Normalized Channel Steepness Index Research Articles

Role of coseismic bedrock landslides in the landscape evolution of high-relief mountainous terrain: Insights from detrital 10Be dilution modeling

Episodic landslides supply vast quantities of debris from hillslopes to channels, resulting in the dilution of cosmogenic nuclides in fluvial sediment. This study revisited the nuclide dilution concept and proposed a novel model framework to quantify landslide-derived sediment yields to interpret the responses of entire landscape systems to tectonic forcing in an active orogen. The model was applied to datasets of detrital 10Be concentrations obtained from the Minjiang catchment in the eastern margin of the Tibetan Plateau, where the impacts of coseismic landslides were documented during the 2008 Wenchuan earthquake. Presumable model parameters were evaluated through multifaceted geospatial analyses by adopting the normalized channel steepness index as a proxy for background denudation rate, which was then converted to the corresponding nuclide concentration; the fluvial channel geometry was adopted for evaluating pre-event fluvial sediment storage. The scaling factors for quantifying the landslide debris influx were obtained via inversion of the diluted 10Be concentrations and corresponding landslide inventory to verify the feasibility of the model. The calibrated model was then applied at the regional scale to evaluate the long-term net denudation of the hillslopes with a certain earthquake recurrence interval. The resulting spatial distribution of increased denudation is consistent with very-long-term exhumation rates derived from low-temperature thermochronology, implying the critical role of coseismic landslides in mass removal from hillslopes to counterbalance long-term tectonic uplift.

Using Disorder Metrics to Distinguish Discharge‐Driven From Drainage Area‐Driven Incision and Quantify Deviations in Channel Steepness

AbstractThe rate of channel incision in bedrock rivers is often described using a power law relationship that scales erosion with drainage area. However, erosion in landscapes that experience strong rainfall gradients may be better described by discharge instead of drainage area. In this study, we test if these two end member scenarios result in identifiable topographic signatures in both idealized numerical simulations and in natural landscapes. We find that in simulations using homogeneous lithology, we can differentiate a posteriori between drainage area and discharge‐driven incision scenarios by quantifying the relative disorder of channel profiles, as measured by how well tributary profiles mimic both the main stem channel and each other. The more heterogeneous the landscape becomes, the harder it proves to identify the disorder signatures of the end member incision rules. We then apply these indicators to natural landscapes, and find, among eight test areas, no clear topographic signal that allows us to conclude a discharge or area‐driven incision rule is more appropriate. We then quantify the distortion in the channel steepness index induced by changing the incision rule. Distortion in the channel steepness index can also be driven by changes to the assumed reference concavity index, and we find that distortions in the normalized channel steepness index, frequently used as a proxy for erosion rates, is more sensitive to changes in the concavity index than to changes in the assumed incision rule. This makes it a priority to optimize the concavity index even under an unknown incision mechanism.

Excess topography and outburst flood: Geomorphic imprint of October 2023 extreme flood event in the Teesta catchment of Eastern Himalayas

The 2023 South-Lohnak Lake outburst flood event across the upstream Teesta catchment triggered short-lived, high-magnitude flooding and substantial socioeconomic disruption downstream. We performed landscape analysis across the Teesta catchment using topographic metrics to understand the geomorphic response to this extreme flood event. We estimated the various topographic metrics such as ksn anomaly (normalized channel steepness index) (∼500–2500 m0.9), SL-index (stream-length gradient index) (∼5000–7000 m), and KsnQ (channel steepness-weighted discharge) along the trunk channel draining through the South-Lohnak Lake, which shows high magnitude in flooded regions and numerous spikes in their longitudinal profiles across mass-wasting regions downstream. We used the KsnQ metric as an event characteristic to investigate the changes in the channel morphology due to high-magnitude flooding. There was a sudden increase in the magnitude of the KsnQ metric when the river traversed through the Chungthang dam over the high ranges of excess topography (∼0–1700 m). This shows that the downstream channel morphology changes rapidly during this flood event, and KsnQ is a significant indicator of geomorphic change. To understand the spatial relationship between the physical drivers that trigger this outburst flood, we quantified the causal relationship between glacial-hydrological drivers over the upstream Zemu-sub catchment. Our observations suggest that precipitation intensity and surface temperature had a significant direct causal influence on snowmelt and snow depth (in terms of water equivalent) over the event duration with a 5-day and 1-day lag composite. Through the inclusion of lagged composites and causal linkages, the drivers across the glaciated landscape serve as event anomalies, which trigger the glacier hillslope failure and subsequent high-magnitude outburst flooding. Therefore, we suggest that the interaction of topographic discontinuity with hydrological extremes and their causal interdependencies influences this outburst event in the upper reaches, followed by high-magnitude flooding in the downstream reaches of the Teesta River. However, the long-term geomorphic consequences of such events on the evolution of the regional landscape remain unclear.

