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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. The deposits here
are not only brought by the Beas river alone but also by some of its major glacier fed tributaries
like Manalsu, Alain, Dhuangan etc which also bring down huge amount of debris at certain
intervals. The C:A axis ratio here is quite high about 0.65, higher than the previous two areas
indicating that as the huge bulk of deposits move downhill away from their source they get
slowly eroded losing their angular nature they become more rounded in shape. Thus from the
morphometric analysis of the clasts of three different section of the study area, it can be clearly
deduced that as the clasts move away from their glaciated source region their shape and size
changes from angular and slabby to rounded ones indicating dominant fluvio-glacial action
towards the lower sections that are constantly reworking the deposits.
Plate 5.28: Measurement of clasts in Baukar Thatch, Beas Kund and Bahang, Manali.
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