landscape adjustments has made analyses of fluvial systems fundamental for understanding the topographic development of orogens. However, the transient nature of uplift and erosion has posed a challenge for inferring the roles that tectonics and/or climate have played on generating topographic relief. The Mt. Alpi region in the southern Apennines has a heterogeneous distribution of elevated topography, erosionally-resistant lithology and uplift, making the area optimal for conducting topographic and river analyses to better understand the landscape development of a transient orogen. Stream length-gradient, normalized channel steepness, stream convexity and first-order channel gradient indices from 10 m digital elevation data from the region exhibit stream profile inconsistencies along the current drainage divide and a dominance of high values subparallel but inboard of the primary chain axis irrespective of known transient landscape factors, suggesting that the current river network may be in a state of transition. The location of these stream profile anomalies both near the modern drainage divide and subparallel to an isolated swath of high topography away from catchment boundaries is thought to be the topographic expression of an imminent drainage divide migration driven primarily by the ~ northeast-vergent extension of the western chain axis.

Barbed tributaries flowing in southeast directions, an asymmetric drainage divide with both the South Fork Grand River and the North Fork Moreau River, and the Jump-off escarpment-surrounded basin (interpreted here to be a large abandoned headcut) are examples of topographic map evidence suggesting the north oriented Little Missouri River valley eroded headward across a large southeast oriented anastomosing complex of ice-marginal melt water flood flow channels that once crossed Harding County, South Dakota. Additional evidence includes southeast oriented tributaries to the northeast oriented South Fork Grand River and multiple divide crossings (e.g. through valleys and wind gaps) on the Boxelder Creek-Little Missouri River divide (in eastern Montana and west of the Little Missouri River) and suggests deep regional erosion occurred as the north oriented Little Missouri River valley eroded headward into and across the region. Harding County is located south and west of the southwest limit of coarse-grained glacial erratic material and ice-marginal melt water flow routes logically should have crossed it. Deep melt water erosion of Harding County and adjacent eastern Montana regions to the west is not consistent with many previous drainage history and glacial history interpretations, but is consistent with deep erosion by continental ice sheets.

Continental-scale drainages host the world’s largest rivers and offshore sediment accumulations, many of which contain significant petroleum reserves. Rate of sediment supply in these settings may be a signal of external controls (e.g., tectonics) on landscape evolution, yet deciphering these controls remains a major challenge in interpreting the ancient stratigraphic record. Integration of new and published detrital zircon U-Pb ages from the United States Rocky Mountain region and Gulf of Mexico (GOM) sedimentary basin demonstrates profound changes in the U.S. continental drainage divide that controlled the rate of sediment delivery to the northern GOM during Paleocene–Eocene time. Sedimentation rate increased dramatically during deposition of the lower Wilcox Group, reaching approximately three times the Cenozoic average, accompanied by pronounced shoreline regression and delivery of a large volume of sand to the basin floor. We hypothesize that this increase in sediment delivery to the GOM resulted from drainage capture of a significant portion of the Sevier-Laramide structural province (∼900,000 km2) that included the headwaters of the California and Idaho Rivers. Capture of the California River drainage may have occurred in the vicinity of the Hanna Basin of eastern Wyoming that previously emptied northward into a shallow seaway, but was subsequently diverted southward to the Rockdale delta, which accumulated within the Houston embayment during the time of deposition of the lower Wilcox Group. Detrital zircon U-Pb ages from Wilcox samples within the Rockdale delta show a remarkable similarity with contemporaneous Laramide synorogenic units, including enrichment in detritus derived from the Cordilleran arc and basement terranes of western North America relative to older and younger units in the Houston embayment. A subsequent order of magnitude decline in sedimentation rate to the GOM can be partly attributed to well-documented drainage closure (∼800,000 km2) that accompanied lake formation in interior Laramide basins (ca. 53–51.8 Ma). Our results demonstrate that tectonically induced drainage migration in the high-relief segments of continental-scale drainages can have a pronounced effect on the rate of sediment transfer to continental margins.