Fluvial geomorphic parameters of the Shuiluo River Catchment and their tectonic implications, SE Tibetan Plateau

The Shuiluo River Catchment (SRC) is the front zone of the southeast compression and uplift of the Tibetan Plateau, with intense tectonic activity. In the basin, a series of regional large NW–SE trending active faults are developed. Studying clearly the geomorphic evolution of the SRC is conducive to further understanding the uplift and expansion mechanism of the SE edge of Tibetan Plateau. Our research was based on geographic information system, numerical analysis tool, and digital elevation model data, to extract six geomorpic parameters (hypsometric integral, asymmetry factor, basin shape ratio, valley floor width–valley height ratio, normalized channel steepness index and index of relative active tectonics) in SRC. After eliminating the impacts of climate, catchments area, and glacier, the geomorphic evolution of the SRC is mainly affected by geological structure and differential tectonic uplift movement; in the upstream and midstream (upper part), the shape of valleys and stream longitudinal profile shapes are affected by lithology; affected by geological structure and tectonic uplift, the tectonic activity in the midstream and downstream is relatively strong, and the intensity of activity in the downstream is stronger than that in the midstream, which may suggest that the faults’ activity in the downstream is stronger; the index of relative active tectonics values of the SRC are consistent with the regional seismic intensity, field-work and low-temperature thermochronology which indicates it is reasonable to use the fluvial geomorphic parameters to study the regional geomorphic evolution. The morphological parameters we extracted show different values in different regions of SRC, which may be the result of differential uplift in the southeastern of the Tibetan Plateau.

Segmentation of the Tashkurgan normal fault in the eastern Pamir: Insights from geomorphology and thermochronology and implications for fault-slip transfer

At the northwestern end of the India–Asia collision zone, in the eastern Pamir interior, the Kongur Shan extensional system extends for ∼250 km as a composite system of normal faults. As the southernmost segment of the extensional system, the Tashkurgan fault can be divided into a northern and southern segment by the intersection of the Tahman and Tashkurgan faults. To evaluate the tectonic activity along the Tashkurgan fault and explore the extensional characteristics of the southern Kongur Shan extensional system, we integrate geomorphologic analysis with thermochronologic data and modeling. Geomorphic indices, including local relief, normalized channel steepness index (ksn), and river χ-plots, show that the southern Tashkurgan fault is more active than the northern Tashkurgan fault. On the footwall of the northern Tashkurgan fault, most thermochronologic data, which include biotite 40Ar/39Ar (Arbt), zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th-Sm)/He (AHe) dates, record emplacement-related cooling, and only a few AHe dates possibly record exhumation of <2 km since ∼7 Ma ago. On the footwall of the southern Tashkurgan fault, almost all of the ZHe, AFT, and AHe dates record significant late Miocene to present exhumation; thus, we perform three-dimensional thermokinematic modeling for the normal slip along this fault segment. Modeling results indicate a probably constant slip rate on the southern Tashkurgan fault at a value of 1.4–1.5 mm/a, which corresponds to 6–7 km of both horizontal extension and footwall uplift since 6.5 Ma ago. All together, the geomorphic and thermochronologic evidences imply that the southern Tashkurgan fault is responsible for the ∼E–W extension along the southernmost portion of the Kongur Shan extensional system, while the northern fault segment plays a minor role in the extension. This result, combined with the previously published magnitude of extension along the southern Kongur Shan fault, indicates that the extension at any site along the southern Kongur Shan extensional system can be primarily attributed to normal faulting along a single border fault, which is a typical characteristic of an interbasin transfer zone with a transfer fault.

Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

AbstractTo investigate the recent landscape evolution of the orogenic Turkish–Iranian Plateau (TIP) and the Lesser/Greater Caucasus ranges, we perform a quantitative analysis of topography and drainage networks at a regional scale. This analysis focuses on climatic–topographic swath profiles, local relief distribution, longitudinal river profiles, normalized channel steepness index (ksn), paleo‐river profile, and chi analysis (χ). In general, we find that the evolution of topographic relief and river networks are locally controlled by Late Cenozoic volcanism, contrasts in rock strength, and neotectonic activity along regional tectonic structures. However, our results show that the influence of these factors on the landscape evolution of the Greater Caucasus is significantly different from the Lesser Caucasus and TIP. This study shows that a combination of enhanced aridity, rapid uplift of orographic barriers along the TIP margins, and exposure of resistant rock types associated with the regional volcanic activity resulted in low‐relief plateau and the Lesser Caucasus surfaces that are preserved in the upper/middle Kura–Arax and Qezel‐Owzan river catchments. High local relief in the flanks of the Greater Caucasus and west Alborz, downstream increase in channel steepness, and perturbations in the χ plots of the three main rivers indicate that the topography is in a transient state.We reconstruct the paleo‐river profiles from the relict section of the upper Kura–Arax and Qezel‐Owzan rivers and show that the last drastic fall of the Caspian base‐level, which occurred during the Late Miocene–Early Pliocene, can explain the incision of ~500–1000 m gorges (i.e., Amardos) below major knickpoints. Furthermore, local cross‐divide differences of the χ parameter reveal that disequilibrium in the plan‐form geometry of the drainage networks, attributed to the upstream migration of the regional knickpoints towards the plateau interior and integration of plateau areas into the external fluvial system.

Controls on topography and erosion of the north-central Andes

Abstract We present 17 new 10Be erosion rates from southern Peru sampled across an extreme orographic rainfall gradient. Using a rainfall-weighted variant of the normalized channel steepness index, ksnQ, we show that channel steepness values, and thus topography, are adjusted to spatially varying rainfall. Rocks with similar physical characteristics define distinct relationships between ksnQ and erosion rate (E), suggesting ksnQ is also resolving lithologic variations in erodibility. However, substantial uncertainty exists in parameters describing these relationships. By combining our new data with 38 published erosion rates from Peru and Bolivia, we collapse the range of compatible parameter values and resolve robust, nonlinear ksnQ–E relationships suggestive of important influences of erosional thresholds, rock properties, sediment characteristics, and temporal runoff variability. In contrast, neither climatic nor lithologic effects are clear using the traditional channel steepness metric, ksn. Our results highlight that accounting for spatial rainfall variations is essential for disentangling the multiple influences of climate, lithology, and tectonics common in mountain landscapes, which is a necessary first step toward greater understanding of how these landscapes evolve.

Spatial distribution of rock uplift in the Bongarà district (Peruvian Andes) and implications for the genesis of supergene ore deposits

Topography and river landscape morphometry of two hydrographic basins, the Utcubamba River and the Chiriaco River basins (Bongará district, Amazonas region) allowed to determine the relationship between the irregular distribution of vertical motions (e.g., rock uplift) and the genesis of supergene Zn deposits. The latter derives from variable weathering of pre-existing carbonate-hosted Zn sulfides orebodies, in three distinct localities: Florida Canyon, Mina Grande and Cristal. The research was carried out through the evaluation of the parameters such as elevation, local relief, swath profile, river longitudinal profiles and transformed river profiles (χ-long profiles), and slope/area analysis to derive the normalized channel steepness index (ksn). The NE-ward sharp increase in mean and minimum elevation coupled with a jump in the mean ksn values, suggests that the Chiriaco River basin has experienced more recent rock uplift than the Utcubamba River basin. In fact, the Utcubamba River experienced a long-lasting uplift, resulting in a rugged local relief and lowering the mean and minimum elevations, and exhumation and weathering of the Triassic-hosted sulfide mineral deposits at Florida Canyon. In the Chiriaco River basin, the younger uplift has promoted the weathering of the more surficial Jurassic-hosted Mina Grande and Cristal mineral deposits. The morphometric approach proved to be effective in recognizing fertile areas with near-surface orebodies also in regions characterized by distinct types of ore deposits.

