The chapter notes will familiarise students with India's primary geographic features, including mountains, plains, deserts, plateaus, and islands. The notes will assist students in comprehending the process of Indian landmass creation, which includes the rise of the Himalayas, the deposition of alluvium, formation of deltas and coastal plains to plateaus that were the oldest landmass in the Indian subcontinent.
What is the 'Theory of Plate Tectonics'?
According to the Theory of Plate Tectonics, Earth's Crust (Lithosphere) is made up of 7 major and several minor plates which float over the upper molten layer of Mantle (Asthenosphere).
These plates could either be Oceanic or Continental. The Oceanic plates are denser compared to the Continental Plates because they are made of Basalt which is essentially a dense igneous rock. Continental Plates on the other hand are made of Granite which metamorphosize into less dense granitic rocks.
These plates interact with each other in 3 ways:
1. Convergent Boundaries (Moving towards each other)
2. Divergent Boundaries (Moving apart from each other)
3. Transform Boundaries (Grinding against each other)
What physical features form due to interaction of the Tectonic Plates?
Convergent Boundaries: When two plates move towards each other they form a convergent boundary.
The denser plate of the two would usually slide under the lighter one, this movement is called subduction. It results in formation of volcanic arcs and deep ocean trenches such as the 'Ring of Fire' which is formed due to interaction between the oceanic Pacific Plate and surrounding continental plates such as Eurasian Plate, Indo-Australian Plate, North American Plate among other smaller ones.
If the plates have similar density then they will form collision boundaries also known as Orogenic belts which result in formation of high mountains such as the Himalayas, Andes and Alps.
The process of convergence is also called folding.
Divergent Boundaries: When two plates move apart they form a divergent boundary.
The movement of oceanic plates away from each other results in formations of mid-oceanic ridges which results in ocean floor spreading.
The movement of continental plates away from each other results in formation of Rift Valleys and ridges such as the Great Rift Valley in East Africa. The rifts also lead to formation of huge lakes such as Lake Victoria in Africa or Lake Baikal in Russia.
Transform Boundaries: When two plates grind against each other they form transform boundaries. They have limited convergence or divergence in their respective movements.
These types of movements result in creation of faults such as the famous San Andreas Fault or Dead Sea Transform. As a result of grinding these zones are prone to earthquakes.
Formation of Indian landmass
India has a variety of physical features from large flood plains, high mountains, deserts, coastal plains and islands. These physical features have been formed due to various geological processes such as weathering, erosion and depositions over different geological periods.
These geological processes have modified India's relief to its present form. We find different kinds of rocks and resultantly different kinds of soil across Indian landmass.
Timeline of Indian Landmass Formation
Around 250 million years ago, most of the landmass existed as a supercontinent called 'Pangea' which was surrounded by the super ocean 'Panthalassa'.
The convection currents in the molten layer of Mantle split the supercontinent pangea into two parts:
- Laurasia: The Northern landmass that included present day continents of North America, Asia and Europe which lie in the northern hemisphere with the exception of the Indian peninsula. It comprised other major landmasses such as Siberia (Angaraland), Laurentia, Baltica among others.
- Gondwana: The Southern landmass that includes Indian peninsula, Australia, South Africa, South America and Antarctica as one single land mass
The convection currents further split these landmasses into the present day tectonic plates which are still drifting.
How were the Himalayas formed?
The Indo-Australian plate split from the southern Gondwana land and started drifting northwards before colliding with the Eurasian plate.
This collision led to the folding and upliftment of sediments accumulated in the Tethys Sea into mountain ranges of western Asia and the Himalayas.
The system of Himalayas geologically represents a very unstable and youthful topography with high peaks, deep valleys and flowing rivers.
How were the Northern Indian Plains formed?
The collision of the Indian plate with the Eurasian plate also resulted in subsidence or sinking of the northern part of the Indian peninsula creating a large basin.
This depression between the Himalayas in the north and the peninsular plateau got gradually filled with sediments brought by rivers from the two regions. This deposition of sediments led to the formation of the fertile alluvial soil in the northern plains of India.
