Structure and Physiography — Study Notes

1. Introduction

The Indian subcontinent has a remarkable and diverse physical structure, ranging from the highest mountains in the world to flat plains, from ancient plateaus to island groups. The physical features of India are the result of its long geological history, which is closely connected with the movement of the Indian plate. The northward movement of the Indian plate and its collision with the Eurasian plate gave rise to the Himalayas, while the ancient peninsular block remained stable.

The physical division of India is usually studied under six major physiographic units: the Himalayan mountains, the Northern plains, the Peninsular plateau, the Indian desert, the Coastal plains and the Islands. The physiography of India influences its climate, drainage, soils, natural vegetation and human activities. In this chapter we study the geological structure of India and the main features of each physiographic division.

2. Geological Structure of India

India's geological structure is divided into three major geological divisions: 1. The Peninsular block: An ancient, stable block composed of crystalline and metamorphic rocks, including the Deccan Plateau, which has remained stable for hundreds of millions of years. 2. The Himalayan and other extra-Peninsular mountain systems: Geologically young fold mountains, formed by the collision of the Indian plate with the Eurasian plate, made of sedimentary rocks and marine deposits. 3. The Indo-Ganga-Brahmaputra plain: A vast alluvial plain formed by the deposition of sediments by the Indus, Ganga and Brahmaputra rivers and their tributaries, lying between the Himalayas and the Peninsula.

These three divisions correspond to three distinct physiographic units, and each has its own characteristic structure, rocks and relief.

3. The Himalayan Mountains

The Himalayas are the youngest and highest mountain range in the world, stretching in an arc of about 2,400 kilometres from west to east, between the Indus in the west and the Brahmaputra in the east. They are fold mountains formed by the collision of the Indian and Eurasian plates. The Himalayas are divided into three parallel ranges:

1. The Greater Himalayas (Himadri): The northernmost and highest range, with an average height of about 6,000 metres. It contains the highest peaks, including Mount Everest (8,848 m) and K2 (8,611 m). This range is made of the oldest rocks and is covered with snow throughout the year.
2. The Lesser Himalayas (Himachal): The middle range, with an average height of 3,700 to 4,500 metres, including ranges like the Pir Panjal, Dhaula Dhar and Mahabharata ranges. These mountains are composed mostly of highly compressed and altered rocks. Hill stations like Shimla and Mussoorie lie here.
3. The Shiwaliks (Outer Himalayas): The southernmost and lowest range, with an average height of 900 to 1,200 metres, composed of unconsolidated sediments brought down by rivers from the higher ranges. Valleys like Dehra Dun lie between the Shiwaliks and the Lesser Himalayas.

4. The Northern Plains

The Northern plains lie between the Himalayas in the north and the Peninsular plateau in the south. They are formed by the alluvial deposits of the Indus, Ganga and Brahmaputra rivers and are among the most fertile and densely populated plains of the world. The plains cover an area of about 7 lakh square kilometres and have a thickness of alluvium ranging from 1,000 to 2,000 metres.

The Northern plains are divided into three sections: 1. Punjab plains: Formed by the Indus and its tributaries (Jhelum, Chenab, Ravi, Beas and Sutlej), covering western parts. 2. Ganga plains: Extending between the Ghaggar and the Teesta rivers, covering the largest part, including Uttar Pradesh, Bihar and West Bengal. 3. Brahmaputra plains: In the eastern part, in Assam, formed by the Brahmaputra river.

The plains are subdivided into regions like Bhabar (a narrow belt of pebbles along the foothills), Terai (a marshy, damp belt south of Bhabar), Bangar (older alluvium, higher and less fertile) and Khadar (newer alluvium, lower and more fertile, renewed each year by floods).

5. The Peninsular Plateau

The Peninsular plateau is the oldest landmass of India, made of ancient crystalline, igneous and metamorphic rocks. It is a part of the ancient Gondwanaland. The plateau is roughly triangular in shape, with its base in the north and apex in the south at Kanyakumari. It is divided into two major parts by the Narmada river:

1. The Central Highlands: The northern part of the plateau, lying north of the Narmada. It includes the Aravalli hills (the oldest mountain range of India) and is divided into the Malwa plateau, the Bundelkhand and the Chota Nagpur plateau. The western part is the Malwa plateau.
2. The Deccan Plateau: The southern part, lying south of the Narmada, bounded by the Western Ghats in the west and the Eastern Ghats in the east. It is divided into the Maharashtra plateau (Deccan lava), the Karnataka plateau and the Telangana plateau. The black soil found here is formed from volcanic lava.

