Structure and Physiography of India
• Earth is approximately 4600 million years old.
• Overtime 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 earth.
• Indian plate was south of equator, millions of years 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 Eurasian plate moved towards south eastern direction and Indian plate to the north.
• This northward movement of the Indian plate is still
continuing and it has significant consequences on physical environment of Indian .
• It is primarily through the interplay of these endogenic and exogenic forces and lateral movements of plates that 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 divisions follow the physical features:
1. The Peninsular Block
2. The Himalayas and other Peninsular Mountains
3. Indo-Ganga-Brahmaputra Plain.
1. The Peninsular Block:
Peninsular Block Extension:
• 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 Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of this block.
• The north-eastern parts are separated by Malda fault in West Bengal from Chotanagpur plateau.
a. Peninsular block formation
- 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.
2. The Himalayas and other Peninsular Mountains
- The Himalayas 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 planes.
- 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.
3. Indo-Ganga-Brahmaputra Plain
- The third geological division of India comprises the plains formed by the river Indus, Ganga and Brahmaputra.
- Originally, it was a geo-synclinal depression which attained its maximum development during the third phase of the Himalayan mountain formation approximately 64 million years ago.
- Since then, it has been gradually filled by the sediments brought by the Himalayan and Peninsular
rivers.
- The relief and physiography of India has been greatly influenced by the geological and geomorphological processes active in 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 vast north Indian plain.
• Based on these macro variations, India can be divided into following physiographic divisions:
A) The Northern and North-eastern Mountains
B) The Northern Plain
C) The Peninsular Plateau
D) The Indian Desert
E) The Coastal Plains
F) The Islands.
A. The North and North-eastern Mountains
• The North and North-eastern Mountains consist of Himalayas and the North-eastern hills.
• The Himalayas consist of a series of parallel mountain ranges.
• 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 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 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.
• Some of the important ranges are the Greater Himalayan range( which includes the Great Himalayas and the Trans-Himalayan range), the Middle Himalayas (Himachal or lesser Himalaya) and the Shiwalik (outer Himalaya).
Shiwalik Range:
• Located in between the Great Plains and Lesser Himalayas. The altitude varies from 600 to 1500 meters.
• Runs for a distance of 2,400 km from the Potwar Plateau (west) to the Brahmaputra valley (east).
• The width of the Shiwaliks varies from 50 km in Himachal Pradesh to less than 15 km in Arunachal Pradesh.
• They are an almost unbroken chain of low hills except for a gap of 80-90 km which is occupied by the valley of the Tista River and Raidak River.
• Valleys are part of synclines and hills are part of anticlines or anti-synclines
Middle Himalayas or Himachal:
• In between the Shiwaliks in the south and the Greater Himalayas in the north.
• The Lower Himalayan ranges are 60-80 km wide and about 2400 km in length.
• Elevations vary from 3,500 to 4,500 m above sea level.
• The Lower Himalayas have steep, bare southern slopes (steep slopes prevent soil formation) and gentler, forest covered northern slopes.
Greater Himalayas
• Inner Himalaya, Central Himalaya or Himadri.
• It is mainly formed of the crystallines (granites and
gneisses) overlaid by metamorphosed sediments (limestone).
• This mountain arc convexes to the south just like the other two ranges.
• The Himadri terminates abruptly at the syntaxial bends.
• One in the Nanga Parbatin the north-west and the other in the Namcha Barwain the north-east.
Himalayas can be regionally divided into the following sub-divisions:
1. Kashmir or Northwestern Himalayas
• It lies betweenthe Indus and the ravi river.
• Comprise a series of ranges such as the Karakoram, Ladakh, Zaskar and PirPanjal.
• 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 PirPanjal 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 Zafran, a local variety of saffron.
• Some of the important passes of the region are Zoji La on the Great Himalayas, Banihal on the PirPanjal, 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. Himachal and Uttaranchal Himalayas
• It lies betweenthe Ravi in the west and the Kali (a tributary of Ghaghara) in the east.
• Drained by two major river systems of India, i.e. Indus and Ganga.
• 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 Nag tibha in 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 35-45 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.
3. 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 Teesta, 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 while the southern part, particularly the Darjiling Himalayas, has a mixed population of Nepalis, Bengalis and tribal 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 of the Shiwalik formations.
• In place of Shiwaliks here, the ‘duar formations‘ are important, which have also been used for the development of tea gardens.
4. 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.
• Bhramaputa flows through a deep gorge after crossing Namcha Barwa.
