Landform Evolution Research Articles

Debris‐Flow Process Controls on Steepland Morphology in the San Gabriel Mountains, California

AbstractSteep landscapes evolve largely by debris flows, in addition to fluvial and hillslope processes. Abundant field observations document that debris flows incise valley bottoms and transport substantial sediment volumes, yet their contributions to steepland morphology remain uncertain. This has, in turn, limited the development of debris‐flow incision rate formulations that produce morphology consistent with natural landscapes. In many landscapes, including the San Gabriel Mountains (SGM), California, steady‐state fluvial channel longitudinal profiles are concave‐up and exhibit a power‐law relationship between channel slope and drainage area. At low drainage areas, however, valley slopes become nearly constant. These topographic forms result in a characteristically curved slope‐area signature in log‐log space. Here, we use a one‐dimensional landform evolution model that incorporates debris‐flow erosion to reproduce the relationship between this curved slope‐area signature and erosion rate in the SGM. Topographic analysis indicates that the drainage area at which steepland valleys transition to fluvial channels correlates with measured erosion rates in the SGM, and our model results reproduce these relationships. Further, the model only produces realistic valley profiles when parameters that dictate the relationship between debris‐flow erosion, valley‐bottom slope, and debris‐flow depth are within a narrow range. This result helps place constraints on the mathematical form of a debris‐flow incision law. Finally, modeled fluvial incision outpaces debris‐flow erosion at drainage areas less than those at which valleys morphologically transition from near‐invariant slopes to concave profiles. This result emphasizes the critical role of debris‐flow incision for setting steepland form, even as fluvial incision becomes the dominant incisional process.

DEM-based analysis of tectonic geomorphologic characteristics and tectonic activity intensity of the Dabanghe River Basin in South China Karst

Abstract The Dabanghe River Basin, in the west of Guizhou Plateau, consists of numerous prominent geological structural features, such as the Shuicheng–Wangmo, Yadu–Ziyun, and Yongningzhen Faults, the Huangguoshu Waterfall, and the Guanjiao Knickpoint. The topographic conditions and structural systems are highly complex, making this a suitable area to study neotectonics. However, research on the geomorphology of the region is lacking. Combined with geomorphic parameters, quantitative exploration of tectonic geomorphic and tectonic activity in the Dabanghe River Basin is of great significance to reveal the formation of the Huangguoshu Waterfall, the development of landforms in western Guizhou, and the regularity of uplift of Guizhou Plateau. Therefore, based on a Digital Elevation Model, GIS software extracted and calculated six geomorphic parameters of the basin: Hypsometric Integral, Asymmetry Factor, Basin Shape Ratio, Stream-Gradient, and Valley Floor Width–Valley Height Ratio (VF) indexes. The tectonic geomorphic characteristics of the Dabanghe River Basin were analyzed, combined with the tectonic activity level classification method, and the Index of Relative Active Tectonics (IAT) of each sub-catchment was calculated. The geomorphic parameters of the basin were found to indicate its geomorphic characteristics well. The tectonic activity in the study area midstream is the most active, and the geomorphic evolution of some upstream and downstream reaches is affected by lithology, topography, and structure. The tectonic geomorphology of the basin is significantly affected by the fault system. Under the control of the Yadu–Ziyun Fault, the tectonic activity in the basin gradually weakens from west to east, and the differential tectonic activity (strong in the mid-reach and eastwards decrease) is consistent with observed seismic intensity. It is confirmed that our research results are consistent with the regional geological background and geomorphic characteristics through field geological survey. Therefore, this study confirms that the use of tectonic geomorphic parameters to classify active tectonics can be an important method to evaluate the stability of the crust in the region and further extends the application of geomorphic parameters in tectonics.

