Structure And Physiography
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. Over millions of years, Indian plate broke into many parts and the Australian plate moved towards the south-eastern direction and the Indian plate to the north. 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:
1. The Peninsular Block,
2. The Himalayas and other Peninsular Mountains and
3. Indo-Ganga-Brahmaputra Plain.
1. The Peninsular Block
The northern boundary of the Peninsular Block - line running from Kachchh along the western flank of the Aravalli Range near Delhi and then roughly parallel to the Yamuna and the Ganga as far as the Raajmahal Hills and the Ganga delta. Krabi Ang long and the Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of this block. The north-eastern 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. Due to Indo-Australian Plate- vertical movements and block faulting. Eg: Rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains. 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.
2. 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. 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
3. 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 the alluvial deposits range from- 1,000-2,000m.
Physiography
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:
I). The Northern and North- eastern Mountains,
II). The Northern Plain,
III). The Peninsular Plateau,
IV). The Indian Desert,
V). The Coastal Plains and
VII). The Islands.
I). The Northern and North- Eastern Mountains
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 Darjeeling and Sikkim regions lie in an east west 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 approximate 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. Himalayas are not only the physical barrier, they are also a climatic, drainage and cultural divide. There are large-scale regional variations within the Himalayas. On the basis of relief, alignment of ranges and other geomorphological features, the Himalayas can be divided into:
a). Kashmir or Northwestern Himalayas,
b). Himachal and Uttaranchal Himalayas,
c). Darjeeling and Sikkim Himalayas,
d). Arunachal Himalayas and
e). Eastern Hills and Mountains.
a). Kashmir or Northwestern Himalayas
It comprises a series of ranges such as 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 famousDal 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 Karewas formations, which are useful for the cultivation of Zafran, a local variety of saffron.
Passes- Zoji La on the Great Himalayas, Banihal on the Pir Panjal, Photu La on the Zaskar and Khardung La on the Ladakh range. Fresh lakes are Dal & Wular and Saltwater lakes are Pangong Tso & Tso Moriri. 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 landform. The southernmost part of this region consists of longitudinal valleys known as Duns.
b). The Himalayas And Uttarakhand Himalayas
Between the Ravi in the west and the Kali (a tributary of Ghaghara) in the east and drained by two major systems called 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. Himalayas is an extension of the Ladakh cold desert, which lies in the Spiti subdivision of district Lahul and Spiti.
These are the Great Himalayan range, the Lesser Himalayas (which is locally known as Dhauladhar in HimachalPradesh and Nagtibhain Uttarakhand) and the Shiwalik range from the North to the South. The two distinguishing features are: Shiwalik and Dun formations.
Some important duns located in this region are the Chandigarh-Kalk a dun, Nalagarh dun, DehraDun, Harike dun and the Kota dun, etc.(DehraDun is the largest of all the duns). In the Great Himalayan range, the valleys are mostly inhabited by the Bhotia‘s. 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 Shiwaliks : The word Shiwalik has its origin in the geological formation found in and around a place called Sivawala near DehraDun which was once a headquarters of the Imperial Survey. 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.
c). Darjeeling 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 (Kanchan Giri), and deep valleys. The higher reaches of this region are inhabited by Lepcha tribes while the southern part, particularly the Darjeeling Himalayas, has a mixed population of Nepalis, Bengalis and tribals from Central India.
The British, introduced tea plantations in this region. In place of the Shiwaliks here, the ‘duar formations’ are important, which have also been used for the development of tea gardens. Sikkim and Darjeeling Himalayas are also known for their scenic beauty and rich flora and fauna, particularly various types of orchids.
d). 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. Important Mountain peaks- Kangtu and Namcha Barwa. These ranges are dissected by fast-flowing rivers from the north to the south, forming deep gorges. Brahmaputra flows through a deep gorge after crossing Namcha Barwa. Important rivers- Kameng the Subansiri, the Dihang, the Dibang and the Lohit. These are perennial with the high rate of fall, thus, having the highest hydro-electric power potential in the country. Tribes from west to east - Monpa, Daffla, Abor, Mishmi, Nishi and the Nagas. Shifting or slash and burn cultivation (Jhumming) practiced here. Most of the interactions are carried through the duar region along the Arunachal-Assam border.
e). The Eastern Himalayas
They are known by different local names. In the north, they are known as Patkai Bum, Naga hills, Manipur, hills and in the south as Mizo or Lushai hills. These are low hills, inhabited by numerous tribal groups practising 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 so 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 Irrawaddy of Myanmar.
