CHAPTER - 6 PERIGLACIAL ENVIRONMENT, …shodhganga.inflibnet.ac.in/bitstream/10603/29280/12/12_chapter 6.pdf · the principal method of transport comprises downslope movement of debris

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CHAPTER - 6

PERIGLACIAL ENVIRONMENT, PROCESSES AND LANDFORMS

6.1 Introduction to Periglacial environment In literal meaning Periglacial is an adjective originally referring to climatic and

geomorphic conditions found in the edges of Pleistocene ice sheets and glaciated areas (as

proposed by the Polish geologist Lozinski, 1912) but has later on been widely used in

geomorphology to describe any place where geomorphic processes related to intense frost action

occur. Since that time, the term has undergone substantial revision and no universally accepted

definition came into being. Some researchers have suggested rigorous definitions based solely

upon climate like Troll (1944). Peltier (1950) also suggested that the periglacial climate was

charecterised by mean annual air temperatures of between -150 C and -10 C, precipitation of

between 120 and 1400 mm per annum. He also identified periglacial environment to have

‘intense frost action, strong mass movement, and the weak importance of running water’. In its

original meaning a periglacial area was not buried by glacial ice but was subject to intense

freezing cycles and exhibits permafrost weathering and erosion characteristics. The severe frost

action and frozen ground promote significant mechanical weathering, fine and coarse-grain

sorting, and mass movements (Péwé, 1969 & 1975). As Péwé suggested though Permafrost is

not prerequisite, it is practically ubiquitous in the periglacial environment. Washburn (l979)

identified periglacial as ‘.... primarily terrestrial, non-glacial processes and features of cold

climates characterised by intense frost action regardless of age and proximity to glaciers’. The

term 'Periglacial' is employed in this broad sense to-day. Hence, the term periglacial refers to

the conditions, processes and landforms associated with cold, non-glacial environments.

Approximately 25 percent of the earth's land surface qualifies as periglacial at this time (Gerrard

1992, c.f. Chattopadhyay, 1998).

Periglacial geomorphology developed in the 1940s–1960s as a branch of climatic

geomorphology. In the initial stages periglacial geomorphology focused on Quaternary studies

and Palaeo-Environmental reconstructions, later on it emphasized on current geomorphic activity

in cold regions, as per Embleton & King, (1975). In the 1960s–1970s periglacial geomorphology

was dominated by the freeze- thaw phenomena along with frost action as the sole periglacial

geomorphic activity. Such a view was severely criticized in the 1980s–1990s based both on

monitoring studies and on time–space multiscale approaches that attempted to search for the real

past and present processes responsible for the landform geometry. According to Andre, (2009)

the role of rock properties and the pre-Quaternary history of slope systems were re-evaluated and

taken into account, thereby minimizing the dominance of only cold climatic conditions and

related processes. The interest of genuine periglacial landforms as geo-indicators of climate

change was growing. Polar and Alpine regions are nowadays considered as the prime location for

analyzing climatic changes, and presently periglacial geomorphologists are greatly involved in

the detection, monitoring and prediction of environmental changes which is well indicated

through periglacial landform evolution. Thus, the evolution of periglacial geomorphology over

the past six decades has been in accordance with the quantitative and technological revolution

and its application in the field of Quaternary Geomorphology as a whole.

French (1976) identified four types of periglacial environments.

1. High arctic climates in polar latitudes; with large seasonal but small diurnal temperature

fluctuations (e.g., the Canadian arctic).

2. Continental subarctic climates with large seasonal but small diurnal temperature pattern;

extreme annual temperature range (e.g., interior Alaska including the upper Copper River

watershed).

3. Alpine climates in the middle latitudes with large seasonal and diurnal temperature

fluctuations (e.g., the summits of the European Alps, Himalaya etc).

4. Other climates of low annual temperature range in azonal locations widely distributed

with small seasonal and diurnal temperature fluctuations (e.g., some subarctic islands and some

summits of the South American Andes and the Hawaiian Seamounts).

Presently, two distinct domains of periglacial environment in the world are considered:

1) Arctic and Sub-arctic zones (ice-free polar desert and Northern forests) where thick layer

of permafrost or perennially frozen ground occurs, and

2) Alpine zones (mountain regions above timber-line and close to snow-ice and glaciers).

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6.2 Periglacial processes and landforms Periglacial environment is dominated by some typical processes leading to the formation

of unique landform patterns. Some processes are Zonal in nature like the frost action and

weathering processes along with some types of mass movements while others are Azonal

operating in either humid (fluvial) or semi arid (Aeolian) environments (Dylik, 1964 & French,

1976). Even if the Late Pleistocene period is considered periglacial conditions occurred a number

of times, but of varying duration and intensity and they too are charecterised by three conditions,

namely a) intense frost action, b) presence of continuous or discontinuous perennially frozen

grounds and c) strong wind action.

The processes that are charecterised in the periglacial regions of the present day are

discussed as follows:

A. Frost Weathering or Gelifraction is the chief process, preparing bed rock for erosion. It

includes the various weathering processes like development of permanently frozen ground

(Permafrost) with ice segregation combined with thermal contraction of ground under intense

freeze and thaw. It also initiates disintegration of surface rocks by frost wedging and a

complex of frost activity within the seasonally thawed layer like frost heaving, soil churning,

frost cracking, frost shattering etc as conceived by Ball and Goodier (1970). In areas outside

the permafrost ground during warmer season water penetrates in the rock body through

cracks and fissures and on freezing (as a result of 9% volume increase) it exerts pressure thus

breaking down the rock in smaller fragments.

The frost action process is most important in periglacial landscape modification, of which

freeze-thaw cycle is the dominant one. Three basic frost action processes are separately

enlisted below, though they occur in a combined manner. They are:

Plate 6.1: Frost wedging on the bed rock in Rohtang pass area

Plate 6.2: Partly snow covered snow shattered rocks along with development of ice wedges in Rohtang Pass area.