The plateau slopes gently from west to east, so most rivers flow eastwards and drain into the Bay of Bengal. The Western Ghats are higher than the Eastern Ghats and form the edge of the plateau.

6. The Indian Desert

The Indian desert, also called the Thar desert, lies in the north-western part of India, mainly in Rajasthan, with extensions into Gujarat and Punjab. It is a sandy plain with low, shifting sand dunes (barchans). The desert receives very little rainfall, about 15 to 25 centimetres annually. The Luni is the only river of this region. The desert was formed due to the absence of moisture-bearing winds and the blocking of monsoon winds by the Aravallis. The dunes of the desert are stabilised by xerophytic vegetation.

7. The Coastal Plains

The coastal plains are the narrow strips of land between the sea and the landward margin of the Peninsular plateau. They are divided into: 1. The Western Coastal Plain: A narrow plain between the Western Ghats and the Arabian Sea, divided into the Kathiawar-Gujarat coast, the Konkan (Mumbai to Goa), the Kannad and the Malabar coast (Kerala). It is narrower than the eastern plain. 2. The Eastern Coastal Plain: A wider, broader plain between the Eastern Ghats and the Bay of Bengal, divided into the Northern Circars and the Coromandel coast. The deltas of rivers like the Mahanadi, Godavari, Krishna and Kaveri are found here.

8. The Islands

India has two main groups of islands: 1. The Andaman and Nicobar Islands: Located in the Bay of Bengal, these are a group of about 572 islands, divided into the Andaman group (north) and the Nicobar group (south), separated by the Ten Degree Channel. They are of volcanic and coral origin. 2. The Lakshadweep Islands: Located in the Arabian Sea, south of the Malabar coast, these are a group of about 36 islands of coral origin. The Kavaratti is the administrative headquarters.

Quick Revision Tables

Physiographic Divisions of India

Himalayan Ranges

Mind Map

Important Diagrams (SVG)

Diagram 1: Major Physiographic Divisions of India

Diagram 2: Himalayan Ranges

Common Mistakes

1. Writing that the Himalayas are the oldest mountains of India; they are the youngest fold mountains, while the Aravallis are the oldest.
2. Confusing the three Himalayan ranges: Himadri is the highest, Himachal is the middle, and Shiwaliks are the lowest and southernmost.
3. Confusing Bhabar (pebbly belt along the foothills) with Terai (marshy belt south of Bhabar).
4. Writing that the Narmada divides the Peninsular plateau into two parts; remember the Narmada is the divider between the Central Highlands and the Deccan Plateau.
5. Saying the Western Ghats are lower than the Eastern Ghats; the Western Ghats are higher and continuous.
6. Confusing the Andaman-Nicobar islands (Bay of Bengal, of volcanic/coral origin) with the Lakshadweep islands (Arabian Sea, of coral origin).
7. Believing the Thar desert receives high rainfall; it receives only about 15-25 cm annually.
8. Writing that the Northern plains are made of volcanic rocks; they are made of thick alluvial deposits of the rivers.

Exam Tips

1. Memorise the six physiographic divisions and their main characteristics for map and descriptive questions.
2. Learn the three Himalayan ranges with their heights: Himadri (about 6,000 m), Himachal (3,700-4,500 m), Shiwaliks (900-1,200 m).
3. Know the subdivision of the Northern plains: Punjab, Ganga and Brahmaputra plains, and the four belts Bhabar, Terai, Bangar and Khadar.
4. Draw labelled diagrams of the physiographic divisions and the Himalayan ranges.
5. Remember that the Western Ghats are higher than the Eastern Ghats and that most peninsular rivers flow eastwards.
6. List the peaks: Everest (8,848 m) and K2 (8,611 m) in the Greater Himalayas.
7. For the islands, remember the Ten Degree Channel separates the Andamans from the Nicobars.

Conclusion

The structure and physiography of India are the product of a long geological history, dominated by the movement of the Indian plate and its collision with Eurasia. India is divided into six major physiographic units: the young, high Himalayas with their three parallel ranges; the fertile alluvial Northern plains; the ancient, stable Peninsular plateau divided into the Central Highlands and the Deccan Plateau; the arid Indian desert; the narrow Western and broader Eastern coastal plains; and the island groups of Andaman-Nicobar and Lakshadweep. These divisions determine the drainage, climate, soils and vegetation of India and provide the physical framework within which the human geography of the country has developed. The next chapter examines the drainage systems that drain these physiographic units.

Keywords: Himalayas, Himadri, Himachal, Shiwaliks, Northern plains, Deccan Plateau, Central Highlands, Thar, Western Ghats, Lakshadweep.