II). The Northern Plains
Formed by the alluvial deposits brought by the rivers – the Indus, the Ganga and the Brahmaputra. This Plain extended 3,200 km from east to the west with an average width of 150-300 km and with maximum depth of 1,000-2,000 m.
The alluvial plains can be further divided into the Khadar and the Bhangar.
Bhabar : It is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope.
South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby creating marshy and swampy conditions known as the Tarai.
This has a luxurious growth of natural vegetation and houses a varied wildlife. The south of Tarai is a belt consisting of old and new alluvial deposits known as the Bhangar and Khadar respectively.
These plains have characteristic features of mature stage of fluvial erosional and depositional landforms such as sand bars, meanders, ox- bow lakes and braided channels.
The Brahmaputra plains are known for their riverine islands and sandbars.
Periodic floods and shiing river courses forming braided streams.
The mouths of these mighty rivers also form some of the largest deltas of the world, for example, the famous Sunderbans delta.
These river valleys have fertile alluvial soil cover which supports a variety of crops like wheat, rice, sugarcane and jute.
III). The Peninsular Plateau
Rising from the height of 150 m above the river plains up to an elevation of 600-900m is the irregular triangle known as peninsular plateau.
Delhi ridge in the northwest, (extension of Aravalis), the Raj mahal hills in the east, Gir range in the west and the Cardamom hills in the south constitute the outer extent of the Peninsular plateau. However, an extension of this is also seen in the northeast, in the form of Shillong and Karbi-Anglong plateau.
The Peninsular India is made up of a series of patland plateaus such as the Hazaribagh plateau, the Palamuplateau, the Ranchi plateau, the Malwa plateau, the Coimbatore plateau and the Karnataka plateau, etc.
The general elevation of the plateau is from the west to the east, which is also proved by the pattern of the flow of rivers.
Physiographic features - Tors, block mountains, ri valleys, spurs, bare rocky structures, series of hummocky hills and wall-like quartzite dykes offering natural sites for water storage.
The western and north- western part of the plateau has an empathic presence of black soil. This Peninsular plateau has undergone recurrent phases of upliment and submergence accompanied by crustal faulting and fractures.
These spatial variations have brought in elements of diversity in the relief of the Peninsular plateau.
The north-western part of the plateau has a complex relief of ravines and gorges. The Ravines of Chambal, Bhind and Morena are examples.
On the basis of the prominent relief features, the Peninsular plateau can be divided into three broad groups:
(a). The Deccan Plateau,
(b). The Central Highlands and
(c). The North- eastern Plateau
(a). The Deccan Plateau
Bordered by the Western Ghats in the west, Eastern Ghats in the east and the Satpura, Maikal range and Mahadeo hills in the north.
Western Ghats are locally known by different names such as Sahyadri in Maharashtra, Nilgiri hills in Karnataka and Tamil Nadu and Anaimalai hills and Cardamom hills in Kerala.
Western Ghats are comparatively higher in elevation and more continuous than the Eastern Ghats.
Anamudi‘ (2,695 m), the highest peak of Peninsular plateau is located on the Anaimalai hills of the WesternGhats followed by Dodabetta (2,637 m) on the Nilgiri hills.
Most of the Peninsular rivers have their origin in the Western Ghats. Eastern Ghats comprising the discontinuous and low hills are highly eroded by the rivers such as the Mahanadi, the Godavari, the Krishna, the Kaveri, etc.
Some of the important ranges include the Javadi hills, the Palconda range, the Nallamala hills, the Mahendragiri hills, etc.
The Eastern and the Western Ghats meet each other at the Nilgiri hills.
(c). The Central Highlands
They are bounded to the west by the Aravali range. The Satpura range is formed by a series of scarped plateaus on the south, generally at an elevation varying between 600-900 m above the mean sea level.
This forms the northernmost boundary of the Deccan plateau. It is a classic example of the relict mountains which are highly denuded and form discontinuous ranges.
The extension of the peninsular plateau can be seen as far as Jaisalmer in the West, where it has been covered by the longitudinal sand ridges and crescent-shaped sand dunes called barchans.
This region has undergone metamorphic processes in its geological history, which can be corroborated by the presence of metamorphic rocks such as marble, slate, gneiss, etc
The general elevation of the Central Highlands ranges between 700-1,000 m above the mean sea level and it slopes towards the north and northeastern directions.
Most of the tributaries of the river Yamuna have their origin in the Vindhyan and Kaimur ranges. Banas is the only significant tributary of the river Chambal that originates from the Aravalli in the west.