Plate 6.3: Evidences of frost shattering and frost heaving in moist geliflucted slopes in Beas Kund region. 149 

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The lowering of temperature of ice rich frozen soils leads to a thermal contraction of the

ground leading to development of fissures due to frost cracking, which varies with soil type

and its ice content.

When soil freezes water within the soil segregates into ice lenses, thereby forming

segregated ice. Ice segregation in seasonally thawed layers causes some distinct geomorphic

processes such as frost heaving of soil, upfreezing of stones, frost sorting, needle ice

formation, stone tilting and frost mound development i.e. localized updoming of surface

sediments by ice crystal growth.

Increase in volume of water by approximately 9% on freezing during the freeze cycle

leads to two important frost action processes. They are frost wedging and mass displacement

and development of cryostatic pressure.

B. Mass Movement or Gelifluction the principal method of transport comprises downslope

movement of debris under the influence of gravity. Though this process is not unique to the

periglacial regions, the mass movement process gets highly induced and activated in the

periglacial environment due to dominance of frost action, high moisture content of the active

soil layer and permafrost. The various mass movement processes are: slow flow of water

saturated soil like gelifluction (solifluction), frost creep and slopewash. Slip involves active

layer failures and ground ice slumps. Fall involves rockfall and rock avalanches. Other rapid

mass movement includes earth flow, debris flow e.t.c. all of which lead to active

development of slopes.

C. Other Processes include the following:

Fluvial action charecterized by marked seasonal discharge pattern and huge suspended and

bedload sediments, valley slope asymmetry, periglacier valley sandar.

Strong wind or aeolian action comprising nivation and snow patch effects in regions of

sparse vegetation and large amount of glacially derived unsorted debris.

The erosive process nivation is formed by the combined action of frost shattering,

gelifluction and slopewash processes. However, the present day Quaternary

geomorphologists tend to exclude nivation process from the periglacial domain.

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Table 6.1: Periglacial processes and resultant landforms.

Periglacial Process Resultant Landform

Frost Weathering

or Gelifraction

Frost Action Tor, Rock Glacier, Pro Talus Rampart, Talus Slope, Scree

Slope, Block fields and Block Slopes, Debris mantled slope of coarse angular sediments, often relict.

Frost Heave Hills (Pingos) and mounds (Palsas, Thufurs), Ice Wedges, Patterned Ground

Other minor processes are – Frost shattering (wedging,

splitting), Frost Cracking etc.

Repeated cracking and incremental accretion of ice creates ice wedges, segregated ice that is wedge-shaped in cross section and occupies the polygonal network of thermal

contraction cracks.

Mass Movement

or Gelifluction

Frost Creep Cryoplanation Terraces & Cryopediments. Solifluction

(gelifluction) Solifluction (Gelifluction) Terraces, Turf-banked & Stone-

banked Solifluction Lobes and lobate sheets. Rockfall & Rock

avalanches Avalanches, Asymetrical Valley profiles.

Earth flow and Debris flow

Reduction of Relief and Surface Irregularities

Others Fluvial processes

Large Gullies in upslopes. Braided periglacial streams due to fluctuating discharge and high variable sediment loads

in downslope

Aeolian processes Grooved, fluted, polished surfaces of boulders often mantled with loess.

(Compiled by the author)

It has been found difficult to arrange all possible types of periglacial landform features

found in different cold climatic regions (Arctic, Sub-arctic, Alpine and others) of the world. A

scheme of classification of periglacial features modified from that of standard classification by

Ballantyne, 1980 and Chattopadhyay, 1982, 1985 has been presented here.

Fig 6.1: Classification of periglacial features

How to distinguish periglacial deposits from glacial deposits in an extensively glaciated

landscape:

In an extensively glaciated area problems can arise in distinguishing periglacial deposits

(soliflucted material) from glacial deposits. Presence of erratics and striations on rocks are

common denominators to identify a drift as glacially deposited, but these features can often

incorporate in solifluction deposits subsequent to the disappearance of glacial activity. It has

been suggested by many workers (Pecsi, 1969; Ballantyne, 1981; Chattopadhyay, 1982) that n

such case an intensive field study is required in which major elements of consideration would be:

i) the clast orientation, ii) the packing of material, and iii) the particle shape indices.

In the glacial deposits (e.g., till) the clasts are generally oriented parallel to the direction of

ice movement; this contrasts with the clasts in solifluction deposits, being aligned up-and-down

the slope as a result of cryoturbation. Also glacial deposits are more compact in texture and

show no bedding, whereas solifluction deposits are identified as rhythmically stratified slope

deposits. Perhaps the most important distinction between these two types is related in the

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particle-shape indices. Under periglacial conditions the particle-shape characteristics of frost-

shattered detritus are dependent upon relative frequency of horizontal and vericlal planes of

weakness. Slabby clasts with low c:a (bredth : length) axis ratios are characteristic of soliflucted

material on many rock types where horizontal planes of weakness are frequent. By contrast,

clasts of glacially deposited material are often pre-dominantly blocky with greater c:a axis ratios.

6.3 Periglacial environment in the Himalaya: An Assessment and Literature

Review The Himalayan periglacial environment is essentially identified as Alpine periglacial

zone. The extent of available literature dealing with periglacial environment and processes in the

Himalaya so far is not only very limited but also have, in most cases, incomplete as well as

confusing owing to the absence of methodical observation and knowledge in this branch of

geomorphology.

Firstly, in many cases glacial drift deposits have mistakably been identified as the product of

periglacial processes;

Secondly, lumps of shattered debris actually resulted under paraglacial processes (a process

which operate to shatter the deglaciated valley walls following rapid retreat of glaciers) often

posed challenge to the Geomorphologists to separate them from the periglacially derived ones

particularly since they normally occur in the same cold environment, and

Thirdly, the presence of shattered blocks in the periglacial environment which have resulted

entirely from activities of tensional and compression forces acting in the seismically sensitive

rock structure in this young fold mountain system also create problems. They often look quite

similar to that produced by frost shattering under periglacial processes.