Catchment-wide erosion rates were defined using 10Be terrestrial cosmogenic nuclides for the Eastern Cordillera of the Colombian Andes to help determine the nature of drainage development and landscape evolution. The Eastern Cordillera, characterized by a smooth axial plateau bordered by steep flanks, has a mean erosion rate of 11 ± 1 mm/ka across the plateau and 70 ± 10 mm/ka on its flanks, with local high rates of > 400 mm/ka. The erosional contrast between the plateau and its flanks was produced by the increase in the orogen regional slope, derived from the progressive shortening and thickening of the Eastern Cordillera. The erosion rates together with digital topographic analysis show that the drainage network is dynamic and confirms the view that drainage divides in the Eastern Cordillera are migrating towards the interior of the mountain belt resulting in progressive drainage reorganization from longitudinal to transverse-dominated rivers and areal reduction of the Sabana de Bogota plateau. This article is protected by copyright. All rights reserved.

We propose a novel way to measure and analyse networks of drainage divides from digital elevation models. We developed an algorithm that extracts drainage divides, based on the drainage basin boundaries defined by a stream network. In contrast to streams, there is no straightforward approach to order and classify divides, although it is intuitive that some divides are more important than others. We thus propose a divide-network metric that orders divides based on the average distance one would have to travel down on either side of a divide to reach a common stream location. Because measuring these distances is computationally very expensive, we instead sort divide segments in a tree-like network, starting from endpoints at river junctions. The sorted nature of the network allows assigning distances to points along the divides, which can be shown to scale with the average distance downstream to the common location. Furthermore, because divide segments tend to have characteristic lengths, an ordering scheme in which divide orders increase by one at junctions, mimics these distances. We applied our new algorithm to a natural landscape and to results from landscape evolution model experiments to assess which parameters of divides and divide networks are diagnostic of divide mobility. Results show that stable drainage divides strive to attain a constant hillslope relief as well as flow distance from the nearest stream, provided a distance of > ~ 5 km from endpoints. Disruptions of such pattern can be related to mobile divides that are lower than stable divides, closer to streams, and often asymmetric in shape. In general, we observe that drainage divides high up in the network, i.e., at great distance from endpoints, are more vulnerable than divides closer to endpoints of the network and are more likely to record disturbance for a longer time period. We compared different topographic metrics to assess drainage divide mobility and found that cross-divide differences in hillslope relief proved more useful for assessing divide migration than other tested metrics. Finally, we introduced a new metric to assess divide junction stability, based on the connectivity of junctions with adjacent drainage divide segments.

A primary goal of geomorphology is to infer from topographic form the processes that drive landscape evolution. Often implicit is the assumption that orogen-scale ( > 10 10 m2 planform area) transient landscape changes on Earth are driven by equally large-scale transient tectonics, climate, or sea level. Here we argue that meso-scale (105–1010 m2) uplift perturbations may affect landscapes on scales that far exceed their size and duration. We study the consequences of transient variations in uniform surface uplift that are localized in space, such as may occur in volcanic landscapes or during landslide emplacement. These localized uplift perturbations define a class of landforms that are larger than typical hillslope lengths but smaller than orogens, and grow at rates that are rapid compared to fluvial bedrock erosion. We use 1D and 2D landscape evolution models to show that uplift perturbations drive transient lateral migration and vertical amplification of nearby ridges, sometimes generating a spatially distributed imbalance between uplift and erosion that causes plateau-like topography. Relaxation to steady-state conditions, in which erosion balances uplift everywhere, depends on the degree to which wave-like adjustment within channels or of ridges dominates subsequent landscape erosion. We find that the spatial structure and timescales of landscape response are predictable given uplift perturbation parameters. In 2D models, localized uplift generates a radial pattern of channel network and drainage divide reorganization that remains long after the perturbation is eroded. The spatial pattern of ridges and channels in a landscape thus may record both the scale and pace of perturbations to the uplift field.

