Revision Notes: Structure & Physiography - NCERT Textbooks (Class 6 to Class 12) - UPSC

Introduction

• The Himalayas along with other Peninsular mountains are young, weak and flexible in their geological structure unlike the rigid and stable Peninsular Block.
• These mountains are tectonic in origin, dissected by fast-flowing rivers which are in their youthful stage.
• Various landforms like gorges, V-shaped valleys, rapids, waterfalls, etc. are indicative of this stage.

Indo-ganga-brahmaputra Plain

• The third geological division of India comprises the plains formed by the river Indus, the Ganga and the Brahmaputra.
• Originally, it was a geo-synclinal depression which attained its maximum development during the third phase of the Himalayan mountain formation approximately about 64 million years ago.
• Since then, it has been gradually filled by the sediments brought by the Himalayan and Peninsular rivers.
• Average depth of alluvial deposits in these plains ranges from 1,000­2,000 m.
• The relief and physiography of India have been greatly influenced by the geological and geomorphological processes active in the Indian subcontinent.

Physiography

• ‘Physiography’ of an area is the outcome of structure, process and the stage of development.
• The north has a vast expanse of rugged topography consisting of a series of mountain ranges with varied peaks, beautiful valleys and deep gorges.
• The south consists of stable table land with highly dissected plateaus, denuded rocks and developed series of scarps.
• In between these two lies the vast north Indian plain.

Based on these macro variations, India can be divided into the following physiographic divisions:

• The Northern and North-eastern Mountains
• The Northern Plain
• The Peninsular Plateau
• The Indian Desert
• The Coastal Plains
• The Islands

The North and Northeastern Mountains

• The North and Northeastern Mountains consist of the Himalayas and the Northeastern hills.
• The Himalayas consist of a series of parallel mountain ranges.
• Some of the important ranges are the Greater Himalayan range, which includes the Great Himalayas and the Trans-Himalayan range, the Middle Himalayas and the Shiwalik.
• The general orientation of these ranges is from northwest to the southeast direction in the northwestern part of India.
• Himalayas in the Darjiling and Sikkim regions lie in an eastwest direction, while in Arunachal Pradesh they are from southwest to the northwest direction.
• In Nagaland, Manipur and Mizoram, they are in the north south direction.
• The approxiate length of the Great Himalayan range, also known as the central axial range, is 2,500 km from east to west, and their width varies between 160-400 km from north to south.
• The Himalayas stand almost like a strong and long wall between the Indian subcontinent and the Central and East Asian countries.
• Himalayas are not only the physical barrier, they are also a climatic, drainage and cultural divide.
• Himalayas can be divided into the following sub-divisions:
  (i) Kashmir or Northwestern Himalayas
  (ii) Himachal and Uttaranchal Himalayas
  (iii) Darjiling and Sikkim Himalayas
  (iv) Arunachal Himalayas
  (v) Eastern Hills and Mountains

(i) Kashmir or Northwestern Himalayas

• comprise a series of ranges such as the Karakoram, Ladakh, Zaskar and Pir Panjal.
• The northeastern part of the Kashmir Himalayas is a cold desert, which lies between the Greater Himalayas and the Karakoram ranges.
• Between the Great Himalayas and the Pir Panjal range, lies the world famous valley of Kashmir and the famous Dal Lake.
• Important glaciers of South Asia such as the Baltoro and Siachen are also found in this region.
• The Kashmir Himalayas are also famous for Karewa formations, which are useful for the cultivation of Zofran, a local variety of saffron.
• Some of the important passes of the region are Zoji La on the Great Himalayas, Banihal on the Pir Panjal, Photu La on the Zaskar and Khardung La on the Ladakh range.
• Some of the important fresh lakes such as Dal and Wular and salt water lakes such as Pangong Tso and Tso Moriri are also in this region.
• This region is drained by the river Indus, and its tributaries such as the Jhelum and the Chenab.
• Jhelum in the valley of Kashmir is still in its youth stage and yet forms meanders - a typical feature associated with the mature stage in the evolution of fluvial land form

(ii) The Himachal and Uttarakhand Himalayas

• The northernmost part of the Himachal Himalayas is an extension of the Ladakh cold desert, in which all the three ranges of Himalayas are prominent.
• These are the Great Himalayan range, the Lesser Himalayas (which is locally known as Dhaoladhar in Himachal Pradesh and Nagtibha in Uttarakhand) and the Shiwalik range from the North to the South.
• In this section of Lesser Himalayas, the altitude between 1,000-2,000 m.
• The important hill stations such as Dharamshala, Mussoorie, Shimla, Kaosani and the cantonment towns and health resorts such as Shimla, Mussoorie, Kasauli, Almora, Lansdowne and Ranikhet, etc.
• The two distinguishing features of this region from the point of view of physiography are the ‘Shiwalik’ and ‘Dun formations’. Some important duns located in this region are places of pilgrimage such as the Gangotri, Yamunotri, Kedarnath, Badrinath and Hemkund Sahib are also situated in this part.
• The region is also known to have five famous Prayags (river confluences).

(iii) The Darjiling and Sikkim Himalayas

• They are bordered by Nepal Himalayas in the west and Bhutan Himalayas in the east.
• It is relatively small but is a most significant part of the Himalayas.
• Known for its fast-flowing rivers such as Tista.
• It is a region of high mountain peaks like Kanchenjunga (Kanchengiri), and deep valleys.
• The higher reaches of this region are inhabited by Lepcha tribes.

(iv) The Arunachal Himalayas

• Extend from the east of the Bhutan Himalayas up to the Diphu pass in the east.
• The general direction of the mountain range is from southwest to northeast.
• Some of the important mountain peaks of the region are Kangtu and Namcha Barwa.
• These ranges are dissected by fast-flowing rivers from the north to the south, forming deep gorges. 
• The Brahmaputra flows through a deep gorge after crossing Namcha Barwa.
• Some of the important rivers are the Kameng the Subansiri, the Dihang, the Dibang and the Lohit.
• These are perennial with the high rate of all, thus, having the highest hydro-electric power potential in the country.
• An important aspect of the Arunachal Himalayas is the numerous ethnic tribal community inhabiting in these areas.
• Some of the prominent ones from west to east are the Monpa, Daffla, Abor, Mishmi, Nishi and the Nagas. Most of these communities practise Jhumming.
• It is also known as shifting or slash and burn cultivation.
• This region is rich in biodiversity which has been preserved by the indigenous communities.
• Due to rugged topography, the inter-valley transportation linkages are nominal.
• Hence, most of the interactions are carried through the duar region along the Arunachal-Assam border.

(v) The Eastern Hills and Mountains

• These are part of the Himalayan mountain system having their general alignment from the north to the south direction.
• They are known by different local names. In the north, they are known as Patkai Bum, Naga hills, the Manipur hills and in the south as Mizo or Lushai hills.
• These are low hills, inhabited by numerous tribal groups practicing Jhum cultivation.
• Most of these ranges are separated from each other by numerous small rivers.
• The Barak is an important river in Manipur and Mizoram.
• The physiography of Manipur is unique by the presence of a large lake known as ‘Loktak’ lake at the centre, surrounded by mountains from all sides.
• Mizoram which is also known as the ‘Molassis basin’ which is made up of soft unconsolidated rocks.