N.K. Chauhan 
The Himalayas are the world's youngest and highest mountain range extended almost uninterrupted for a distance of 2,500 km and covering an area of around 5 Lakh square km.
The southern slopes of the Himalayas facing India are steeper and those facing the Tibetan side are generally gentler.
The Himalayas are wider in the west than in the east. The width varies from 400 km in Kashmir to 150 km in Arunachal Pradesh.
The Himalayas take a sudden southward turn after crossing Dihang gorge in Arunachal Pradesh and forms series of mountains located north to south.
Origin and development
According to Wegener's Continental Drift theory, during the Carboniferous period (~360 to 300 million years ago) all the continents were one single continental mass (Super Continent) - Pangaea(Pan=all + Gea=earth) and a Mega Ocean surrounded this supercontinent named Panthalassa(Pan=all + Thalassa=ocean).
Image SourceAround 200 million years ago Pangaea started splitting and broke down into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively.
India was a part of Gondwanaland.
During the Mesozoic era (~250 to 65 million years ago), the space between Laurasia and Gondwanaland got filled with Tethys Sea and it gradually got widened.
About 80 million years ago, when India was ~ 6,400 km south of the eurasian continent but moving towards it, the tethys sea floor was subducting northwards beneath eurasian plate to form a convergent oceanic-continental plate margin.
Mountain building activity took place in Orogenetic Stage (~50 million years ago) when Himalayas and Alps(Europe) were formed with the folding of sediments of Tethys Sea.
Image Source
About 50 million years ago, the two large landmasses, Indian and Eurasia plates, driven by plate movement, collided. As a result, the sediments accumulated in Tethys Sea (brought by rivers) were compressed, squeezed and series of folds were formed, one behind the other, giving birth to folded mountains of the Himalayas.
The Eurasian plate was partly crumpled and buckled up above the Indian plate but due to their low density and high buoyancy neither continental plate could be subducted. This caused the continental crust to thicken due to folding and faulting by compressional forces pushing up the Himalaya and the Tibetan Plateau.
The thickening of the continental crust marked the end of volcanic activity in the region as any magma moving upwards would solidify before it could reach the surface.
Indian plate is still moving northwards at the rate of 5 cm/year and crashing into the rest of Asia, thereby constantly increasing the height of Himalayas.
North-South Division of the Himalayas
Himalayas comprise a series of three ranges running more or less parallel to one another, they are supposed to have emerged in three different phases following one after the other.After the Great Himalayas were formed, the second phase took place about 25-30 million years ago when the Middle Himalayas were formed.
The Shiwaliks were formed in the last phase of the Himalayan orogeny.
1) The Great Himalayas(Himadri & Trans-Himalaya)
Great Himalayas are the Northernmost range with an average height of 6000 metre and width of 120 km.1.1) Trans Himalayas
The Trans-Himalayas Mountain Region or Tibet Himalayan Region is located to the north of the Great Himalayas which is consists of Karakoram, Ladakh, Zaskar and Kailash mountain ranges.It is also called the Tibet Himalayan Region because most of the part of these ranges lies in the Tibet.
1.1.1) Karakoram ranges
Karakoram ranges hold the largest amounts of snow and ice among all of the Himalayan ranges.The Karakoram is home to some of the largest glaciers such as Siachen (2nd longest glacier outside of polar regions), Biafo (longest glacier outside of polar regions), Baltoro, Hispar, Trango etc.
India's highest peak lies in the Karakoram Range called K2 (Gaudvin Austin), which is located in Pakistan Occupied Kashmir (POK), also called Krishnagiri.
1.1.2) Ladakh ranges
Ladakh ranges are to the south-east of the Karakoram ranges, it separates the rivers "Indus" and "Shyok".Khardung La Pass (India's 2nd highest motorable pass) falls in these ranges.
These ranges extend into China where they are known as the Kailash ranges.
They include Mt. Kailash and Mansarovar Lake.
Pangong Tso and Spanggur Tso are the two saltwater lakes situated in these ranges.
1.1.3) Zanskar ranges
To the south of the Ladakh ranges are the Zanskar ranges, which cut across by the Zanskar river.These ranges extend into Uttarakhand.
These ranges contains some prominent peaks like Mt. Kamet, Nanda Devi, Kedarnath etc.
Liphu Lekh Pass that leads to Mansarovar and Mt. Kailash forms a part of these ranges.
Spiti Valley, Lahaul Valley, and Kinnaur Valley are also a part of these ranges.
