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CHAPTER - 5 PLEISTOCENE GLACIATION AND FLUVIO-GLACIAL ENVIRONMENT IN THE HIMALAYA 5.1 Introduction: Pleistocene Glaciation in the Himalaya Glacier is a large mass of terrestrial ice made up of superficial snow, which is crystallized from the annual precipitation and meltwater. This accumulation of ice crystal, snow, air, water and rock debris slowly moves out from the place of origin i.e. snowfield under the influence of gravity thereby transporting and depositing the sediment load down the valley. In the cold environment, the formation of a glacier is directly related to the climate and topography of the region. Climate is of fundamental importance as it aids in inception i.e. snow accumulation pattern and growth of glaciers. The form of the landscape determines the threshold condition for glacial occurrence as well as its size, shape and longevity. Therefore the morphology of any glacier is considered to be unique to its location on the earth surface. Glacial geomorphology studies the landforms that result from the extension and subsequent wastage of glaciers and ice sheets on an area of the earth surface. In a sufficiently cold environment, snow tends to accumulate on the ground covering a wide area and with the passage of time this accumulated snow changes its physical character. As it becomes more compact, heavier and granular it is called ‘firn’ in German meaning snow which fell last year and ‘névé’ in French meaning loose mass of compacted granular snow and ice. Continued pressure causes most of the air voids in the ice granules to be expelled so that the granules become even more closely packed. Glaciers form where the accumulation of snow and ice exceeds ablation. As the snow and ice thicken, they reach a point where they begin to move, due to a combination of the surface slope and the pressure of the overlying snow and ice.When the ice reaches the true solid state composed of interlocking ice crystals, it is said to form Glacier Ice, which is normally opaque and of a blue grey colour. Generally, it is estimated that 10 – 11 m3 of snow yield approximately 1 m3 of ice (Hambrey and Alean, 2004). The level up to which the snow melts in summer i.e. the lower edge of the permanent snowfield is called Snow Line. The altitude of snowline directly depends on climate and its height varies with latitude from sea level like in the western Himalayan region it is approximately 5,800m while in the eastern 106 Himalayas it is approximately 4,420m. In the study area Upper Beas Basin these are found very vividly and are shown through the Plates below: Plate 5.1: Fresh snow, snow patches and snow fields in the study area - Rohtang Pass. Plate 5.2: Glaciers Ice with crevasse in the study area – Beas Kund region. Plate 5.3: Snow Line in the study area Upper Beas Basin at an altitude of about 5,300mts 107 A glacier is conceived to be a system, with inputs and outputs and interaction with other systems like atmosphere, ocean, river, landscape etc. Mass and energy enter the system in the form of precipitation, rock debris, gravity, solar radiation and geothermal heat and leave in the form of water vapour, melt water, ice, rock debris and heat at varying rates. In this open system input in the form of snow and ice is collectively known as Accumulation or Alimentation and the region aided with low temperature and higher altitude as Accumulation zone, while output occurs in the form of melting and evaporation of the glacier known as Ablation and the region with comparatively higher temperature and lower altitude as Ablation Zone. The figure below illustrates these phenomena. Thus growth of a glacier occurs in region where accumulation exceeds ablation while glacier recedes in those regions where output is more than input. The work of a glacier modifies the landscape which is known as the glacial landscape. Comparatively Lower to Higher Temperature Fig. 5.1: An idealized Glacial System. Thus, it is obvious that formation of a glacier is a function of climate and topography and its morphology is unique to its location on the earth’s surface. The scheme of classification of glaciers based on morphology as mentioned below is developed and modified from the works of Ommanney (1969), Ostrem (1974), Armstrong et al. (1973), Sugden and John (1976) and Benn and Evans (1996). Wide variety of glacier morphologies ranging from the smallest niche to the largest ice sheet is categorized below: 108 Table 5.1: Morphological classification of glaciers. First Order Classification A. Ice Sheet and Ice Cap unconstrained by topography B. Glaciers constrained or controlled by topography C. Marine Glaciers Second Order Classification Ice Dome Ice Stream Outlet Glacier Ice field Valley Glacier Transection Glacier Cirque Glacier Piedmont Lobe Niche Glacier Glacieret Ice Apron Ice Fringe Ice Rise Glacier Ice Shelf Sea-ice Ice Shelf 5.2 Glacial and Fluvio-Glacial environments in the Himalaya: Literature Review The Himalayan mountain chain, the youngest mountain belt of the world running in an arcuate shape for about 2,500 Km between Indus Gorge in the west and Brahmaputra Gorge in the east; displays more than 90 peaks above 6,096m and several glacial, periglacial, paraglacial & fluvio-glacial landform features. During the various phases of the Himalayan orogeny the sediments comprising the rocks of the Himalaya were deposited in the huge geosynclines and were uplifted, folded and faulted. During the Miocene orogeny’s uplift, several longitudinal ranges and basins were formed. In the Himalayas, during the glacial stages these ranges were extensively covered by the continental ice sheets or glaciers. The countless Himalayan glaciers during Pleistocene are believed to have descended to the altitudes of 1,676m to 1,829m in different parts of the entire range. In the interglacial phases due to extensive ice melt, sea level rose up to 100m (approx), thereby transgressing the coastal areas considerably. Evidences in support of it are found in the north western Himalayan region like the boulders of Dhauladhar Granitoid Gneiss in lower regions of Kangra (1,000m) and glacial evidence at Mamul in Dalhousie area (1,600 m). The Kashmir valley also bears evidence of 6 major glacial and 6 interglacial phases, as found from the works of Pal and Srivastava, (1982) and Kaul, (1990). In 109 the interglacial phases the Himalayan terrain were further broadened because of large scale glacial erosion, sub-aerial action, and subsequent blocking of river valleys downhill as they become sites for myriad types of glacial deposition of sediments, moraines and unsorted materials by rapid mass movements. Moreover the fluvio-glacial channels that were generated, had little power to transport it further down due to lack of velocity, current, enough water, excess bed load etc. The resultant deposits formed the fluvio-glacial terraces that vary from 3 to 5 in numbers in various parts. In most parts of the Himalaya the glacial tongues now rest at 3,353m or above while their erosional or depositional