Tectonic geomorphology of Bozdoğan and Karacasu grabens, western Anatolia

Western Anatolia is one of the most rapidly extending and seismically active regions in the world. The circa N-S extension since the Early Miocene caused the formation of E-W trending major grabens and intervening horsts, having earthquake potentials with magnitude ≥5. The E-W oriented Büyük Menderes graben cross-cuts the broadly N-S oriented Bozdoğan and Karacasu grabens, of which the boundary faults of the latter are the source of seismic activity. Geomorphic indices, including drainage basin asymmetry, mountain front sinuosity, valley-floor width to valley height ratio, stream length-gradient index and normalized channel steepness index, were used to evaluate the boundary fault segments of the Bozdoğan and Karacasu grabens. The results indicate that both grabens are tectonically active and therefore regions of earthquake potential, consistent with the epicenters of earthquakes. Thus, it can be inferred that fault segments of second-order grabens, which are crosscut by the boundary faults of seismically active main depressions, are apparently reactivated by ongoing tectonism and may represent seismic activity. This suggestion applies also for similar basins located in the western Anatolia.

Tectonic geomorphology of the Ottawa-Bonnechere Graben, Eastern Canada: implications for regional uplift and intraplate seismicity

In intraplate areas where regional tectonic strain is accommodated by the reactivation of pre-existing structures, the level of seismic hazard associated with faults may be underestimated due to the poor surface expression of faults, scattered earthquake distribution, and long earthquake recurrence intervals. The cause(s) of seismicity in eastern Canada remains unresolved. This is partially because surface expressions of faults have been eroded during glacial and deglacial periods and in the Ottawa-Bonnechere Graben (OBG) are undetectable until a seismic event. Morphotectonic analysis has been widely applied to assess relative tectonic activity in various geological settings. To establish whether active uplift is occurring and to investigate the spatial distribution of relative uplift rates, 131 bedrock drainage basins in OBG were analysed. The aim of this was to (1) test the applicability of geomorphic indices for quantifying active deformation, (2) quantify the spatiotemporal distribution of relative uplift rates, and (3) explore the implications for faulting mechanisms, deformation styles, and ultimately regional seismic hazard. We measured valley floor width-to-height ratio ( Vf), basin elongation ratio ( Re), basin hypsometric integral, and normalized channel steepness index ( ksn). The results show that high relative uplift rates exist in all the six bedrock escarpment sections investigated, suggesting that they are presumably related with regional broad wavelength uplift (epeirogeny) caused by a complex interaction between far-field tectonic stress and glacial isostatic adjustment (GIA). Our analysis showed that Vf, Re, and ksn reveals no considerable spatial differences in high relative uplift rates, consistent with the Canadian Base Network GPS uplift rates. Highlights Geomorphic indices are applied in a low relief and low-medium seismicity area. Geomorphic indices reveal a broad wavelength regional uplift and show relative tectonic activity in the OBG. Relatively high geomorphic indices values provide longer term deformation history compared to global positioning system (GPS) records. Landscape formation and river incision is driven by a complex interaction between GIA and far-field tectonic stresses. Relative uplift rate results show similar patterns to published GPS uplift rates. Possible link between relative tectonic activity and current seismicity.

Long-term uplift pattern recorded by rivers across contrasting lithology: Insights into earthquake recurrence in the epicentral area of the 2016 Kumamoto earthquake, Japan

Topography results from the interplay between rock uplift and erosion, and studying river responses to active tectonics may enable the rates and spatial distribution of rock uplift to be inferred. Normalized channel steepness index (ksn) is widely used to infer rock uplift rates, and rock erodibility plays a significant role in determining the variation of channel steepness in response to external forces. Various measures may be applied to evaluate rock erodibility; however, since they are essentially qualitative, it is difficult to quantify relationships between rock mass strength and channel forms. In this study, we inferred long-term rock uplift rates along the Futagawa fault, an active normal-dextral fault, and the Idenokuchi fault, an active normal fault, in southwestern Japan, based on morphological characteristics of rivers across substrates with contrasting erodibility. The widely used detachment-limited model predicts that, when the rock uplift rate is spatially uniform, the ratio of erodibility of different rock types can be written by an inverse ratio of their ksn values. We employed this theoretical prediction to quantitatively calibrate the effects of rock mass strength on channel steepness. Within the study area, channel steepness was larger in the eastern part where volcanic rocks were exposed than in the western part where less resistant sedimentary rocks predominated. We calculated ratios of substrate erodibility using drainage basins close to the Futagawa fault that experienced similar rock uplift. Calibrated ksn exhibited a clear difference between the eastern and the western part of the fault, suggesting that contrasting erodibility alone cannot explain the observed channel steepness. We also confirmed that the observed channel steepness could not be explained without differential rock uplift, even when considering the combined effects of channel width, precipitation, and erosion process. The distribution of long-term rock uplift rates inferred from calibrated ksn and vertical slip rates of the fault compiled from published papers agree with the distribution of vertical displacement of the earthquake that occurred on the fault in 2016, suggesting that earthquakes similar to the 2016 event have occurred repeatedly in the study area.

