- 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 was to the south of the equator millions ofyears ago
- it 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. 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.
THE HIMALAYAS AND OTHER PENINSULAR MOUNTAINS
1. The Himalayas along with other Peninsular mountains are young, weak and flexible in their geological structure unlike the rigid and stable Peninsular Block.
- Consequently, they are still subjected to the interplay of exogenic and endogenic forces, resulting in the development of faults, folds and thrust plains.
- 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.
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 1,0002,000m.
- The relief and physiography ofIndia has been greatly influenced by the geological and geomorphological processes active in the Indian subcontinent.
- ‘Physiography’ of an area is the outcome ofstructure, 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:
- Kashmir or Northwestern Himalayas
- Himachal and Uttaranchal Himalayas
- Darjiling and Sikkim Himalayas
- Arunachal Himalayas
- Eastern Hills and Mountains.
1. 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 ofZafran, 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
2. The Himachal and Uttarakhand Himalayas
- lies approximately between the Ravi in the west and the Kali (a tributary ofGhaghara) in the east.
- drained by two major river systems of India, i.e. the Indus and the Ganga.
- Tributaries of the Indus include the river Ravi, the Beas and the Satluj, and the tributaries of Ganga flowing through this region include the Yamuna and the Ghaghara.
- The northernmost part of the Himachal.
- Himalayas is an extension of the Ladakh cold desert, which lies in the Spiti subdivision of district Lahul and Spiti.
- All the three ranges of Himalayas are prominent in this section also.
- These are the Great Himalayan range, the Lesser Himalayas (which is locally known as Dhaoladhar in Himachal Pradesh and Nagtibhain Uttarakhand) and the Shiwalik range from the North to the South.
- 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 the Chandigarh-Kalka dun, Nalagarh dun, Dehra Dun, Harike dun and the Kota dun, etc.
- Dehra Dun is the largest of all the duns with an approximate length of 3545 km and a width of 22-25 km.
- In the Great Himalayan range, the valleys are mostly inhabited by the Bhotia’s.
- These are nomadic groups who migrate to ‘Bugyals’ (the summer glasslands in the higher reaches) during summer months and return to the valleys during winters.
- The famous ‘Valley of flowers’ is also situated in this region. The 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
- The word shiwalik has its origin in the geological formation found in and around a place called Sivawala near Dehra Dun which was once a headquarter of the Imperial Survey and which subsequently established its permanent headquarters at Dehra Dun.
- In Kashmir Valley, the meanders in Jhelum river are caused by the local base level provided by the erstwhile larger lake of which the present Dal Lake is a small part.
3. The Darjiling and Sikkim Himalayas
- 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 Lepchatribes while the southern part, particularly the Darjiling
- Himalayas, has a mixed population of Nepalis, Bengalis and tribals from Central India.
- The British, taking advantage of the physical conditions such as moderate slope, thick soil cover with high organic content, well distributed rainfall throughout the year and mild winters, introduced tea plantations in this region. absence ofthe Shiwalik formations.
- In place of the Shiwaliks here, the ‘duar formations’ are important, which have also been used for the development of tea gardens.
4. 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 Bhramaputa 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 offall, 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.
5. The Eastern Hills and Mountains
- 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 practising Jhum cultivation.
- 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 deposits.
- Most of the rivers in Nagaland form the tributary of the Brahmaputra.
- While two rivers of Mizoram and Manipur are the tributaries of the Barak river, which in turn is the tributary of Meghna;
- the rivers in the eastern part of Manipur are the tributaries of Chindwin, which in turn is a tributary of the Irrawady of Myanmar.