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

Introduction

  • The earth is approximately 460 million years old.
  • Over these long years, it has undergone many changes brought about primarily by the endogenic and exogenic forces.
  • These forces have played a significant role in giving shape to various surface and subsurface features of the earth.
  • The Indian plate which was to the south of the equator millions of years ago was much larger in size and the Australian plate was a part of it.
  • Over millions of years, this plate broke into many parts and the Australian plate moved towards the south eastern direction and the Indian plate to the north.
  • This northward movement of the Indian plate is still continuing and it has significant consequences on the physical environment of the Indian subcontinent.
  • It is primarily through the interplay of these endogenic and exogenic forces and lateral movements of the plates that the present geological structure and geomorphologic processes active in the Indian subcontinent came into existence.
  • Based on the variations in its geological structure and formations, India can be divided into three geological divisions. 

Question for Revision Notes: Structure & Physiography
Try yourself:
What are the two primary forces responsible for shaping the surface and subsurface features of the Earth?
View Solution

These geological regions broadly follow the physical features:
  • The Penisular Block
  • The Himalayas and other Peninuslar Mountains
  • Indo-Ganga-Brahmaputra Plain. 

The Peninsular Block

  • The northern boundary of the Peninsular Block - line running from Kachchh along the western flank of the Aravali Range near Delhi and then roughly parallel to the Yamuna and the Ganga as far as the Rajmahal Hills and the Ganga delta.
  • Karbi Anglong and the Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of this block.
  • The northeastern parts are separated by the Malda fault in West Bengal from the Chotanagpur plateau.
  • In Rajasthan, the desert and other desert-like features overlay this block.
  • The Peninsula is formed by a great complex of very ancient gneisses and granites, which constitutes a major part of it.
  • As a part of the Indo-Australian Plate, it has been subjected to various vertical movements and block faulting.
  • The rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains are some examples of it.
  • The Peninsula mostly consists of relict and residual mountains like the Aravali hills, the Nallamala hills, the Javadi hills, the Veliconda hills, the Palkonda range and the Mahendragiri hills, etc.
  • The river valleys here are shallow with low gradients.
  • Most of the east flowing rivers form deltas before entering into the Bay of Bengal.
  • The deltas formed by the Mahanadi, the Krishna, the Kaveri and the Godavari are important examples.

Question for Revision Notes: Structure & Physiography
Try yourself:
Which physical features form the Peninsular Block?
View Solution

The Himalayas And Other Peninsular Mountains

  • 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.

Question for Revision Notes: Structure & Physiography
Try yourself:
Which physiographic division of India is characterized by rugged topography consisting of mountain ranges and deep gorges?
View Solution

(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.
The document Revision Notes: Structure & Physiography | NCERT Textbooks (Class 6 to Class 12) - UPSC is a part of the UPSC Course NCERT Textbooks (Class 6 to Class 12).
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FAQs on Revision Notes: Structure & Physiography - NCERT Textbooks (Class 6 to Class 12) - UPSC

1. What is the structure of the Earth's crust?
Ans. The Earth's crust is composed of a variety of rocks and minerals that form different layers. The uppermost layer, known as the lithosphere, is made up of the continents and ocean floors. The lithosphere is broken into several tectonic plates that move around the Earth's surface. Beneath the lithosphere is the asthenosphere, which is partially molten and allows the tectonic plates to move.
2. What are the major physiographic features of the Earth?
Ans. The Earth's major physiographic features include mountains, plateaus, plains, and valleys. Mountains are formed by tectonic activity or volcanic eruptions and are characterized by their steep slopes and high elevations. Plateaus are elevated flatlands that are generally surrounded by mountains. Plains are large, flat areas that cover a significant portion of the Earth's surface. Valleys are low-lying areas between mountains or hills that are often formed by erosion.
3. How do tectonic plates move?
Ans. Tectonic plates move due to convection currents in the Earth's mantle. As hot molten rock rises from the mantle, it creates a flow that moves the plates apart. This process is known as divergent boundary movement. At other times, two plates may collide, causing one to slide beneath the other in a process known as subduction. This creates a convergent boundary. Alternatively, two plates may slide past each other in a process known as transform boundary movement.
4. What is the role of erosion in shaping the Earth's surface?
Ans. Erosion is a natural process that wears down the Earth's surface through the action of wind, water, and other environmental factors. Erosion can produce a variety of landforms, including valleys, canyons, and deltas. Over time, erosion can also alter the shape of mountains and plateaus, smoothing out rough terrain and creating new landforms.
5. How do glaciers shape the Earth's surface?
Ans. Glaciers are large masses of ice that slowly move across the Earth's surface, eroding the land beneath them. As glaciers advance, they pick up rocks and other debris, which become embedded in the ice. As the glacier melts, it deposits this debris, creating features like moraines and drumlins. Glaciers can also carve out valleys, creating deep, U-shaped depressions in the Earth's surface.
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