features suggest that at one glacial stage they had come down to the altitude of 900 m in Nayyar-Alakananda valley in Garhwal and 1,000 m in middle Beas valley in Kangra regions. The frequent climatic fluctuations in the Quaternary period are responsible for the shrinkage and advance of these glaciers and shift of the snowline. As considered by Pal (1987), in the present decade the summer snow line has risen up and is confined to the altitude of about 4,500 m, where the permanent glaciers are located and form the Glacial Zone of the Himalaya. The Inner Periglacial Zone is limited from 5,000m down to about 3,800 m which forms the winter snow line and then it is followed by the Outer Periglacial Zone that lies between 3,800 m down to 2,280m or so, which receives occasional snowfall only during winter months. As mentioned by Frakes (1980) that unlike the huge continental ice sheets in Europe, America and Soviet Union, smaller ice masses occupied the highlands and mountainous areas throughout Asia. The extensive loess deposits of northern China extends nearly to the base of the Pleistocene and suggests that the history of Asian glaciation is not yet fully known, and if delineated to some extent their position in time are poorly fixed. Owen and Sharma (1996) gave an account of the glacial history of northwest Garhwal of the Central Himalaya. On the basis of sediments and landforms, they identified one glacial stage called the Bhagirathi Glacial Stage, when extensive valley glaciers advanced down the Bhagirathi valley to Jhala, 40.5km from the snout of Gangotri Glacier. This glaciation is considered equivalent to the Last Glaciation elsewhere in the world, where the maximum extent of ice occurred ca. 63 ka BP. A series of sharp-crested moraines are present between 1 and 3 km, beyond the snouts of most of the present glaciers. These moraines formed during the mid Holocene (<5 ka BP), are termed as the Shivling Glacial Advance. Small moraines are inset into 110 these, dated at about 200 to 300 BP are named as the Bhujbasa Glacial Advance; and considered equivalent to the Little Ice Age in other parts of the world. Since the Bhujbasa Glacial Advance, there has been progressive retreat of glaciers, initially by downwasting and retreat, and then by simple retreat. This retreat has accelerated during the last few decades. Impressive paraglacial fans are associated with deglaciation representing very rapid re-sedimentation during and soon after ice retreat. Derbyshire and Owen (1997) reviewed the pattern and extent of glaciation in the NW Himalayas and Karakoram Mountains of Pakistan, and recognised at least three glacial events, progressively less extensive with time, in most regions. The timing and status of these glacial successions are poorly known due to poor dating constraints that arise from a lack of adherence to strict stratigraphic procedures. Therefore recommendations are made for a more rigorous approach to the study of Himalayan Quaternary glacial histories. According to Benn and Owen (1998) new dates for late Quaternary glaciations in the Himalayas show that, during the last glacial cycle, glaciations were not synchronous throughout the region. Rather, in some areas glaciers reached their maxima at the global glacial maximum of c. 18–20 ka BP, whereas in other areas glaciers were most extensive at c. 60–30 ka BP. Comparison of these data with palaeoclimatic records from adjacent regions suggest that, on millennial timescales, Himalayan glacier fluctuations are controlled by variations in both the South Asian monsoon and the mid-latitude westerlies. Taylor and Mitchell (2000) recognised three glacial Stages and a minor advance in the Zanskar range of the north-western part of the Himalaya within the Indian Territory. A glaciated palaeosurface >280 m above river level with associated erratics represents the oldest and most extensive glaciation, the Chandra Stage. A change in valley form from broad glacial troughs to narrow V-shaped gorges along with large subdued moraine ridges delimits a separate later extensive valley glaciation, the Batal Stage, with its maximum at 78.0±12.3 ka BP. Distinct sets of moraine ridges represent a less extensive younger glaciation, the Kulti Stage, which dates close to the global Last Glacial Maximum. A minor advance, the Sonapani, is represented by sharp crested moraine ridges within 2km of current ice bodies, possibly belonging to the Little Ice Age. They also calculated the Glacier Elevation Indexes (GEIs) for this area. They also deduced from the recent high-resolution palæo-monsoon records which shows complex peaks in 111 monsoon intensity, that, there was a more favourable combination of precipitation and temperature earlier rather than later during the last glaciation. Till recently analysis of quantitative chronologies for the glacial successions that occured throughout the Himalaya has been almost totally lacking. Owen, Finkel and Caffee (2002) with the help of two new techniques - Optically Stimulated Luminescence and Cosmogenic Nuclide Surface Exposure Dating, enabled the age of many glacial features and helped us to study the extent and timing of Himalayan glaciation in the late Quaternary. New data show that the local Last Glacial Maximum (LGM) occurred during the early part of the last glacial cycle, in most areas during marine isotope stage 3 (MIS-3). MIS-3 was a time of increased insolation, when the South Asian summer monsoon strengthened and penetrated further north into the Himalaya. The concomitant increased precipitation, occurring as snow at high altitudes, produced positive glacier mass balances, thereby allowing glaciers to advance. On the other hand, during the global LGM, 18–24 ka, Himalayan glaciation was very restricted in extent, generally extending <10 km from contemporary ice margins. Lower insolation at this time produced a weaker monsoon cycle, which in turn resulted in lower snowfall and snow accumulation at high altitudes. Only modest advances occurred at this time due to reduced temperatures locally. According to Benn and Owen (1998), Phadtare (2000), Juyal et al. (2004), Pant et al. (2006) the Himalayan terrain responds sensitively to changing precipitation and temperature fluctuations during the Quaternary period. Juyal et. al. (2004) and Juyal, and Sundriyal, (2009) summarised their work during 2005 to 2008 pertaining to the reconstruction of later Quaternary climatic history in Himalaya using a variety of archives ranging from sediments (glacial, fluvial, lacustrine), peat bogs and tree rings. They have also presented a brief summary of the recent studies carried on in Himalayan glacier in the context of global warming. Characteristic landforms produced by the sediments discharged from the glacier meltwater have been reported by many geomorphologists from different parts of the world, which are recognised as fluvio-glacial deposits and landforms (Price, 1973). Extensive fluvioglacial deposits that occur around the upper catchment areas of the major glacier-originated rivers in the Himalayan region have been spectacularly manifested. 