Keywords

1 Introduction

Landscape geomorphology epitomizes the balance between processes that produce and destroy topographic relief by uplifting and erosion (D’Arcy and Whittaker 2014). The landform evolution mechanism is regulated by various processes, such as lithology, tectonics, and climate change (Solanki et al. 2020). In high-level terrain, active tectonics during the recent geological period can be reflected by river incisions and sediment yields; diversion of channels, the formation of hanging tributaries and so on (Bull and McFadden 1977; Molin and Fubelli 2005; Kale and Shejwalkar 2008; Pati et al. 2018; Das 2020). However, alluvial plains like the Ganga plain respond to the neotectonics by abandoned river terraces, forming terminal fans, change in soil properties, and morphometric variations of the present and paleochannels. Morphometric analysis has widely been used to investigate the relationship between landform geometry and active faults (Kale and Shejwalkar 2008; Singh and Tandon 2008; Raj 2012; Pati et al. 2018; Gailleton et al. 2019; Das 2020). Quantitative landscape measurements may provide important information on geomorphic evolution and the degree of tectonic activity during recent geological times. Geomorphic indices are highly convenient tools for understanding active tectonics as these indices provide insights into particular sites that are rapidly adapting to variable tectonic deformation. The morphotectonic and field-based studies are widely used to locate undergoing tectonic deformation (Azor et al. 2002; Kirby and Whipple 2012; Han et al. 2017; Moodie et al. 2018; Pati et al. 2019; Patel et al. 2020).

The Solani, a tributary of the river Ganga has experienced frequent seismic activity with moderate-size earthquakes, epicentered around 10 km depth. Several studies have been performed to understand geology, stratigraphy, earthquake recurrence, and GPS measurements in the area (Jade 2004; Bhosle et al. 2008; 2009; Patel et al. 2020). The scale and methodology used in the earlier studies are highly generalized to apprehend the tectonic deformation of the area. However, a geomorphic evaluation supporting to the ongoing tectonic uplift is lacking in this area. Besides, any response to the neotectonic activity of the Himalayan segment can be studied along the respective foothill segments and their river systems. This study investigates the impact of the neotectonic activity on the Solani River basin using morphometric analysis, OSL chronology of alluvial terraces, and seismicity.

2 Study Area

2.1 Location

The study area lies between latitude 29–31°N and longitude 77–79°E. Politically it partly falls in Uttarakhand and Uttar Pradesh state of India. Thus, its northern extent is up to the Himalaya and southern extent is up Bijnor Uttar Pradesh. The Solani River is a tributary of the Ganga River, which originates from the Himalayan foothills (Fig. 1). This monsoon-fed river has a catchment area of ~2009 km2. It’s ~150 km course passes through the Himalayan piedmont, consisting of boulders, pebbles, and massive sandstones of Mio-Pliocene age and sandy to loamy Quaternary soils of the Ganga plain, until meeting the Ganga River.

Fig. 1
figure 1

Drainage map of the Solani River basin showing different orders of streams. The inset map shows the location of the study area

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2.2 Geology

The Solani River basin is a part of the western Ganga plain and lies in the Yamuna-Ganga interfluve (Fig. 2). The Solani River originates from the Himalaya foothills at Mohand. This incised river flows through a longitudinal fault (Solani fault), where the lower order tributaries follow less distance, and the trunk river continues further south and merges with the Ganga River near Bijnor of Uttar Pradesh. The river basin is restricted by the Ganga River in the east, the Yamuna River in the west, and the Siwalik in the north. Seismically active, the Mahendragarh-Dehradun Fault (MDF) following the Delhi-Haridwar ridge (Patel et al. 2020), passes along the western boundary of the basin (Fig. 3). Except the steep slope along the northern foothill piedmonts, running along the Siwalik’s foothills, the river basin lacks any topographic prominence. The piedmont in the northern end is a narrow (10–25 km vast), elongated landscape, drained by several parallel to sub-parallel ephemeral streams. The piedmont is composed of gravel, sand, and clays, whereas the abundance of gravels decreases significantly from north to south. The river basin experiences semi-arid to sub-humid climate where annual precipitation varies from 500 to 1200 mm, out of which 80–85% is received between July and September (Kumar et al. 1996).

