Chapter Five
Summary and Conclusion
Perfunctory references of glacial landforms by the explorer naturalist of the 19th early
20 th centaury have helped immensely while reconstructing the paleoclimate of the
Himalayas. Contain a glacial repository oflate Quaternary landform. These landforms
have now been used as proxy data for delineating glacial extent and magnitude.
The conclusions resulting from this investigation would provide a framework for the
. understanding of the evolution and dynamics of Himalayan environment especially
the limit and phases. This study has led to the identification of the number and extent
of glacials in the Late Quaternary in the Bhagirathi valley along with characterization
of the geomorphology and the relative role of earth surface processes in shaping the
landscape. This work adds to and enriches the knowledge of paleoclimate and the
paleoglaciation of the region, for interpreting glacial chronologies (timing and phases
of glaciation) and landforms in the Garhwal and can be extended to other similar areas
acroce the Himalayas. To achieve desired result for this study multiparametric method
have been applied to obtain absolute ages (OSLlCRN), ELA calculation
(A WMlAARlTHAR), as well as mapping of snout position (GPS survey/ chain-tape
survey) for Gangotri glacier forefield and environment.
5.1 Major Landforms
The major glacial landforms associated with various environmental conditions at
Gangotri glacier area in the Bhagirathi valley are rock glacier, lateral moraine,
hummocky moraine, glaciofuvial outwash terraces, paraglacial fan, and debris flow
fan.
Rock glacier exists above 4300 m, covering 6 per cent of the studied area.
Extensively debris covered rock glacier above Tapovan il') beheaded from its
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headwall. Complex assemblages of lateral moraines extend down valley from
Tapovan to Bhujbas. The crests of the lateral moraine are 120 m higher than the
present glacier ice surface. The highest lateral moraine is clearly visible on the south
side of Bhagirathi River, above snout, which rises 240 m from the valley floor.
Lateral moraines account for more than 30 per cent of the surveyed area between
Bhujbas and Tapovan. Assemblage of hummocky moraine exists within 1.5 km of the
present ice margin of the Gangotri glacier. These hummocky moraines are present in
the north of the Bhagirathi River within an area of 1.25 km 2 • Striations are present on
recently deglaciated area on the north side, bedrock near snout. Melt water of the
Gangotri glacier has formed four sets of terraces within 1.5 km of the snout. These
glaciofuvial outwash terraces account for 12 per cent of the surveyed area. Paraglacial
debris flow fans have reworked the material from these outwash terraces to a
considerable extent. The surfaces of paraglacial fans have prominent leveed channels.
Rockfall and scree slope account for area of 6 per cent and 5 per cent respectively.
Stone stripes from the highest lateral moraine terrace, cover 4 percent of mapped
area. End moraines are restricted only within I km from the contemporary glacier ice
extent, with only prominent end moraine at Ihala at 2490 m and another near Pandu
Gupha at 3000 m. Absence of end and push moraine indicate that these landform have
poor preservation potential because of the variability of meltwater and switching of
channels. Rock glaciers in the region indicate a decreasing precipitation pattern. The
altitude and aspect of the Bhagirathi valley shows a strong control on the climate
precipitation and distribution of landform processes. There is a decreasing trend in
.
retreat of snout position. In the 1960s rate, of retreat ~as 30 m -I, which reduced to 24
m-I by 1990s. But in year 2006-07 the rate was only 8.4 m because of extended cold
spell and good snowfall in late winters.
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5.2 Quaternary Glacial History
There have been four phases of advances, each smaller than the earlier, evolved from
a large number of dated material and landforms. On the basis of absolute dates and
morphostratigraphic evidence, maximum expansion of glaciers occurred 58.5 ka ± 4.6
in the Bhagirathi valley. At its maximum, an extensive valley glacier descended to an
altitude of 2490 m near Jhala. This end moraine was earlier dated to 63 ka B.P.
(Sharma and Owen, 1996). OSL dates for the glaciogenic sediments around Gangotri
village confirm to a relatively large advance reaching at least Bhaironghati (2786 m
asl) between ca. 13.1 ka to 17.6 ka. Sharma & Owen (1996) had considered this to be
the waning part of the Bhagirathi Stage Maxixmum. This study identifies this as a
stage and proposes to name of Sudarshan Stage advance. Even the exposure on the
northern. flank of the river near Bhujgarhi (3776 m) also yields OSL ages between 4.2
ka to 9.1 ka BP. This strengthens proposal for additional advance that reached as far
as 2784 m asl down valley. This advance is now constrained as early Holocene.