Geomorphologists like Brozovic, Burbank and Meigs (1997) reported the upper limit of

active periglacial processes in the Karakoram area in the Kashmir Himalaya.

Information on periglacial environments, processes and landforms in the Nepal Himalaya

is relatively adequate. Many Oriental and Oxidental geographers studied periglacial

environmental conditions in Nepal Himalaya. Fuji & Higuchi (1976) studied ground temperature

conditions and its relation to permafrost occurrences in the Khumbu Himal and Hiddin valley in

Nepal. Fort (1987) studied solifluction and deflation processes under periglacial conditions in the

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dry continental Himalaya in the Mustang district of Nepal. Fukui, Fujii, Ageta & Asahi (2007)

reported the ascent of the lower limit of permafrost in Khumbu Himal area from 5,300 m in 1973

to 5,400 to 5,500 m in 2004 under gradual global warming. Heimsath and McGlym (2008)

measured headwall retreat rate under periglacial weathering processes in the high altitude regions

of parts of the Nepal Himalaya.

The eastern Himalayan region has drawn attention of the periglacial geomorphologists

only recently. Kar (1969) conducted field work in periglacial zones of Sikkim and Darjeeling

Himalayas and made deduction on the mechanism of slope development under periglacial

conditions. He also tried to identify various periglacial landform features but most of the fluvial

and fluvio-glacial features were wrongly identified to be periglacial ones, as mentioned by

critics. Chattopadhyay (1984, 1985, 1998 & 2005) made systematic classification of periglacial

landforms in the Sikkim Himalaya around Kanchenjunga and studied the characteristics features

of these landforms. Starkel (2003) gave an account of solifluction terraces in the uplifting

mountain areas of the Himalaya and attributed them to the periglacial processes. Regmi and

Watanabe (2004) presented a paper on slow mass movement in Kanchenjunga area in 19th

Himalaya–Karakoram-Tibet workshop in NISEKO, Japan. They observed the solifluction

processes operating under periglacial conditions as well as measured and monitored ground

temperature and soil moisture. In the same workshop Iwata, Karma, Ageta, Sakai, Narama, and

Naito (2004) reported periglacial features including rock glaciers in the Lunana area in Bhutan

Himalaya.

6.4 Periglacial processes and landforms identified in the mountains of the

Upper Beas Basin The Upper Beas Basin in the Kullu valley encompasses the Alpine Periglacial

environmental condition. The region is quite conducive for periglacial processes under the

existing Alpine periglacial condition and exhibits a wide variety of typical landforms produced

thereby.. The active periglacial zone in the study area extends from above the timber line

(3,800m) to the perpetual snow line (4,600m). Above the timber line the greater part of the

ground surface is of relatively low slope gradient and is covered in most parts by the patches of

green grassy Alpine meadow, locally known as ‘Thatch’ and exhibits numerous periglacial

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features. This area is often traversed by old morainic ridges as remnants of past Pleistocene

glaciation. Periglacially derived detritus (in the form of scree slope and associated features)

cover the steeper mountain slopes of the higher altitudes up to the perpetual snow-line.

The major difficulty for a systematic geomorphological study of this part of Himalayas is the

absence and inaccessibility of any detailed geological and geographical report mainly due to

strategic reason. As no systematic investigation and analyses of periglacial landforms have been

done in this part so far, the literature published till now have only passing mention of the

Quaternary environmental condition of the Western Himalaya in general.. Owing to the absence

of methodical observation and knowledge in this branch of geomorphology certain landforms

have often been mistakably identified and have raised confusion as mentioned in previous

chapter 6.3. In spite of the difficulties an attempt has been made to make a detail survey of the

most prominent and accountable landform features in the Upper Beas Basin. The principal

characteristics of periglacial landform features of this area can be interpreted as follows:

The footprints of periglacial phenomena in distinguished forms are distributed above the

timberline.

The past climate of this region was sufficiently cold, with greater temperature range to permit

extensive frost shattering. This view is supported by the presence of frost shattered material

in the form of debris slopes, talus slopes and block slopes with clasts of large volumes

covered with lichens and moss.

The past periglacial climate in this region in the late glacial times was much more intensive

during which landforms comprising massive blocks of rock fragments occurred and with

gradual disappearance of this harsh periglacial condition these features have turned into relict

forms.

All major periglacial landforms occur outside the morainic limits and there are evidences that

in many cases the surface profile of the morainic drifts have been reworked by periglacial

activity

In the past, when the periglacial climate was more intensive (during the later part of the

Pleistocene) the massive features like Block slope, block fields and debris slopes developed

extensively in this region under large scale frost shattering and frost wedging under this harsh

climate that subsequently moved down slope, giving rise to the major slope features. The

present day periglacial activity in this region operates at smaller scale producing rockfall

features from cliffs and the associated talus slopes, along with slow down slope movement of

gelifluction lobes and terraces.

Types of periglacial landform features found in the study area

Owing to steeper slopes and presence of glacial drift deposits along with extensive cliff

walls all possible types of periglacial landforms are not found on the mountains around the

Upper Beas basin. Moreover, the solifluction and associated features at the lower levels that

could have occurred during the harsher periglacial climate in the past now remain under

vegetation cover and it is difficult to identify them. Periglacial landforms were studied in two

selected areas namely Baukar Thatch (near the Beas Kund) and Rohtang Pass. The principal

types of periglacial features occurring in these two areas were found to have preserved in the

form of:

A. Talus Slope: Talus slope is the hill slope covered with a veneer of shattered angular rocks

and fines with a cliff-wall behind, showing the area from where the materials have been

derived under frost riving and frost shattering processes. Talus slopes are usually concave

with the steeper section occurring towards the top of the slope and they have a thickness less

than 5 m that mantles a bedrock surface. Talus slope reflects a balance between accumulation

by rockfall on one hand which is greatest near the foot of the free face and spreading of

material outwards from the base by slush avalanches and debris flow as well as presence or

absence of basal erosion. A photographic evidence of Talus Slope in Kothi near Rohtang