Fig. 2
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Simplified geological map of NW Himalaya (modified after Singh et al. 2016)

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Fig. 3
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Schematic diagram showing the basement configuration of the western Ganga plain. The Dehli–Haridwar ridge passes through the western boundary of the Solani River basin (modified after Gahalaut and Kundu 2012; MDF: Mahendragarh-Dehradun Fault, GBF: Great Boundary Fault, LF: Lucknow Fault, MF: Moradabad Fault, SF: Saharanpur Fault, GF: Gorakhpur Fault)

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3 Materials and Methodology

Methodology followed in this study includes morphometric analysis, field study, and seismic data analysis.

3.1 Morphometric Analysis

We used ALOS data of 12.5 m resolution to evaluate the morphotectonics of the Solani River basin (Fig. 4). The datasets were validated using the Survey of India (SOI) topographic maps (1:50,000 scale) and Google Earth image. For the morphostructural analysis, the datasets were processed in ArcGIS 10.8 software on WGS 1984 datum. Field studies were carried out to validate the observations from the remote sensing based studies.

Fig. 4
figure 4

a ALOS DEM of the Solani River basin showing topographic perception, b Slope map

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3.1.1 Bifurcation Ratio (Rb)

Rb is defined as the ratio of the number of streams in any given order to the number of streams in the next higher-order in the basin (Schumm 1956). It is a significant parameter that denotes the basin’s water-carrying ability and related flood potential (Mahala 2020). A higher Rb value indicates a steep slope with impermeable or less permeable lithology, and a lower Rb value indicates the geological heterogeneity, higher permeable rocks with less structural control (Hajam et al. 2013). The Rb varies from 2.33 to 4.36, with a mean Rb of 3.46 for the Solani River basin (Table 1). This indicates that the basin falls under the normal category (Pandey and Das 2016). The high bifurcation ratio is found between 1st (4.36) and 2nd (4.04) order, and streams up to the 2nd order flow through strongly dissected and steep gradient of the piedmont area.

Table 1 Different geomorphic parameters studied for the Solani River basin
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3.1.2 Stream-Length Ratio (R L )

RL is the ratio of the average length of the stream to one order to the next lower order (Horton 1945). It is an essential link between the discharge of the surface flow and the erosion of the basin. RL for the Solani basin varies from 0.68 to 3.77, with an average RL of 1.85 (Table 1). Higher values observed in the ratio of 1st and 2nd (1.95), 2nd and 3rd (1.77), and 3rd and 4th (3.37), which are strongly dependent on topography and slope, and in turn are controlled by the tectonic activity.

3.1.3 Elongation Ratio (Re)

Re is the ratio between the diameter of the circle of the same area as the drainage basin and the maximum length of the basin (Schumm 1956). It is believed that the elongated shapes of the basins are due to the guiding effect of thrusting and faulting in the basin (Zaidi 2011). The basins with lower Re values are susceptible to erosion (Sreedevi et al. 2009) because of moderate to high relief of the basin. The elongation ratio for the Solani River basin is 0.52 (Table1).

3.1.4 Longitudinal River Profile (LRP)

LRP is a very sensitive linear feature of tectonic deformation in the earth’s crust (Holbrook and Schumm 1999; Whittaker et al. 2007; Viveen et al. 2012; Fekete and Vojtko 2013; Goren et al. 2014). Convex segments of LRP are called knickpoints or knickzones depending upon their length, which can be examined to determine their coincidence with tectonic disruptions (Molin and Fubelli 2005). Knickpoints in the LRP could serve as useful indicators of active structures along a river (Wobus et al. 2005). Fault movements will produce several small knick points in the channel profile (Zhang et al. 2011). In this study, LRP has been prepared for the Solani River (Fig. 5) using ALOS DEM. Avoiding the river confluences, the river shows multiple other local convexities along the LRP. Hence we interpret these knick points are related to tectonics.