Triggering mechanism and brittle-ductile dynamics of active faults in the south-central Saurashtra horst, Gujarat, western India: A geospatial, geological, and geophysical approach

The seismically active Saurashtra horst is located within the intraplate volcanic continental margin of western India. The region is prone to moderate and low-magnitude earthquakes within the depth range of ∼ 3 to ∼ 24 km. We observed that the earthquakes in this region are associated with seismically active brittle and ductile crustal layers. To understand the dynamics of the earthquake generation process, we applied an integrated geological and geomorphological approach, supplemented by subsurface geophysical (magnetotelluric) studies. Additionally, the active surface deformation has been measured using the PSInSAR and GLA techniques. Based on the stream offset and geomorphic landform development pattern several NW-SE and NE-SW oriented strike-slip faults have been identified. The PSI-derived displacement analysis reveals that the area is deforming at the rate of ± 5 mm/yr. Furthermore, subsurface crustal heterogeneity with increasing depth has been identified using the magnetotelluric technique, which is reflected in the form of basaltic lava flows, plutonic emplacement within the granitic basement, and the presence of semi-crystallized magmatic bodies below the brittle-ductile level. Additionally, we proposed a model to depict the plutonic emplacement within the highly fractured/faulted granitic basement and their relationship to the earthquake generation process. Our model shows that crustal heterogeneity and the migration of hydrothermal fluid from the semi-crystallized magmatic body along the active fault cause earthquake nucleation processes within the brittle and ductile layers. We concluded that the upwelling magmatic fluid above the brittle-ductile transition (BDT) acted as a lubricant for the nucleation and triggering of the earthquake along the active faults. Similarly, the fractured ductile crust is weakened by fluid migration, which causes high fluid pressure in the ductile crust thereby decreasing the confining pressure and endorsing the velocity weakening in the aseismic layer, responsible for the shear instability that causes deep crustal earthquakes. More specifically, the lithological heterogeneity at brittle and ductile regimes is an important factor for the earthquake nucleation process in this part of the Indian plate.

Channel migration in the northeastern margin of the Tibetan Plateau and its implication for fluvial response to the interaction between rapid tectonic activity, climatic fluctuation and human influence

Fluvial response to allogenic and autogenic controls concerns the understanding of landform evolution related to the interaction between tectonic movements, climate, surface process and human activity. Paleo-channels, as part of geomorphic archives, have been widely employed to study this issue during recent decades. Previous work has however concentrated on the mechanisms driving river migration. A new approach, in which multiple elements are considered, is employed here in the examination of paleo-channel formation in the Jiudong Basin, located at the northeastern margin of the Tibetan Plateau and characterized by active tectonic deformation, a dry climate and ancient human activity. Based on geomorphic and sedimentary analysis, eight paleo-channels formed by the Taolai and Hongshuiba rivers (two tributaries of the Beida River catchment) have been identified. AMS14C dating of the overlying lacustrine sediments defined their respective abandonment at ca. 22.2, 20.9, 15.3, 18.8, 13.9, 11.9, 3.5 and 1.1 cal. Ka BP. The migration histories of the two rivers have been reconstructed, and then well correlated with reference to archives of tectonic, climatic and human influence. Our results suggest that these controlling factors seem to be coupled and have a competitive relationship in driving river migration. In the northeastern margin of the Tibetan Plateau, channel migration can therefore be regarded as a result of fluvial response to the interaction between rapid tectonic activity, climatic fluctuation and human influence.

Morphology of the north-western wall of Eos Chaos, Valles Marineris: Evidence for glaciation during late Amazonian high obliquity

Glacial landforms have been reported from various regions on Mars; most notably from the mid-to-high latitude regions. We studied Eos Chaos, located towards the eastern boundary of Valles Marineris, for the possible glacial processes occurring in the low-latitude areas on Mars. A thorough investigation of the morphology of the north-western wall of Eos Chaos was carried out using planetary datasets such as context camera (CTX) and High-resolution Imaging Science Experiment (HiRISE) images from NASA's Mars Reconnaissance Orbiter (MRO) mission and Mars Color Camera (MCC) images from ISRO's Mars Orbiter Mission-1 (MOM-1). We identified various geomorphological features that may have resulted from diverse geological processes. The glacial processes are manifested by the morphological features such as tongue-shaped lobate flows, alternative dark and light strata (~10-15 m thick), light-toned fragmented sediments, kettle lake-like structures, surface striations, sublimation hollows, and pit and knob structures. The flow features correspond to three stages of evolution: developing (~0.3 km length), intermediate size (1.5 km length), and mature (~15 km length). These three stages culminated in developing a model depicting the evolution of the glacial landforms of the region based on morphological features. We deduce that the glacial landforms of the region were formed during episodes of higher planetary spin axis obliquity during the late Amazonian.

