Himalayan Neotectonics and Channel Evolution

Neotectonics keeps its prominent signatures on river channel evolution. This chapter reviewed emergence, flourishment and advancement of the study of neotectonics, adjustment of fluvial forms and processes to neotectonics within the territory of Indian Subcontinent. Based on this review, we confirm the theme of the volume and suggest profuse scope of further research on the Himalayan Neotectonics and Channel Evolution in the Indian Subcontinent ranging from basin-scale to channel-site scale. We also introduced other chapters of the book.

Geomorphology of the Bhagirathi-Alaknanda catchments draining across the northwest Himalayas was studied to understand the role of differential tectonic uplifts over landscape erosional rates and landscape shaping. We plotted longitudinal profiles of Bhagirathi and Alaknanda and identified the major thrust zones along these trunk streams. For the comprehension of differential uplift, steepness and concavity indices were computed in between major thrusts along the longitudinal profiles. The regions experiencing very high erosion were recognized through anomalously high normalized steepness index (k_sn) and dense distribution of knickpoints on the drainage network. Further estimation of average erosion and deposition rates between the major thrusts was done through establishing linear correlation of average normalized steepness index and readily available in-situ ¹⁰Be cosmogenic dating-derived erosion rate data. Our results indicated a very high erosion rate (2.87 mm/yr) between Main Central Thrust I and II (Vaikrita Thrust), related to intense uplift, high recurrence of landslides and profound fluvial incision. Regions from MBT to further south towards Ganga plain showed strong aggradation at an average rate of 3.03 mm/yr.

The Trans-Himalayas in India comprise of the Ladakh, Karakoram and Zanskar (also spelled as Zaskar) ranges. These ranges are marked out by the presence of several active major thrust faults, which are epicenters of recurrent seismic activity. Their alignments control the main stream courses of the area, resulting in sharp bends, obtuse junctions, steep defiles and abrupt changes in channel morphology, wherever streams transition across different morpho-structural units. The present study focuses on the drainage composition and topographic characteristics of the Leh and Nubra valleys in the Ladakh region, along the courses of the Indus, Zanskar, Shyok and Nubra rivers. The morphometric attributes and spatial variation in terrain aspects of the basins developed within the aforementioned three ranges and draining into these four rivers are examined using the ALOS PALSAR Digital Elevation Model (DEM) to elicit watershed and channel parameters related to tectonics. Thrust faults digitized from the available geological maps of the region are compared with the principal streams extracted from the above DEM dataset through an overlay analysis to discern the influence exerted by the principal thrust faults and other structural lineaments on the drainage alignment. Segment-wise stream gradient indices reveal the abrupt changes in longitudinal profile and resultant changes in channel morphological characteristics as the rivers traverse these various structural and lithological entities. These attributes of the drainage character are compared with the various lithological and geomorphic entities of the area, to elicit the river character in each physiographic unit.

This study investigates the influence of neotectonics on the Solani River basin, using morphometric parameters, seismic signatures, and field-based study of unpaired river terraces. Morphometric parameters such as linear, areal, relief parameters, slope, aspect, stream-length (SL) index, and longitudinal river profile (LRP) suggest that the neotectonic activity triggered by the Himalayan tectonics affect the Solani River basin. Local convexity in the LRP indicates differential uplift along the associated faults. However, minor variation in knick points in LRP has been interpreted as rapid erosion due to unconsolidated to semi-consolidated nature of the sediments. The SL index of the Solani River ranges from 29.4 to 5233.2. The SL values along the river length indicates anomalies around the active fault zones. Mountain front sinuosity (S_mf) adjacent to the river basin ranges from 1.04 to 1.13, suggesting tectonically active nature of the region. Unpaired terraces reported at Roorkee and Toda-Kalyanpur at the right bank of the river are evidence of neotectonics. Three unpaired terraces reported at Roorkee, have riser-height of 1, 1.5, and 3 m and tread-width of 50, 40, and 70 m. While the riser and tread could not be measured at Toda-Kalyanpur due to their deformed nature. These E-W aligned terraces present 1.5 km south of the present river course dated back to 2.5 Ka (T₁) and 1.6 Ka (T₂). These terraces were formed due to the river shifting in response to the uplift of the river basin along with the Ganga plain. The upliftment rate along the Himalaya in the area shows a good coherency with few of the morphotectonic signatures of the basin. Other morphometric parameters such as hypsometry, asymmetry, valley width height ratio, did not yield supporting result, probably due to the DEM error and the unconsolidated nature of the sediments.