Pass is shown in Plate 6.4

Plate 6.4: Talus Slope in Kothi near Rohtang Pass 156 

B. Block Fields or ‘Felsenmeer’: These are extensive fields of angular boulders, rocks, and

coarse debris and rubble accumulations, with a gentle gradient below 10 . They are formed in

areas of exposed rock surfaces, relatively hard and well bedded which are susceptible to

intense frost wedging along major joints and bedding planes. The block fields are usually

conceived as relic features, but as the age and rate of formation of block fields and related

features like block slope (discussed below) cannot be clearly stated, they are of limited use in

Pleistocene periglacial reconstruction. A photographic evidence of Block Fields or

‘Felsenmeer’ near Beas Kund region is shown in Plate 6.5

0

Plate 6.5: Block Fields or ‘Felsenmeer’ near Beas Kund region

C. Block Slope: Block slope is a slope covered with large angular blocks with very little amount

of fines. The blocks are assumed to have developed in situ and have been derived under

intensively cold climate through the process of large scale frost shattering. (discussed in detail

in Chapter 7.5) Block Slope near Beas Kund region is shown in Plate 6.6

Plate 6.6: Block Slope near Beas Kund region 157 

D. Debris Slope: Debris slope is a relatively smooth slope profile, with no abrupt break of

slopes, covered with a veneer of debris comprising both stones and fines resulting from frost

shattering and solifluction of rocks. In common with that of Block Slope the debris in this

instance, is produced in situ. They have no free face or bedrock outcrop and depending upon

lithology the slope angle varies from 100 to as high as 25–300. The slope profile is

dominantly convexo-concavo in form. Debris Slope near Beas Kund region is shown in Plate

6.7

Plate 6.7: Debris Slope near Beas Kund region

E. Protalus Rampart: It is a ridge of coarse angular rock debris found near the base of a steep

inland face consisting of frost-shattered debris. They are formed at the base of a large semi

permanent or permanent snow bank which existed below the free face, with the blocks

detaching them from the free face through frost wedging and then sliding down the surface of

the snow bank. Therefore when snow melts these ridge like accumulations are seen to

develop some distance away from the base of the steep slope. Protalus Rampart near Rohtang

Pass region is shown in Plate 6.8

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Plate 6.8: Protalus Rampart near Rohtang Pass region

F. Solifluction (Gelifluction) Lobes and Lobate Sheets: Solifluction (Gelifluction) Lobes and

Lobate Sheets are the micro features that occur on the slopes of the periglacial environment

in the form Crescentic (lobate) steps facing down slope. This indicates their contemporary

down slope movements. These Lobes and Lobate Sheets are composed of a mixture of coarse

and fine material. Under the process of frost creep and solifluction (gelifluction) these lobes

move slowly down slope. They can be formed of both fines and coarse material (debris lobe)

and mainly fines (soil lobe). Soil lobes and lobate sheet are found to have covered with turf

and thus they are popularly known as turf-coved solifluction (gelifluction) lobes. Solifluction

(Gelifluction) Lobes and Lobate Sheets near Rohtang Pass region is shown in Plate 6.9

Plate 6.9: Solifluction (Gelifluction) Lobes and Lobate Sheets near Rohtang Pass region

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G. Patterned Ground: The surface of the periglacial regions are often covered by some micro-

relief features composed by a complex variety of patterns and small scale relief

configurations which are commonly termed patterned ground. According to Washburn

(1969) the origin of most forms of patterned ground are uncertain, they are polygenetic and

they may be both active and relict. These features are formed under the process of frost

sorting of the coarse and fine materials. The main geometric forms are – circles, polygons,

stripes, nets and steps, all of which may be sorted and unsorted. In the study area mainly non-

sorted polygons are found. Patterned Ground at Baukar Thatch near Beas Kund region is

shown in Plate 6.10

Plate 6.10: Patterned Ground at Baukar Thatch near Beas Kund region

H. Ploughing Blocks: Ploughing Blocks or Gliding Boulders are mainly found in the

subarctic and alpine environment. According to Chattopadhyay (1983) and Tufnell (1972,

1976) these are individual blocks resting on the solifluction (gelifluction) sheets showing a

furrow at the rear and a mound (bow-wave) in front. The altitudinal distribution of Ploughing

blocks is used for mapping the lower limit of Gelifluction in slopes of periglacial regions.

Ploughing Blocks at Baukar Thatch near Beas Kund region is shown in Plate 6.11

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Plate 6.11: Ploughing Blocks at Baukar Thatch near Beas Kund

The above mentioned periglacial landforms vary in pattern, type of occurrence, characteristics,

approximate slope gradient upon which they occur, location and age (relict/contemporary), the

detail of which is presented in the following table 6.2.

Table 6.2: Distinguished periglacial features and their pattern of distribution in the study area

Periglacial features Characteristics and composition Appx, slope angle

Type of occurrence Location Relict/

Contemporary

Talus slopes Accumulation of frost-shattered

angular blocks of various sizes at the base of near-vertical cliffs.

>30° Extensive

Both inside and outside glacial drift

limits

Both relict and contemporary.