The United States Supreme Court settled legal disputes concerning four different Larimer County (Colorado) locations where water is moved by gravity across the high elevation North Platte-South Platte River drainage divide, which begins as a triple drainage divide with the Colorado River at Thunder Mountain (on the east-west continental divide and near Colorado River headwaters) and proceeds in roughly a north and northeast direction across deep mountain passes and other low points (divide crossings) first as the Michigan River (in the North Platte watershed)-Cache la Poudre River (in the South Platte watershed) drainage divide and then as the Laramie River (in the North Platte watershed)-Cache la Poudre River drainage divide. The mountain passes and nearby valley and drainage route orientations and other unusual erosional features can be explained if enormous and prolonged volumes of south-oriented water moved along today’s north-oriented North Platte and Laramie River alignments into what must have been a rising mountain region to reach south-oriented Colorado River headwaters. Mountain uplift in time forced a flow reversal in the Laramie River valley while flow continued in a south direction along the North Platte River alignment only to be forced to flow around the Medicine Bow Mountains south end and then to flow northward in the Laramie River valley and later to be captured by headward erosion of the east-oriented Cache la Poudre River-Joe Wright Creek valley (aided by a steeper gradient and less resistant bedrock). Continued uplift next reversed flow on the North Platte River alignment to create drainage routes seen today. While explaining Larimer County North Platte-South Platte drainage divide area topographic map drainage system and erosional landform evidence this interpretation requires a completely different Cenozoic history than the geologic history geologists usually describe.

Extensive areas with low-relief surfaces that are almost flat surfaces high in the mountain ranges constitute the dominant geomorphic feature of the Three Gorges area. However, their origin remains a matter of debate, and has been interpreted previously as the result of fluvial erosion after peneplain uplift. Here, a new formation mechanism for these low-relief surface landscapes has been proposed, based on the analyses of low-relief surface distribution, swath profiles, χ mapping, river capture landform characteristics, and a numerical analytical model. The results showed that the low-relief surfaces in the Three Gorges area could be divided into higher elevation and lower elevation surfaces, distributed mainly in the highlands between the Yangtze River and Qingjiang River. The analyses also showed that the rivers on both sides of the drainage divide have not yet reached equilibrium, with actively migrating drainage divides and river basins in the process of reorganizing. It was concluded that the low-relief surfaces in the Three Gorges area did not share a common uplift history, and neither were they peneplain relicts, but rather that the effect of “area-loss feedback” caused by river capture has promoted the formation of upland low-relief surface landscapes. A future work aims to present the contribution of accurate dating of low-relief surface landscapes.

Kansas has played a significant role for the growth of wind energy in the United States. Kansas ranks sixth among states for wind-energy capacity, and is third in the nation for per-capita production of electricity from the wind. Wind farms are sited in topographically high positions on uplands, drainage divides, escarpments, and other rural sites in which there are few or no obstacles to interrupt near-surface wind flow. The best regions of the state include the High Plains, especially in southwestern Kansas, the Blue Hills and Flint Hills, and on the Missouri-Arkansas drainage divide in the Osage Cuestas. Rapid development of wind energy has taken place in these regions during the past few years, except for the Flint Hills, which is an exclusion zone for new wind farms. Bird and bat mortality remains an issue, but with appropriate wildlife mitigation much more wind energy could be developed in Kansas. Aesthetic issues include visibility and noise. Developing safe and renewable energy resources that have...

This study investigates the combined effects of Quaternary climate change and tectonically induced topography on the Yarlung River drainage-system evolution in the eastern Himalaya. Our work integrates field mapping, geomorphological analysis, stratigraphy, sedimentology, optically stimulated luminescence dating, radiocarbon dating, and detrital-zircon dating of a Holocene valley-fill sequence in a Yarlung River tributary. This holistic approach reveals an aggradational event, which started at or soon after 24–20 k.y. B.P. and continued to or after 9.2–8.0 k.y. B.P. across the Himalayan drainage divide between the east-flowing Yarlung River in the north and the south-flowing Subansiri River in the south. The aggradational event was associated with a major phase of glacier advance during a period of warm and wet climate conditions in the eastern Himalaya; it was expressed by the deposition of a valley-fill sequence across the modern Yarlung-Subansiri drainage divide. South-flowing fluvial sediments across the divide and the elevation distribution of the fluvial terraces require the existence of a major glacier dam that either blocked a tributary or the main trunk of the Yarlung River. Although we are unable to differentiate the two competing scenarios, our work reveals that combined Holocene climate change and tectonically induced topography have played a major role in controlling rapid shifts in drainage geometry at a time scale of

