Role of tributary glaciers on landscape modification in the Gangotri Glacier area, Garhwal Himalaya, India

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1 Role of tributary glaciers on landscape modification in the Gangotri Glacier area, Garhwal Himalaya, India Dhruv Sen Singh* and Ajai Mishra Department of Geology, University of Lucknow, Lucknow , India Studies on glacier landforms are helpful in the palaeoclimatic reconstructions. However, it may lead to misinterpretation if the secondary processes that modify the landforms and landscape are not taken into consideration. The tributary glaciers are identified as an important agent, which form, affect and modify the landforms/landscape. The landforms and landscape readjust according to the new set of conditions created by tributary glaciers, and get modified. Therefore, to study the geomorphological landforms and their palaeoclimatic implications, the role of transverse tributary glaciers is of prime importance. THE Quaternary period is well known for its repeated climatic changes. One of the most prominent features of the Quaternary times is the periodic glacier activity during cold periods that have given rise to a rich record of the glacial landforms. Therefore, by studying the landforms of the glaciers, it is possible to reconstruct, in considerable detail, the environmental conditions and processes responsible for creating the glacial topography. Such reconstructions are valid and hold good, if the situation is ideal and no other process affects and modifies the landforms. However, there are several processes that cause and affect the existing landscape and modify it. The floods, rock falls, rock slides, debris flow, mass movement and small channels (nalas) coming out from the tributary glaciers are significant processes which are not directly related to the glacial processes, but occur in a glaciated terrain and are important in affecting the glacial processes. These processes are grouped together under a new term, paraglacial processes, which are essentially the non-glacial processes in the glacial region. Flash floods caused by bursting of glacial lakes are well known in the Himalayas 1 where the lake had been formed by landslides 2. The progressive thinning of the Himalayan glaciers during the past century has resulted in the formation of new moraine dammed lakes 3. Floods in the Bhagirathi valley 4, Garhwal Himalaya are often related to the slope failures. However, the tributary glaciers and their role as a cause of flooding and landform modifications were not considered earlier. In the present paper, the role of tributary glaciers of the Gangotri Glacier in regulating the floods and in shaping the landforms and redistribution of sediments within the valley has been emphasized. Gangotri Glacier is situated in the Uttarkashi District of Uttaranchal, between N and E, draining in a northwesterly direction (Figure 1). It is about 30 km long 5 and 0.5 to 2.5 km wide, and covers an area of about 75 km 2. The satellite data (IRS-1D, LISS-III) show that there are numerous small-sized glaciers, which feed and contribute into the main glacier to form the Gangotri group of glaciers (Figure 2). These small-sized glaciers, named as tributary glaciers, are generally transverse to the main glacier and vary from NE-SW and NW-SE in orientation 6. These are small in size (length 3 20 km) and large in number (30) (ref. 5). Meru and Ghanohim are the tributary glaciers which feed the main glacier from left and Raktavarn, Chaturangi, Swachhand and Manda feed from the right (Figure 3, Table 1) 5. Depending upon their present-day location with respect to the main glacier, these tributary glaciers are classified into two categories, active and inactive. Active tributary glaciers are those which are still connected to the main glacier, contributing ice budget to it and are also forming the new landforms. Inactive tributary glaciers are (Table 2) 5 those which are now detached from the main glacier but were connected to it in the past. These are neither contributing ice budget to the main glacier nor forming any new landform. Whatever they are contributing nowadays is only in the form of melt water coming out of them. So we prefer to call these remnant tributary glaciers as inactive. However, the inactive tributary glaciers are modifying the pre-existing landforms only because of their melt water. The nalas coming out from inactive glaciers meet the Bhagirathi Glacier *For correspondence. ( dhruvsensingh@rediffmail.com) Figure 1. Location map. CURRENT SCIENCE, VOL. 82, NO. 5, 10 MARCH

River. During heavy rains, these inactive glaciers bring huge amount of sediments. Sometimes, these sediments (debris) block the fluvial channels and form small ephemeral short-lived lakes.