The present study deals with the study of tectonically regulated landform development within the meander pattern of the Alaknanda River in Lesser Garhwal Himalaya. We used high-resolution satellite imageries supplemented by field investigation to identify landform features exclusively regulated because of tectonic forces. The style of geomorphic landform and deformation pattern reveals the presence of strike-slip transverse faults within a zone of North Almora Thrust (NAT). The structural and lithological controls on the Alaknanda River system in Srinagar valley are manifested by steepness changes and deviations of drainage patterns. We identified several geomorphic anomalies such as an abrupt change in the flow direction, incised meandering, offset river channels, paleo-channels, multi-levels of terraces, knick points, and pools in the longitudinal profile associated with active tectonic in the area. Furthermore, we used morphotectonic landforms and a digital terrain model to generate a litho-tectonic map of the Srinagar valley. The results of the study show that the sinuosity index of the river is 1.34 which shows a sinuous to meandering trend. All 8 sets of meander segments are controlled by tectonic features i.e. fault, and lineaments. Six levels of terraces are the results of episodic upliftment. The meandering course is correlated with tectonic features hence it concluded that the river channel is closely controlled by structural features in the study area.

The Indian state of Tripura and the adjacent parts of eastern Bangladesh are characterised by six N–S aligned westerly arcuate anticlinal ridges of the Chittagong–Tripura Fold Belt (CTFB), uplifted during the Pleistocene. The Buri (107 km in 2017) originates from the western flank of the CTFB’s Baramura Range (247 m) and drains into the Meghna system of the Ganga–Brahmaputra–Meghna Delta. Maps and images of 1931–34 (Survey of India ‘inch’ maps), 1962 (Corona photos), 1975 (Landsat-1 MSS image), and 2017 (Resourcesat-2 L4-fmx image) show that the river markedly changed its planform during the last 84.5 years. Based on valley directions and characteristics, the Buri is divided into 37 reaches. Of these, sinuosity indices (SI) of 36 are calculated for the four survey/imaging years to determine the extent of change. Shuttle Radar Topography Mission elevation data (3 arc second tiles) of the region are utilised to bring out structural signature on drainage using profile shape, normalised stream length-gradient (SLk) index, and basin asymmetry factor (AF). χ-map of the Buri and its surrounding basins is taken into consideration to observe the topographic stability of this region. Finally, long-term rainfall records close to the Buri Basin (932 km²) are analysed as proxies for change in discharge. The results show that the Buri is antecedent to all anticlinal axes along its course. Overall, its 1931–34—2017 SI decreased in 64% of the reaches (1.58–2.76 to 1.02–1.17). Within the hills, increase in 1931–34—2017 channel SI coincided with high SLk values (>2) as well as profile convexity in two stretches, suggesting neotectonic uplift. In two other convexity zones, the 1931–34—2017 SI decreased contradictorily, possibly due to local aggradation or modification. An AF of 31 indicates that the Buri Basin has a probable tilt to the north. The χ-map of the area shows that the water divide is migrating towards the basin at its headwater region. Any statistically significant change in long-term rainfall records close to the basin is not present. Landuse alterations in the basin is also small, and unlikely to impact planform changes. In its deltaic stretch, the reasons for drastic change in the Buri’s sinuosity index (1.40–4.13 to 1.08–1.26) can principally be ascribed to channelisation that reduced its length by 55% between 1931–34 and 1962; sinuosity of the river is slowly increasing thereafter.