Fig. 5
figure 5

Longitudinal river profiles and SL Index along the Solani River plotted together. a Google Earth image of the piedmont zone shows many first-order streams, b confluence of the river in the lower part of the basin shows minor knickpoints, k1, k2, and k3 are the major knickpoints in the river profile

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3.1.5 Stream Length Gradient Index (SL Index)

Hack (1973) proposed a parameter known as the SL index to determine the geomorphological equilibrium. The SL index describes a stream network’s morphology using the distribution of the topographic gradients along rivers (Font et al. 2010). It is sensitive to slope changes and allows to evaluate the tectonic activity, rock resistance, and topography (Keller and Pinter 2002) and is strictly related to the stream power (Moussi et al. 2018). A high SL index value may indicate if a particular region is experiencing tectonic activity or has any structural control. The SL index values of the Solani River range from 29.4 to 5233.2 (Fig. 5). The maximum value of SL index for the Solani River is 5233.2 (Piedmont region), and the minimum value is 29.4 (Plain region).

3.1.6 Mountain-Front Sinuosity Index (Smf)

Mountain-front sinuosity has been applied to study mountain front tectonics by several researchers (Ramírez-Herrera 1998; Frankel and Pazzaglia 2005; Azañón et al. 2012; Mahmood and Gloaguen 2012; Dar et al. 2013; Elias 2015; Topal et al. 2016; Bhakuni et al. 2017; Giaconia et al. 2012) in different parts of the globe (Bull and McFadden 1977; Keller and Pinter 2002; Silva et al. 2003; Pérez-Peña et al. 2010; Giaconia et al. 2012). Along the active mountain fronts, uplift prevails over erosional processes, yielding straight fronts with low values of Smf. Along less active fronts, erosional processes generate irregular or sinuous fronts with high values of Smf (Azañón et al. 2012; Topal et al. 2016). Bull and McFadden (1977) defined mountain front sinuosity (Smf) as an index that reflects the balance between erosional forces and tectonic processes that control the embayment of the mountain front to make it linear.

Mountain-front sinuosity was defined by Bull (1977) as Smf = Lmf /Ls.

Where, Smf: mountain front sinuosity.

Lmf: length of the mountain front along the foot of the mountain along the pronounced break in slope.

Ls: length of the mountain front measured along a straight line.

Smf reflects the balance between erosion forces that tend to cut embayment into a mountain front and tectonic forces that tend to produce a straight mountain front coincident with an active range-bounding fault (Verrios et al. 2004). Smf of highly active mountain fronts generally ranges from 1.0 to 1.5, that of moderately active fronts ranges from 1.5 to 3, and that of inactive fronts ranges from 3 to more than 10 (Elias 2015). Some other studies have proposed that the values of the Smf index lower than 1.4 are indicative of tectonically active fronts (Silva et al. 2003). It is possible to understand tectonic activity and Quaternary landscape evolution through the application of such geomorphic analyses. Young mountain fronts tend to have low values of Smf, as they have not experienced significant range-front erosion and are responding to active tectonic uplift on a relatively steep fault, keeping it approximately straight (Topal et al. 2016). In the present study, the Smf varies from 1.1 to 1.2, indicating the active nature of the region with pronounced uplift (Fig. 6).

Fig. 6
figure 6

a Piedmont zone showing many first and second-order streams, b major paleochannels in the area, c profile along the HFT shows upliftment

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3.2 Field Study

The Solani River basin was studied by detailed fieldwork. During the fieldwork, three unpaired terraces at Roorkee, and two unpaired terraces at Toda Kalyanpur have been studied (Figs. 7 and 8).