Assessment of soil erosion using WSA and SPR techniques for Giri watershed, Himachal Pradesh, NW Himalaya, India

A watershed is the result of several geomorphic processes such as weathering, erosion, degradation and aggradation which are influenced by several factors viz. tectonics, lithology, climate, landslides and mass wasting processes etc. In a tropical climate, watersheds contribute a significant amount of eroded material which is reflecting the impact of lithology, precipitation, tectonics, relief and anthropogenic activities. In the Himalayan region besides significant heterogeneity in lithology, stratigraphy, structure and tectonics, it is observed that variability is exhibited in climatic conditions over a small region. These factors contribute to the development of geomorphic landforms and are best studied in watersheds or river basins. In the present study, Giri Watershed (GW) is assessed to contemplate susceptibility to erosion for 66 sub-watersheds using geomorphic parameters. The prioritization of subwatersheds has been done using Weighted Sum Analysis (WSA) and Sediment Production Rate (SPR) methods. The quantitative analysis of subwatersheds is categorized into different priority classes viz. very high, high, moderate, low and very low, among which 27 subwatersheds have very high to high susceptibility to erosion.

Paleotopography-constrained numerical modeling of loess landform evolution

Numerical modeling of landform evolution is the key to understanding the formation of land surfaces. However, landform evolution occurs under certain initial topographic conditions, while existing landform evolution models often use a plane or a randomly produced surface to establish the initial topographic conditions. This misunderstanding of the initial topographic conditions causes the landform evolution results to deviate greatly from the real terrain. Therefore, the initial topographic conditions must be reconstructed and integrated into the current numerical landform evolution model. In this paper, the Loess Plateau of China was selected as a typical sample area. The paleotopography was reconstructed and integrated into the numerical landform evolution model. Based on the evolutionary mechanism of loess landforms, modules of surface erosion, matter diffusion and precipitation were selected to construct a numerical model of loess landform evolution. Moreover, randomly produced terrain was used as the initial conditions during the landform evolution process and compared with the paleotopography-constrained evolution results. In addition, the results of the landform evolution process were evaluated with different terrain factors, and the uncertainty of the model was assessed by comparing different model conditions. The results show that, due to the control of paleotopography, the evolution results can maintain the main morphological structure of valleys in the loess landscape. Without considering the paleotopography, a large difference exists between the evolution results and the true ground terrain. These results show that paleotopography is an important feature of loess landform evolution modeling and is indispensable for reasonably expressing the process of landform evolution. Finally, the numerical modeling of loess landform evolution with the consideration of paleotopography can not only help to achieve a better understanding of the loess landform evolution process but also provide a reference for feature dependent landform evolution modeling in different landform applications.

OSL chronology reveals Late Pleistocene floods and their impact on landform evolution in the lower reaches of the Keriya River in the Taklimakan Desert

OSL chronology reveals Late Pleistocene floods and their impact on landform evolution in the lower reaches of the Keriya River in the Taklimakan Desert

Interacting effects of climate change and invasions by alien plant species on the morphodynamics of temperate rivers

AbstractThis review explores the implications of climate change for the functioning of plant species as biogeomorphic engineers of temperate river systems, including the potential for an increasing role of invasive alien plant species (IAPS). First, we introduce engineer plants as important controls, along with flowing water and transported sediments, on the morphodynamics of river systems and the likelihood that climate change may affect the contributions of species within their native habitats. We then examine through the prism of the fluvial biogeomorphic succession model how climate change may accelerate the establishment of IAPS, the possible consequences for the performance and/or persistence of native engineer plant species, and thus the potential pathways of influence for IAPS on river morphodynamics. Finally, we present examples of the impacts of invasions by specific plant species along particular river systems and consider their potential biogeomorphic impact against a backdrop of climate change. Loss, replacement, or displacement of native plant species in the river corridor by IAPS can potentially alter biogeomorphic phenomena by directly increasing or decreasing erosion and/or sedimentation and the associated development of fluvial landforms. In the shorter term, increased climate disturbance may provide more establishment opportunities for opportunistic IAPS. In the longer term, under heavy establishment, IAPS may alter the coupled assembly of plant communities, fluvial landforms and ecosystem development, potentially resulting in river landscape metamorphosis and significantly changed habitat conditions.This article is categorized under: Science of Water > Water and Environmental Change Water and Life > Nature of Freshwater Ecosystems Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