Post-rift geomorphological evolution of a passive continental margin (Paraíba region, northeastern Brazil): Insights from river profile and drainage divide analysis

The post-rift erosional history of elevated passive continental margins (EPCMs) has been considered of low-rate tectonics across many regions worldwide. However, research in the northeastern Brazilian passive continental margin suggests variations in the post-rift tectonic styles, timing and rates. This is especially the case of the Paraíba region, where there are reports of uplift affecting Quaternary strata. However, transient fluvial features potentially developed during this event remain to be investigated. In this study, we document transient responses of a fluvial landscape promoted by variations in Quaternary tectonic uplift in the Paraíba region, where outcrops are scarce. The aim was to trace the Quaternary post-rift geomorphological evolution and the mechanisms of development of the northeastern Brazilian margin. A digital elevation model (DEM) was utilised to provide long river profiles based on the χ approach, normalized channel steepness index (ksn), and drainage divide analysis. The results indicated non-linear χ-profiles, migration of knickpoints upstream along the river profiles, and incised channels in elevated areas close to the inner margin plateau. In addition, there were cross divide differences in topographic metrics, with divide movements following a high elevation, chevron-shaped plateau. These transient fluvial features were mostly recorded over lithologies of relatively similar strength, in or near pre-existing basement structures. Thus, they were attributed to a topographic rejuvenation due to variations in tectonic uplift during the Late Quaternary. This tectonic geomorphological interpretation supports previous studies that the late development of the eastern South American EPCM was marked by a period of locally increased tectonics, potentially driven by far-field compressive stresses concentrated along main shear zones.

Impact of Changing Concavity Indices on Channel Steepness and Divide Migration Metrics

AbstractThe concavity index, , describes how quickly river channel gradient declines downstream. It is used in calculations of normalized channel steepness index, , a metric for comparing the relative steepness of channels with different drainage area. It is also used in calculating a transformed longitudinal coordinate, , which has been employed to search for migrating drainage divides. A value of 0.45 is typically assumed in studies. Here we quantify the variability in across multiple landscapes distributed across the globe. We describe the degree to which both the spatial distribution and magnitude of and can be distorted if is assumed rather than constrained. Differences between constrained and assumed of 0.1 or less are unlikely to affect the spatial distribution and relative magnitude of values, but larger differences can change the spatial distribution of and in extreme cases invert differences in relative steepness: relatively steep reaches can appear relatively gentle as quantified by . These inversions are function of the range of drainage area in the considered watersheds. We also demonstrate that the coordinate, and therefore the detection of migrating drainage divides, is sensitive to varying values of . The median of most likely across a wide range of mountainous and upland environments is 0.425. This wide range of variability suggests workers should not assume any value for , but should instead calculate a representative for the landscape of interest, and exclude basins for which this value is a poor fit.

Applicability of Geomorphic Index for the Potential Slope Instability in the Three River Region, Eastern Tibetan Plateau.

Geomorphic indices (e.g., the normalized channel steepness index (Ksn) and the stream length-gradient index (SL)) highlight changes in fluvial shapes and gradients. However, the application of these indices was seldom used to identify potential landslide zones. In this study, we used the Ksn and SL indices to detect the significant variations in the stream power along river reaches, which are anomalies associated with landslides, in the Zengqu River watershed, the upper reaches of the Jinsha River. Most of the landslide anomalies originate along the trunk and surrounding tributaries below the knickpoint of the mainstream. This suggests an erosional wave is migrating upstream throughout the drainage area. The fluvial incision may generate over-steepened hillslopes, which could fail in the future. In addition, the divide asymmetry index (DAI) predicts the direction of the divide as the headwaters migrate toward lower relief, higher elevation surfaces. Landslides are expected to occur as the unstable divide migrates. The proposed methodology can benefit the detection and characterization of potential landslide zones. It should improve hazard and risk analysis and the identification of drainage network areas associated with landslides.