• Some of the important rivers are Kameng, Subansiri, Dihang, Dibang and Lohit.
• These are perennial with the high rate of fall, 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. Eastern Hills and Mountains.
• Part of 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 (it has worlds only floating Keibul Lamjo National park) 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.
• Rivers in eastern part of Manipur are tributaries of Chindwin, which in turn is a tributary of the Irrawady of Myanmar.
B. The Northern Plains:
• Formed by the alluvial deposits brought by the rivers – the Indus, the Ganga and the Brahmaputra.
• Extend approximately 3,200 km from the east to the west.
• Average width of these plains varies between 150-300 km.
• From the north to the south, these can be divided into three major zones:
- the Bhabar,
- the Tarai and
- the alluvial plains.
• The alluvial plains can be further divided into the Khadar and the Bhangar.
• Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope.
• As a result of this, the streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone.
• 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 creating marshy and swampy conditions known as the Tarai.
• Bhangar old alluvium deposit and khaddar new alluvium deposit.
• 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 sand bars. (Majuli, in the Brahmaputra river, is the largest inhabited riverine island in the
world).
• Most of these areas are subjected to periodic floods and shifting 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.
C. 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 the Peninsular plateau.
• Delhi ridge in the northwest, (extension of Aravalis), the Rajmahal 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 Palamu plateau, the Ranchi plateau, the Malwa plateau, the Coimbatore plateau and the Karnataka plateau, etc.
• This is one of the oldest and the most stable landmass of India.
• 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.
• Some of the important physiographic features of this region are tors, block mountains, rift 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 emphatic presence of black soil.
• This Peninsular plateau has undergone recurrent phases of upliftment and submergence accompanied by crustal faulting and fractures. (The Bhima fault needs special mention, because of its recurrent seismic activities).
• The north-western part of the plateau has a complex relief of ravines and gorges.
• The ravines of Chambal, Bhind and Morena are some of the well-known examples.
On the basis of the prominent relief features, the Peninsular plateau can be divided into three broad groups:
1. The Deccan Plateau
• This is 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.
• Their average elevation is about 1,500 m with the height increasing from north to south.
• 'Anaimudi' (2,695 m), the highest peak of Peninsular plateau is located on the Anaimalai hills of the Western Ghats 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 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 (here Satyamangalam Tiger reserve is located).
2. The Central Highlands
• They are bounded to the west by the Aravali range.
• Central Highlands of India are a biogeographic region in India formed by the disjunct ranges of the Satpura and Vindhya Hills
• The Satpura range is formed by a series of scarped plateaus on the south, 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.
3. The North-eastern Plateau:
• It is an extension of 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.
• Today, the Meghalaya and Karbi Anglong plateau stand detached from the main Peninsular Block.
• The Chhota Nagpur Plateau is a plateau in eastern India, which covers much of Jharkhand state as well as adjacent parts of Odisha, West Bengal and Chhattisgarh.
• The Meghalaya plateau is further sub-divided into
three:
(i) The Garo Hills;
(ii) The Khasi Hills;
(iii) The Jaintia Hills, named after the tribal groups inhabiting
this region.
• An extension of this is also seen in the KarbiAnglong 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.
D. 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.Low precipitation and high evaporation makes it a water deficit region.
• Luni river flowing in the southern part of the desert is
of some significance.
•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.
E. The Coastal Plains
• On the basis of the location and active geomorpho-
logical processes, it can be broadly divided into two:
a. Western Coastal Plains:
• 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
NavhaSheva, Marmagao, Mangalore, Cochin, etc. are
some of the important natural ports located along the
west coast. Western coast may be divided into following divisions.,
1. Kachchh and Kathiawar coast in Gujarat.
2. Konkan coast in Maharashtra.
3. Canara 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 special
attraction for tourists.
b. Eastern Coastal Plains:
The 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 in to 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).
F. The Islands:
• There are two major island groups in India – one in
the Bay of Bengal and the other in the Arabian Sea.
The Islands of 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 entire group of island is divided into two broad
categories – the Andaman in the north and the Nicobar in the south.
• However, some smaller islands are volcanic in origin. Barren island, the only active volcano in India.
• These islands receive convectional rainfall and have
an equatorial type of vegetation.
The islands of the Arabian Sea:
• Include Lakshadweep and Minicoy. These are
scattered between 8°N-12°N and 71°E -74°E longitude, they are coral origin.
• 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 Canannore Island.
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