1.2) Great Himalayas (Himadri)
Great Himalayas one of the longest-running fold mountain ranges in the world, extend for about 2400 km.14 of the 28 tallest peaks in the world (higher than 8000 m), are situated in the Himadri e.g. Mt. Everest, Mt. Kanchenjunga, Mt. Makalu etc.
The extent of this range is between the Nanga Parbat peak (8126 m.) in the west and the Namcha Barua peak (7756 m.) in the east.
The highest peak of the world, Mount Everest, (8848 m) is situated in this range.
Rongbuk glacier (largest in the Himadri), Gangotri, Zemu etc. are part of Great Himalayas (Himadri).
Great Himalayas are separated from the lesser Himalayas by longitudinal valleys which are filled with sediments.
These are called the Doons, prominent Doons include Paatli Dun, Chaukamba Dun, Dehra Dun etc.
2) The Lesser Himalayas (Middle or Himachal)
The Lesser Himalayas lies between the Himadri and Siwalik range.The average height of this range is 4000 metre and average width is 60-80 km.
These mountain ranges are divided into the Pir Panjal range and the Dhauladhar range.
This range is not continuous like Great Himalayas from West to East, but broken in many ranges and known locally by different names.
Pir Panjal range is cut across by the Jhelum and Chenab river and is the longest range of the lesser Himalayas.
Pir Panjal Pass, Banihal Pass (connects Jammu and Srinagar) are part of Pir Panjal ranges.
Dhauladhar ranges are the extension of Pir Panjal into Himachal Pradesh, they are cut across by the river Ravi.
Mussoorie ranges are also a part of the lesser Himalayas, they divide the waters of Sutlej and Ganga.
3) The Outer Himalayas (Shiwalik)
The Outer Himalayas or Shiwalik formed in Pliocene or Cenozoic period is the outermost range with an average height of 900-1200 metre and average width of almost 10-50 km.They are known by different names in different places - Jammu hills in Jammu, Dudhwa ranges in Uttarakhand, Darjeeling hills in West Bengal etc.
River Teesta cuts across these ranges in Sikkim, beyond Sikkim, these ranges merge with the lesser Himalayas.
The Himadri and Himachal ranges have been formed much before the formation of Siwalik range.
The rivers rising in the Himadri and Himachal ranges brought gravel, sand and mud along with them, which was deposited in the rapidly shrinking Tethys Sea.
In course of time, the earth movements caused folding of these relatively fresh deposits of sediments, giving rise to the least consolidated Shiwalik range.
Bhabar is a region south of the Lower Himalayas and the Sivalik Hills in Uttarakhand state of India.
It is the alluvial apron of sediments washed down from the Sivaliks along the northern edge of the Indo-Gangetic Plain.
West-East Division of the Himalayas
Sydney Burrard divided the entire length of the Himalayas into the following four divisions on the basis of the river valleys:1) Punjab/Kashmir/Himachal Himalayas
The 560 km long stretch of the Himalayas between the Indus and the Satluj rivers is known as the Punjab Himalayas or Kashmir Himalayas or Himachal Himalayas.Karakoram, Ladakh, Zaskar, Pir Panjal and Dhaola Dhar are the major ranges in this section, and the important snow-capped peaks are Trisul, Nunkun, Kamath and Nanga-Parbat (Highest in Punjab Himalayas).
Image SourceJammu and Kashmir region
The Jammu and Kashmir region is characterized by high snow-covered peaks, deep valleys, interlocked spurs, and High Mountain passes.The Kashmir Himalayas are also famous for Karewa formations.
Karewas refer to the lake deposits consist of clays, silts and sands, found in the flat-topped terraces of the Kashmir valley and on the flanks of the Pir Panjal range.
The occurrence Karewas at the altitudes of 1500-1800m on the flanks of the Pir Panjal strongly suggests that the Himalayas were in process of uplift as late as Pliocene and Pleistocene (1.8m to 10k years ago).
Karewas are famous for the cultivation of Zafran, a local variety of saffron(kesar) and other dry fruits.
Himachal Pradesh Region
The three ranges - the greater, the lesser, and the outer Himalayas are well represented in the Himachal Pradesh Region.The northern slopes of the Himachal Himalayas are covered with thick forests, plains, and lakes and the southern slopes are rugged with forest-clad.
These areas are highly productive and well known for orchards and scenic beauty.
Dalhousie, Shimla, Chamba, Kullu- Manali and Dharam sala are the important hill station in this region.