How does the topography of the peninsular plateau influence drainage and other physical features?
Due to the eastward tilt of the peninsular plateau, the rivers originating in the Western Ghatshave higher elevation and they flow in the east direction. The flow of rivers also resulted in erosion of the Eastern Ghats giving them their unique passes and wider coastal plains.
The tilt is also responsible for shallower waters on the eastern coast of India and as a result a lack of natural harbours as compared to the western coast.
The tilt may be attributed to differences in rocks that make up the different parts of the peninsular plateau. Most rocks however are igneous and metamorphic with gentle rising hills and wide valleys.
Major Physiographic Divisions of India
The physical features of India can be grouped under the following physiographic divisions
1. The Himalayan Mountains
2. The Northern Plains
3. The Peninsular Plateau
4. The Indian Desert
5. The Coastal Plains
6. The Islands
1. The Himalayan Mountains
The Himalayas are one of the tallest and most rugged mountain barriers in the world. They are geologically young features and stretch in an arc shape over a distance of 2400km over the northern borders of India. They extend from Indus in the west to Brahmaputra in the east.
The mountains are the major sources of water and forest wealth.
What is the difference between western and eastern halves of the Himalayas?
● The Himalayas vary in thickness from 400 Km in Kashmir(west) to 150 Km in Arunachal Pradesh (east).
● The eastern Himalayas have greater variation in height compared to the western half.
The Longitudinal or North-South Division of Himalayas
The Himalayas consist of following 3 parallel ranges from north to south:
● Himadri (The Great or Inner Himalayas) : It is the northernmost , loftiest and most continuous range of Himalayas with peaks having an average height of 6000 metres. It is home to some of the tallest mountains in the world including Mt. Everest, Kanchenjunga, Nanga Parbat and Annapurna among others.
They are snow bound throughout the year and have a number of glaciers descending from them. Their core is composed of granite and they are known to have asymmetrical folds.
● Himachal (The Lesser Himalayas) : The Himachal range lies south of the Himadri and consists mostly of highly compressed and altered rocks. The altitude varies between 3700-4500 metres and they have an average width of 50 Km.
It has many important sub ranges such as the Pir Panjal, Dhaula Dhar and Mahabharat. It is well known for its hill stations and the famous valleys of Kashmir, Kangra and Kullu lie in this range.
● Shiwaliks (The Outer Himalayas) : They are the southernmost range having an average width of 50 Km and altitude that varies between 900-1100 metres. They are composed of unconsolidated sediments brought by rivers.
The valleys between Himachal and Shiwaliks are called Duns. They are covered with thick gravel and alluvium. DehraDun, Patli Dun and Kotli Dun are some well known Duns.
The Latitudinal or West-East Division of Himalayas
The Himalayas have also been divided from west to east as regions demarcated by rivers as follows:
Punjab Himalayas : They are the part of Himalayas that lies between the rivers Indus and Satluj. They are also known as Kashmir and Himachal Himalayas.
Kumaon Himalayas : They are the part of Himalayas that lies between the rivers Satluj and Kali.
Nepal Himalayas: They are the part of Himalayas that lies between the rivers Kali and Tista.
Assam Himalayas: They are the part of Himalayas that lies between the rivers Tista and Dihang.
What are the Purvachals?
Post the Brahmaputra river, the Himalayas take a sharp bend southwards and are known as Purvanchal or Eastern Hills. They are composed of sedimentary rocks such as sandstone. They run through the north-eastern states of India and comprise of:
● Patkai Hills
● Naga Hills
● Manipur Hills
● Mizo Hills
2. The Northern Plains
The northern plains of India have majorly been formed by depositional work of 3 rivers of the Himalayan river system namely : Indus, Ganga, Brahmaputra and their tributaries. The northern plains are the granaries of the country. They provide the base for early civilisations.
Course of a river
- Upper Course : The rivers originate at a high elevation point on a mountain. It then flows rapidly through steep valleys and forms deep gorges and waterfalls. The erosion activity of the river is high in this phase due to greater speed and momentum.