Reconstructing the pattern of late Quaternary climate through sediment-landform assemblages in the Dhauli Ganga valley (upper Ganga catchment), India

The present study focuses on the reconstruction of the pattern of late Quaternary climate variability through sediment-landform assemblages in the monsoon-dominated Dhauli Ganga valley. The South Tibet Detachment System (STDS) is a major litho-tectonic boundary that divides the Dhauli Ganga valley into two broad geomorphic entities. Towards the north of STDS, the valley is wide and “U” shaped, and the rivers have a braid-meandering channel, implying that the valley was carved by glacial sculpturing in the past. Whereas in the south, deep gorges indicate the dominance of fluvial processes. Based on the stratigraphic position and optical chronologies, the lithified moraines were assigned to Marine Isotopic Stage-3 (MIS-3) they were followed by a major deglaciation event represented by moderately lithified outwash gravels. Following this, a second glacier advance of lesser magnitude is dated 21.3 ± 2.2 ka, corresponding to the Last Glacial Maximum (LGM). A gradual recession of the LGM moraines led to the formation of a proglacial lake which probably persisted until around the onset of a pulsating deglaciation stage represented by outwash gravels dated between 13.4 ± 1.6 and 9.4 ± 0.8 ka. This was also the period when the valleys were overwhelmed by a high sediment water ratio, as indicated by temporary impoundments dated between 15.0 ± 1 ka and 10.0 ± 1 ka. Alluvial fan and debris flow sedimentation overwhelm the valley after around 9 ka and continues till the present.Climatically, the older lithified moraines indicate that glaciers advanced during the cooler MIS-4 or MIS-3. The first major deglaciation event seems to represent the pluvial phase of MIS-3. The presence of LGM moraines indicate that the valley responded to the global cooling and associated enhanced westerlies. In contrast, the chronology of outwash gravels suggests that the valley witnessed insolation driven by the early Holocene strengthened Indian Summer Monsoon (ISM). The undated youngest alluvial fans/debris flows are assigned the mid to late Holocene age (<9.5 ka) and seem to have deposited during the declining phase of ISM (low solar insolation). The study suggests that the landform evolution responded to both the global and regional climate variability indicating the sensitivity of the paraglacial valleys in the monsoon-dominated region to the late Quaternary climate variability.

Effect of weathering on short‐ and long‐term mechanical behaviour of granitic soils from the Benggang area under unloading conditions

AbstractAs regional soils collapse during the development of Benggang landforms, the release of geostress results in soil disintegration. This phenomenon is associated with soil instability, and it necessitates a study on the mechanical behaviour of decomposed granitic soils in response to unloading in the Benggang area. This study addressed the short‐ and long‐term mechanical behaviour of granitic soils with various degrees of weathering in response to unloading. Triaxial unloading and multi‐stage unloading creep tests were performed, including a comparative study of consolidated undrained (CU) triaxial tests. The deformation characteristics of granitic soils differed with the degree of weathering and the initial stress level. The most significant adverse effect of creep behaviour under unloading and undrained conditions was found in granitic soils with the greatest loss rate of maximum shear stress in contrast to the cases of CU compression and one‐time unloading. Additionally, increasing time‐dependent deformation was observed with increasing degree of weathering and initial stress level, which suggested that creep behaviour under unloading conditions accelerated soil erosion and instability in the Benggang area. The results of this study highlighted the potential influences of geostress release and time‐dependent deformation on soil instability in the Benggang area and advanced the understanding of mechanical mechanisms during the development of Benggang landforms.

The role of topography in landform development at an active temperate glacier in Arctic Norway

AbstractTopography exerts a strong control on how glaciers respond to changes in climate. Increased understanding of this role is important for both refining model predictions of future rates of glacier recession and for reconstructing climatic change from the glacial geological record. In this paper, we examine the geomorphological and sedimentological evidence in the foreland of Fingerbreen, a temperate outlet of the plateau icefield Østre Svartisen. The aim is to investigate the relationship between processes of landform generation and the changing influence of topography as recession progressed. The Fingerbreen foreland is dominated by bouldery Little Ice Age moraines and extensive areas of striated bedrock. A heavily fluted zone occurs in the central part of the foreland that is cross‐cut by annual transverse and sawtooth moraines. Systematic investigations of the structural architecture of moraines at various locations in the foreland provide evidence for a range of moraine‐forming processes, which can be linked to the topographic setting (e.g. deposition on a reverse bedrock slope) and drainage conditions. This includes push and bulldozing of proglacial sediments and squeezing of sub‐glacial sediments and submarginal freeze‐on of sediment slabs. We also identify variations in moraine spacing as a result of topography. This research demonstrates the importance of topography when interpreting moraine records in the context of climate and glacier dynamics.

