Physiography of India

Learning Outcomes

1. Understand the structure and relief of the Indian subcontinent.
2. Identify key physiographic divisions of India and their characteristics.
3. Recognize the importance of the Himalayan and Peninsular drainage systems.
4. Comprehend the influence of plate tectonics on India’s geology.
5. Explore the role of endogenic and exogenic forces in shaping India’s landscape.

The Indian subcontinent showcases a complex geological structure that has evolved over millions of years, influenced by the endogenic (internal) and exogenic (external) forces. These forces, in combination with plate tectonics, have shaped the surface and subsurface features of the region. India’s geological history reflects this continuous evolution. A fundamental understanding of Plate Tectonics and the movement of the Indian plate is crucial for grasping the subcontinent’s formation and physiography. The Indian plate, once located south of the equator, has moved northward, resulting in significant geological and environmental consequences. Based on geological formations, India is divided into three main regions:

1. The Peninsular Block
2. The Himalayas and Peninsular Mountains
3. The Indo-Ganga-Brahmaputra Plain

The Peninsular Block

The Peninsular Block represents an ancient and stable landmass, mostly consisting of granites and gneisses. It extends from Kachchh in the west to the Rajmahal Hills in the east. The Karbi Anglong and Meghalaya Plateau are its northeastern extensions. The Rajasthan desert and other desert-like features form its western fringe. Major physiographic features of the Peninsula include:

1. Structure: The region’s Cambrian origins have left it standing as a rigid block, with some parts submerged or altered by tectonic activities. Notable features include the Narmada and Tapi rift valleys and the Satpura Block Mountains.
2. Residual mountains: These include the Aravali, Nallamala, Javadi, Veliconda, Palkonda, and Mahendragiri hills.
3. River valleys: Rivers in the Peninsular block have shallow valleys and low gradients, and many east-flowing rivers form deltas before entering the Bay of Bengal.

The Himalayas and Other Peninsular Mountains

The Himalayas, along with other Peninsular mountains, are characterized by their young, weak, and flexible geological structure, contrasting with the stable Peninsular Block. The continuous interplay of endogenic and exogenic forces has led to the formation of folds, faults, and thrust plains. This region is also dissected by fast-flowing rivers that create landforms such as gorges, V-shaped valleys, and waterfalls. Key features include:

1. Parallel Ranges: The Himalayas consist of a series of parallel ranges, with the Greater Himalayan range being the most prominent.
2. Mountain Orientation: In various parts of India, the Himalayas have different orientations, such as east-west in Darjiling and Sikkim, and north-south in Nagaland, Manipur, and Mizoram.
3. Length and Width: The Great Himalayan range spans 2,500 km and has a width of 160-400 km.

Indo-Ganga-Brahmaputra Plain

This geological division includes the plains formed by the Indus, Ganga, and Brahmaputra rivers. It originated from a geo-synclinal depression that developed during the third phase of the Himalayan mountain formation. These plains are now filled with alluvial deposits from both Himalayan and Peninsular rivers. Notable aspects include:

1. Alluvial Deposits: These plains have deposits ranging from 1,000 to 2,000 meters in depth.
2. Fluvial Features: The plains display mature fluvial landforms such as meanders, oxbow lakes, and braided channels.

Physiographic Divisions of India

India’s physiography reflects great diversity, with the northern part dominated by rugged mountain ranges, while the south features a stable tableland. Based on major physical variations, India is divided into six physiographic regions:

1. The Northern and Northeastern Mountains
2. The Northern Plain
3. The Peninsular Plateau
4. The Indian Desert
5. The Coastal Plains
6. The Islands

The Northern and Northeastern Mountains

The Northern and Northeastern Mountains consist of the Himalayas and Northeastern Hills. The Himalayan ranges form a physical, climatic, and drainage divide between the Indian subcontinent and Central and East Asia. Their significant features include:

1. Mountain Ranges: The Great Himalayas and Shiwaliks.
2. Orientation: These ranges generally run northwest-southeast, with variations in the Darjiling, Sikkim, and Arunachal Pradesh regions.

The Northern Plains

The Northern Plains extend 3,200 km from the east to the west and are formed by alluvial deposits brought by the Indus, Ganga, and Brahmaputra rivers. These plains consist of distinct zones:

1. Bhabar Zone: A narrow belt parallel to the Shiwaliks, where rivers deposit heavy materials.
2. Tarai Zone: A marshy belt where rivers re-emerge and flow without defined channels.
3. Alluvial Plains: Characterized by features such as sand bars, meanders, and oxbow lakes.

The Peninsular Plateau

The Peninsular Plateau is an irregular triangle, rising from the river plains to an elevation of 600-900 meters. It is one of the oldest and most stable landmasses in India. Major features include:

1. Western and Eastern Extent: Bordered by the Western Ghats in the west and the Eastern Ghats in the east.
2. Major Plateaus: The Hazaribagh, Palamu, Ranchi, Malwa, Coimbatore, and Karnataka plateaus form a significant part of this region.
3. Tectonic Activity: This region has undergone recurrent upliftment and crustal faulting, resulting in features like rift valleys and block mountains.

Important Note
The Peninsular Plateau showcases distinct physiographic features, such as tors, block mountains, and rift valleys, contributing to India’s diverse geography.

The Indian Desert

The Great Indian Desert lies to the northwest of the Aravalis. Characterized by its undulating topography, this desert is dotted with longitudinal dunes and barchans. Significant points include:

1. Low Rainfall: This region receives less than 150 mm of rainfall annually.
2. Physical Features: Wind actions have carved out mushroom rocks, shifting dunes, and oases.

The Coastal Plains

India’s long coastline can be divided into two broad sections:

1. Western Coastal Plains: These are submerged plains with natural ports like Cochin and Marmagao.
2. Eastern Coastal Plains: These are emergent coasts with well-developed deltas, such as the Mahanadi and Godavari deltas.

Important Note
The Kayals (backwaters) of the Malabar coast are unique to the western coast and serve as key sites for tourism and fishing activities.

The Islands

India has two major island groups:

1. Bay of Bengal Islands: These include the Andaman and Nicobar Islands, home to India’s only active volcano.
2. Arabian Sea Islands: The Lakshadweep Islands are built on coral deposits and consist of about 36 islands.

Important Note
The Andaman and Nicobar Islands experienced a devastating tsunami on December 26, 2004, highlighting the region’s vulnerability to natural calamities.

Physiographic Comparison Table

|
| Indian Desert | Arid, undulating region with longitudinal dunes and barchans | Low rainfall, episodic river systems |
| Coastal Plains | Submerged (western) and emergent (eastern) coasts with natural harbors and deltas | Ports, backwaters, and fertile deltas |
| Islands | Coral-based islands in the Arabian Sea and volcanic islands in the Bay of Bengal | Strategic maritime importance |

MCQ
Which waterbody separates the Andaman from the Nicobar Islands?
Answer: 10° Channel.