We detect transition to agropastoral land use in a mountain landscape by radiocarbon dating physical signatures (sedimentation rates, charcoal concentrations, magnetic susceptibility) of conversion from native forest to pasture contained within colluvial stratigraphic sections. Focus is on two study sites located on toeslopes directly beneath zero-order hollows draining several hectares in the commune of Larrau (Pyr�� Atlantiques, France) along the international drainage divide of the western Pyrenees. Sample sites maximize likelihood of spatially and temporally uniform slopewash sedimentation. This constitutes a place-based approach to decipher the chronology of agropastoral activities within individual fields, which is applicable to other mountain ranges of the world. Stratigraphic columns were augured in contiguous 10 cm sample levels, which produced temporal resolution of decades to several centuries. We interpret relatively high concentrations of charcoal, rapid sedimentation, and magnetic susceptibility patterns as evidence of the intentional use of fire to transform forests into pastures. Results indicate that intentional burning and clearing probably were initiated by the Late Neolithic (ca. 5000 e6000 cal. BP). However, intense burning, extensive forest clearance, and erosional degradation occurred later during the Bronze Age at one site, and during the Iron Age at the other site. This non-synchronous pattern of charcoal abundance and sedimentation rates is consistent with human agency of land clearance driving the chronology rather than paleoclimatic drivers. Stratigraphic zones of rapid sedimentation at both sites constitute “legacy” sediment of great antiquity. Our results are consistent with similar shifts in fire regimes and vegetation assemblages derived from direct association with anthropogenic proxies (e.g. pastoral pollen taxa, fungal spores of sheep dung, and archaeological sites) elsewhere in the Pyrenees and other European mountains. Consequently, our method may provide a good indicator of human presence and land-use activities for mountainous areas where paleoenvironmental records from bogs, lakes, and archaeological sites are limited.

Foreland basin sedimentary strata are key records of orogenic development, but identifying detrital thermochronometers of appropriate temperature sensitivity to detect provenance shifts can be challenging. Here, we utilize the medium-temperature apatite U-Pb system as a detrital thermochronometer. With a closure temperature range of ∼375−550 °C, it is a system sensitive to the typical peak temperatures attained by the amphibolite-eclogite cores of many magma-poor Phanerozoic orogens, while apatite itself is a common accessory mineral that is virtually ubiquitous in clastic rocks. We present apatite U-Pb data from the Oligocene−Miocene Barreme and Valensole basins of the Alpine foreland in SE France, together with data from the rutile U-Pb, apatite fission-track (AFT), and zircon U-Pb systems. At ca. 26−25 Ma, an abrupt cessation of detrital apatites yielding Alpine U-Pb ages derived from the eclogite-facies core of the Western Alps records a major westward migration of the primary drainage divide of the orogen. This shift, not visible in AFT and zircon U-Pb data, was synchronous with uplift and exhumation of the Argentera external basement massif. The drainage connection from the foreland to the eclogite-facies core of the Western Alps was restored by ca. 13 Ma and likely as early as ca. 16 Ma, and the primary drainage divide location has likely remained stable since this time. The synchronicity of late Oligocene−early Miocene uplift and initial exhumation of the external basement massifs around the western Alpine arc suggests that a major westward drainage divide migration occurred throughout the Western Alps at that time.

Major drainage divides (separating the water flow draining to different seas) may significantly affect the dispersal, distribution, and genetic structure of semiaquatic animals. Assessing this effect is important for the proper management of both endangered and invasive riparian species. Here, I determined the fine-scale impact of the drainage divide between the Baltic Sea and the Black Sea drainage basins on the genetic structure and dispersal of the Eurasian otter (Lutra lutra) in the Bieszczady Mountains (Poland and Slovakia). I investigated the genetic structure of the otter population and assessed 3 alternative dispersal models using 6 landscape genetics methods. The analyses were based on 48 individual genotypes obtained from 622 fecal and gland secretion samples collected in 2008–2011. Results indicate that the major drainage divide is not a barrier to gene flow for this population. This was established by analyses of population genetic structure and confirmed by analysis of the spatial distribution of samples originating from closely related individuals. In line with these findings, the best-supported dispersal model assumed that otters migrate through mountain passes, away from streams, thus revealing that they are able to cross a drainage divide. The genetic structure of the population studied exhibits an isolation-by-distance pattern; however, the locations of several repeatedly recorded or closely related individuals revealed the occurrence of long-distance movements. Confirmation of the high mobility of otters and their ability to cross a major drainage divide ridge suggest that landscape obstacles and discontinuity of river network are unlikely to stop otter dispersal, gene flow, and recolonization of new areas.