112 The major difficulty for a systematic geomorphological study of this part of Himalayas is the absence of any detailed geological and geographical report. As has been mentioned earlier the literatures published so far have only passing mention of the Quaternary environmental condition of this area which has further been complex and confusing. Recent works by some Indian geomorphologists have thrown some light on the characteristic features of the Quaternary environment and landform features of the Upper Beas Basin in the Western Himalaya. 5.3 Evidences of Glacial processes and landforms in the Upper Beas basin Glacial processes and landforms occur markedly over the mountain slopes in this part of the Upper Beas Basin. It is worth mentioning in this context that glacial process was at a much higher scale in the Late Pleistocene and early Holocene periods (approximately between 20,000 BP and 8,000 BP) when extensive area was covered with ice sheets and large glaciers and also glacier movement was at a higher rate. With gradual climatic amelioration perpetual snowline in this part of the Himalaya (in common with other parts of this mountain) continued to rise upward, glaciers shortened in size and as a result the rate of glacial processes (both erosional and depositional) have decreased. The advance and retreat of glaciers due to variation in mass balance generates glacial processes, which creates erosional and depositional features in glacial geomorphic landscape. The spectacular topography of the Upper Beas Basin is a result of the glaciation in the remote past. Glacial processes in the form of abrasion, corrosion and plucking at a higher rate during the Late Pleistocene period were responsible for the occurrence of glacial landform features like Cirques or Corries, Arêtes and Peaks, Truncated Spur etc on the high mountain areas or the water-divide region surrounding the main Beas river valley. These landform features continue to be exposed from Late Pleistocene through the Holocene periods. Depositional landform features in the form of Morainic Drifts also developed extensively which were later on reworked under fluvial action. Evidences of glacial erosional and depositional features are widespread over the mountain slopes and through the trough of the valley of river Beas, particularly in the northern part beyond Manali. They occur in the form of both large scale and small scale features. 113 Glacial Erosional Processes in Upper Beas Basin A study of the glacial processes that have dominantly occurred in the Upper Beas Basin during the Late Pleistocene and early Holocene periods and also those that are occurring today, are discussed here in order to reconstruct the genesis of the glacial landform features. As modified from Sugden and John (1976) the variables that control the process and pattern of erosion and thereby result in the variety of size and distribution of erosional landforms in the study are as follows: First of all, Glaciological Variables like the characteristics of ice, their motion, flow direction, thermal regime, amount of debris held in the basal ice and drainage system configuration. Secondly, Substratum Characteristics that includes physical characteristic of the bed like structure, lithology, joints, permeability, degree of sustenance of hard rock beds to erosion and weathering and thickness and composition of unconsolidated sediments. Thirdly, Topographic Variables covers the entire morphological attributes of the region, starting from small scale ruggedness to large scale relative relief of the Upper Beas Basin catchment area. Fourthly, Temporal Variables encompasses all the changes in the above variables over time. The glacial processes that are identified in the Upper Beas Basin are dominantly Abrasion and Plucking, which extensively cause the formation of the present day glaciated landscape of upper part of the study area, from above Manali. The erosional processes are discussed here as follows: a) Abrasion: As conceived by Sugden and John (1976) and Benn and Evans (1998) abrasion is a process where the bedrock is scoured by debris carried in the basal layers of the glaciers and encompass the processes of Striation and Polishing by which the roughness of the rock surface is reduced. The variables that affect glacial abrasion process in the study area are: • Thickness of the ice, because greater the thickness, greater will be the effect of vertical pressure on any particle beneath the glacier and more intensive will be the process of abrasion. 114 • The speed or the velocity of the sliding of the glacier is also important as it controls the amount of debris passing over a given area of bedrock thereby positively affecting the amount of abrasion. • Existence of high concentration of debris or till in the basal ice will increase the intensity of abrasion as clean ice cannot erode the solid rock. • Transportation of debris to the base of glacier is necessary for constant renewal of the abrasion process. In the study area due to seasonal changes, ice melts at the bottom of the glaciers due to warmer summers, this causes the rock fragments to slide downward to the base and along with the velocity and inclined slope the abrasion process accentuates. • The warm-based glacier has a thin layer of water at its base that act as a lubricant and helps in basal sliding that enhances the intensity of abrasion by supplying larger particles to the base and removing smaller particles through buoyancy effect. • Relative hardness of rock particles and bedrock also affect the intensity of abrasion, as the bedrock of the study area is made up of hard resistant gneissic, granitic and quartzite rock therefore striation and polishing is of lesser extent. b) Plucking or Quarrying: The process of plucking by overriding ice involves detachment of rock fragments by fracturing of fresh unjointed bedrocks. Here rocks are mechanically disintegrated, loosened and weakened by ice or debris within the ice. The plucking process depends on the rock type and structure, joint spacing that helps in loosening of large blocks of rock from the parent body and depth of glacial excavation. Glacial Erosional Landform Features in Upper Beas Basin Thus, it can be deduced that amount of plucking and the composition of its material controls the intensity and extent of abrasion. In the study area both the processes of abrasion and plucking go hand in hand, to create the unique glacial erosional landforms. Some of the major erosional landforms and the processes that are involved for the development of glacial landforms along with their pattern of contemporary distribution in the study area is presented in the table below and is discussed in detail. Due to the steepness of the topography and huge dimension of 115 the erosional landforms, basic identification and causes of their formation through the different phases are dealt here in detail rather than analysis of morphological attributes. Table 5.2: Major erosional processes and resultant landforms along with the pattern of their