Tectonic Plate Theory:-
The tectonic plate theory describes the large scale motion of the earth’s lithosphere. This theory is based on continental drift which explains the formation of various continents over millions of years; as we see them today.
Based on the relative movement between two tectonic plates, there are three types of plate boundaries. They are as follows:
Convergent Boundary: In this case, the two adjacent tectonic plates move towards each other.
Divergent Boundary: In this case, the two adjacent plates move away from each other.
Transform Boundary: In this case, the two adjacent plates move along their borders.
About 225 million years ago, the earth contained a single landmass; called Pangaea. That landmass was divided into two landmasses, viz. Laurasia and Gondwana Land; about 200 million years ago. As the figures; given here show; the landmasses further broke into different parts and experienced continental drifts at various stages. The Gonwana Land included the modern day India, Australia, South America, South America and Antarctica.
Formation of India
The Indian Peninsula drifted towards the north and finally collided with the much larger Eurasian Plate. As a result of this collision, the sedimentary rocks which were accumulated in the geosynclines (known as Tethys) got folded and formed the mountain systems of the West Asia and Himalaya.
Due to the uplift of the Himalayas in the Tethys Sea, the northern flank of the Indian Peninsula got subsided and formed a large basin. That basin was filled with sediments from the rivers which came from the mountains in the north and from the peninsula in the south. Thus, an extensive flat land of alluvial soil was formed which is known as the northern plains of India.
MAJOR PHYSIOGRAPHIC DIVISIONS:
The landmass of India can be divided into following major physiographic divisions:
1.The Himalayan Mountains
2.The Northern Plains
3.The Peninsular Plateau
4.The Indian Desert
5.The Coastal Plains
The Himalayan Mountains
The Himalayas are the youngest mountains in the world and are; structurally; the folded mountains. The Himalayas run along the northern border of India. The Himalayas form an arc which is about 2,400 km long. The width varies from 400 km in Kashmir to 150 km in Arunachal Pradesh. The altitudinal variations are greater in the eastern part than in the western part. There are three parallel ranges in its longitudinal extent.
(1) The Great or Inner Himalayas:-
This is the northernmost range and is also known as ‘Himadri’. This is the most continuous range. It contains the loftiest peaks. The average height of peaks in this range is 6,000 metres. All the prominent Himalayan peaks are in this range. The folds of the Great Himalayas are asymmetrical in nature and the core of this part is composed of granite. Because of the lofty heights, the peaks of this range are perennially snow-bound.
(2) The Lesser Himalaya or Himachal:This lies towards the south of the Great Himalayas. The altitude of peaks in this range varies from 3,700 m to 4,500 m. Average width of this range is 50 km. This range is mainly composed of highly compressed and altered rocks.
(3) The Shiwaliks:-
This is the outermost range of the Himalayas. The altitude varies between 900 and 1100 km in this range and the width varies between 10 to 50 km. These ranges are composed of unconsolidated sediments. The longitudinal valleys lying between the Himachal and Shiwaliks are called ‘Dun’.
Himalayan Regions from East to West:
Punjab Himalayas:- This part lies between the Indus and Sutlej. From west to east, this is also known as Kashmir Himalaya and Himachal Himalaya; respectively.
Kumaon Himalayas: This part lies between Sutlej and Kali rivers.
Nepal Himalayas: This part lies between the Kali and Tista rivers.
Assam Himalayas: This part lies between the Tista and Dihang rivers.
Eastern hills and mountains: The Brahmaputra marks the eastern border of the Himalayas. Beyond the Dihang gorge, the Himalayas bend sharply towards south and form the Eastern hills or Purvachal. These hills run through the north eastern states of India. They are mostly composed of sandstones. These hills are composed of the Patkai Hills, Naga Hills, Manipuri Hills and Mizo Hills.
The Northern Plain
The northern plain of India is formed by three river systems, viz. the Indus, the Ganga and the Brahmaputra; along with their tributaries. This plain is composed of alluvial soil which has been deposited over millions of years. The total area of the northern plain is about 7 lakh square kilometer. It is about 2400 km long and about 240 to 320 km broad.
The northern plain is divided into three sections, viz. the Punjab Plain, the Ganga Plain and the Brahmaputra Plain.