Distinct modes of meltwater drainage and landform development beneath the last Barents Sea ice sheet

The flow of glacial ice is impacted by basal meltwater drainage systems that fluctuate on a continuum from distributed, high-pressure environments to channelized, lower pressure networks. Understanding the long-term development of dominant drainage modes and impacts on ice flow and landform development is a crucial step in predicting palaeo and contemporary ice-mass response to changes in climate. The spatial and temporal scales at which different drainage modes operate are largely unknown, and the geomorphological legacy of subglacial meltwater networks that evolve over a glaciation provide composite records of drainage system development. Here, we use high-resolution bathymetric data from shallow banks in the central Barents Sea to map the geomorphological imprint of meltwater drainage beneath the collapsing marine-based Barents Sea Ice Sheet (BSIS). We observe a succession of distinct meltwater landforms that provide relative timing constraints for subglacial drainage modes, indicating that extensive networks of channelized drainage were in operation during deglaciation. Interlinked basins and channels suggest that meltwater availability and drainage system development was influenced by filling and draining cycles in subglacial lakes. Networks of eskers also indicate near-margin meltwater conduits incised into basal ice during late-stage deglaciation, and we suggest that these systems were supplemented by increased inputs from supraglacial melting. The abundance of meltwater during the late stages of BSIS deglaciation likely contributed to elevated erosion of the sedimentary substrate and the mobilisation of subglacial sediments, providing a sediment source for the relatively abundant eskers found deposited across bank areas. A newly discovered beaded esker system over 67 km long in Hopendjupet constrains a fluctuating, but generally decelerating, pace of ice retreat from ∼1,600 m a−1 to ∼620 m a−1 over central Barents Sea bank areas during a 91-year timespan.

Soil erosion modeling using computer-graphic methods and geographic information systems

The surface of the earth, exposed to gravitational forces, wind, water and ice, is continuously evolving within spatial and temporal proportions. The erosion processes that form the land surface are extremely complex and difficult to quantify over large areas. Remote sensing provides important data that allows us to gain insight into the interactions between physical processes and environmental conditions that control the erosion and development of landforms. Recent advances in mapping technologies, such as the use of LiDAR, hyperspectral imaging, and ground-penetrating radar, have significantly increased the spatial and temporal function of the analysis of these processes. New research suggests that fundamental changes in the initial theories of erosion processes may be made to align with new scientific findings. Analysis and modelling based on the science of geospatial information (GIS) play an important role in better understanding and predictability aimed at minimizing the negative impacts of soil erosion and its deposition. In this paper it is presented the views, theory and methods of modelling soil erosion, sediment transport and sedimentation in watercourses based on the application of computer graphics methods and the use of geographic information systems. The mathematical equations that stand in the algorithmic backgrounds of the models for the control of soil erosion are applied for the calculation of the intensity of erosion, and the modelling of this process of soil degradation. The presented methods explain the movement of eroded material from basins, its deposition downstream, and the influences of these processes on the evolution of natural landscapes of the studied areas. Some approaches that used GIS applications in simple and advanced models are discussed, and models used in the world and in the Western Balkans region are presented.

The impact of natural and anthropogenic factors on the landforms and landscapes of mountains and their forelands

This paper is an introduction to a collection of nine studies that are intended to fill the gap in the literature associated with landform development and landscape changes related to natural forces and human activities in the Central European Mountains and their close forelands. The papers are grouped into four general categories that describe the influence of climate on glacial landforms and snow avalanches, the evolution of slopes in high mountains, the development of mid-mountain relief, and changes in fluvial systems in mountains and their forelands. This paper summarises the contributions of these studies to this special issue and attempts to outline possible avenues of future research on landforms and landscapes in mountainous areas.

