Structure and Physiography | Class 11 Geography Notes

Geological Structure of India

India’s geological structure forms the foundation for its diverse physiographic features. The country can be divided into three broad geological divisions based on rock formations and tectonic history: (i) The Peninsular Block, (ii) The Himalayas and other Peninsular Mountains, and (iii) The Indo-Ganga-Brahmaputra Plain. The Peninsular Block is an ancient, stable landmass composed mainly of crystalline and granitic rocks dating back to the Cambrian period and earlier. It extends from Kachchh in the west, along the Aravali range near Delhi, parallel to the Yamuna and Ganga rivers, up to the Rajmahal hills and the Ganga delta in the east. Extensions of this block include the Karbi Anglong and Meghalaya plateaus in the northeast and parts of Rajasthan in the west. The Peninsular Block has undergone vertical movements and block faulting, leading to features such as rift valleys (Narmada, Tapi, Mahanadi) and block mountains (Satpura range). The Himalayas and other Peninsular mountains, in contrast, are geologically young, weak, and flexible, formed by tectonic folding and faulting due to the ongoing collision of the Indian and Eurasian plates. These mountains are dissected by fast-flowing rivers, exhibiting youthful landforms like gorges, V-shaped valleys, rapids, and waterfalls. The Indo-Ganga-Brahmaputra Plain is a vast alluvial plain formed by sediments deposited in a geo-synclinal depression created during the Himalayan orogeny about 64 million years ago. The alluvial deposits here are very thick, ranging from 1000 to 2000 meters in depth. This geological diversity results in significant variations in relief and physiography across India.

📊 Diagram: Figure 2.1: A Gorge

🧪 Activity: Calculate and compare the gradient of Himalayan and Peninsular rivers using river profiles.

🔗 Connection: Prepares for detailed study of India’s physiographic divisions and their characteristics.