Glaciers and Snow-line in Himalayas
The ‘snow-line’ or the lowest limit of perpetual snow has different altitude in different parts of the Himalayas. In the Assam Himalaya the snowline is at about 4400 m or higher, whereas in the Kashmir Himalaya it varies from 5100 to 5800 m. This is, to be more precise, 4420 m high in Assam Himalaya, 5200 m in Bunkum Himalaya, 5185 m in Punjab Himalaya, 5500 m over Ladakh range and 5200 m in the Hindu Kusch Mountains.
On the Tibetan side the altitude of the snow line is about 900 m higher owing to the great desiccation of the region and absence of moisture. The scarcity of rainfall also affects the height of snow line in the western Himalayas. Also due to the higher altitude of the snow line most of the peaks of the Lesser Himalaya arc free from snow. However, there are traces of earlier glaciation as is evidenced by the morainic deposits and occurrence of cirques and lake-basins in the Pir Panjal range.
The Greater Himalayas have a number of glaciers some of which are among the largest in the world outside the Polar circles. The glaciers of the Himalayas and Central Asia have been largely studied by the Geological Survey of India and explorers like de Filippi, Bullock-Workman, Dainelli, Montgomerie, Conway, Longstaff, Visser and others.
The majority of the Himalayan glaciers are from 3 to 5 km in length but there are some giant glaciers of more than 50 km o. length, such as Siachen, Hispar, Biafo, Baltoro, Batura (all in Karakoram Mountains). These glaciers of Karakoram are the remnants of the Pleistocene Ice Age. The majority of the glaciers are of valley type but hanging glaciers are not uncommon.
The diurnal rate of movement is between 8 and 13 cm at the sides and from 20 cm to about 30 cm in the middle. The hanging and transverse valley glaciers have a more rapid movement than the longitudinal valley glaciers. The lowest limit of descent of these glaciers is not uniform in all parts of the Himalayas.
It is 3965 62 m in Sikkim, 3660 m in Kumaun and 2500 m in undertl1 Kashmir Himalayas. One main peculiarity of the of ate T Himalayan glaciers is the presence of extensive superficial moraine matters and rock wastes which completely cover the upper surface of the glaciers,lion of i The Himalayan glaciers are gradually receive Suring. In many of them large amounts of moraine cover Arc, to the ice near the snout. During summer season they toward melt and the water escapes through crevasses form-well suing englacial streams issuing out of tunnel-like caves, shield1 They are not only source of the Himalayan rivers but basis o maintain regular supply of water during off-monsoon that ‘Ii period. According to Dr. Banerji major rivers origi- the up nating from the Himalayas obtain about 60 per cent interim of their quantity of water from these glaciers be-pp. 46 teen December and June and about 35 per cent that ‘the during remaining part of the year.
aggradational plain formed by the alluvial deposits , of the Indus, Ganga and the Brahmaputra and the! I tributaries. The plain stretches from west (from the P banks of the Ravi and Satluj) to east (the Gangi delta) to a length of 2400 km with varying width between 150 and 500 km and surface area of about 750,000 sq. km.
It is about 90-100 km. wide in Assam, 160 km near the Rajmahal Hills, 200 km in Bihar, 280 km near Allahabad and 500 km in Punjab- Rajasthan. With an average elevation of about 150m ranging from tide level near the mouth of the Ganga to nearly 300 m (Punjab and Upper Ganga Plains) near the foot-hills the region is characterised by extremely low gradient (about 13 cm/km).
The plain merges into the Thar Desert in the south-west. A low watershed of the Delhi ridge (278 m) along the right bank of the Yamuna River separates the Satluj plains (a part of the Indus Plain) from the Ganga plains.
The Great Plains largely consist of alluvial deposits brought from the rivers originating in the Himalayan and the peninsular regions. The deposits include great thickness of sand, clay, loam and silt. The clay elements are predominant in the deltaic tracts while sands dominate in the upper reaches.
The exact thickness of the alluvium has not yet been fully determined. Oldham estimated the depth of the alluvium between 4000-6000 m and Burrard considered the existence of a fault with 32 km downthrow near the Himalaya. Later Glennie estimated the thickness at about 2000 m. According to the recent studies the average depth of the alluvium has been estimated to about 1300-1400 m which goes on decreasing towards south and finally merging with the irregular edge of the Peninsular block. But in a narrow zone along the foothills of the Himalayas the thickness of the alluvium even reaches more than 8000 m.
The variation in thickness largely depends on the alluvial-morphological processes. The cones of the Kosi in the north and the Son in the south exhibit greater alluvial thickness while the intra-cone areas have relatively shallower deposits (A. Geddes, 1960, pp. 262-263). The physiographic scenery varies from extremely arid and semi-arid landscape of the Rajasthan Plain to the humid and per-humid landscape of the delta and the Assam valley in the east.
The Great plains are remarkably homogeneous with little variation in relief features for hundreds of kilometres. The monotony of the physical landscape is broken on micro level by the river bluffs, levees, dead arms of the river channels, the ravines and khols. Changing river courses in the areas of frequent over-floodings present interesting geomorphic processes in the plains.
This flood although cause immense damage to life and property but lay down fresh layer of silts providing rich fertile soils. The southern boundary of the plain runs along the northern edge of the peninsular block which sometimes make steep cliff along the right bank of the Ganga.