- Middle Course : On reaching the foot of the hills, the rivers slow down due to less slope and start depositional activity. The volume of the water increases as the river is now joined by its tributaries thereby eroding the banks of the river thus making it wider. During the lower part of this course the river slows down further forming flood plains. Due to slow speed, the rivers form meanders, ox-bow lakes, alluvial fans and riverine islands at this stage.
- Lower Course : During the lower stages of its course, the rivers split into distributaries as the rate of silt deposition increases. At this point the river is said to be 'Braided'. This region is also referred to as the deltaic region and is characterised by marshy lands. Rivers meet the oceans during their last course forming deltas. Estuaries can also be found in regions where tidal action constantly washes the mouth of the river.
Sections of the Northern Plains of India
The northern plains of India are broadly divided into 3 sections on the basis of rivers which drain them. These are:
1. Indus Plains or Punjab Plains : These plains are drained by Indus and its 5 major tributaries namely: Jhelum, Satluj, Chenab, Ravi and Beas. The land drained by these 5 rivers is called 'Punjab' - 'Punj' means five and 'Ab' means water. A majority of these plains lie in Pakistan.
2. Ganga Plains : The Ganga plains lie between the rivers Ghaggar in west to Teesta in the east. It is spread over the states of Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand and West Bengal.
3. Brahmaputra Plains : These plains are mainly found in Assam where the river is drained by Brahmaputra and its tributaries such as Dihang, Dibang and Lohit. During the lower courses of Brahmaputra lies the largest inhabited riverine island of Majuli.
Division of Northern Plains on basis of Relief
The northern plains can be divided into these 4 major regions based on the variations in their relief feature:
● Bhabar : It is a narrow belt of pebbles around 8-16 Km in width which can be found lying parallel to the foots of the Shiwaliks. As a river flows through this bhabar belt , it disappears into the ground.
● Terai : The rivers re-emerge from the ground in this region making it wet, swampy and marshy. This is usually a thickly forested region and a lot of India's national parks such as Dudhwa, Jim Corbett can be found in this region.
● Bhangar : This is the largest part of the northern plains and is majorly composed of older alluvium with calcareous deposits called Kankar. It lies above the flood plains and presents a terrace like feature.
● Khadar : These are the younger deposits of alluvium and are renewed almost every year. They are very fertile and ideal for agriculture.
3. The Peninsular Plateau
The peninsular plateau is the oldest landmass of Indian territory and was formed due to breaking and drifting of the Gondwana land. It is composed of old crystalline, igneous and metamorphic rocks. It features broad and shallow valleys and rounded hills.
The plateau is a storehouse of minerals, which has played a crucial role in the industrialisation of the country.
The plateau consists of 2 broad divisions:
- Central Highlands : This region lies to the north of Narmada river and represents a triangular region which is bounded by Vindhya ranges to its south and Aravallis to its northwest. The Aravallis are highly eroded and broken hills and extend from Gujarat to Delhi in the southwest-northeast direction.
It tapers from west to east with its western extension merging into the sandy and rocky terrain of Rajasthan. As we move eastwards in the Central Highlands, the plateau tapers into regions locally known as Bundelkhand, Bagelkhand and Chota Nagpur plateau.
- Deccan Plateau : This is also a triangular region which lies to the south of Narmada. It is flanked by Satpura range to its north which extends eastwards in the Kaimur Hills, Mahadev and Maikal ranges. The western and eastern ghats from the western and eastern edges of the deccan plateau.
The western part of the plateau is rich in black soil and is known as Deccan Trap. This was formed due to volcanic action and are hence igneous in nature.
What is the Karbi-Anglong Plateau?
An extension of the Deccan plateau lies towards north-east India and is locally known in Meghalaya as Karbi- Anglong plateau and North Cachar hills. A small gap separates it from the chota nagpur plateau region which is believed to be a result of compression of the peninsular plateau at the time of collision of Indian plate with Eurasian plate.