2) The Kumaun Himalayas
Kumaun Himalayas is the west-central section of the Himalayas, extending 320 km from the Sutlej River to the Kali River.The area lies largely within the state of Uttarakhand and northwest of Nepal comprising part of the Siwalik Range in the south and part of the Great Himalayas in the north.
The highest peak in this division is Nanda Devi(7,817 metres), another important peaks are Kamet(7,756 metres), Trisul, Kedarnath, Dunagiri, Badrinath, Jaonli, Gangotri, and Bandarpunch.
Pindari, Gangotri, and Milam are important glaciers in this division.
At elevations above 4,300 metres, snow covers the mountains throughout the year, at lower elevations herders take sheep and goats to graze during the short summers.
Deodar cedar forests supply timber that is sold on the plains to the south.
The major hill stations are Mussorie, Nainital, Ranikhet, Almora, and Bageshwar.
3) Nepal Himalayas
Nepal Himalayas are the highest part of the Himalayan mountain ranges, extending upto 800 km from the Kali River to the Tista River.The range occupies most of Nepal and extends into the Tibet autonomous region of China and Sikkim state in India.
Everest (8,848 metres), Kanchenjunga (8,586 metres), Makalu (8,463 metres), Dhaulagiri I (8,167 metres), Manaslu I (8,163 metres), and Annapurna I (8,091 metres) are part of this region.
4) Assam Himalayas
Assam Himalayas also known as Eastern Himalayas run eastward for 720 km from the Tista River in the west to the great southward bend of the Brahmaputra River (Dihang) in the east.
Image SourceIt is extending eastward across Sikkim(India) and Bhutan, into northern Assam and Arunachal Pradesh (India), and along the border with the Tibet (China).
Namcha Barwa(7,756 metres) is the highest peak of the region, other important peaks are Kula, Chomo, and Kangto
On the southern border of Arunachal Pradesh, it takes a southerly turn, and ranges are arranged in North-South direction passing through Nagaland, Manipur, Mizoram, and Tripura called Purvanchal.
Patkai Hills
The Patkai Bum are the hills on India's north-eastern border with Myanmar.They were created by the same tectonic processes that created the Himalayas in the Mesozoic.
The Patkai hill range are not as rugged as the Himalayas and the peaks are much lower.
Three mountain ranges come under the Patkai:
1) Patkai-Bum (Arunachal Pradesh, Nagaland and Myanmar)
2) Garo-Khasi-Jaintia (Meghalaya)
3) Lushai Hills (Manipur and Mizoram)
highest point is Phawngpui Tlang, also known as 'Blue Mountain'.
The Garo-Khasi range is in the Indian state of Meghalaya. The Mawsynram and Cherrapunji, on the windward side of these hills are the world's wettest places, having the highest annual rainfall.
Indian states along the Patkai range are Assam, Manipur, Meghalaya, Mizoram and Nagaland.
Related Info
The Karakoram Range ends on the northern side of the Pangong Tso. The Kailash Range originates from the southern bank and runs northwest to southeast for over 60 km.The Kailash Ridge is characterised by rugged, broken terrain with heights varying between 4,000-5,500m, and its key features include Helmet Top, Gurung Hill, Spanggur Gap, Muggar Hill, Mukhpari, Rezang La and Rechin La.
The Ridge dominates Chushul Bowl; an important communications centre.
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Great Himalayas is the oldest range of Himalayas(Oligocene(25-40 million years ago)), after this the Middle Himalayas(Mid Miocene(14 million years ago)) and Shiwalik(Pliocene(5-1.7 million years ago)).
Bhabar or Bhabhar (8-10 km) is a region south of the Lower Himalayas and the Sivalik Hills in Uttarakhand state of India. It is the alluvial apron of sediments washed down from the Sivaliks along the northern edge of the Indo-Gangetic Plain.
The tree line is the edge of the habitat at which trees are capable of growing. The value of tree line in eastern and middle himalayas lies between 3600-3800m, while in western and north western himalayas it declines to 3300-3600m.
The Kashmir Valley is bound by Great Himalayas on the northeast and the Pir Panjal Range on the southwest.
Kullu valley is a broad open valley in Himachal Pradesh located between Pir Panjal and Dhauladhar. It is formed by the Beas River between Manali and Largi.
In 1984 Bachendri Pal became the first Indian woman to reach the summit of Mount Everest. Junko Tabei, a Japanese mountaineer was the first woman in the world to reach the summit of Mount Everest and the first woman to ascend the Seven Summits, climbing the highest peak on every continent.
Santosh Yadav is the first woman in the world to climb Mount Everest twice, and also the second woman in India to successfully climb Mount Everest.
