Module 53. Geology and Physical Geography of India

India’s geology and physical geography are the result of millions of years of tectonic activity, climatic changes, and erosional processes that have shaped a land of immense diversity. From the towering Himalayas in the north to the coastal plains of the peninsula, India’s landscape reflects a wide range of geological structures, physiographic regions, and natural resources that have profoundly influenced its history, ecology, and human settlements.

Geological Structure of India

The geological formation of India is primarily divided into three broad units based on age and structure: the Peninsular Block, the Extra-Peninsular or Himalayan Region, and the Indo-Gangetic Plain.

1. The Peninsular Block:The Peninsular region, often termed the “old landmass of India,” is the most stable and ancient part of the country. It is composed largely of Precambrian rocks, some dating back over 3.5 billion years. The major geological divisions within this region include:
   • The Archaean Crystalline Complex: Found in regions such as Karnataka, Tamil Nadu, and parts of Jharkhand and Odisha, comprising granite, gneiss, and schist formations.
   • The Dharwar System: Noted for its mineral wealth, especially iron, manganese, gold, and mica; prominent in Karnataka and Andhra Pradesh.
   • The Cuddapah and Vindhyan Systems: Represent Proterozoic sedimentary basins found in Andhra Pradesh, Madhya Pradesh, and Rajasthan, hosting limestone, sandstone, and shale formations.

   The Deccan Plateau, forming the bulk of the Peninsular Block, is of volcanic origin, composed of extensive basaltic lava flows known as the Deccan Traps. These were formed by immense volcanic eruptions around 66 million years ago during the Cretaceous-Palaeogene period.

2. The Extra-Peninsular or Himalayan Region:The Himalayas are young fold mountains, formed by the collision of the Indian Plate with the Eurasian Plate about 50 million years ago. The resulting orogenic activity created a series of parallel ranges:
   • The Greater Himalayas (Himadri), containing the highest peaks such as Mount Everest (Sagarmatha) and Kanchenjunga.
   • The Lesser Himalayas (Himachal), characterised by folded sedimentary and metamorphic rocks.
   • The Siwalik Range, consisting mainly of unconsolidated sediments derived from the erosion of the upper ranges.

   The Himalayas are geologically active, with ongoing uplift and frequent seismic activity, particularly along the Main Central Thrust (MCT) and Main Boundary Fault (MBF).

3. The Indo-Gangetic Plain:This alluvial plain, lying between the Peninsular Block and the Himalayas, was formed by the deposition of sediments brought down by the Ganga, Brahmaputra, and Indus river systems. It represents one of the most fertile and densely populated regions in the world, consisting of recent and sub-recent alluvium.

Physiographic Divisions of India

India can be broadly divided into six major physiographic regions, each with distinct relief and geological characteristics:

1. The Northern and Northeastern Mountains:This region includes the Himalayas and the Purvanchal Hills. The Himalayas act as a climatic barrier, intercepting monsoon winds and influencing weather patterns. The Purvanchal Hills in the northeast are the continuation of the Himalayan ranges through Nagaland, Manipur, Mizoram, and Tripura, composed mainly of folded sedimentary rocks.
2. The Northern Plains:Stretching from Punjab in the west to Assam in the east, the Northern Plains are primarily formed by the alluvial deposits of the Indus, Ganga, and Brahmaputra rivers. The plain is subdivided into:
   • The Bhabar and Terai belts near the Himalayan foothills.
   • The Bangar (older alluvium) and Khadar (newer alluvium) zones further south.
3. The Peninsular Plateau:The plateau is divided into several distinct units:
   • The Central Highlands, including the Malwa Plateau and Bundelkhand uplands.
   • The Deccan Plateau, bounded by the Western and Eastern Ghats.
   • The Chota Nagpur Plateau, rich in minerals like coal, iron, and mica.This region exhibits a radial drainage pattern, particularly from the Western Ghats.
4. The Indian Desert:Known as the Thar Desert, it lies mainly in western Rajasthan and is characterised by sandy plains, dunes, and sparse vegetation. The desert experiences scanty rainfall (below 150 mm annually) and high diurnal temperature variation.
5. The Coastal Plains:India’s coastline extends over 7,500 kilometres, divided into:
   • The Western Coastal Plain, narrow and divided into the Konkan, Kannad, and Malabar coasts.
   • The Eastern Coastal Plain, broader and containing the deltas of the Mahanadi, Godavari, Krishna, and Kaveri rivers.
6. The Islands:India possesses two major island groups:
   • The Andaman and Nicobar Islands in the Bay of Bengal, of volcanic origin and part of the submerged mountain chain extending from Myanmar.
   • The Lakshadweep Islands in the Arabian Sea, formed from coral deposits.

Geological Evolution and Plate Tectonics

India’s geological evolution is closely linked to plate tectonic movements. About 200 million years ago, India was part of the supercontinent Gondwanaland along with Africa, Australia, and Antarctica. Following the breakup of Gondwanaland, the Indian Plate drifted northwards and collided with the Eurasian Plate, giving rise to the Himalayas and the Tibetan Plateau.
This tectonic history explains:

• The presence of Gondwana sedimentary rocks in central India, rich in coal deposits.
• The seismic activity across the Himalayan belt.
• The depositional plains formed by Himalayan rivers due to ongoing uplift and erosion.

Drainage Systems and River Patterns

India’s drainage system is broadly categorised into Himalayan Rivers and Peninsular Rivers.

• Himalayan Rivers (e.g., Ganga, Indus, Brahmaputra) are perennial, fed by glaciers and rainfall, exhibiting a meandering course and large catchment areas.
• Peninsular Rivers (e.g., Godavari, Krishna, Narmada, Tapi) are mostly rain-fed, flowing through hard rock terrain, showing seasonal variations in discharge.

The Narmada and Tapi rivers are notable exceptions as they flow westward, forming estuaries, unlike the east-flowing rivers which form deltas.

Natural Resources and Geological Significance

India’s geological formations are rich in mineral resources. The Chota Nagpur Plateau and Dharwar regions hold significant reserves of iron ore, coal, mica, manganese, and bauxite. The sedimentary basins of Assam, Gujarat, and the western coast are known for petroleum and natural gas deposits. The Deccan Traps also play an important role in soil formation, leading to the development of fertile black cotton soil (regur) in Maharashtra and Madhya Pradesh.

Climatic and Environmental Implications

The diverse physiography of India contributes to the variety of climatic zones, ranging from the alpine conditions of the Himalayas to the arid deserts of Rajasthan and tropical rainforests of the Western Ghats. This geographical diversity influences India’s biodiversity, agriculture, and water resources, making it one of the most ecologically varied regions in the world.
The continued tectonic movements and climatic fluctuations pose challenges such as earthquakes, landslides, and soil erosion, particularly in seismically active and mountainous regions.