1.Punjab Plains: The Punjab plains form the western part of the northern plain. This is formed by the Indus and its tributaries; like Jhelum, Chenab, Ravi, Beas and Sutlej. A major portion of this plains is in Pakistan. Doabs abound in this plain.
2.Ganga Plains: This plain extends between Ghaggar and Tista rivers. The northern states, Haryana, Delhi, UP, Bihar, part of Jharkhand and West Bengal lie in the Ganga plains.
3.Brahmaputra Plains: This plain forms the eastern part of the northern plain and lies in Assam.
Based on the relief features; the northern plain can be divided into four regions, viz. bhabar, terai, bhangar and khadar.
1.Bhabar: After descending from the mountains, the rivers deposit pebbles in a narrow belt. The width of this belt is about 8 to 16 km and it lies parallel to the Shiwaliks. This region is known as bhabar. All the streams disappear in this region.
2.Terai: The terai region lies towards south of the bhabar belt. In this region, the streams reappear and make a wet, swampy and marshy region.
3.Bhangar: Bhangar is the largest part of the northern plain and is composed of the oldest alluvial soil. They lie above the flood plains. They resemble terraces. The soil of this region is locally known as kankar and is composed of calcareous deposits.
4.Khadar: The floodplains formed by younger alluvium are called khadar. The soil in this region is renewed every year and is thus highly fertile.
The Peninsular Plateau
The peninsular plateau is a tableland. It is composed of the oldest rocks because it was formed from the drifted part of the Gondwana land. Broad and shallow valleys and rounded hills are the characteristic features of this plateau.
The plateau can be broadly divided into two regions, viz. the Central Highlands and the Deccan Plateau.
a.The Central Highlands: The Central Highlands lies to the north of the Narmada river. It covers the major portion of the Malwa plateau. The rivers in this region flow from southwest to northeast; which indicates the slope of this region. It is wider in the west and narrower in the east. Bundelkhand and Baghelkhand mark the eastward extension of this plateau. The plateau further extends eastwards into the Chhotanagpur plateau.
b.The Deccan Plateau:- The Deccan Plateau lies to the south of the Naramada river. It is triangular in shape. The Satpura range makes its northern part. The Mahadev, Kaimur Hills and Maikal range make its eastern part. The slope of the Deccan Plateau is from west to east. It extends into the north east which encompasses Meghalaya, Karbi-Anglong Plateau and North Cachar Hills. Garo, Khasi and Jaintia hills are the prominent ranges; starting from west to east.
c. The Western and the Eastern Ghats:- They make the western and eastern edges of the Deccan Plateau. The average elevation of Western Ghats is 900 – 1600 metres; compared to 600 metres in case of Eastern Ghats. The Eastern Ghats stretch from Mahanadi Valley to the Nilgiris in the south. The Western Ghats cause oceanographic rains as they face the rain-laden winds from west.
The Indian Desert:-
The Indian desert lies towards the western margins of the Aravali Hills. This region gets scanty rainfall which is less than 150 mm in a year. Hence they climate is arid and vegetation is scanty. Luni is the only large river but some streams appear during rainy season. Crescent-shaped dunes (barchans) abound in this area.
The Coastal Plains
The Peninsular plateau is flanked by stretch of narrow coastal strips. They run along the Arabian Sea on the west and along the Bay of Bengal on the east. The western coast lies between the Western Ghats and the Arabian Sea. It is divided into three sections. The Konkan; which comprises of Mumbai and Goa makes the northern part. The Kannada Plain makes the central pat and the Malabar coast makes the Malabara coast.
The western coastal plain is wider and level and it runs along the Bay of Bengal. It is divided into two parts. The northern part is called Northern Circar. The southern part is called the Coromandel Coast. Extensive deltas are formed by large rivers like Mahanadi, Godavari and Kavery. Chilika lake is an important feature along the eastern coast.
The Lakshadweep Islands are in the Arabian Sea. Its area is 32 sq km. The administrative headquarters of Lakshadweep is at Kavaratti island. This group of islands is rich in terms of biodiversity.
The Andaman and Nicobar Islands are bigger in size and has more number of islands. This group of islands can be divided into two groups. The Andaman is in the north and the Nicobar is in the south. These islands too have rich biodiversity.