An eastern extension of the Central Highland is formed by the Rajmahal hills, to the south of which lies a large reserve of mineral resources in the Chotanagpur plateau.
(d). The North-Eastern Plateau
It is an extension of the main peninsular plateau.
It is believed that due to the force exerted by the north-eastward movement of the Indian plate at the time of the Himalayan origin, a huge fault was created between the Rajmahal hills and the Meghalaya plateau. Later, this depression got filled up by the deposition activity of the numerous rivers. The Meghalaya and Karbi Anglong plateau stand detached from the main Peninsular Block.
The meghalaya plateau is subdivided into:
- The Garo Hills
- The Khasi Hills
- The Jaintia Hills
An extension of this is Karbi Anglong hills of Assam. Similar to the Chotanagpur plateau, the Meghalaya plateau is also rich in mineral resources like coal, iron ore, sillimanite, limestone and uranium.
This area receives maximum rainfall from the south west monsoon. As a result, the Meghalaya plateau has a highly eroded surface. Cherrapunji displays a bare rocky surface devoid of any permanent vegetation cover.
IV). The Indian Desert
To the northwest of the Aravali hills lies the Great Indian desert, it is a land of undulating topography dotted with longitudinal dunes and barchans. This region receives low rainfall below 150 mm per year; hence, it has arid climate with low vegetation cover. It is because of these characteristic features that this is also known as Marusthali. The Luni river flows in the southern part of the desert. Low precipitation and high evaporation makes it a water deficit region. There are some streams which disappear after flowing for some distance and present a typical case of inland drainage by joining a lake or playa. The lakes and the playas have brackish water which is the main source of obtaining salt.
V). The Coastal Plains
On the basis of the location and active geomorphological processes, it can be broadly divided into two: The western coastal plains and The eastern coastal plains.
1. The Western coastal plains
Example of submerged coastal plain. It is believed that the city of Dwaraka which was once a part of the Indian mainland situated along the west coast is submerged under water. Because of this submergence it is a narrow belt and provides natural conditions for the development of ports and harbours. Kandla, Mazagaon, JLN port Navha Sheva, Marmagao, Mangalore, Cochin, etc. are some of the important natural ports located along the west coast.
Western coast may be divided into following divisions:
(i). The Kachchh and Kathiawar coast in Gujarat,
(ii). Konkan coast in Maharashtra,
(iii). Goan coast and Malabar coast in Karnataka and Kerala respectively.
The rivers flowing through this coastal plain do not form any delta. The Malabar coast has got certain distinguishing features in the form of ‘Kayals’ (backwaters), which are used for fishing, inland navigation and also due to its special attraction for tourists. Every year the famous Nehru Trophy Vallamkali (boat race) is held in Punnamada Kayal in Kerala.
The Eastern Coastal Plains
Eastern coastal plain is broader and is an example of an emergent coast. There are well- developed deltas here, formed by the rivers flowing eastward into the Bay of Bengal. These include the deltas of the Mahanadi, the Godavari, the Krishna and the Kaveri. Because of its emergent nature, it has less number of ports and harbours. The continental shelf extends up to 500 km into the sea, which makes it difficult for the development of good ports and harbours.
VI). The Islands
There are two major island groups in India :
1. The Bay of Bengal
2. The Arabian Sea
(a). The Islands of the Bay of Bengal
The Bay of Bengal island groups consist of about 572 islands/islets. These are situated roughly between 6°N-14°N and 92°E -94°E. The two principal groups of islets include the Ritchie’s archipel ago and the Labyrinth island. The entire group of islands is divided into two broad categories — the Andaman in the north and the Nicobar in the south. They are separated by a water body which is called the Ten degree channel. These islands are an elevated portion of submarine mountains. However, some smaller islands are volcanic in origin. Barren island, the only active volcano in India is also situated in the Nicobar islands. The coastal line has some coral deposits, and beautiful beaches. These islands receive convectional rainfall and have an equatorial type of vegetation.
(b). The Islands Of The Arabian Sea
It includes Lakshadweep and Minicoy. They are between 8°N-12°N and 71°E -74°E longitude. These islands are located at a distance of 280 km-480 km off the Kerala coast is built of coral deposits. There are approximately 36 islands of which 11 are inhabited. Minicoy is the largest island with an area of 453 sq. km. The entire group of islands is broadly divided by the Eleventh degree channel, north of which is the Amini Island and to the south of the Cannanore Island. The Islands of this archipelago have storm beaches consisting of unconsolidated pebbles, shingles, cobbles and boulders on the eastern seaboard.
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