The Himalayan Mountains are young fold mountains which run in the west to east direction. They run over about 2,400 km. The width of the mountains varies from 2,400 km in Kashmir to 150 km in Arunachal Pradesh. The Himalayas is not a single mountain range, but there are many parallel ranges in the system. The southernmost is known as Siwaliks, the youngest range. Next to Siwaliks are Lesser Himalayas, Greater Himalayas (Himadri) and Trans Himalayan range from south to north. These ranges are young to old respectively. These mountain ranges are also divided into Western Himalayas (or Kashmir Himalayas), Central Himalayas (or Kumaun Himalayas) and Eastern Himalayas (or Assam Himalayas). North of the Himalayas is the Tibetan Plateau. It is called “the roof of the world”. However, the Tibetan Plateau is very dry because the plateau and the mountains act as a gigantic rain shadow. The rain falls instead on the south side of the mountains. This has greatly influenced the climate of the Indian subcontinent.