Numerical model simulations and experiments have suggested that when migration of the main drainage divide occurs in a mountain belt, it can lead to the rearrangement of river catchments, rejuvenation of topography, and changes in erosion rates and sediment flux. We assess the progressive mobility of the drainage divide in three lithologically and structurally distinct groups of bedrock in the High Atlas (NW Africa). The geological age of bedrock and its associated tectonic architecture in the mountain belt increases from east to west in the study area, allowing us to track both variations in rock strength and structural configuration which influence drainage mobility during erosion through an exhuming mountain belt. Collection of field derived measurements of rock strength using a Schmidt hammer and computer based extraction of river channel steepness permit estimations of contrasts in fluvial erodibilities of rock types. The resulting difference in fluvial erodibility between the weakest and the strongest lithological unit is up to two orders of magnitude. Published evidence of geomorphic mobility of the drainage divide indicates that such a range in erodibilities in horizontal stratigraphy of the sedimentary cover may lead to changes in erosion rates as rivers erode through strata, leading to drainage divide migration. In contrast, we show that the faulted and folded metamorphic sedimentary rocks in the centre of the mountain belt coincide with a stable drainage divide. Finally, where the strong igneous rocks of the crystalline basement are exposed after erosion of the covering meta-sediments, there is a decrease in fluvial erodibility of up to a factor of three, where the drainage divide is mobile towards the centre of the exposed crystalline basement. The mobility of the drainage divide in response to erosion through rock-types and their structural configuration in a mountain belt has implications for the perception of autogenic dynamism of drainage networks and fluvial erosion in mountain belts, and the interpretation of the geomorphology and downstream stratigraphy.

The Taebaek Mountain Range (TBR) initially formed via extension of a back-arc basin in the East Sea during the early-Miocene (ca. ~22 Ma) and exemplifies a typical escarpment on a passive continental margin. The TBR acts as a major watershed and divide across which topography changes from gentle western side slopes to steep eastern slopes. Compared to the geologic history of the flanking extensional basin, which is well known from analysis of its sedimentary fill, the post-extensional geomorphic history of the escarpment and basin margin has been minimally studied because of a lack of terrestrial archives. We determined the rate and cause of divide migration of the TBR using a suite of relatively new geomorphic and geochronologic tools. We used geomorphic analyses of relief, slope, river long profiles, swath profiles, and χ parameters to study this transient topography. Catchment-wide denudation rates (CWDR) using 10Be facilitated comparisons of denudation rates of cross-divide paired basins. Denudation rates east of the divide from drainages with steep slopes average nearly two times counterparts with gentle slopes west of the divide. Gilbert metrics used to assess divide mobility strongly suggest that catchments in the eastern TBR may have captured counterpart catchments in the west. Both CWDR and Gilbert metric results reveal that retreat of the main TBR divide likely accelerated in the late Quaternary following tectonic inversion, surface uplift, and tilting or flexure in the eastern TBR. Geomorphic disequilibrium across the current divide of the TBR continues until the present.

20 pages, 20 figures, 1 table, supplementary data https://doi.org/10.1016/j.geomorph.2019.106954, Active tectonics in North Africa are fundamentally driven by NW-SE directed slow convergence between the Nubia and Eurasia plates, leading to a region of thrust and strike-slip faulting. In this paper, we analyse the morphometric characteristics of the northern Tunisia sector. We aim to identify unknown active tectonic structures, and to further understand the mechanisms driving the drainage evolution in this region. The interpretation of morphometric data was ground-truthed with field data. Our analysis indicates that recent fluvial captures have been the main factor driving fluvial network reorganization in NE Tunisia. The Medjerda River has increased its drainage area during the Quaternary by capturing adjacent axial valleys to the north and south of its drainage divide. These captures are probably driven by the gradual uplift of adjacent axial valleys by reverse/oblique faults or associated folds like El Alia-Teboursouk and Dkhila faults. Our fieldwork found that these faults cut Holocene sediments thus showing recent fault activity. The growth and stabilization of the axial Medjerda River, contrary to the natural transverse drainage development of mature orogens, might be caused by a combination of crustal shortening structures and mantle dynamic processes. The Medjerda River flows SW-NE from the South Atlassic dextral transfer zone to the regional topographic low defined by the Gulf of Gabes and the Straits of Sicily, which in turn, may be influenced by the underlying Tunisian slab in the region, The authors were supported by research projects CGL2011-29920, CTM2007-66179-C02-01/MAR, by research group 2014 SGR 940 (Generalitat de Catalunya), by the CTM2011-30400-C02-01 HADES Project from the Spanish Ministry of Science and Innovation and by the CGL2015-67130-C2-1-R LITHOSURF Project from the Spanish Ministry of Economy and Competitiveness, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