2 River. During heavy rains, these inactive glaciers bring huge amount of sediments. Sometimes, these sediments (debris) block the fluvial channels and form small ephemeral short-lived lakes. Bursting of such lakes leads to flood and these floods redistribute the sediments and modify the landscape. Some of the material is deposited in the nearby areas, filling part of the valley. Transportation of the debris depends on the slope gradient of the valley wall and energy of the water. The Gangotri group of glaciers has undergone many major and minor changes in its spatial extent 7, which is evidenced by the presence of lateral and recessional Figure 2. Gangotri and its tributary glaciers as seen in satellite data IRS-1D. 568 CURRENT SCIENCE, VOL. 82, NO. 5, 10 MARCH 2002

3 moraines occupying different elevations and positions 8. In the past, Gangotri Glacier was 40 km downstream from its present position 9. Along with the recession of the main glacier towards Gaumukh, the tributary glaciers also recessed in their own path and became inactive 10. Even today on the way from Gangotri to Figure 3. Gangotri and its tributary glaciers. Gaumukh, the inactive transverse tributary glaciers can be seen. Important ones are near Bhujbas (Bhujbas Dhar, Figure 4 a) at the right bank of the river and another near Chirbas (Manda, Figure 4 b) on the left bank of the river. On 6 June 2000 near Bhujbas, heavy rains transported large amount of sediments from the left (Figure 5) bank tributary glaciers and deposited enormous amount of material into the valley. In these rainless areas, the precipitation was recorded as 80 mm in a single day. The debris consisting of boulders, pebbles, cobbles, sand and silt dammed the Bhagirathi River to form a short-lived extensive lake. Bursting of this lake caused flash floods in which the entire area, including DST huts and tents located at Bhujbas were affected (Figure 6). The water level of the river rose by about 3 m and water spread in an area of about 3 4 km 2. The poorly sorted material consisting of boulders and gravels was redistributed in the valley (Figure 6). The boulders range in size from 100 to 400 cm in diameter. The clasts aligned themselves in the downstream direction along the direction of flow (N60W). In some places about m thick sediments were deposited (Figure 7 a and b). The river is situated more towards the left valley wall. Since the left valley wall has more slope gradient than the right valley wall 10, the fluvial channel could be blocked easily by the sediments of the left bank tributary glaciers in comparison to the right bank tributary glaciers. The main glacial landforms in the study area are lateral moraines, medial moraines, recessional moraines, debris cone, pillar-like structures, and river valley terraces 11. The tributary glaciers continuously modify all these land forms. The lateral continuity of the lateral moraines is being disrupted by the tributary glaciers 10, the medial Table 1. Details about tributary glaciers of the main Gangotri Glacier Glacier Height (m) Length (km) Area (km 2 ) Feeding bank Maiandi Bamak Swachhand Ghanohim Gl. N. of Bharat Khunta Peak Gl. E. of Topo h. s Gl. opposite Ghanohim Bamak Kirti Bamak Suralaya Bamak Gl. between Vasuki and Suralaya Bamak Gl. between Meru and Kirti Stambh Gl. W. of Bhagirathi *Parvat Chaturangi Bamak Meru Bamak Raktavarn Pilapani Bamak Nilambar Bamak Thelu Bamak Bhujbas Dhar Swetvarn Bamak Bhrigupant Bamak Manda Bamak Matri Bamak CURRENT SCIENCE, VOL. 82, NO. 5, 10 MARCH

moraines are formed by the confluence of the Gangotri Glacier with the tributary glaciers.

5 km upstream from Gangotri township towards Gaumukh, the point beyond which the nalas meeting the river are not prominent.

4 moraines are formed by the confluence of the Gangotri Glacier with the tributary glaciers. The recessional moraines are reworked and transported by the nalas coming out from the inactive tributary glaciers. This may be the reason for the presence of recessional moraines, after 15.5 km upstream from Gangotri township towards Gaumukh, the point beyond which the nalas meeting the river are not prominent. These tributary glaciers and their melt water also modify the debris cone and pillar-like structures. Thus, tributary glaciers are important in giving final shape to the Gangotri Glacier landforms. Table 2. Inactive tributary glaciers between Gangotri to Gaumukh Glacier Raktavarn Pilapani Bamak Nilambar Bamak Thelu Bamak Bhujbas Dhar Swetvarn Bamak Bhrigupant Bamak Manda Bamak Matri Bamak Bank of the river During interglacial periods, especially when the glacier is retreating at an increased rate 6,7 (20 35 m/y), more tributary glaciers would be detached from the Gangotri Glacier. The number of inactive tributary glaciers would increase and would cause more floods and intensify the modification of landforms. The deposits of tributary glaciers are similar to those of the main glacier, and are often confused because of the lithological similarity. Therefore caution should be taken at the time of sample collection for various studies, otherwise the material deposited by the tributary glaciers may be confused with that deposited by the main glacier, thereby leading to wrong interpretations. This difference can be made in the field by the mode of occurrence. Because of lithological and directional similarity, the same problem may be encountered for the lateral moraines of the tributary glaciers, which may be often confused with the recessional moraines of the Gangotri Glacier. The Gangotri Glacier is the sustainable source of the major river Ganga and assists the irrigation and power generation sectors. It is important to consider potential Figure 5. bank nala, which brought the sediments and dammed the river to form a lake on 6 June Figure 4. Inactive glacier near (a) Bhujbas (Bhujbas Dhar) and (b) Chirbas (Manda). 570 Figure 6. DST hut, Bhagirathi valley showing scattered debris after flood. CURRENT SCIENCE, VOL. 82, NO. 5, 10 MARCH 2002