Fig. 7
figure 7

a–c are the field photos of terraces, d schematic diagram of the Solani River terraces at Roorkee

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Fig. 8
figure 8

a Schematic diagram of the Solani River terraces at Todakalyanpur, b–d are the field photos of the terraces

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3.3 Seismic Activity

Paleoseismology uses elements of tectonic geomorphology, sedimentology and stratigraphy to assess the position timing and displacement of past earthquakes (Kondo and Owen 2013). Recent technological advances including remote sensing, geodesy, fault trenching and computational dating have helped to accelerate knowledge and analysis of past earthquakes. Efficient seismic hazard mapping requires the creation of ground acceleration maps based on high resolution, accurate geomorphic and quaternary geological mapping. Geomorphology is the primary tool for neotectonics, earthquake geology, paleoseismology studies and evaluation of seismic hazards. The geomorphology of active fault plays a dominant role in the collection of such data (Kondo and Owen 2013). Neotectonic activity in the present area of study has been well recorded by several seismic events in recent years (Fig. 9). These seismic events indicate active tectonics in the area.

Fig. 9
figure 9

Seismicity map of the western Ganga plain shows seismicity pattern in and around the Solani River basin. a Seismic Hazard map (data compiled from http://asc-india.org, inset shows seismic zone of India with the location of the study area), b Distribution of faults and seismic pattern (for abbreviations refer to Fig. 3, seismic data taken from Prabhu and Raghukanth 2015)

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4 Neotectonic Movements and Channel Evolution

It is difficult to describe any parameter that would systematically isolate the tectonic effect on a river basin. However, the morphometric analysis of the Solani basin has provided evidence for the influence of neotectonics. Kumar et al. (1996) delineated many paleochannels on a regional scale, which shows the river’s northeastward shift of channel. Modern channels also show meandering and northeastward shifting (Fig. 10). This long-term unidirectional shift may be due to tilting of the tectonic clock due to the ongoing NE-SW compression. LRP shows the local convexity corresponds the knickpoints and tributary junction. However, ignoring the confluences, all other local convexities are due to local structural perturbations. The SL index plotted along the LRP is showing a good correlation. The stream length gradient index and LRP coroborate each other, indicating neotectonic influence in the river basin.

Fig. 10
figure 10

a Mapping of paleochannels shows river shifting towards the east (modified after Kumar et al. 1996), b the migration of recent Solani channels

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Paleochannels in the area begin near to Roorkee and end near to Hastinapur (Fig. 10). The “folklore”, as verbally stated by the natives, are are the Burhi (Old) Ganga channel (Kumar et al. 1996) (through depicted by the Aeolian ridges and without any significant channels, Fig. 11). The Hindu epic Mahabharat states that Hastinapur was the capital of the Kaurava-King Prikhsit, and he had to shift his capital from Hastinapur due to floods in the Ganga (Thaper 1966). The Mahabharat Era is closely related to the Painted Gray Ware (PGW) culture, and the later dated back to 600–1000 B.C. (Lal 1954–55, 1981). The flooding time of Hastinapur was dated 800 B.C. (Thaper 1966). This suggests the Ganga River flowed on this upland region (about 15 m higher than the Ganga flood plain, where the present Ganga River flows) sometime before 600 B.C.