The activity of normal faults in the Central-Western Pyrenees is mainly detected by the disruption of paleic landforms surviving to Plio-Quaternary incision: the remnants of a Low-Relief Topography (LRT) that probably originated asynchronically during the Oligocene and Miocene. We propose a new method for mapping the LRT remnants that combines automatic analysis of digital topography and cross-checking with regional databases of Quaternary landforms. We focus on an area where the location of the main-drainage divide seems to be influenced by the activity of the Bedous-Pic de Midi du Bigorre set of faults and by the North Maladeta Fault. Neotectonic markers defined by the remnants of LRT envelops are tectonically displaced up to similar to 700m by the previously identified faults, but also along new faults observed in between them. A western prolongation of the North Maladeta Fault has been identified for the first time, implying a 75km total trace length, almost twice the previously published value. A restoration of the fault block motion was performed assuming a regional uplift across the range, enhanced in the northern part of the Axial Zone. This uplift leads to an outer arch extension along the Maladeta-Bedous Fault System. The resulting paleo-topography shows a broad southern paleo-flank (up to similar to 120km long) with a gentle regional gradient (similar to 1 degrees) and a much shorter and steeper northern paleo-flank (similar to 4 degrees gradient, up to 30km-long). This configuration suggests that the LRT remnants now located North of the main divide were connected to the Ebro Basin. The results are supported by previous studies on age and source provenance of major alluvial systems mantling the northern and southern flanks of the chain., Research was supported by the Institut de Recerca Geomodels and the RISKNAT Group (2017SGR126SGR-AGAUR distinction).

The Greater Caucasus Mountains are a young (∼5 m.y. old) orogen within the Arabia-Eurasia collision zone that contains the highest peaks in Europe and has an unusual topographic form for a doubly vergent orogen. In the east-central part (45°E–49°E), the range is nearly symmetric in terms of prowedge and retrowedge widths and the drainage divide is much closer to the southern margin of the range (prowedge side) than it is to the northern margin (retrowedge side). Moreover, the divide does not coincide with the topographic crest, but rather the crest is both shifted northward by as much as 40 km and traversed by several large north-flowing rivers. Both the topographic crest and drainage divide appear to coincide with zones of active rock uplift, because they are characterized by bands of high local relief and normalized channel steepness values (>300). This uplift pattern could result from a synchronous initiation of the two uplift zones or propagation of deformation either northward or southward. The two propagating scenarios differ fundamentally in their predictions for the relative ages of topographic features; northward propagation predicts that the topographic crest is younger than the drainage divide, and the southward scenario predicts the converse. Because available geologic and topographic data are consistent with both propagation directions, we use a landscape evolution model to test all three scenarios. Model results indicate that the current topography and drainage network is best explained by a northward propagation of deformation from the south flank into the interior of the east-central Greater Caucasus. Such propagation implies recent out-of-sequence deformation within the Greater Caucasus due to reactivation or development of new structures within the core of the orogen. It remains unclear if such deformation is a transient response to an accretion cycle or stems from a fundamental change in the structural architecture of the orogen.

The Kalahari Desert contains extensive networks of ephemeral and fossil drainage which are potential indicators of past and present neotectonic activity and climate-driven environmental change. An absence of topographic data has hindered our understanding of their development. We present long-profile information for twenty-nine valley networks derived from Shuttle Radar Topographic Mission (SRTM) digital elevation data. In total, 8354 km of valley talweg was measured for x, y and z information. Most valleys exhibit concave-up profiles. Fifty-five previously unknown knickpoints were identified. The majority coincide with lithological boundaries or fractures, but many developed in response to Neogene uplift and/or downwarping or occur where valleys cross palaeolake shorelines. The headwaters of four valleys cross the Kalahari–Limpopo drainage divide and predate the presumed Miocene uplift of the Kalahari–Zimbabwe axis, suggesting that they are of considerable antiquity.

