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| Photo by James Wheeler |
The Himalayas have been divided on geographical, regional, and geological basis. However, the geographical basis is more pronounced and widely accepted. Geographically entire Himalayan region can be divided into the following three categories:-
- The Himalayan Ranges.
- The Trans Himalayas.
- The Eastern Hills.
The Himalayan Ranges
The Himalayas are not a single chain of mountains, but a series of several, more or less parallel or converging ranges. As we have discussed, the formation of the Himalayas took place in three different phases (Origin of Himalayas), which resulted in the formation of three different ranges. These ranges are separated by deep valleys. Like in all young fold mountains, we find a densely dissected "ridge and valley topography" in the Himalayas. Some of the most beautiful Himalayan valleys are the vale of Kashmir and the Karewas, the Kangra and Kullu valley in Himachal Pradesh; the Dun valley; the Bhagirathi valley (near Gangotri), and the Mandakini valley (near Kedarnath).
The individual ranges have a very steep gradient towards the south but present a very gentle slope towards the north. In the eastern section, the Himalayas rise abruptly from the plain of the Bengal and Oudha and suddenly attain great elevation within a short distance from the foot of the mountains. Thus the peaks of Kanchenjunga and Everest are only a few kilometers from the Northern plains. Most of the Himalayan Ranges fall in India, Nepal, and Bhutan, but the northern slope of some ranges lies in Tibet while the western extremities lie in Pakistan, Afghanistan, and Central Asia.
This Himalayan Ranges could be further divided into three parallel ranges from the Indo-Gangetic plain to the Tibet plateau according to their age of formation:-
- The Shiwalik Range.
The Shiwalik Himalaya formed in the last stage of formation of Himalaya. It comprises the outermost range of the Himalayas and is also known as the outer Himalayas. It has a hogback-like appearance due to its steep northern slope. Flat scraps, anticlinal crests, and synclinal valleys are the chief characteristics of this range. This range runs parallel to the lesser Himalayas for a distance of about 2400 km from the Potwar Plateau to the Brahmaputra valley. The width of the Shiwaliks varies from 50 km in Himachal Pradesh to less than 15 km in Arunachal Pradesh. It is almost an unbroken succession of low hills except for a gap of 80-90 km which is occupied by the valley of Tista river. The altitude of Shiwaliks varies from 600 to 1500 meters.
The Shiwaliks are formed of the great thickness of Mio-Pleistocene sand, gravels, and conglomerates which have been brought by the rivers flowing from the higher ranges of the Himalayas. These have been folded and faulted by the earth's movements. Shivalik have different names in different areas like Jammu Hills in Jammu, Dafla, Miri, Abora, and Mishmi Hills in Arunachal Pradesh.
As the Shiwaliks are last in the formation of the Himalayas, they obstructed the flow of rivers from the upper reaches of the Himalayas and formed big lakes in the valleys. The silt and sediments brought by the rivers got deposited in these lakes. After the rivers had cut their course through the Shiwalik Ranges, the lakes are drained away leaving behind plains called Duns in the west and Duars in the east. Dehradun in Uttarakhand is the best example of such a plain which is 75 km long and 15-20 km wide. It is covered with boulder and clay deposits. The Eastern part of the Shiwalik is covered with thick forests but the forest cover becomes thin in the west. The southern slopes of this range are almost completely devoid of the forest covers in Punjab and Himachal Pradesh and are highly dissected by several seasonal streams locally called Chaos.
Other divisions (i.e. the Middle Himalayas and the Great Himalayas) will be discussed in the next post.