This study is an endeavour for analysing the neotectonic signatures reflected at basin scale for few selected rivers in the eastern part of Himalayas through the application of morphotectonic indices. River catchments around the Jaldhaka re-entrant have been considered in this study due to its proven sensitivity to neotectonic perturbations. Since, the impact of neotectonics has already been sensed on the piedmont segment, the nature of sensitiveness of the fluvial forms at the entire catchment scale to tectonic deformations has been the focal theme of this study. The selection of the eleven morphotectonic indices was done pondering on three major geomorphic perspectives; basin form components, basin and valley relief components and channel long profile form parameters. The nature of the geomorphic signatures found at the basin scale, river valleys and along the river courses have steered towards an ongoing adjustment of the fluvial units with active tectonism. Invariably the catchments are experiencing a state of dynamic equilibrium where adjustment between the fluvial activity and tectonic upliftment along the major thrusts is characteristic of fluvial form modifications within the studied catchments. The neotectonic perturbations have its indentations reflected in the channel long profile form adjustments with characteristic differences of channel responses related to different expressions of surface warping. Spatial associations of the knick points has been observed in a close correspondence with the Himalayan thrusts and surface deformations, developed on the alluvial reaches of the foredeep plain are explicitely associated with the neotectonic twitching.

Himalayan Foreland Basin (HFB) has been a fluvio-geomorphic domain of hyper-avulsive rivers associated with numerous abandoned channels. This study contemplates the evolution of a presently abandoned channel named Dharala and the echoes of neotectonic controls in it. Analysing the old data inventory in the forms of old maps since 1767 and colonial literature along with fine resolution digital datasets and validation of those using geomorphic markers and sedimentary archives have been the major stance of this study during establishing the facts of channel development. While marking out the tectonic controls in the process of channel development morphotectonic approach was embarked using the indices related to channel planform; Regional Sinuosity, Topographical Sinuosity index, Meander Arc Angle and Meander Shape Index along with channel orientation parameters; channel parallelism to neotectonic confinement and meander bends direction. Dharala River, one of the major branches of Torsa River, was formed primarily through capturing palaeo channels of Jaldhaka River and later on reworked by the major share of discharge of Torsa River. The abnormality in the channel planform with respect to the locational extent, sudden deflections in channel direction around the points where Dharala had encountered lineaments or fault lines had certified the positive controls of neotectonic features. Precisely, intense meandering with sinuosity ranging from 1.20 to 3.12, possible deformations in channel long profile with relatively flatter middle segment, channel segments deflected along the lineaments and fault lines with 42% of the total number of major turns in channel direction that had encountered neotectonic confinements, confined meandering with 21% of total bends oriented in the NNE-SSW direction and the existence of micro-terraces and entrenched channel segments had showcased neotectonic controls on the development of Dharala River.

The NNW-SSE trending Manabhum Anticline is an impressive hill in the foredeep area of the Naga-Schuppen belt near Mishmi Hill on the southern bank of the Brahmaputra. We present a detailed geological study of this area to better establish its Quaternary tectonics. Rocks exposed in the core of the Manabhum anticline are Pleistocene in ages and Holocene sediments are also involved in the deformation. We have prepared a geological map at the 1:25,000 scale and for the first time dated nine representative samples of rocks and sediments from this area. Three distinct age ranges have been obtained; ~220 ka- ~130 ka, ~ 67 ka- ~36 ka, and less than 10 ka. We interpret the Manabhum Hill as an asymmetric antiformal fold that is actively developing in a compressive regime near the Eastern Himalayan Syntaxis (EHS) zone. We present evidence that it has been highly active tectonically during Pleistocene-Holocene time and maybe a key to understand how collision has accommodated and evolved in the eastern syntaxis.