Block Slopes Mountain slopes covered with moderate to large size frost-

shattered angular blocks 15°-30°

Extensive

Outside glacial drift

limits

Relict(stones covered with

lichens)

Block Field

Extensive ground of horizontal and near-horizontal surface covered with frost-shattered

angular blocks, coarse debris and rubble

below 100 Extensive

Both inside and outside glacial drift

limits

Relict(stones covered with

lichens)

Debris Slopes

Mountain slopes covered with a near- continuous veneer of frost-

shattered debris consisting of small to moderate size blocks

with some fines

15°-30°

In patchy areas only

Both inside and outside glacial drift

limits

Contemporary

Protalus Rampart

An arcuate rampart consisting of boulders and other coarse

shattered debris marking the downslope edge of a melted

snowbank

>30° In some areas

At the foot of the valley

wall Relict

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Compiled by the author

Gelifluction/ Solifluction Lobes and Lobate Sheets

Lobate features on slope consisting of stones and fines 20°-30° Only in

patchy areas

Outside glacial drift

limits

Relict (stones covered with

lichens)

Patterned Ground (Polygons)

Poygons formed of blocky clasts with finer material in the centre 2°-10° Only in

patchy areas

Outside glacial drift

limits

Both relict and contemporary

Ploughing Blocks

Individual boulders on grassy moist slope showing a distinct

line of furrow behind as the mark of past movement

5°-15°Only in patchy areas

Outside glacial drift

limits

Both relict and contemporary

6.5 Analysis of Selected Periglacial landform features in the Upper Beas

Basin. Among the identified features as above Block Slope, Solifluction (Gelifluction) Lobes

and Lobate Sheets and Ploughing Blocks were studied in the field in detail and analyzed

quantitatively, the result of which is presented below.

BLOCK SLOPES:

It has already been mentioned that Block slope is a slope covered with large angular

blocks with very little amount of fines. The blocks are assumed to have developed in situ and

have been derived under intensively cold climate through the process of large scale frost

shattering. This feature was found to be widespread in some areas around Baukar Thatch (Beas

Kund) and Rohtang pass.

A quantitative study was done on the samples collected from the selected stretches of

block slope as mentioned above. The following table demonstrates the findings of this survey.

Table 6.3: Quantitative report on size characteristics of clasts collected from Block slopes Sample size: 50 in each site

Site Mean Length of Axes (m) Mean volume (m3)

Mean C:A Axis ratio A B C

Site: Fresh Debris Slope around Baukar Thatch in Beas Kund area, Slope Gradient: 32º, Aspect: North North East

Middle Slope (3,472m)

0.50 (St.Dev.0.23)

0.39 (St.Dev.0.14)

0.24 (St.Dev.0.10)

0.07 (St.Dev.0.09)

0.50 (St.Dev.0.12)

Foot Slope (3,422m)

1.14 (St.Dev.0.47)

0.86 (St.Dev.0.37)

0.56 (St.Dev.0.21)

0.82 (St.Dev.0.51)

0.51 (St.Dev.0.13)

Site: Near Rohtang Pass, Altitude: 3827m, Slope Gradient: 33º, Aspect: South east 1 Km away from 0.67 0.39 0.13 0.07 0.21

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the zero point at Rohtang Pass

(St.Dev.0.45) (St.Dev.0.26) (St.Dev.0.07) (St.Dev.0.19) (St.Dev.0.08)

Based on Field survey, data vide Table…. in Appendix

Discussion: Characteristics of clasts of two selected Block slope areas, (Beas Kund and Rohtang

Pass), as have been presented in the above table (Table 6.3) can be interpreted in the light of the

existing periglacial environmental condition in these areas. Geological formations of these two

areas are different; the Beas Kund area is formed of gneissic rocks, whereas schists and phyllites

are the basic rocks in the Rohtang Pass area. Both the areas are above 3,400m and the slopes were

found to have developed upon moderately high degree (32º and 33º) convexo-concave

depositional slope. In the Beas Kund area samples were selected from both Middle and Foot

slope and from the Rohtang Pass area they were selected only from Middle slope, as the foot of

the slope in this part descends deep into the Beas gorge covered with dense vegetation.

Some interesting features have emerged from the analyses which can be explained and interpreted

as follows:

a) Although geologically different, the clast samples collected from the Middle slope in these

two areas show almost the same size in terms of their axes and volumes. The clasts samples

collected from the Foot slope in the Beas Kund area are markedly larger in size (Mean A axis

value 1.14m, and Mean Volume 0.82m3) compared to those collected from the Middle slope,

with some amount of fines, (Mean A axis 0.50m and Mean Volume 0.07m3). Higher S.D.

value for the volume of clasts (S.D. 0.51) found for the samples taken from the Foot slope at

the Beas Kund area, gives a certain indication that the volume of blocks vary widely in this

part. Compared to this smaller S.D. value for the volume of clasts (S.D. 0.09) in the Middle

slope of this part is suggestive of their fairly similar size distribution pattern. Again block

volumes of the samples collected from the Middle slope of Rohtang Pass area are very similar

to those found in the case of the Middle slope of the Beas Kund area.

b) It is believed that the materials of smaller clasts existing in the Middle slope of both the areas

are the product of the contemporary periglacial process acting under relatively mild climatic

condition, whereas the blocks of larger size occurring at the foot of the Block slope in the Beas

Kund area with lichen cover, were produced under harsher periglacial climatic condition that

prevailed in the past during the Late-Pleistocene Period. This is well depicted in Plate 6.12.

Plate 6.12: Block slopes with smaller clasts in the Middle slope and larger size at the foot of the Block slope in the Beas Kund area with lichen cover

c) Response of frost wedging and shattering to the clasts also differs significantly according to

geological formations in these two areas. It is known that gneissic rocks usually break down

irregularly under frost shattering but as the frost penetrates in schist and phyllite through the

lines of fissility they break down giving rise to blocks of slabby form. Clasts of the Block

slope in the Beas Kund area, formed predominantly of gneissic rock, are having higher C:A

axis ratio (0.50 to 0.51) compared to those in the Rohtang Pass area (C:A axis ratio of 0.21)

where slabby blocks have been resulted due frost shattering of Schistose and Phyllitic rocks.

Usually in the periglacially derived block assemblage clasts tend to have their A axis oriented

toward the aspect of the slope upon which they occur (Ballantyne, 1981, Chattopadhyay, 1982).