During the Bhujbas Glacial Advance glaciers reached positions 2-3 km beyond the
present snouts. This advance occurred -400 years ago comparable with little ice age
elsewhere.
The increase in ice cover was about two and halftimes compared to that of the present
day which resulted due to an ELA depression of 700 m. These ages suggest that
glaciations in NW Garhwal were not synchronous with the other parts of the worlds
baring the LIA advance. The variation in waning in glacier ice related to the
Bhagirathi stage in the upper parts is best exemplified by the lateral moraines of
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Bhrigupanth and Manda glaciers which have a down. Minor fluctuations during the
Shivling and Bhujbas Glacial Advances show ELAs depressions of 120-30 m,
respectively. The ELA values show that a small depression may result in a substantial
fluctuation in snout position, amounting to 2-3 kilometers of the frontal advance. ELA
reconstructions in the region clearly indicate the control of aspect on the glaciers.
5.3 Environmental Concerns in the Bhagirathi valley
Development activity like road construction and the increasing flow of pilgrims, every
year has led to the serious problem of deforestation in the Bhagirathi valley. Use of
firewood for meeting fuel needs has been depleting the vegetation cover rapidly. The
bark of bhujpatra (birch) tree is considered vary sacred by the pilgrims as it is
believed that the Hindu religious scripts were written on it. This had a serious impact
on the population of the birch tree in the region and Bhojbas, 12 km upstream from
Gangotri town.
Another major activity taking place in the region is dam construction. Tehri and
Manari are two such examples. In this region ample amount of loose and fragile
material of lateral moraine give rise to heavy load of suspended sediment in the river.
This further affect the down stream dams decreasing their longevity.
5.4 Major Conclusions and Contributions
The major conclusions and contributions ofthis study are outlined below.
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•
Gangotri glacier expansion (BSM 58.6 ka) is not a synchronous with the last
glacial maximum (LGM) expansion in other parts of the world. However, the
Bhujbas advance constrained by CRN technique between 210-440 years is
comparable with the LIA advance elsewhere.
•
It is obvious from the ages obtained for boulders at Tapovan that the terminus
of the Gangotri glacier was much higher possibly at the junction of Kirti
bamak prior to the 1.3-1.6 ka CRN
•
Average ELA depression of700 m (530m by AWM) was sufficient to expand
Gangotri glacier and its tributaries to form extensive valley glacier down up to
Jhala 2490m, increasing ice cover by almost 3 times in region. Therefore, it is
considered that a small depression may result in substantial down valley
increase in snout position.
•
Glacier environment, dominated by supraglacial and proglacial environment
result in a poor preservation potential for end, push and hummocky moraines
in the valley glacier forefields. Variability in glacier meltwater, ice-collapse
and rapid resedimentation rapidly rework and alter these landforms in such
environment.
•
The altitudinal organization of landforms has produced a distinctive landform
association which is important for understanding landscape evolution and
changes through tiIJ1e, and for hazard assessment. The landforms of the
Bhagirathi valley are polygenetic in evolution.
•
The climate of the Bhagirathi valley is becoming semi-arid as indicated by the
formation of rock glaciers in the region, as well as instrument precipitation
data for Uttaranchal, Himachal Pradesh, and Jammu & Kashmir.
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•
The summer monsoon rainfall is insignificant in terms of moisture supply for
the glacier mass balance. Monsoon rainfall shows negative relation with
glacier mass balance, instead of moisture supply from westerlies.
•
The ELA gradient for the Bhagirathi valley and the Himalaya from east to
west indicates that the moisture supply has been from the west during the
maximum expansion of glaciers and subsequent advances, probably related to
the westerlies.
•
Huge population pressure, with increasing number of pilgrims is largely
responsible for environmental degradation in this region.
•
Deforestation, High way construction, huge quaternary glacial sediments,
highly variable monsoonal rainfall and discharge are responsible for very high
suspended sediment load in the Bhagirathi River which ultimately would
affects the longevity of dams down stream (Manari and Tehri).
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