Evidence for and against landscape transience in the Northern Qinling Mountains, China

The Northern Qinling Mountains, China, have experienced large earthquakes over the last millennium, including the 1556 Shaanxi earthquake, thought to be the deadliest earthquake in recorded history. Past studies suggest rapid Holocene fault throw rates, but exhumation and basin wide erosion rates are an order of magnitude slower. We explored channel profiles and normalized channel steepness index (ksn) values to evaluate evidence for landscape transience and potential acceleration in channel incision triggered by changing tectonic activity. We find that precipitation and lithological differences cannot explain the differences in channel steepness in the area. We integrate drainage area along channel profiles to plot a transformed coordinate, χ, against elevation, a technique that can identify signatures of changing channel incision rates. If there is acceleration in fault throw rates in a fault crossing the outlet of multiple basins, one would expect channel convexities located at similar χ locations as well as clustering of knickpoints at similar elevations. Instead, we find channel profiles are remarkably straight in χ-elevation space in basins that drain across the Qinling Northern Piedmont Fault (QNF) and Huashan Piedmont Fault (HPF). The landscape does contain a number of knickpoints but these do not cluster in elevation. Some basins in the area contain convexities but these convexities to not reappear in adjacent basins. These lines of evidence suggest that if fault throw rates have accelerated regionally along the QNF and HPF, they have not had time to substantially perturb channel profiles. Simple calculation of adjustment timescales for steady state channels suggests that the erosion rates, at least in channels not containing convexities, have been stable for timescales on the order of a million years.

Active Deformation and Relief Evolution in the Western Lurestan Region of the Zagros Mountain Belt: New Insights From Tectonic Geomorphology Analysis and Finite Element Modeling

AbstractTo unravel how and where coseismic and interseismic deformation impacts the spatial and temporal patterns of rock uplift of the Lurestan sector of the Zagros Mountains, we performed an investigation of the large‐scale features of topography and river network coupled with 2‐D finite element modeling. Geomorphological analysis and constraints from parameters such as elevation, local relief, normalized channel steepness index (ksn), river longitudinal profiles, and transformed river profiles (chi plots) were used to unravel the time‐space distribution of vertical motions. Whereas the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphology. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. The outputs illustrate how coseismic slip controls localized uplift of a prominent topographic feature—the Mountain Front Flexure—located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located farther to the NE, in the interior of the orogen.

Active Tectonics of the Frontal Himalayas: An Example from the Manzai Ranges in the Recess Setting, Western Pakistan

The Himalayan main frontal thrust (MFT) accommodates most of the present-day Indo–Asia convergence with related periodic earthquakes. The seismicity and deformation mechanism varies considerably across the frontal Himalayas. We mapped a segment (Manzai Ranges) of the MFT at the western margin of the Himalayas and analyzed its deformation mechanism and active tectonics using geomorphic indices and the Interferometric Synthetic Aperture Radar (InSAR) Small Baseline Subset (SBAS) technique. Two frontal thrust faults (Khirgi and Jandola) were mapped using Sentinel-2B band ratios in the study area. Water gaps were present in the form of deflected streams at the tip of the growing anticlines. The C-band RADAR interferometry (Sentinel-1A) showed an average uplift of 5–9 mm/year in the satellite line of sight (LOS) from May 2018 to October 2019. The velocity profiles show an uplift variation across the anticlines and may be related to the displacement transfer from the zone of compression in the Manzai Ranges to the zone of transpression in the Pezu–Bhittani Ranges. Four types of morphometric analyses were carried out to assess the relative tectonic activity, namely mountain front sinuosity index (Smf), valley floor width to height ratio (Vf), normalized longitudinal river profile, and normalized channel steepness index (Ksn). The landscape response to active tectonics in the study area was recorded as a deep fluvial incision in V-shaped valleys, convex river profiles, topographic breaks as knickpoints, and a high Ksn index. The geomorphic parameters show a relative increase in tectonic uplift and deformation from the Kundi anticline to the Khirgi and Manzai anticline. We concluded that the frontal structures in the western Himalayas are still going through an active phase of deformation and landscape development with both seismic and aseismic creep.

