The Himalayas are the youngest mountains in the world and are, structurally, the folded mountains. The Himalayas run along the northern border of India. The Himalayas form an arc which is about 2,400 km long. The width varies from 400 km in Kashmir to 150 km in Arunachal Pradesh. The altitudinal variations are greater in the eastern part than in the western part. There are three parallel ranges in its longitudinal extent.
This is the northernmost range and is also known as ‘Himadri’. This is the most continuous range. It contains the loftiest peaks. The average height of peaks in this range is 6,000 metres. All the prominent Himalayan peaks are in this range. The folds of the Great Himalayas are asymmetrical in nature and the core of this part is composed of granite. Because of the lofty heights, the peaks of this range are perennially snow-bound, i.e. they remain snow-capped throughout the year.
This lies towards the south of the Great Himalayas. The altitude of peaks in this range varies from 3,700 m to 4,500 m. Average width of this range is 50 km. This range is mainly composed of highly compressed and altered rocks.
This is the outermost range of the Himalayas. The altitude varies between 900 and 1100 km in this range and the width varies between 10 to 50 km. These ranges are composed of unconsolidated sediments. The longitudinal valleys lying between the Himachal and Shiwaliks are called ‘Dun’.
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Eastern Hills and Mountains: The Brahmaputra marks the eastern border of the Himalayas. Beyond the Dihang gorge, the Himalayas bend sharply towards south and form the Eastern hills or Purvachal. These hills run through the north eastern states of India. They are mostly composed of sandstones. These hills are composed of the Patkai Hills, Naga Hills, Manipuri Hills and Mizo Hills.
The northern plain of India is formed by three river systems, viz. the Indus, the Ganga and the Brahmaputra; along with their tributaries. This plain is composed of alluvial soil which has been deposited over millions of years. The total area of the northern plain is about 7 lakh square kilometer. It is about 2400 km long and about 240 to 320 km broad.
The northern plain is divided into three sections, viz. the Punjab Plain, the Ganga Plain and the Brahmaputra Plain.
Punjab Plains: The Punjab plains form the western part of the northern plain. This is formed by the Indus and its tributaries; like Jhelum, Chenab, Ravi, Beas and Sutlej. A major portion of this plains is in Pakistan. Doabs abound in this plain.
Ganga Plains: This plain extends between Ghaggar and Tista rivers. The northern states, Haryana, Delhi, UP, Bihar, part of Jharkhand and West Bengal lie in the Ganga plains.
Brahmaputra Plains: This plain forms the eastern part of the northern plain and lies in Assam.
Based on the relief features; the northern plain can be divided into four regions, viz. bhabar, terai, bhangar and khadar.
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