contemporary distribution in Upper Beas Basin. Processes Scale of Landforms Large Scale Erosional Small Scale Type of Erosional Processes Areas of Occurrence Forms involved U-Shaped Glaciated Valleys Hanging Valleys Over the mountain summits and Depression Cirques &Arêtes throughout the upper catchment Abrasion Corrie Lakes section of Beas river and its and Plucking tributary valleys like Solang, Cols and Passes Hamta etc, mainly beyond Manali Nivational Hollows Truncated Spurs Eminence Peaks or Horns Striae, Grooves and On valley walls and rock outcrops, Abrasion Depression Polished Surface in the above mentioned regions, Polishing & & Streamlined particularly in the recently Striation Chattermarks deglaciated mountain slopes Compiled by the Author Relief Type Large-scale Landform Features: Large–scale erosional landforms are associated with glaciers, ice streams or snow patches; it also includes bedforms and small scale erosional features superimposed on them. The main large scale erosional landforms in the study area – Upper Beas Basin, are U-Shaped Glaciated Valleys, Hanging Valleys, Cirques or Corries &Arêtes, Corrie lakes, Truncated Spurs and Peaks and Cols. U-Shaped Glaciated valleys are the cross profiles of glaciated troughs, mainly asymmetric in shape, flat floored with one gentle and the other steeper slope and are sometime parabolic in shape too. The valley sides and floor of the U-Shaped glacier valley or trough is eroded by valley glacier collectively by the erosional processes of abrasion and plucking. The Plate 5.4 and 5.5 below shows the U-Shaped glacier valley near the source of Beas River, Beas Kund glacier and Hamta valley. The valley glaciers are tongues of moving ice flowing from highland areas, where the ice accumulates since from Pleistocene and are enclosed between valley walls that were often preglacial river valleys (Clowes and Comfort, 1988). It can be understood that this preglacial river valley was initially V-Shaped in cross section with interlocking spurs. During the Pleistocene period due to intense glaciation, they were eroded, deepened and widened to form the U-Shaped glacier valley. The ice tongues during Pleistocene 116 period extended up to Mandrol, which is near Kullu i.e. lower part of the study area, where still today evidences of lateral moraines are found. Therefore presently U-Shaped valley is noticed vividly in the uppermost part of the catchment of the River Beas starting from Beas Kund up to Dhundi, after which the U-Shaped valley is reworked by fluvial action. Plate 5.4: U-Shaped glaciated valley in the upper part of river Beas, near Beas Kund Plate 5.5: U-Shaped glacial trough in Hamta valley, near Hamta glacier in the upper part of Beas basin. Truncated Spurs originated when the glaciers moved down slope on the preglacial VShaped valley and on its way eroded the floor as well as the sides of the valley particularly the rocks of the Interlocking Spurs that protruded in the valleys i.e. on the path of motion or down 117 sliding of the glaciers. This resulted in the formation of Truncated Spurs which gives great steepness to the sides of glacial troughs. In the study area, as shown in Plate 5.6 presently the Truncated Spur seen from Marhi and Rohtang region reveals that truncation of valley sides of glacial troughs slowly became less steeper towards the valley floor than when ice was present, as weathering and mass wasting movement from upper slopes has caused scree to collect at their bases. Plate 5.6: Steep Truncated Spurs in the upstream of river Beas near Rohtang, bearing evidence of glaciation in U-Shaped valley. Hanging Valleys are found to be perched above the main glacial trough as erosion rates in troughs that carry the major trunk glacier are greater than those below tributary glaciers. They are usually concave in form and join the main valley at a slope of 350 – 500 and terminate at higher altitudes above the main valley. The character and distribution of joints in the bedrock gives the profile of the hanging valley a lot of variation than that of the main valley. The Plate 5.7 below shows one of the main hanging valleys of Beas Kund glacier which is presently exposed, to retreat of Beas Kund Glacier. 118 Plate 5.7: De-glaciated exposed Hanging valley developed along the U-Shaped glacial trough following retreat of the Beas Kund Glacier Cirques or Corries and Arêtes are found almost universally in all mountainous glaciated topography. This erosional landform is confined to both the areas of present or former glaciation. They are charecterised by a steep headwall, flat rock floor or over-deepened basin, both connected by a concave slope and simple arcuate or amphitheater shape. The structure of the cirque is mainly controlled by bedrock structure, thickness and steepness of glacier to generate stress, along with abrasion and plucking erosional process forming the lower backwall and floor while the upper backwall is formed by frost action. The cirques glaciers are small ice masses accumulating in and flowing from rock hollows that are slowly enlarged by subglacial erosion and subaerial slope retreat supplies debris to the glacial surface. When two or more cirques or glacial troughs are adjacent, they are separated by knife edged ridges or Arêtes. Various types of cirques divided by Arêtes are noticed in the study area like active and relict; simple, compound, staircased etc. as shown in Plate 5.8, 5.9 & 5.10. Very little work has been conducted in the western Himalayas, mainly in the study area regarding identification of Cirques at different levels, considering the snow line, on the basis of which number and period of Pleistocene glacier advances can be deduced. 119 Plate 5.8: Ideal Compound Cirques recently being deglaciated near Beas Kund divided by sharp Arêtes. Plate 5.9: Retreating glacier within a Cirque with exposed medial moraine on one side and Arete on the other, along with ground rubble. Plate 5.10: A Cirque near Beas Kund 120 Various attempts are made to reconstruct the evolution of cirques, whose size increases along with the increase in degree of enclosure and long profile. This indicates that cirque develops from hollows by progressive retreat of backwall and downcutting of the floor. Summing up the views of Matthes, 1900; Wright, 1914; Russell, 1933; Boye, 1952; Watson, 1966; Evans and Cox, 1974; Vilborg, 1977; Thorn, 1979; Ballantyne and Harris, 1994 it is seen that evolution of a Cirque from a Nivation Hollow can occur with progressive growth of the occupying snow and ice from a snow patch in a Nivation Hollow, through a larger snow patch in a Nivation Cirque to a glacier in a true Cirque. The enlargement of hollows on the mountainside can occur by snow patch erosion or Nivation along with freeze and thaw activities, chemical weathering and transportation by solifluction, slope wash, snow creep and melt water; accelerated by permanent or semi-permanent snow. Some Nivational Hollows are noticed in the study area as shown in Plate 5.11. Plate 5.11: Nivational Hollows in the less steeper slopes near