Fig. 11
figure 11

Field photographs of the alluvial ridges in the Solani River deposits around Gadharauna

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The Solani River basin records neotectonic activities in the Ganga plain along its course. Unpaired tectonic terraces at Roorkee and Toda Kalyanpur at the river’s right bank are evidence of faulting and river shifting (Figs. 7 and 8). At Roorkee, three terraces have been identified, having riser of 1, 1.5, and 3 m height and tread of 50, 40, and 70 m width, respectively, while riser and tread cannot be measured at Toda-Kalyanpur due to the deformation. These terraces are about 2 km south from the present river course. Different generations of river terraces in the Ganga plain are generally distinguished by their respective degree of soil development. However, the presently studied terraces have no signature of soil development, indicating that they are very recently developed. These terraces were formed by upliftment of the Ganga plain due to compression along the Himalayan front and subsequent river shifting. The Ganga plain is tectonically active by its coupled nature with the Himalaya (Parkash et al. 2011). River courses in the Ganga plain are continuously shifting in one direction due to the area’s compression and upliftment. The results allow in reconstructing the Holocene evolution of the river valley and correlating the processes that led to the terrace formation.

Four unpaired terraces (T0–T3), were recognized along the right bank of the Solani River (Vorha 1987). The T3 lies 14–18 m above the present Solani River bed (T0), Terrace T3 and T2 were dated using the Thermo Luminescence (TL) technique by Vhora (1987) and assigned ages 2500 and 1600 cal. B.P., respectively. The date for the T3 terrace is the same order of magnitude, as indicated by the PGW culture. Unpaired tectonic terraces and the morphometric parameters suggest temporal activity of the Solani fault.

Unpaired terraces and different faults are indicative of the ongoing tectonic activity in the area. These terraces, composed of fluvial deposits, prominently stand above the modern river channel. Morphotectonic parameters indicate tectonic movements along the MDF, which is close to the Solani basin (Patel et al. 2020). Paleochannels of Solani River are linear in nature, associated with terraces, are indicative of migration of the river (Fig. 6b).

The Himalaya along with the Solani basin experience strong compressional stress (Zoback 1992). Due to the tectonic activity along the Solani, Yamuna, and Ganga faults, the upper Ganga-Yamuna block was raised, and the Ganga-Ramganga block was thrown down (Kumar et al. 1996, Fig. 12). This is clear evidence of the tectonic upliftment of the area. Since its origin, the Ganga plain has undergone numerous geomorphic changes due to tectonic activity (Mohindra et al. 1992). Finite element modelling of the Ganga plain by Parkash et al. (2000) indicates that SW compression (Fig. 12) develops longitudinal faults (parallel to sub-parallel with the Himalayan trend) and extensional transverse normal faults (an angle to the Himalayans trend). Using the Global Positioning System (GPS), Jade (2004) indicates the displacement of the Indian plate to the northwest. The above works support the mechanism for the creation of longitudinal and transverse faults in the Ganga plain studied by several researchers (Singh et al. 2006; Bhosle et al. 2007, 2008; Pati et al. 2018, 2019; Verma et al. 2017; Patel et al. 2020). The present study confirms the existence of active tectonics in the area and highlights its role in shaping the Solani River basin.

Fig. 12
figure 12

a Surficial faults and tectonic blocks in the area. 1—Solani block, 2—Ganga Solani block, 3—Khoh block, 4—Upper Ganga-Yamuna block, 5a1—Modinagar subblock, 5a2—Khurja sub-block, 5a3—Etah sub-block, and 6—Ganga-Ramganga block (modified after Kumar et al. 1996), b Finite element model after Parkash et al. (2000) shows compression from SW develops longitudinal faults in the area. GPS movement was taken from Jade (2004) (Inset figure)

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5 Conclusions

The tectono-geomorphic investigations of the Solani River basin was conducted in the western Ganga plain on the basis of ALOS DEM analysis. The morphometric analysis, seismic, and field-based study helps us to reach the following conclusions.

  1. 1.

    The Solani River basin is a sixth-order river basin with the dominance of lower-order streams.

  2. 2.

    The unpaired terraces at Roorkee and Toda Kalyanpur are evidence of neotectonics.

  3. 3.

    Seismicity and morphometric parameters indicate the river basin is tectonically influenced.

  4. 4.

    Tectonic influence in the Solani River basin is due to its position adjacent to a highly compressed zone of the Himalayan front, where significant upliftment has been recorded.