Detecting neotectonics in the lowlands of Amazonia through the analysis of river long profiles

There has been a considerable number of studies focusing on the analysis of river long profiles based on stream power incision models aiming to detect areas affected by neotectonics. Most of these studies have successfully uncovered active tectonics in mountainous landscapes, with some examples in areas of low reliefs around the globe. However, this kind of investigation has rarely been used in large tropical lowlands, such as the Amazonian lowlands, where the application of river long profiles is still challenging. The main aim of the present work was to test the functionality of methods based on river profiles to detect neotectonic reliefs in lowland landscapes. The Negro River basin was selected for this investigation, assuming the several indications of tectonic activity during the late Pleistocene and Holocene. We tested the normalized channel steepness index (ksn), with the identification of knickpoints and interpretation of swath profiles, computed from the 30 m digital elevation model provided by the Shuttle Radar Topography Mission. The results showed streams with profiles bounded by a set of knickpoints represented by very low ksn values in the right (average ksn = 8) and left (average ksn = 10) margins of the Negro River. These values contrast with the high range of ksn values generally found for rivers of tectonically active mountainous landscapes. Even with low values, we verified that a slight increase in ksn values was enough to detect transient rivers related with strike slip faults in Amazonia lowlands. The swath profiles also showed sectors on relief compatible with changes in the base level of the tributaries, with the record of knickpoints and an increase in ksn values. The experimental results obtained in this work motivate further quantitative investigation in Amazonian lowlands by testing geological data with new robust techniques from river profiles.

Assessing landscape response to tectonics in the Jalisco block and adjacent areas (west-central Mexico) using topographic analysis

To elucidate how landscapes respond to either tectonic and climatic changes through time, geomorphologists use the analysis of river and basin morphometry. Many studies have evaluated how rivers, and consequently hillslopes, respond to changes in the rate of rock uplift in compressional settings. The case of extensional settings, however, has received less attention. We examine the case of landscape response to tectonics in west-central Mexico to identify zones where there is notable increase in the tectonic activity. The study of west-central Mexico is challenging for the morphometric analysis since there is an interplay between the development of extensional structures and pulses of volcanism, mainly from Eocene to Oligocene and Pliocene to Pleistocene, that have buried large parts of the landscape. For our purpose we use the normalized channel steepness index (ksn) to evaluate how this index correlates with other morphometric parameters such as the hillslope gradient, hillslope convexity and concavity, terrain rugosity and first order stream gradient (Fosg). We use the landform units map as the spatial unit of analysis and from this, we estimate the morphometric properties of the landscape. The results of the morphometric analysis indicate that the topography of Eocene to Oligocene volcanic landscapes are well explained (~70%) by the ksn and in less degree for Pliocene to Pleistocene landscape where ksn accounts for ~55–66% of landscape morphometry. Our results also indicate that the ksn is the best suited among all morphometric variables used in this study and confirm that the landscape of west-central Mexico is dominated by river incision. Landscape incision is particularly high on the northern part of the Jalisco block, mainly along the Ameca river and its tributaries such as Atenguillo river, and north of the Jalisco block, along the Santiago river and on tributaries incising the Sierra Madre Occidental. Finally, the morphometric analysis indicates that even for the case where the volcanic rocks and sediments are filling up large parts of the landscape, river incision resulting from the tectonic activity is capable to cut into lavas, propagating the change imposed by the tectonic activity.

Landscape expressions of tectonics in the Zagros fold-and-thrust belt

This study uses geomorphic indices, including normalized channel steepness index (ksn), integrated relief and hypsometric index (HI), to investigate how landscape responds to tectonic and climatic drivers in the Zagros fold-and-thrust belt, and show how geomorphology can be a sensitive indicator of tectonic processes. There is a broad association of relatively high ksn values (>50 m0.9) with the upper elevation limit for seismogenic thrusting, which occurs regionally at the 1250 m topographic contour. Higher ksn values occur beyond this seismicity cut-off in the Bakhtyari Culmination, but are rare in the Fars region. We measured HI values for 17,380 third order river basins across the Zagros. In many areas the low/high HI transition (0.3) is typically at the elevation limit of seismogenic thrusting. There are two important exceptions. In the Dezful Embayment/Bakhtyari Culmination the low/high HI transition lies at higher elevations than the thrust seismicity cut-off. In the Fars region, the HI transition lies at lower elevations than the seismicity cut-off. We explain these differences by the different climates of the two areas: wetter conditions and vigorous drainage systems in the Dezful/Bakhtyari region retard orogenic plateau growth; drier climate and low power rivers in the Fars region promote plateau growth. Orographic precipitation may itself have a tectonic control; regional basement strength variations have caused intense thrusting and high relief in the Bakhtyari Culmination. Integrated relief of five across-strike Zagros topographic swath profiles is in the range 2.2–2.8 108 m2. We argue that this consistency within ~25% relates to the comparable strain rates across different sectors of the Zagros, regardless of local structural, drainage network or climatic variations.