11. Singh, D. S., Natl. Acad. Sci. India, Allahabad, 2000, pp. 126 127. 12. Burbank, D. W., Geol. Bull. Univ. Peshawar, 1983, 16, 43 49. ACKNOWLEDGEMENTS.

5 11. Singh, D. S., Natl. Acad. Sci. India, Allahabad, 2000, pp Burbank, D. W., Geol. Bull. Univ. Peshawar, 1983, 16, ACKNOWLEDGEMENTS. The Department of Science and Technology, Government of India, New Delhi is acknowledged for financial assistance (DST No. ES/91/020/97). We thank Prof. I. B. Singh, Head, Department of Geology, University of Lucknow, for providing working facilities and also for continuous encouragement. We also thank Dr Deepak Srivastava, Director, Glaciology Division, GSI, Lucknow, and Dr R. Kar, BSIP, Lucknow for discussion. Received 8 June 2001; revised accepted 3 January 2002 Fertility of Late Archaean basement granite in the vicinity of U-mineralized Neoproterozoic Bhima basin, peninsular India P. Senthil Kumar* and R. Srinivasan National Geophysical Research Institute, Uppal Road, Hyderabad , India Figure 7. a, Iron rods at the bank of the river before floods; b, Iron rods showing 1.5 m of resedimentation after flooding in a single event. effects of such events in terms of hazard assessment and their role in resedimenting the valley deposits, both within the mountains and on the Indo-Gangetic Plains 12. Therefore it is important to study the tributary glaciers to consider their effects for lake formation and lake bursting in terms of flooding and landforms modification. 1. Coxon, P., Owen, L. A. and Mitchell, W. A., J. Quat. Sci., 1996, 11, Butler, R. W. H., Owen, L. A. and Prior, D. J., Geol. Today, 1988, 4, Mayewski, P. A., Pregent, G. P., Jeschke, P. A. and Ahmad, N., Arct. Alp. Res., 1980, 11, Prasad, C. and Rawat, G. S., Himalayan Geol., 1979, 9, Inventory of Major Glaciers in Indian Himalayas, Geodatic and Research Branch, S.O.I., Naithani, A. K., Nainwal, H. C., Sati, K. K. and Prasad, C., Curr. Sci., 2001, 80, Puri, V. M. K. and Shukla, S. P., Geol. Surv. India Publ., 1995, 21, Singh, D. S. and Mishra, A., Convent. IAS, Cochin, 2000, vol. XVII, p Sharma, M. P. and Owen, L. A., Quat. Sci. Rev., 1996, 15, Mishra, A. and Singh, D. S., Seminar on Geology and Natural Environment of the Lesser Himalaya, Nainital, 2001, p Late Archaean granitoids constituting the basement for the Neoproterozoic Bhima Group are exposed along the southern margin of the Bhima basin in southern India. These are rich in accessory minerals such as sphene, allanite, apatite and zircon, which are the main carriers of uranium and thorium. In situ gamma-ray spectrometric analysis reveals that these granitoids have higher abundances of Th, U and K (Th range ppm, mean 26 ppm; U range 3 21 ppm, mean 8 ppm; K range %, mean %) relative to granitoids occurring farther away from the basin. Thus, they belong to the class of fertile granitoids from the point of view of uranium mineralization. The granitoids have been mylonitized and hydrothermally altered in the Gugi Ukkinal fault zone, which constitutes the zone of uranium mineralization discovered recently along the southern margin of the Bhima basin. Uranium apparently derived from hydrothermal leaching of basement granitoid rocks may have got deposited in the fault zone at the contact of carbonate rocks, which provided favourable geochemical environment (Eh ph conditions) for uranium precipitation. LATE Archaean granitoid rocks consisting of radioelement-rich accessory minerals the fertile granitoids have contributed to uranium mineralization at the interface *For correspondence. ( senthilngri@rediffmail.com) CURRENT SCIENCE, VOL. 82, NO. 5, 10 MARCH

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