Rohtang. Peaks or Horns form when two or more cirques intersect back to back thereby forming sharp edged peaks or horns as shown in Plate 5.12. Cols and Passes The sharp saw-tooth like ridges which is called Arête in French consists of alternating sags or depressions known as glacial Cols produced by intersection of opposed cirques and pointed Peaks or Horns as shown in Plate 5.13. When these Cols are wider and flatter they are known as Passes. The Upper Beas basin is endowed with numerous Mountainous Passes, most important are Rohtang Pass, Hamta Pass etc as shown in Plate 5.14 121 Plate 5.12: Sharp edged Peaks on the Pir Panjal ranges as viewed from Kothi Plate 5.13: Cols or Sags between two sharp edged Peaks Plate 5.14: Rohtang Pass the most important pass of the study area 122 A Cirque as mentioned above is like a basin which extends forward from the headwall and terminates at a bedrock rise called Threshold (Thornbury, 1998). Cirque lakes or Tarns as they are known in British Isles are small lakes of glacier melt water that form during summer within this Cirque basin. Beas Kund in the study area is an ideal Cirque Lake which is conceived to be one of the important sources of River Beas as shown in Plate 5.15 Plate 5.15: Beas Kund conceived to be the original source of River Beas is an ideal Corrie Lake Small - Scale Landform Features: Small – scale landform features are superficial erosional marks. A very wide range of small scale erosional landforms are noticed in a glaciated topography. In the study area – Upper Beas Basin, the small scale erosional forms are mainly Striae, Grooves and Polished Surface and Chattermarks as shown in Plate5.16; they are engraved on the surface of the bedrocks by glaciers. They are hard to find out in the study area due to the hardness of the rocks in the valley heads and presently, as the glaciated region are being reworked intensely by periglacial action due to overall climatic change. Striae, Grooves and Polished Surface are innumerable scratches incised in to the bedrocks, usually short in length and are recognised as an evidence of scouring by particles embedded in the glacier ice. The intensity of the marks in the polished surface depends upon the shape and comparative hardness of the abrasion tools. Grooves are developed due to rotation of cutting tools in the deeper surface (Ben and Evans, 1998 and Kaul, 1990). In the study area these features are mainly seen on the glacially abraded valley walls of exposed upper catchment areas of Beas River, Solang Nala, and Hamta Nala etc and on some rock outcrops. 123 Plate 5.16: Striae, Grooves, Polished Surface and Chattermarks on the glacially abraded valley wall near Beas Kund glacier. Chattermarks are fracture marks or cracks on the bedrock, usually occurring at the base of shallow grooves, only a few centimeters wide and record the removal of flakes of rocks by plucking as well as indicates the direction of ice flow, (Ben and Evans, 1998). They usually occur as a series of closely spaced fractures, often one inside another due to repeated due to repeated quarrying. In the study area these features are mainly seen on the glacially plucked or quarried valley walls of exposed upper catchment areas of Beas River, Solang Nala, and Hamta Nala etc. Glacial Transportation in Upper Beas Basin The glacial erosional processes and the landforms carved out by erosional activities are only possible when the eroded rock particles are transported subsequently. The glaciers are efficient in transporting enormous volumes of rock debris of various sizes over considerable distance. On the basis of the position of debris within the glacier the transportation process can be categorised into 3 zones. They are as follows: • Supraglacially: debris carried on the surface of the ice like mechanical weathering of the slopes above the glacier supplies materials that is carried on the surface of the glacier. • Englacially: debris carried within the glaciers as the debris eroded from the ice-rock interface below mixes within the glacial mass or along the flow lines of the glacier ice. 124 • Subglacially: debris carried or dragged beneath the glacier along the ice-rock interface mainly due to glacial erosion of the rock floor over which it flows. Glacial Depositional Processes in Upper Beas Basin When the glacier or ice sheets melt, large quantities of debris are deposited on the landscape, mainly around the glacial snout, bottom and marginal areas. As mentioned in transportation of glacial deposits, there are three main zones of glacial deposits within a glacier that are primary in nature i.e. laid down uniquely by glacial properties - Supraglacial, Englacial, and Subglacial. They are carried along one or more transport paths including active or passive glacial transport. Depositional process refers to the mechanism that lay down the final deposit and comprises glacier as the dominant agent and river, wind and gravitation as secondary ones. Here the glacial depositional process is mainly taken into consideration as it is unique to the glacial environment of the study area. The depositional process influences the geometry of bed, sediment properties like grain size distribution, particle morphology etc. The Glacial Deposits, collectively called glacial drift can be divided into 3 main types. They are enlisted below as modified from Clowes and Comfort (1988). They are as follows: a) Glacial Till: also called ‘drift’ or ‘boulder clay’ in Britain as suggested by Charlesworth (1957) previously and ‘glacial diamictite’ by Flint (1971) later on. it is unsorted and unstratified debris deposited directly by ice. It is massive in structure without smooth lamination or graded bedding as referred by Goldthwait (1971). It is composed of fragments of rocks of all shapes and sizes, ranging from large boulders to small clay particles mixed randomly. b) Ice contact stratified drift: are deposited near the melting ice (snout of the glacier) in which the debris is partly sorted and roughly stratified by water action. c) Outwash deposits: are transported by glacial melt water and are thereby well sorted and stratified according to particle size. Glacial Depositional Landform Features in Upper Beas Basin As the glacial depositional features are created directly by the advance and retreat of glaciers, therefore they bear many evidences of Pleistocene glacial advances, thereby changing 125 the landscape. Among the varied types of depositional landforms, Moraines are the most remarkable ones. Usually they have lineated topography and the relief types produced are eminence; they are either aligned parallel or transverse to ice flow direction. The moraine distribution reveals a strong relationship between landform orientation and direction of ice flow. In the study area moraines are composed of Glacial Till (unsorted and unstratified debris) dominantly and towards the peripheral zone of the glaciated and periglaciated region from where the fluvio-glacial activities become dominant, the deposits are Ice contact stratified drift and Outwash deposits. Here