The Great Himalaya

Also known as Inner Himalaya, Central Himalaya or Himadri.
Average elevation of 6,100 m above sea level and an average width of about 25 km.
It is mainly formed of the central crystallines (granites and gneisses) overlain by metamorphosed sediments [limestone].
The folds in this range are asymmetrical with steep south slope and gentle north slope giving ‘hog back (a long, steep hill or mountain ridge)’ topography.
This mountain arc convexes to the south just like the other two.
Terminates abruptly at the syntaxial bends. One in the Nanga Parbat in north-west and the other in the Namcha Barwa in the north-east.
This mountain range boasts of the tallest peaks of the world, most of which remain under perpetual snow.

Mount Everest was first located by George Everest, the then Surveyor General of India in 1841 and in 1852 it was established as the highest peak of the world by the Great Trigonometrical Survey of India.

The Trans Himalayas:

The Himalayan ranges immediately north of the Great Himalayan range.
Also called the Tibetan Himalaya because most of it lies in Tibet.
The Zaskar, the Ladakh, the Kailas and the Karakoram are the main ranges.
It stretches for a distance of about 1,000 km in east-west direction.
Average elevation is 3000 m above mean sea level.
The average width of this region is 40 km at the extremities and about 225 km in the central part.
The Nanga Parbat (8126 m) is an important range which is in The Zaskar Range.
North of the Zaskar Range and running parallel to it is the Ladakh Range.
Only a few peaks of this range attain heights of over 6000 metres.
The Kailas Range (Gangdise in Chinese) in western Tibet is an offshoot of the Ladakh Range. The highest peak is Mount Kailas (6714 m). River Indus originates from the northern slopes of the Kailas range.
The northern most range of the Trans-Himalayan Ranges in India is the Great Karakoram Range also known as the Krishnagiri range.
Karakoram Range extends eastwards from the Pamir for about 800 km. It is a range with lofty peaks [elevation 5,500 m and above]. It is the abode of some of the greatest glaciers of the world outside the polar regions.
Some of the peaks are more than 8,000 metre above sea level. K2(8,611 m)[Godwin Austen or Qogir] is the second highest peak in the world and the highest peak in the Indian Union.
The Ladakh Plateau lies to the north-east of the Karakoram Range.
It has been dissected into a number of plains and mountains [Soda Plains, Aksai Chin, Lingzi Tang, Depsang Plains and Chang Chenmo]

Purvanchal or Eastern Hills

Eastern Hills or The Purvanchal are the southward extension of Himalayas running along the north-eastern edge of India.
At the Dihang gorge, the Himalayas take a sudden southward bend and form a series of comparatively low hills which are collectively called as the Purvanchal.
They run along the India-Myanmar Border extending from Arunachal Pradesh in the north to Mizoram in the south.

Patkai Bum hills are made up of strong sandstone; elevation varying from 2,000 m to 3,000 m; merges into Naga Hills where Saramati (3,826 m) is the highest peak.
Patkai Bum and Naga Hills form the watershed between India and Myanmar.
South of Naga Hills are the Manipur hills which are generally less than 2,500 metres in elevation.
The Barail range separates Naga Hills from Manipur Hills.
Further south the Barail Range swings to west into Jaintia, Khasi and Garo hills which are an eastward continuation of the Indian peninsular block. They are separate from the main block by Ganga and Brahmaputra rivers.
South of the Manipur Hills are the Mizo Hills (previously known as the Lushai hills) which have an elevation of less than 1,500 metres. The highest point is the Blue Mountain (2,157 m) in the south.