Evidence for preservation of organic carbon interacting with iron in material displaced from retrogressive thaw slumps: Case study in Peel Plateau, western Canadian Arctic

In northern high latitudes, rapid warming is set to amplify carbon-climate feedbacks by enhancing permafrost thaw and biogeochemical transformation of large amounts of soil organic carbon. However, between 30 % and 80 % of permafrost soil organic carbon is considered to be stabilized by geochemical interactions with the soil mineral pool and thus less susceptible to be emitted as greenhouse gases. Quantification of the nature of and controls on mineral-organic carbon interactions is needed to better constrain permafrost-carbon-climate feedbacks, particularly in ice-rich environments resulting in rapid thaw and development of thermokarst landforms. On sloping terrain, mass wasting features called retrogressive thaw slumps are amongst the most dynamic forms of thermokarst. These multi-decadal disturbances grow due to ablation of an ice-rich headwall, and their enlargement due to warming of the Arctic is mobilizing vast stores of previously frozen materials. Here, we investigate headwall profiles of seven retrogressive thaw slumps and sediments displaced from these mass wasting features from the Peel Plateau, western Canadian Arctic. The disturbances varied in their headwall height (2 to 25 m) and affected land surface area (<1 to > 30 ha). We present total and water extractable mineral element concentrations, mineralogy, and mineral-organic carbon interactions in the headwall layers (active layer, permafrost materials above an early Holocene thaw unconformity, and Pleistocene-aged permafrost tills) and in displaced material (suspended sediments in runoff and material accumulated on the debris tongue). Our data show that the main mechanism of organic carbon stabilization through mineral-organic carbon interactions within the headwall is the complexation with metals (mainly iron), which stabilizes 30 ± 15 % of the total organic carbon pool with higher concentrations in near-surface layers compared to deep permafrost. In the displaced material, this proportion drops to 18 ± 5 %. In addition, we estimate that up to 12 ± 5% of the total organic carbon is stabilized by associations to poorly crystalline iron oxides, with no significant difference between near-surface layers, deep permafrost and displaced material. Our findings suggest that the organic carbon interacting with the sediment mineral pool in slump headwalls is preserved in the material mobilized by slumping and displaced as debris. Overall, up to 32 ± 6 % of the total organic carbon displaced by retrogressive thaw slumps is stabilized by organo-mineral interactions in this region. This indicates that organo-mineral interactions play a significant role in the preservation of organic carbon in the material displaced from retrogressive thaw slumps over years to decades after their development resulting in decadal to centennial scale sequestration of this retrogressive thaw slump-mobilized organic carbon interacting with the soil mineral pool.

Evolution of the first mouth bar, distributaries and floodplains of the Pearl River Delta

As one of the most densely populated areas in the world, the Pearl River delta has been well studied in its postglacial sedimentary stratigraphy and the effects of Holocene sea-level rise. However, the effects of fluvial force on its geomorphological evolution are much less understood. This paper analyzed the Holocene sedimentary archives and reconstructed the geomorphologic history of an area where the West and North Rivers join and enter the deltaic basin. The reconstruction is based on the analyses of particle size, total organic carbon, organic carbon isotope ratios and microfossil diatoms of five radiocarbon-dated core sediments. The results show rapid paleo-incised valley infilling since c. 9500 cal. a BP, in response to sea-level rise. During marine regression starting from c. 8000 cal. a BP, a bifurcation occurred, and a mouth bar was developed. While the mouth bar emerged to mean tide level around c. 5500 cal. a BP, the surrounding estuarine subtidal flats were gradually transformed into tidal wetlands by c. 3000 cal. a BP. The immediate adjacent waters to the mouth bar were gradually infilled from c. 3000 cal. a BP onwards which narrowed the distributary channels. This landform evolution in the head area of the Pearl River delta resulted in the gradually strengthening fluvial force and weakening tidal force since the relative sea level approached its stabilization. During the past 3000 years, the continuous strengthening of fluvial force supported the accretion of deltaic floodplains. The discovery of mouth bar formation, channel narrowing and deltaic floodplain accretion in this location brings a new perspective of scientific investigation to river delta geomorphologic evolution in response to natural and anthropogenic factors.