the main concern is the Glacial Till that is seen in the moraines. An advancing glacier is loaded by debris that it deposits, dumps or smears on the valley floor as a thick mantle of till, also called Lodgement Till; later due to deglaciation ablation takes place along with shrinking of ice margins, this causes the spread of sediment load across the landscape and is called Ablation Till. The morainic landforms are extremely short lived and remain as long as the main glacier exists; otherwise they get reworked by other geomorphic agents. Very little research has been conducted on the morphology and genesis of the different depositional geomorphic features in this Upper Beas basin and no such effort has been given to reconstruct the glacial history of the study area with the help of end moraines. As calculated from the IRS satellite imagery of 2007, the entire glaciated zone of the study area is about 60 Km2 of which more than half is covered by depositional features and out of which about 70 % is covered by various types of moraines alone. Even the volume of debris that is related to intensity of erosion and weathering is also very high. The retreat of glaciers associated with worldwide climatic change and deglaciation produced various types of moraines in the study area. It is also conceived that the moraines are progressively older with increasing distance from the cirque. The table below shows the process and landforms of deposition along with their pattern of contemporary distribution in Upper Beas Basin. Table 5.3: Depositional processes, depositional relief forms and their contemporary distribution in Upper Beas Basin. Processes Depositional Scale of Landform Large Scale Type of Landforms Relief type Morainic Drift Lateral Linear Morainic Drift Medial Linear 126 Relief form Processes involved Ice marginal form parallel to ice flow Ice marginal form parallel Transported by glaciers. Controlled deposition Areas of Occurrence Most remarkable through the enclosed valleys Morainic Drift Terminal/End Lobate Morainic Drift Ground NonLinear to ice flow Ice front form transverse to ice flow Subglacial form lacking consistent orientation above the tree-line, (>4000m) Transported by glaciers. Uncontrolled deposition Compiled by the Author The four typical moraines identified in the study area are: • Lateral Moraine: are marginal ice forms parallel to the ice flow. They are linear ridge like morainic drifts produced from the dumping of till within the glacial trough between the glacier and the valley sides. The lateral moraines are mainly composed of sub-rounded to sub-angular boulders, cobbles, pebbles along with rock flour that has been transported subglacially and englacially. The very common in the glaciated region of the study area and are noticed very vividly near the Beas Kund Glacier. These lateral moraines are joined by their counterpart from the hanging valleys usually in acute angles. There is distinct uniformity of height and spacing of the moraines in the glacial valley near Beas Kund, and it ranges from about 10 meters to 100s of meters. As conceived by Kaul (1990) the lateral moraines can be further classified according to size and distance from the existing glacier. They are the Medium High and High Lateral Moraines are considered to be the older ones far away from the present glacier and are formed during the initial phases of deglaciation while the Low Lateral Moraines are nearest to the Cirque glacier formed during the recent phases of deglaciation. Plate 5.17: Low and Medium High Lateral Moraine near Beas Kund Glacier 127 The Low Lateral Moraines as shown in Plate 5.17 are found in the higher parts of the glacial valley near the valley or trough head and are quite steep. Here the moraines are composed of gravels and boulders with some fine materials acting as weak matrix. The amount of silt content is proportionately higher than the later two types. The Medium High and High Lateral Moraines as seen in Plate 5.17 and 5.18 are generally bulky and broad and are located farthest from the valley, often covered by thin veneer of vegetation. They have lesser proportion of finer material and are composed of more boulders, pebbles and cobbles. They have steep leeward side and the outer slopes are dissected by gullies. Plate 5.18: Relict High Lateral Moraine away from the Beas Kund Glacier • Medial Moraines: are formed when the lateral moraines of the inner sides of two glaciers meet or conjoin. They are also formed in regions of compound cirques and are also seen in the study area. • Ground Moraines: are large scale non-linear subglacial landforms lacking consistent orientation and are formed due to uncontrolled deposition by glaciers. Their surface expression is dull and monotonous with un-assorted, irregularly distributed or scattered large and medium sized boulders along with finer cementing materials. In the study area Beas Kund as shown in Plate 5.19 and 5.20, they are formed due to both englacial and subglacial processes of transportation and are dumped by glaciers on the valley floor during the process of melting. 128 Plate 5.19: Closer view of Low Lateral Moraine along with Ground Moraine Plate 5.20: Ground Moraine adjacent to Relict High Lateral Moraine, near Beas Kund Glacier • Terminal or End Moraines: have a frontal location and are lobate in form transverse to the direction of ice flow, usually formed by controlled depositional activity. They are formed by the movement (advance and retreat) of the glacial snout and acts as an important indicator of the last glacial limit. The morphological attributes of the end moraine are related to movement of ice, rate of surface ablation and volume of materials carried by the glacier englacially, subglacially or supraglacially and dumping of the debris at successive height. Plate 5.21 shows a fresh terminal moraine but usually the older ones in the study area are quite difficult to identify because they are destroyed by the process of valley widening by the 129 Beas River and later on due to fluvio-glacial activities. The major proportions of the unstratified debris are angular rock fragments, pebbles and boulders. Plate 5.21: Fresh terminal moraine (glacial snout) as the evidence of contemporary retreat of valley wall glaciers Glaciers in Upper Beas Basin and their recent rate of deglaciation The Inventory of Glaciers and Glacial Lakes and the Identification of Potential Glacial Lake Outburst Floods (GLOFs) Affected by Global Warming in the Mountains of Himalayan Region, Himachal Pradesh Himalaya, India made by International Centre for Integrated Mountain Development (ICIMOD), Chaudhary Sarwan Kumar Himachal Pradesh Agricultural University (CSKHPAU), Asia-Pacific Network for Global Change Research (APN), global change System for Analysis, Research and Training (START) and United Nations Environment Programme (UNEP) in 2004 gives a detail account as well as analysis of the glaciers and glacial lakes of the entire Beas Basin. The western part of Himachal Pradesh is occupied by the Beas river basin, it lies between 31°24’ N - 32° 36’ N latitude and 75° 36’ E -77°.52’ E longitude. The Beas river network comprises Parbati, Binwa, Neugal, Banganga, Gaj, Dehr and Chakki Kunal, Masch, Khairan rivers. The main river flows from east to west. Glaciers are mainly confined to the extreme north eastern part of the basin. The Beas river basin has a total of 358 glaciers and covers an area of 758.18 sq. km with ice reserves of 76.42 km3. The two largest glaciers in the basin have area coverage of 63.18 and 65.68 sq. km, respectively. The highest numbers of 130 glaciers is distributed in the southern aspect, whereas the lowest number of glaciers are distributed in the east and west aspects. There are seven types of glacier in the Beas basin— Cirque, Ice-apron, Ice cap, Mountain, Mountain basin and Valley glaciers. The table below shows the number of glaciers and the area occupied by these glaciers according to their types in the entire Beas River Basin. Table 5.4: Glacier types, numbers and area in entire Beas River Basin. Glacier Type Number Area Cirque 12 2.49 Ice Apron 60 41.47 Ice Cap 9 1.32 Mountain 134 156.43 Mountain Basin 105 186.82 Niche 26 5.41 Valley Glacier 12 364.24 (Modified from Inventory of Glaciers and Glacial Lakes and the Identification of Potential Glacial Lake Outburst Floods (GLOFs) Affected by Global Warming in the Mountains of Himalayan Region, Himachal Pradesh Himalaya, India) Fig 5.2: Map of Beas River Basin showing total Glaciers, Lakes and area covered them. (Modified from Inventory of Glaciers and Glacial Lakes and the Identification of Potential Glacial Lake Outburst Floods (GLOFs) Affected by Global Warming in the Mountains of Himalayan Region, Himachal Pradesh Himalaya, India) 131 Some of the major glaciers of the study area are taken into consideration in the table below; of which Beas Kund glacier, one of the most important one has already shrunk to half within a period of 26 years. Table 5.5: Some of the main glaciers of the study area – Upper Beas Basin. Glacier & its Location in Upper Beas Basin Beas Kund Glacier, 32°23'35.16"N, 77°02'29.24"E Jarnu Glacier, 32°21'54.17"N, 77°04'20.50"E Duhangan Glacier, 32°07'31.42"N, 77°24'30.72"E Orientation Length (M) Area (M2) Thickness (M) Ice Reserve (Km3) Glacier Type Receding Rate NE 2509 1028024 42.36 0.04363 Shrunk To Mountain Half within a basin period of 1980 - 2006 NE 1801 1666581 50.74 0.08473 Mountain data available N 4979 5591506 77.85 0.43518 Mountain No authorised data available basin No authorised Source: TNN (2007), National Institute of Hydrology, ICIMOD, UNEP The detail field investigation reveal the alarming rate of retreats of the major glaciers around the south, south west and southeast facing slopes of the Pir Panjal ranges in the River Beas watershed. The rapid retreat of the Beas Kund glacier indicates increase of the temperature due to environmental degradation and global warming. Rapid decay of glacier body often gives rise to debris-dammed lakes adjacent to the snout and at certain time intervals catastrophic dam bursts can cause flooding, and disturbing the equilibrium of the valley profile in the upper catchment areas of the glacier-fed river. The rapid increase in the number of mountaineers, and trekkers in each year cause marked environmental degradation in recent years. The increasing pressure of cattle population on the alpine meadow area in recent years, who discharge higher amounts of methane gas in atmosphere through their dung and remnants, also cause rapid atmospheric warming. From the satellite imagery analysis of two years, one Landsat – TM satellite image of Upper Beas basin, Kullu valley of the year 1998 and the other Indian Remote Sensing (IRS) – P6 LISS-III image of the year 2007 from National Remote Sensing Agency, India a change detection has been done regarding the aerial coverage under Glaciers with snow patches and snow fields and Periglacial zone. From the table below it is very much clear that the Zone of 132 Glaciers have reduced in area by 258.02% while the periglacial zone next to it has increased by 30%. The rate of deglaciation as calculated is quite alarming. Moreover it can be easily deduced that due to overall climatic warming and recession of glaciers, the snow line is moving upwards and the previous zones of glaciation are slowly getting converted to periglacial zones where the main geo-climatic action is freeze and thaw along with frost action and gelifluction, with no permanent glaciers or snow patches. The table below and the corresponding Fig 5.3 and 5.4 shows the change in the coverage of Glaciers with snow patches and snow fields and Periglacial zone respectively. Table 5.6: Statistical representation of change in area under Glacier with snow fields and snow patches and Periglacier zone in the study area – Upper Beas Basin. Land cover categories 1998 Area in Km2 2007 Area in Km2 Glaciers with snow patches and fields 211.797772 59.1588 -152.63 258.02 Decreased Periglacial zone 138.81772 200.8338 62.02 30.88 Increased Change in Area % change in Remarks (1998-2007) Area (Compiled and Calculated by the author) Due to rapid rate of deglaciation around this part of Western Himalaya the main river Beas and its major tributaries like Solang Nala, Hamta Nala, Manalsu Nala, Sarwari Nala etc all of which are glacier fed will suffer from hydrological imbalance as well as scarcity of water in coming decades. There is enough reason to apprehend that in the absence of perennial snow fields and glaciers the hydrological character of the main rivers will be very much temperamental and be guided by the rainfall alone; they will be lacking water flow in the drier months and be torrential in the rainy season. 133 Fig 5.3: Glacial and Periglacial land cover map of Upper Beas Basin using Landsat TM Imagery, September, 1998. 134 Fig 5.4:Glacial and Periglacial land cover map of Upper Beas Basin using IRS LISS-III Imagery, October, 2007. 135 5.4 Evidences of Fluvio-Glacial landforms and deposits In the arctic and alpine environments typical landform features develop under the combined work of glaciers and melt water streams down the valley. These features are known as Fluvio-Glacial landforms that are formed by deposits brought down by both fluvial and glacial action. Thus, Fluvio-Glacial deposits are characterised as material moved by glaciers and subsequently sorted and deposited by streams flowing from the glacier ice. Along the river banks these Fluvio-Glacial deposits were found to remain almost unaffected while along the foothills, from the edges where the valley wall rises, these features were found to have been reworked to a great extent by rockfall and slope washing. The Plate 5.22 shows the Beas River Valley near Dhundi and Solang River, a tributary of Beas carrying huge load of debris, both being slowly reworked by fluvial action. Plate 5.22: The river valley of Beas and Solang being reworked by Fluvio-glacial action. The deposits are often stratified and may occur in the form of Outwash Plains, Deltas, Kames, Eskers, and Kame Terraces. But in the study area some instances of rhythmically stratified deposits with alternating layers of coarse and fine material are clearly visible as seen in Plate 5.23. The extent and type of stratification is assumed to be largely a function of the environment of deposition, while the shape of the particles is the function of the source of debris, the type of material and the distance to which the material was transported during the melting of glacier ice in the past. Occurrence of the extensive tract of fluvio-glacial deposits through the Upper Beas basin suggests that the Beas glacier was large enough discharging huge amount of material at its melting stage to give rise to such enormous deposits in the form of terraces. 