The Himalaya consists of three parallel ranges in its longitudinal extent and Trans-Himalayas. A number of valleys lie between these ranges.
The Greater Himalayas or Himadri: The northern most range is known as the Great or Inner Himalayas or the ‘Himadri’. It is the most continuous range consisting of the loftiest peaks with an average height of 6,000 metres. It contains all the prominent Himalayan peaks. The folds of Great Himalayas are asymmetrical in nature. The core of this part of Himalayas is composed of granite. It is perennially snow bound, and a number of glaciers descend from this range.
The Lesser Himalaya or Himachal: The range lying to the south of the Himadri forms the most rugged mountain system and is known as Himachal or lesser Himalaya. The ranges are mainly composed of highly compressed and altered rocks. The altitude varies between 3,700 and 4,500 metres and the average width is of 50 Km. While the Pir Panjal range forms the longest and the most important range, the Dhaula Dhar and the Mahabharat ranges are also prominent ones. This range consists of the famous valley of Kashmir, the Kangra and Kullu Valley in Himachal Pradesh. This region is well known for its hill stations.
The Sub-Himalayas or Shiwaliks: The outer most range of the Himalayas is called the Shiwaliks. They extend over a width of 10-50 Km and have an altitude varying between 900 and 1100 metres. These ranges are composed of unconsolidated sediments brought down by rivers from the main Himalayan ranges located farther north. These valleys are covered with thick gravel and alluvium. The longitudinal valley lying between lesser Himalaya and the Shiwaliks are known as Duns. Dehra Dun, Kotli Dun and Patli Dun are some of the well-known Duns.
Trans-Himalayas: The Trans-Himalaya zone with a width of 40km in its eastern and western ends and a width of 222km in its central part, it has important ranges such as the Zaskar Range and the Great Karakoram range. The Karakoram extends towards the south-east to form the Kailash Range in Tibet. The highest peak in the karakoram range is K2 (8611m). The longest glacier is Siachen in the Nubra Valley which is more than 72km.
Source: NCERT India Physical Environment