Landform classification and geomorphological mapping of the Chota Nagpur Plateau, India

Geomorphological map plays a key role to illustrate landscape evolutionary history along with the guidelines of sustainable landuse planning. The Chota Nagpur Plateau is situated in the eastern part of the Indian subcontinent and it is a storehouse of valuable rocks and minerals of Precambrian origin. Classification of geomorphological units is highly required for sustainable landuse planning and natural hazards management. So, the principal objective of this scientific study is to classify the Chota Nagpur Plateau region into micro geomorphological units by applying automated and semi-automated methods. Digital elevation model (DEM) data and satellite imageries (from United States Geological Survey) have been used to improve the precision of this map. Geomorphological mapping techniques such as terrain attributes classification, Topographical Position Index (TPI) and Slope Position Index (SPI) have been applied to extract the major geomorphological units or features. TPI values show that the maximum area comes under the valley bottom with stream (35.26%) followed by the high ridge (24.55%) whereas minimum area coverage is found in the open slope zone (0.02%). Local ridges and mid-slope ridges lie in 8.77% and 4.94% area respectively. The result has been verified through field verification techniques with the help of GPS data. This high-accuracy map should be applied for regional planning and natural hazards management. These techniques also give very good results for terrain classification as well as landforms evolution.

Physically based numerical model for the landscape evolution of soil-mantled watersheds driven by rainfall and overland flow

Soil and gully erosion is a critical threat to sustainable agricultural land management and productivity. Soil erosion by rain splash, sheet runoff, and concentrated flow are complex problems conditioned by the combined interactions of soil physical properties, hydrology, human activity, landscape topography, and climate. Effective management of erosion processes driven by rainfall and surface runoff requires a combined effort of field observation, physical experimentation, and numerical simulation. A physically-based hydrodynamic numerical model, CCHE2D with updated raindrop erosion effects, is applied to simulate landscape evolution processes as a result of raindrop impact and overland flow. The numerical model simulates a thin layer of runoff and concentrated flow over complex terrains, and predicts sediment transport due to raindrop splash detachment, transport and soil surface erosions. Soil erosion and landform evolution simulations due to rainfall are presented for an experimental landscape and a tilled large scale agricultural field. Photogrammetric field data were collected using an unmanned aerial system (UAS) following planting and subsequent rainstorms. Numerical simulation results agreed well with the observed experimental soil surface topography, sediment yield, and drainage network developments. The simulated soil and gully erosion in the tilled field also agreed well with observations. This research successfully demonstrates how high resolution spatial and temporal topographic measurements in experimental and field landscapes can be simulated and interrogated by 2D physically-based hydrodynamic and morphodynamic models. The accurate predictions of tillage field and gully erosion process in agriculture watersheds with complex tillage conditions also indicated the usefulness of the model for studying soil and landscape degradation.

Landform evolution in Asia during the Cenozoic revealed by formation of drainages of Wei River and Indus River

Formation and evolution of the Asian landform was determined by growth of the Himalaya-Tibetan Plateau and evolution of the Asian monsoon climate during the Cenozoic period. In this process, mountain building and degradation, and river drainage reorganization are the most obvious results. On the other hand, developments of large scale drainages preserved in related basin sediments are direct records of evolution of Asian landforms. In this study, we use thick fluvial-lacustrine sediments in the Weihe Basin near the northeastern Tibetan Plateau, and Ocean Drilling Program (ODP) sediment cores from Arabian Sea adjacent to the southwest Himalaya-Tibetan Plateau, to reconstruct erosion processes of the Himalaya-Karakorum and Qinling Mountains and infilling history of the Weihe Basin and northern Arabian Sea during the Cenozoic. Based on independent stratigraphic chronology and source-to-sink analyses, our results show that the large drainages of the Wei River and the Indus River were established at an upper limit of time by middle Eocene. Since the formation of these large drainages is mainly determined by topography and precipitation/runoff, we deduce that key parts of Asian landform such as southwestern/western Tibetan Plateau and Qinling Mountains had grown to a significant elevation to form the proto-Indus and proto-Wei rivers catchment. The modern-analogue Asian topography was established at least by the middle Eocene. Our new results support an early origin of the Asian landforms as responses to the collision of Indian and Eurasian plates and erosion by the Asian hydrology processes.