A quantitative assessment of landform and sediment in Quaternary deposits, focusing upon the Mountain Front Thrust (MFT) manifests neotectonics in the aftermath of the orogeny, is intended in the Darjeeling Sub-Himalayas, to feel the ever-fecund pulses of ground tremors. The Sub-Himalayan hilly terrain, generally without sediment cover, has a distinctive character on two sides of the Mountain Front Thrust in terms of drainage pattern and density, stream order, 1st order stream gradient, and shape and size of watershed basins. The sinuosity of MFT <1.4 elicits tectonic deformation. Comparatively smaller and more elongated watershed basins residing at the southern flank of MFT suggest steepness along with tectonic imprints. Significantly more frequent occurrence of parallel drainage patterns, comparatively lower stream orders, and consequent reduction in drainage density on this thrust front are well anticipated. The River Tista in the area achieves minimum gradient on the crest of the MFT eliciting uplift. Frequent changes in river gradient around MFT without any correlation with lithologic changes testify tectonic effect. The valley floor-width/height ratios (<0.5) derived from this river bear clear attestation to the tectonic youthfulness of the studied terrain. This uplift of the MFT recorded the basin subsidence in fluvial sequence building with thinning of valley cycles through vertical stacking of warped and tilted multi-generated terraces along River Tista in the Sub-Himalayan region. A concomitantly progressive increment of clast sizes and distal crystalline rocks in a vertical succession of sediment piles with southward migration on thrust shoulder along with enhancement of sedimentation rate upstream and channel incision suggests the directive measurements of tectonism, not climatic effect. The common presence of penecontemporaneous deformational structures in the pile is also suggestive of intermittent tectonic disturbances.

This book chapter provides immense documentation of Himalayan foredeep neotectonics and evolutionary processes that focus on landform deformation and channel succession in terms of morphotectonic discussion at a glance. The Himalayan foredeep foothill is composed of successive sediment deposition of 16.0–0.5 Ma BP i.e. Middle Miocene-Middle Pleistocene and late Quaternary Siwalik, which is overlain by young thick sandy to loamy sediments of Holocene near surface (Jain AK, Banerjee DM, Kale SV (2020) Tectonics of Indian subcontinent, society of earth scientists series, ISSN 2194-9204 ISSN 2194-9212 (electronic), ISBN 978-3-030-42844-0 ISBN 978-3-030-42845-7 478 (eBook), 111–433. 10.1007/978-3-030-42845-7). This elongated section is formed by series of alluvial fans, which are deformed and restructured by the neotectonic activities evident by earthquake magnitude in the last 120 years with the presence of Matiali scarp (MBT) 34 ka, Chalsa scarp (MFT) 11–6 ka (Kar et al. Geomorphology 227:137–152, 2014). The MIS-3(marine isotope stage 3) of 34 ka (Mukul M, Singh V (2016) Active tectonics and geomorphological studies in India during 2012–2016. In: Proceedings of the Indian national science academy, p 82 10.16943/ptinsa/2016/48480) initiated the alluvial fan formation (Matiali fan) which had been interrupted by repeated tectonic activities and accompanied by hydrological flow alteration due to climate change as the emergence of LGM (Last Glacial Maximum) and MIS-2 in Holocene (Martinson et al. Quatern Res 27:1–29, 1987). Upliftment and erosion sequences assemblaged by slope differentiation and flow/velocity alteration prompted the reframed alluvial fans and two tire river terraces. The alluvial fan in a fan formation extended towards the south with distinctly identified three geomorphic units as apex, mid fan, and lobes. These fans are cast around as mega fans and meso to micro-scale dimensions. The outcome of the study is recapitulated in one pictorial image to make a clear understanding of its morphological units. In the field, artificially initiated water flow in varying discharge (Q) has been experimented to set an idea of expanded coverage area in both monsoon and flood seasons. The morphotectonic indices on River Kaljani specify the active tectonics over the area where fans have developed in an elongated shape with changed SL and concavity along the channel. It is a comprehensive study of foreland active tectonics of North Bengal foothill. It clarifies the mechanism of deformed landforms and modification of channel succession in response to the active tectonics.