136 Plate 5.23: Rhythmically stratified deposits with alternating layers of coarse and fine material near Solang above Palchan Village. Evidences of Fluvio-glacial landforms are quite marked through the main valley of the Upper Beas River particularly in the upper part beyond Raison. Two most important of them are discussed here as follows: Meltwater channels are present throughout the glaciated northern regions of the Beas River basin at an altitude of about 4000m. They are not structurally controlled but were formed due to glacial and fluvio-glacial processes. Meltwater Channels in the study area originate on freshly deposited or relict debris and large terminal moraines and are therefore called Drift- cut meltwater channels as seen in Plate 5.24. These Meltwater channels form when the valley glaciers terminate in the valley basin and release large quantities of glacier melt water that drain broad outwash plain. After the glacial phases, these meltwater channels develop and they usually have subglacial drainage, they are incised into the interfluves and are deepened during phases of fluvio-glacial erosion that follow subsequently during the present phases of deglaciation. 137 Plate 5.24: Drift-cut Meltwater Channels in the Beas Kund Regions mostly developed on Terminal Moraines River Terraces are one of the most remarkable features of the study area. Fluvio-Glacial deposits in the study area- Upper Beas basin are exhibited by and large in the form of extensive valley-side River Terraces. They are flat, gently inclined land surface mainly produced by fluvio-glacial action and are quite well developed throughout the entire belt. These terraces extend from the existing rivers up to the moraines. They decrease in width with increasing height and the downstream slope is 100 - 200 on an average while upstream it is above 300. They are considered to be important morphostatigraphic unit as they record the paleo time table of consecutive geomorphic processes through ages. It is assumed that during the massive deglaciation from the early Holocene (approximately 8000-10,000 year BP) enormous amounts of morainic drifts from the catchment area of the Beas river in the north (Pir Panjal area ) were brought down by the huge flux of river water and continued to be deposited through the Kullu Valley forming extensive terraces. Sections exposed in many places alongside the main river and its tributaries have spectacular manifestations of debris comprising mixture of glacially derived angular and sub angular clasts and fluvially reworked rounded clasts of various sizes. 138 Plate 5.25: A High River Terrace in the lower part of the study area in Mandrol near Kullu. Plate 5.26: A broad and medium high river terrace in the middle part of the study area near Naggar along the braided river Beas Plate 5.27: A typical cross sectional view of showing rounded and angular blocks embed in the FluvioGlacially deposited regolith of the terraces along the Solang river course. 139 Sections exposed on either side of River Beas, across the terraces particularly from Mandrol village (12km north of Kullu town), near Naggar Village in the middle to the north up to about the Palchan village (12km to the north of Manali town) for a distance of about 40km have spectacular manifestations of thick regolith embedded with both angular (glacially and periglacially derived) and rounded (fluvially reworked) boulders and pebbles. Origin and development of the vast agriculturally prosperous terraces in the Kullu valley can be attributed to the work of glaciofluvial processes during the greater part of the late glacial and post glacial (Holocene) periods. Morphological analysis of fluvio-glacial deposits The morphological attributes of fluvio-glacially derived debris or deposits were analysed in the field in detail at three different points of the study area. The area for study includes three selected positions of the entire study area – Upper Section in Baukar Thatch, Beas Kund (77º05.394' E; 32º21.075' N), Middle Section in Bahang, Manali (77º10.838' E; 32º16.212' N) and Lower Section in Patlikuhl, Kullu (77º08.773' E; 32º06.416' N). The A Axis (length), B Axis (breadth) and C Axis (width) was measured and from it the Volume and C:A axis ratio was calculated. The results shown in Table 5.7 clearly depicts that the C:A axis ratio average volume of the debris varies distinctively from upper, middle and lower parts. Table 5.7: Pattern of the average volume and C:A axis variations of clasts as measured from 3 different points starting from the Upper part through the middle to the lower part of the Upper Beas Basin Locations in 3 different parts of the study area-Upper Beas Basin (50 Samples from each location) Average Volume Average C:A Axis Ratio Baukar Thatch, Beas Kund (77º05.394' E ; 32º21.075' N) Altitude: 3422 mts Slope: 16º Aspect: North 65471.18 Bahang, Manali (77º10.838' E; 32º16.212' N) Altitude: 1997m Slope: 10º Aspect: South 31649.98 Patlikuhl, Kullu (77º08.773' E ; 32º06.416' N) Altitude: 1452 m Slope: 10º Aspect: South 64279.45098 0.496341505 0.50024706 0.654031544 Details of the table in Appendix The clast in the upper part in Baukar Thatch where altitude is quite high about 3422m, slope about 160 and aspect towards north are huge in volume as they are freshly deposited moraines which are being reworked by periglacial climate mainly frost action therefore the 140 average C: A axis ratio is quite low about 0.49 indicating the slabby and angular nature of periglacially sculptured deposits. On the other hand the clast in the middle part in Bahang near Manali, the zone of dominant fluvio-glacial action, where the river valley is quite wide, at an altitude of about 1997m, slope about 100 and aspect towards south, are comparatively smaller in volume, but the average C: A axis ratio is higher about 0.50 indicating the clasts here are slowly becoming sub angular and rounder in nature as they have been dragged downhill for quite some distance and thereby have been eroded. The clast analysis in the lower flatter part of the Beas river valley at Patlikuhl near Kullu where the altitude is quite low about 1452 m, with an average slope of 10º or less and aspect towards South; shows that on an average the clast are highly variable and mixed in size, thus the average volume of the clast is quite large. 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