On this assumption selected number of clasts (number 50) from each of the three Block slopes

(two in Bauker Thatch in Beas Kund and one in Rohtang Pass areas) were measured of their A

axis orientation and the results have been presented in the table (Table 6.4, 6.5 and 6.6) and

diagram (Fig. 6.2, 6.3 and 6.4) below.

164 

Table 6.4 & Fig. 6.2: A axis orientation of clasts of Block slope near Rohtang Pass area. Altitude: 3827m, Slope Gradient: 33º, Aspect: South east

Orientation Frequency N 0 NNE 0 NE 0 ENE 0 E 5 ESE 5 SE 14 SSE 9 S 11 SSW 3 SW 0 WSW 2 W 2 WNW 0 NW 0 NNW 0 TOTAL 51

Table 6.5 & Fig. 6.3: A axis orientation of clasts of Block slope at its middle slope around Baukar Thatch (Beas Kund area)

Altitude: 3,472m, Slope Gradient: 32º, Aspect: North North East

Orientation Frequency N 5

NNE 10 NE 9

ENE 6 E 6

ESE 0 SE 1

SSE 3 S 1

SSW 0 SW 0

WSW 0 W 0

WNW 3 NW 4

NNW 1

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Table 6.6 & Fig. 6.4: A axis orientation of clasts of Block slope at its foot slope around Baukar Thatch

(Beas Kund area) Altitude: 3,422m, Slope Gradient: 32º, Aspect: North North East

Orientation Frequency N 5

NNE 4 NE 0

ENE 1 E 3

ESE 5 SE 1

SSE 4 S 3

SSW 4 SW 0

WSW 2 W 2

WNW 4 NW 6

NNW 6

Discussion: It can be seen in Fig. 6.2 and 6.3, that for the clast samples collected from the two

middle slope segments of Block slopes, the A axes in general have orientation in conform with

the aspect. While those collected from the foot slope as in Fig. 6.4, have in general irregular

orientation. Orientation of A axis for the blocks of middle slope quite clearly suggests that they

are periglacially derived and the process is still in operation. The irregular orientation of A axes

for the clasts at the foot slope would have resulted due to their reorganization through down

slope movement under gravity after the cessation of harsh periglacial condition that prevailed in

the past.

SOLIFLUCTION (GELIFLUCTION) LOBES AND LOBATE SHEETS:

It has already been mentioned (Section 7.4) that Solifluction (Gelifluction) Lobes and

Lobate Sheets are the micro features that occur on the slopes of the periglacial environment in

the form Crescentic (lobate) steps facing down slope. This indicates their contemporary down

slope movements. These Lobes and Lobate Sheets are composed of a mixture of coarse and fine

material. Under the process of frost creep and solifluction (gelifluction) these lobes move slowly

down slope. They are formed of both fines and coarse material (debris lobe) and mainly fines

166 

(soil lobe). Soil lobes and lobate sheet are found to have covered with turf and thus they are

popularly known as turf-coved solifluction (gelifluction) lobes. A quantitative study was done on

the selected stretches of solifluction (gelifluction) lobes and lobate sheets in Rohtang Pass area.

The following table 6.7 gives details of this study.

Table 6.7: Quantitative report on size characteristics of Solifluction (Gelifluction) Lobes measured around the Rohtang Pass area

Altitude: 3827 mts, Slope Gradient: 33º, Aspect: South east No. of Sample: 12

Mean Length (m) Mean Width (m) Riser Height (m) Surface characteristics 1.76 (Std. Dev 0.35) 1.46 (Std. Dev. 0.22) 0.50 (Std. Dev. 0.13) Moist soil regolith covered with

grass and turf Based on Field survey data vide Table…. in Appendix

Table 6.8 & Fig. 6.5: A axis orientation of Gelifluction Lobate Sheets around the Rohtang Pass Area Altitude: 3827 mts, Slope Gradient: 33º, Aspect: South east

Orientation Frequency N 0

NNE 0 NE 0

ENE 0 E 0

ESE 0 SE 8

SSE 1 S 3

SSW 0 SW 0

WSW 0 W 0

WNW 0 NW 0

NNW 0 TOTAL 12

Discussion: It can be seen from the above Table 6.8 and Fig. 6.6 that the orientation of the

Gelifluction Lobate Sheets in the Rohtang Pass area depicts clearly that the A axes in

general have orientation in conform to the aspect. From the observation of their surface form

with bulging frontal part and composition of mainly finer material it can be assumed that

these lobate features are still moving down the slope gradually under frost creep and

gelifluction process.

167 

Table 6.9: Size characteristics of clasts collected from different depth through the section of a Solifluction (Gelifluction) Lobe

Site: 1 Km downhill from Baukar Thatch (77º05.899' E ; 32º21.049' N) near Beas Kund area, Altitude: 3328 mts, Slope: 25-30º, Aspect: North North East,

Ground Condition: Moist vegetation covered Sample size: 25

Depth from the surface

Mean Length of Axes (m) Mean volume (m3) Mean C:A Axis ratio A B C

Maximum 30cm (near surface Ao Horizon)

0.15 (St.Dev.0.03)

0.10 (St.Dev.0.03)

0.04 (St.Dev.0.3)

0.0007403 (St.Dev.

0.000961453)

0.29 (St.Dev.0.15)

Below 30cm (Sub surface A Horizon)

0.30 (St.Dev.0.03)

0.19 (St.Dev.0.05)

0.05 (St.Dev.0.02)

0.002978133 (St.Dev.0.001899639)

0.18 (St.Dev.0.10)

Based on Field survey data vide Table…. in Appendix Discussion: The above data set in Table…..gives an account of the varied size of clasts collected

from near surface and subsurface areas (Ao and A horizons). Measurements of the morphological

attributes of gelifluction lobes and the clast size from 2 different horizons are shown in plate

6.13.

Plate 6.13: Measurements of morphological attributes and horizon wise clast size of Solifluction

(Gelifluction) Lobes and Lobate Sheets near Rohtang Pass and Beas Kund region

• A comparative analysis of the mean length of A, B & C axes, mean volume and mean C:A

axis ratio between the two horizons shows that variation exists between the two vertical

sections.