Which are the prominent ranges present in the Karbi-Anglong plateau?
Three Prominent hill ranges from the west to east are the Garo, the Khasi and the Jaintia Hills.
Topography of Deccan Plateau: The Deccan plateau is higher in the west and slopes gently towards the east resulting in many rivers rich as Mahanadi, Godavari, Krishna and Kaveri flowing eastwards.
The Western Ghats
They lie on the western edges of the Deccan plateau and run parallel to the narrow western coast. They are continuous and can be crossed only through passes. Some important sections of the western ghats are Thal, Bhor and Pal Ghats.
They have an average elevation of 900-1600 metres and the elevation increases as we move from north to south. They act as barriers to the southwest monsoon approaching from the Arabian sea and result in orographic rainfall on the western sides.
The highest peaks include the Anamudi (2,695metres) and the Doda Betta (2,637 metres).
The Eastern Ghats
They lie on the eastern edges of the Deccan plateau and run parallel to the eastern coast. Their elevation is comparatively lower than the western ghats averaging around 600 metres.
They stretch from Mahanadi valley in Odisha to the Nilgiris in the south. They are discontinuous and irregular due to erosion by the eastward flowing rivers which drain into the Bay of Bengal.
Mahendragiri (1,501 metres) is the highest peak in the Eastern Ghats. Shevaroy Hills and the Javadi Hills are located to the southeast of the Eastern Ghats. Popular hill stations of Udagamandalam popularly known as Ooty and Kodaikanal lie in this range
The Indian Desert
The Indian desert lies to the west of the Aravali range. Since the Aravali's lie in the southwest-northeast direction, they don't act as watersheds for the southwest monsoon. This results in low rainfall in the Indian desert region. They recieve a rainfall of less than 150mm per year.
They have an arid type of climate with low vegetation cover. The streams in the region dry during the summer season and appear during the rainy season. Luni is the only major river of the region.
They are covered with sandy plains having smooth elevations and are covered by sand dunes. The crescent shaped dunes are called Barchans and become more prominent near the India-Pakistan border.
The Coastal Plains
The coastal region and island groups provide sites for fishing and port activities. Thus, the diverse physical features of the land have immense future possibilities of development.
The Western Coast: They are narrow in width and are sandwiched between the Western Ghats and the Arabian sea. It consists of 3 major regions running from north to south:
● Konkan : The northern part stretching from Mumbai to Goa
● Kannad : This is the central stretch from Goa to Karnataka
● Malabar : The southern part which stretches along the state of Kerala
The Eastern Coast: They are wider and more level compared to the western ghats. They lie between the Eastern ghats and the Bay of Bengal. Large rivers such as Mahanadi, Godavari, Krishna and Kaveri form deltas on the eastern coast as we move from north to south.
It consists of 2 major regions from north to south:
● Northern Circars: The northern part running along the states of Odisha and Andhra Pradesh
● Coromandel Coast: The southern part which runs along the state of Tamil Nadu
India has two group of islands:
1. Lakshadweep Islands
They are a small island group covering an area of 32 square Km. They were earlier called Laccadive,Minicoy and Amindive and were renamed Lakshadweep in 1973. Its administrative capital is Kavaratti.
They lie close to the Malabar coast on the west of Kerala and are made up of corals. They are rich in flora and fauna and have many uninhabited islands such as the Pitti Island which also has a bird sanctuary.
What are corals?
Corals are short lived microscopic polyps that live in warm, shallow and mud-free waters. The secrete calcium carbonate which is responsible for formation of coral reefs.
The 3 most common kinds of coral reefs are barrier reef, fringing reef and circular or horseshoe shaped atolls.
2. Andaman and Nicobar Islands
They lie in the Bay of Bengal and are larger in number compared to the Lakshadweep. They are believed to be elevated portions of submarine mountains. They are bigger in size and scattered are and broadly divided into 2 sections
Andamans in the North and Nicobar in the South. They lie close to the equator and have equatorial type of climate