Sedimentary records in peripheral basins of mountain belts record changes in erosion dynamics and drainage-network reorganization, but it is often difficult to discriminate between these different controls. Geochemical provenance data on paleo-Indus deposits from the western Himalayan foreland provide constraints on the possible variation of the position of the drainage divide between the Indus and Ganges river systems. Here we present geochemical (trace element and Hf-Nd isotopic) and thermochronological (detrital zircon fission-track [DZFT]) analyses of modern Indus and Miocene Siwalik sediments from northern Pakistan and compare these with published data on the Indus Fan. Available bedrock isotopic data are used to define three end-member sediment sources (Himalaya, Karakorum, and the Kohistan-Ladakh arc) and to calculate the contribution of each of these sources to the foreland basin and Indus Fan. Our results indicate that since the Miocene the contribution of the Himalayan rivers reaching th...

The evolution of drainage systems in and around active orogens may be strongly affected by climatic or tectonic processes. Information on the drainage evolution is stored in the sediments of the foreland depocentres. We investigated the provenance of two key deposits adjacent to the Central Alps, the Pliocene Sundgau gravels and the Pleistocene Hohere Deckenschotter by applying detrital thermochronology. Combined with provenance information from Rhine Graben deposits, we propose a reconstruction of the north Alpine drainage system since the middle Pliocene and discuss potential controlling mechanisms. Our data show that the Rhine Graben received detritus from the Alpine realm already during the Pliocene, indicating two different river systems—the proto-Rhine and the Aare–Doubs—draining the Alpine realm toward the North Sea and Mediterranean Sea. The investigated sediments contain detritus from two central Alpine sources, one showing a regional exhumational equilibrium and the other characterized by increasing exhumation rates. Discharge of the latter source ceased after ~2 Ma, reflecting a northward shift of the main Alpine drainage divide. Between ~2.0 and 1.2 Ma, the drainage system was affected by a major change, which we explain as resulting from a change in the Alpine stress field leading to tectonic exhumation and topography reduction in the area of the southern Aar massif. Generally, it seems that between ~4 and 1.2 Ma, the drainage system was mainly controlled by tectonic processes, despite first glaciations that already affected the north-Alpine foreland by ~2 Ma. The drainage system only seems to have reacted to the late Cenozoic climate changes after ~1.2 Ma, i.e., at the time of the most intense Alpine glaciation. At that time, the course of the Rhine River shifted toward the area of the Hegau volcanics, and the size of the Rhine River catchment became strongly reduced.

Physical and numerical simulations of the development of mountain topography predict that asymmetric distributions of precipitation over a mountain range induce a migration of its drainage divide toward the driest flank in order to equilibrate erosion rates across the divide. Such migration is often inferred from existing asymmetries, but direct evidence for the migration is often lacking. New low-temperature apatite cooling ages from a transect across the northern North Cascades range (Washington, NW USA) and from two elevation profiles in the Skagit River valley record faster denudation on the western, wetter side of the range and lower denudation rates on the lee side of the range. This difference has already been documented further south along another transect across the range; however, in the south, the shift from young cooling ages to older ages occurs across the modern drainage divide. Here, further north, the shift occurs along a range-transverse valley within the Skagit Gorge. It has been proposed that the upper Skagit drainage was once a part of the leeward side of the range but started to drain toward the western side of the range across the Skagit Gorge in Quaternary time. Age-elevation profiles along the former drainage and in the Skagit Gorge restrict the onset of Skagit Gorge incision to the last 2 m.y., in agreement with 4 He/ 3 He data for the gorge floor. Breaching of the range drainage resulted in its displacement 40 km further east into the dry side of the range. In the 2000-m-deep, V-shaped Skagit Gorge, river stream power is still high, suggesting that incision of the gorge is still ongoing. Several other similar events have occurred along the range during the Pleistocene, supporting the proposed hypothesis that the repeated southward incursions of the Cordilleran ice sheet during this period triggered divide breaching and drainage reorganization by overflow of ice-dammed lakes at the front of the growing ice sheet. Since these events systematically rerouted streams toward the wet side of the range and resulted in leeward migration of the divide, we propose that in fact the Cordilleran ice sheet advance essentially catalyzed the adjustment of the mountain chain topography to the current orographic precipitation pattern.