Longitudinally the Himalayas consist of three parallel ranges from south to north and a trans- Himalayan region.

(a) The Sub Himalaya or Siwaliks-it is also known as the outer Himalaya. This is the southernmost range of the Himalayas bordering the Ganga Plain and giving a hog-back appearance with rela­tively steeper slopes towards south. Flat scarps, anticlinal crests and synclinal valleys with an aver­age elevation of 600 m characterise this range. It is bordered at the top by scarps and descends north­wards to flat floored structural valleys called ‘doon’ or ‘dun’ in the west and ‘duar’ in the east which are intensively cultivated and densely populated. The site of Dehradun lies in one such valley (75 km x 20 km) which is covered with boulder and clay depos­its.

The range has a total length of about 2400 km from the Indus gorge to the Brahmaputra valley. It is known by various local names, i.e. the Jammu hills (Jammu & Kashmir), the Dundwarange (Uttaranchal), the Churia Muria hills (Nepal), the Daffla, Miri, Abor and Mishmi hills (Arunachal Pradesh).

Most of the rivers descending from the northern ranges of the Himalayas have carved out wide and steep-sided valleys. The gorges of the Tista and the Raidak have jointly formed a 90 km gap in the Siwalik range. The range is covered with thick, tropical moist deciduous forests. It enjoys good amount of rainfall and suffers heavy erosion. Its southern slopes are barren and highly dissected.

ADVERTISEMENTS:

(b) The Lesser Himalaya or Himanchal-this range lies north of the Siwalik range from which it is separated through M.B.T. It consists of parallel ranges in Nepal and Punjab but of scattered moun­tains in Kumaun. Important ranges include the Dhauladhar, Pirpanjal, Nag Tiba, Mahabharat range and Mussoorie range. Of these the Pirpanjal range of Kashmir is the longest and the most important one. It runs for 400 km between the Jhelum and the Beas.

The Pirpanjal (3494 m) and the Banihal (2832 m) are two important passes in this range, the latter being followed by the Jammu-Srinagar road. The Kishanganga, Jhelum and the Chenab cut through the Pirpanjal range. The famous hill resorts Irke Shimla, Chail, Ranikhet, Chakrata, Mussorie, Nainital, Almora and Darjeeling etc. are situated over this range. Between the Pir Panjal and a westerly range of the Himadri lies the famous valley of Kashmir.

It is a great basin (150 x 80 km) at a height of 1700 m which was previously occupied by a lake. The Kangra valley in Himachal Pradesh extends from the foot of the Dhauladhar range to the south of the Beas river which is a strike valley. The KuIIu valley is a transverse valley in the upper course of the Ravi river. Further eastward lays Kathmandu valley in Nepal at a height of 1500 m covering a total area of 25 sq. km.

The southern slopes of the Lesser Himalayas are steep, rugged and bare while the northern slopes are gentle and thickly forested. The zone between 1500 and 2400 m is covered by evergreen (tropical and temperate) forests (chir, deodar, blue pine, oak, and magnolia) and that between 2400 and 3000 m by coniferous forests (birch, spruce, silver fir and other species). Along the slopes are found a number of small pastures which are called merg in Kashmir (viz. Gulmerg, Sonmerg, Tanmerg) and Bugyal and Payar in Uttaranchal.

ADVERTISEMENTS:

The lesser Himalayas have very few peaks which have perpetual snow cover. The area enjoys snowfall for three to four months during winter season but the weather becomes fine and invigorat­ing during summer season.

(c) The Greater Himalayas or Himadri-this is a most continuous, loftiest and northern most range of die Himalayas. It has a core of Archaean rocks (granites, gneisses and schists) flanked by 41 metamorphosedsedimentaryrocks. The range houses most of die snowy peaks and ridges of the Himala­yas.

The average height of the range is 6100 m, whereas many peaks exceed 8000 m (Mt. Everest 8848 m, Kanchenjunga 8598 m, Makalu 8481 m, Dhaulagiri 8172m, Mansalu 8156, ChoOyu 8153 m, Naga Parbat 8126 m and Annapurna 8078 m). Few passes occur in these ranges though at very high elevation (over 2500 m) and remain snowbound for most part of the year.

The Burzil pass and Zoji La in ^ Kashmir, B ara Lapcha La and Shipki Lain Himachal Pradesh, Thaga La, Niti Pass and Lipu Lekh Pass in Uttaranchal, and Nathu La Jelep La in Sikkim are worthy of mention. The Hindustan-TibetRoad, which joins Shimla with Gartok in western Tibet passes through die Shipki La in die Satluj valley. Another j important trade route connects Kalimpong in West Bengal widi Lhasa the capital of Tibet, through Jelep La in the Chumbi valley in Sikkim.

ADVERTISEMENTS:

The Himadri runs in an arc like shape in a length of 25(X) km from Nanga Parbat (8126 m) in the west to Namcha Barwa (7756 m) in die east.

Major part of die range remains covered with snow throughout die year giving birth to a number of glaciers. Of these Gangotri, and Milam (Kumaun) and Zemu (Sikkim) have a length of more than 20 km. It is an asymmetrical range having very few spurs soudiwards.

In die morth-west the Zaskar range is an extension of diis range north of which flows the Indus River. Here lie Rupshu and Devasai Plains. Between Himadri and Himanchal one finds the famous valley of Kashmir.

The Greater Himalayas consistst of a lower Alpine zone up to 4800 m and an upper, snow bound zone usually above 5000 m. The Alpine zone con­tains rhododendrons, trees with crooked and twisted stems, thick shrubs wide a variety of beautiful flowers and grass (M.S. Krishnan, 1982, p. 9).

ADVERTISEMENTS:

(d) The Trans-Himalayas or Tethys Himala­yas-It is also called the Tibetan Himalayas. This is about 40 km wide and 965 km long consisting of mainly Karakoram, Ladakh and Kailash ranges. Its average height lies between 3100 and 3700 meters.

The range acts as a water divide between the rivers draining into the Bay of Bengal and those emptying their waters to the Tibetan lakes. It has a number of mountain passes situated at height of more than 5200 m (Dig La 5795 m). The range is almost devoid of vegetal cover.

The most important range of the Trans Hima­layas is Karakoram Range which is called as the ‘backbone of high Asia. It determines India’s fron­tiers with Afghanistan and China. It has many lofty peaks (K2 8611 m, Hidden Peak 8068 m, Broad Peak 8047 m, and Gasherbrum II 8035 m) and large glaciers (Siachen of the Nubra valley 72 km, Biafo and Baltaro of the Shigar valley 60 km, and Hispar and Batura of the Hunza valley 57 km). Westward the Karakorams merge into the Pamir Knot while these continue as the Kailash range of Tibet towards south-east. South of the Karakoram lies the Ladakh range (height 5800 m) which acts as a water divide for the Indus and its tributary Shyok River.