168 

169 

• The clast samples collected from the Ao horizon are smaller (Mean A axis value 0.15m, and

Mean Volume 0.0007403m3) with some amount of fines compared to those collected from

the A horizon below. They are markedly larger in size (Mean A axis value 0.30m, and Mean

Volume 0.002978133m3). Higher S.D. value for the volume of clasts in A horizon (S.D.

0.001899639) gives a certain indication that the volume of blocks vary widely in this part.

Compared to this smaller S.D. value for the volume of clasts (S.D. 0.0009614) in the Ao

horizon is suggestive of their fairly similar size distribution pattern.

• Clasts of both the horizons in this area are formed predominantly of gneissic rock, having

C:A axis ratio of 0.29 in Ao (upper) horizon and 0.18 in A (lower) horizon. From the

analyses it emerges that the clasts in both the horizons are markedly slabby. The lower

average of C:A axis ratio of the clasts in the lower horizon (Horizon A) is even smaller. Thus

it can be stated that the regolith in the lower horizon was formed under more intense

periglacial climatic condition and these lobes and lobate sheets are now moving down the

slope slowly under the existing milder periglacial condition.

PLOUGHING BLOCKS:

Ploughing Blocks or gliding boulders are widespread upon the slopes above timber-line,

from about 3,300m upward upon the vegetation covered moist solifluction sheets. On the lower

slopes, they are often stagnated by morainic drift and vegetation. Typical ploughing blocks are

found around Baukar Thatch alpine meadow on the way to Beas Kund and around Rohtang Pass

as shown in Plate 6.14. In these regions ground moisture in the solifluction sheets is maintained

for the greater part of the year due to snowmelt and precipitation. Typical ploughing blocks have

been identified, investigated upon their characteristic features in the field by data collection and

analysed. The following table gives details of this study:

Table 6.10: Quantitative report on size characteristics of Ploughing Blocks measured on the slope near Bauker Thatch (Beas Kund) and Rohtang Pass areas

Location Mean value (m) Mean

volume (m3)

Furrow Length (m)

Bow-wave height (cm) Block

Length Block Width

Block Height

Bauker Thatch near Beas Kund Altitude: 3323m,

1.67 (S.D. 0.97)

1.23 (Std. Dev.

0.77)

0.85 (Std. Dev.

0.49)

3.52 (Std. Dev.

5.63)

1.17 (Std. Dev.

0.95)

20.45 (Std. Dev.

16.97)

Slope: 25-30º, Ground Condition: Moist vegetation covered Sample size:22 Near Rohtang Pass zero point Altitude: 3827m, Slope:33º, Ground Condition: Moist without vegetation covered Sample size:22

1.34 (Std. Dev. 0.61)

0.66 (Std. Dev. 0.41)

0.21 (Std. Dev. 0.05)

0.26 (Std. Dev.

0.39)

1.11 (Std. Dev.

0.38)

22.5 (Std. Dev. 7.23)

Based on Field survey data vide Table…. in Appendix

Plate 6.14: Ploughing Blocks on the mountain slopes around Baukar Thatch mainly composed of gneissic rocks

The difference in geological formation of these two areas has been reflected in the size

variations of ploughing blocks. While the blocks in the Baukar Thatch, formed of gneissic rock,

are larger in volume compared those found the Rohtang Pass area, formed of platy rocks of

schistose origin. A quantitative analysis on the morphological characteristics of ploughing block

samples collected from the Baukar Thatch area is presented below.

Morphological Characteristics

Study of ploughing block morphology have been done in the field on randomly selected

sample of 22 and involved measurement of the following parameters: Block Size (i.e. Block

length, width and height above the ground), Block Volume, Block Orientation, Bow Wave

170 

Height and Length of Furrow. Each morphological feature of the ploughing block is discussed

below in detail:

Block Volume: is calculated by multiplying the Block Length (length along the orientation of the

slope), Block Width (width across the orientation of the slope) and Block Height (height above

the ground surface), as shown in Plate 6.15. While sliding down slope the blocks appear to get

partially embedded within the soft moist grounds up to quite few centimeters. Thus, the height of

the block only above the earth surface is considered.

Block LengthBlock WidthBlock Height

Plate 6.15: Measurement of Block Volume

The sampled blocks range in length from 70 to 370 cms, width from 50 to 290 cms and

height above the round 10 to 180 cms. After accounting the block volume, we get to see that the

largest block volume is 19,314,000 cm3 and smallest is 44,000 cm3. The mean size is

3,528,913.46cm3. The Table 2 and Figure 2 below show the frequency distribution of the

sampled block volume.

171 

Table 6.11 and Fig. 6.6: Percentage Frequency Distribution of Block Volume of Ploughing Block

Block Volume (In cm3) Frequency %

0 - 4,999,000 18 81.7

50,000,000 - 9,999,000 1 4.6

10,000,000 - 14,999,000 1 4.6

15,000,000 - 19,999,000 2 9.1

The Percentage Frequency Distribution data of Block Volume is categorized into four

classes. Majority (81.7%) of the blocks are of smaller size i.e. up to 150 cm long, 120cm wide

and 115 cm height from the ground. The medium volume and large volume blocks comprise

4.6% each. The largest size blocks are 9.1% of frequency distribution i.e. volume ranging from

15,000,000-19,999,000 cm3. Therefore, in the Beas Kund region ploughing blocks are of smaller

volume dominantly, while huge ones are quite lesser in number.

Block Orientation or Block Aspect: Slope gradient of the surveyed region is 250 to 300 upon

which the ploughing blocks occur in association with gelifluction deposits, as shown in Plate

6.16. The diagrammatic representation of ploughing block orientation in Figure 3 depicts that the

general trend of block orientation is towards North (N), North North East (NNE) and North

North West (NNW). Thus in conformal to the slopes, the orientation too is non-variant. This is

because of the unique climatological, vegetal and geomorphological (Periglacial) nature of the

higher slopes of Upper Beas Basin.