The Rangit catchment is nestled within the active tectonic region of the Eastern Himalayas in the mountainous state of Sikkim, India. The role of tectonics in this catchment is visibly indicated by the presence of fluvial systems under the erosional regime and associated geomorphic features, along with frequent seismic activities. The streams in the Rangit Basin and their associated catchments were extracted from the ortho-corrected ALOS PALSAR DEM. To assess the tectonic response in the fluvial systems, several indices such as the asymmetric factor, hypsometric integral, elongation ratio, stream gradient index and valley width-height ratio have been calculated for all 16 sub-catchments along with the trunk-stream of the Rangit River. Besides, morphometric indices such as relief ratio, relative relief, planform curvature, dissection index, ruggedness number and stream power index have been evaluated for these drainage units. These attributes have been collated and further analysed by the multi-criteria Entropy Method. Finally, the Index of Active Tectonics (IAT) values for individual sub-catchments were mapped to determine the intra-basin variation of relative tectonic activity in the Rangit Basin. Before performing the analysis, the parameters were checked for redundancy by the Variance Inflation Factor-induced multicollinearity diagnostics. It can be summarized that the concerned region has extremely rugged topography and characterised by high relative relief, steep gradient and highly dissected segments. Furthermore, it is observed that the left bank tributaries display a higher degree of tectonic control than the right bank tributaries. The Main Central Thrust (MCT), which is located between the Greater Himalayas and the Lesser Himalayas, roughly divides the catchment into right and left bank tributaries. The notable difference in tectonic activity across two flanks of the MCT suggests that the MCT is active during the Holocene.

The dynamicity of the channel is the main characteristic of the Raidak-I River in the eastern Himalayan foothill. The present study evaluates riverbank migration in association with erosion–deposition changes along the river Raidak-I using DSAS models. The present work intends to evaluate the relationship between the riverbank erosion–deposition and geomorphological and tectonic adjustment. For the study, earth observatory data like MSS, TM, ETM+ and OLI datasets of 1972, 1979, 1987, 1995, 2003, 2011, and 2020 have been used to demarcate the bankline position. Temporal analysis reveals that the river has changed its bank position by extensive erosion-accretion processes and modified its floodplain area uses significantly. The historical positions of both banklines indicate that a large portion of the floodplain area depicts an erosion-accretion sequence with time. In the timeframe of the last 48 years, the Raidak-I River has an average erosion–deposition at −0.23 m/year on the right bank and 1.57 m/y on the left bank. A general observation from this research is that the most dynamic or migrant part of the river is zone A and zone B compared to zone C which is relatively stable. In this study, the river course in zone C (both banks) is the most dynamic part of this entire river. The changes by the direct effect of banking migration have a bad impact on the dwellers of the floodplain adjacent village area of the river. The results of this study can represent an important indicator of the vulnerability of the Raidak-I River buffer area and also provide information about the geomorphological instabilities of the study area.

The Morphotectonic characteristics of Chel river was examined through the analysis of Shuttle Radar Topography Mission (SRTM) DEM-based geomorphic indices to investigate the effects of neotectonics on channel characteristics and landform development. The individual and cumulative analysis of geomorphic indices such as Relief Ratio (Rh), Drainage basin asymmetry (Af), Stream length gradient index, Mountain front sinuosity, Basin Shape, Valley floor width to height ratio signify adjustment of Chel river basin to the prevailing tectonics. The elongated basin shape and the derived hypsometric integral value of 0.15 indicate that the basin is in the senile stage and only 15% of the actual landmass is present to be denuded by the erosion agents. The Basin asymmetry factor suggests that the basin is tilted significantly towards the south-west direction in the middle reach but is tilted towards the east in its upper and lower reach. The basin has an irregular mountain front and the derived Smf value of 2.02 implies that the basin falls under the moderate tectonics category. Lower Vf values <0.7 from its source up to mountain front (10 kms approx) suggest the presence of V-shaped valleys due to accelerated vertical erosion induced by landform upliftment. The sudden increase of SL index values even in uniform lithology further indicates the greater role of relative tectonics over lithology. Cross-examination of assessed geomorphic indices with geology confirms the adjustments of river Chel to the differential effects of ongoing tectonic processes over the channel and basin as a whole which has shaped the evolution of the basin to its present-day morphology.

In this study, we addressed the impact of neotectonics on channel evolution of the Kameng River of North–East Himalaya. To the end we used ArcGIS software and derived information on the basin’s asymmetry factor, bearing of lineaments and streamlines and hypsometric variables. Information gathered from images and other secondary sources were processed using basin’s asymmetry factor (AF) and revised asymmetry factor (RAF), variance (R²) for bearing of channel lines explained by bearing of tectonic lineaments, and hypsometric integral (HI) methods. We conclude that neotectonics caused the Kameng basin and its sub-basins tilted and channel links of the Kameng system are evolved following the fault, crack, and joint lines.