172 

Plate 6.16: Measurement of Block Orientation with the help of clinometers

Table 6.12 and Fig. 6.7: Frequency Distribution of Ploughing Block Orientation around Baukar Thatch

Orientation Frequency N 10

NNE 10 NE 0

ENE 0 E 0

ESE 0 SE 0

SSE 0 S 0

SSW 0 SW 0

WSW 0 W 0

WNW 0 NW 0

NNW 2

Furrow Length: Furrow is a typical micro feature that usually occurs adjacent to a ploughing

block. It is a trail of elongated depression formed behind the ploughing block extending from the

rear edge of the block edge to upslope. Its length marks the path of downhill movement of the

ploughing block under gravitational pull as well as active gelifluction and frost creep processes.

The furrow profile usually gets partly vegetation covered by meadow grasses in course of time.

Figure 4 showing percentage frequency distribution of the furrow length shows that the range

173 

varies from 0 to 399 cms with a mean of 117.09cms. Frequency distribution shows 50% of the

ploughing blocks have furrows are under 99 cms long i.e. half of the entire surveyed ploughing

blocks. 31.8% of the ploughing blocks have length ranging from 100 – 199 cms. 13.6 % and

4.6% ploughing blocks have furrows with length varying within 200 – 299 cms and 300 – 399

cms respectively, which is of quite lesser proportion. Another noticeable feature associated with

the furrow length is furrow depth, immediately behind the block, which suggests a recent down

slope movement of the ploughing block. In the study area except of one or two, furrow depth are

not found because of thick grass cover in the trail. This also suggests that the ploughing blocks

are largely relict.

Table 6.13 & Fig 6.8: Percentage Frequency Distribution of Furrow Length of Ploughing Block

Furrow Length (in cm)

Frequency %

0 - 99 11 50

100 - 199 7 31.8

200 - 299 3 13.6

300 - 399 1 4.6

Bow wave Height: Bow wave is a mound of regolith that occurs in front of the ploughing block.

They generally vary in height, width and composition from one region to the other. In the study

area, the bow waves have found to form, of lump of regolith covered with turf as shown in Plate

6.17.

174 

Plate 6.17: Measurement of Bow wave height

Among all samples studied, four had no identifiable bow wave because; these blocks

have followed the furrow of a preceding block. The mean value of the bow wave height is

20.45cm. From the percentage frequency distribution of the bow wave height, it can be deduced

that again 50 % of the bow waves have height below 19 cms which is quite low. The moderate

class of 20 – 39 also forms almost another half of the samples, i.e., 40.8 %. The remaining high

(40 – 59)cm and very high (60 – 79)cm classes are negligible with only 4.6% each. Thus, the

ploughing blocks in the study area have bow waves with low to moderate height. This indicates

that their increased rate of down slope movement have begun in the recent deglaciation period,

when freeze and thaw action became more dominant, resulting in active formation of periglacial

landform features.

Table 6.14 & Fig 6.9: Percentage Frequency Distribution of Bow wave Height of Ploughing Block

Bow - Wave

Height Frequency %

0 - 19 11 50

20 - 39 9 40.8

40 - 59 1 4.6

60 - 79 1 4.6

175 

176 

In the study area, though only 4.6% of the total studied samples are of very large size, yet they

truly represent that very large block volume along with predominant ploughing activity leads to

progressive sinking of the ploughing blocks and formation of Frontal-Lateral bow wave.

Discussion

The selected parameters of ploughing blocks studied were Block Length, Block Width, Block

Height (above the ground), Block Volume and Length of Furrow. A pattern of strength of

correlation between these parameters were calculated, the result of which are given in the

following table:

Table 6.15: Pattern of correlation between the parameters of ploughing blocks studied

Block Length (cms)

Block Width (cms)

Block Height (cms)

Block Volume(cm)3

Furrow Length (cms)

Block Width (cms) 0.964288444 Block Height (cms) 0.826481991 0.77851027 Block Volume(cm)3 0.95155234 0.908686541 0.823268552 Furrow Length (cms) 0.489933155 0.480010552 0.557532408 0.524637726 Bow-wave Height (cms) 0.499606016 0.53877674 0.33903752 0.582230398 0.755343731The analyses reveal very strong and statistically highly significant correlation between:

a) Block Width and Block Length (0.96),

b) Block Volume and Block Length (0.95) and

c) Block Volume and Block Width (0.91).

Among other parameters, strong and statistically significant correlation exists between:

a) Block Height and Block Length (0.83),

b) Block Height and Block Width, (0.78),

c) Block Volume and Block Height (0.82) and

d) Bow-wave height and Furrow length (0.76)

These high values can be yet be disregarded, because of their high morphological dependence

with each other. The strong relationship of Bow-wave height and Furrow length (0.79) indicates

that as a block slides down longer distance, in higher slopes, it ploughs up or excavates greater

amount of regolith to form higher mound (Bow-wave) in its frontal part.

Moderate to low correlation values is deduced from the relationship between:

a) Furrow Length and Block Length (0.48),

b) Furrow Length and Block Width (0.48),

c) Furrow Length and Block Volume (0.52),

177 

d) Bow wave Height and Block Length (0.50),

e) Bow wave Height and Block Width (0.54),

f) Bow wave Height and Block Height (0.34), and

g) Bow wave Height and Block Volume (0.58)

These statistically insignificant relationships suggest that no strong relationship exist between

these parameters. Although Furrow Length and Bow wave Height are directly associated with

the volume and down slope movement of the ploughing block, no significant correlation occurs

among these variables.

Thus, it can be concluded that the quantitative analyses of the nature and characteristics

of ploughing blocks reveal that they have a wide range of variation in their morphology. In

general, the associated micro-features of the ploughing blocks reveal no dominant pattern of

influence upon the movement of the ploughing blocks.

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