Quick Revision Notes: Class 11 Geography

Chapter: Structure and Physiography

Physiography: The physical structure, relief, and surface features of a landmass (भौगोलिक स्वरूप / भू-आकृति).
Relief: The differences in elevation or height of a land surface from place to place.
India's Diversity: India is a land of vast physical diversity with lofty mountains, deep valleys, extensive plains, plateaus, and a long coastline.

India can be divided into three major geological divisions based on its geological history:

The Peninsula Block:
- Composed of ancient gneisses and granites.
- Formed a part of the ancient supercontinent Gondwana Land.
- A stable shield that has undergone recurrent faulting and fracturing (e.g., Narmada and Tapti rift valleys).
The Himalayas and other Peninsular Mountains:
- Young, weak, and flexible fold mountains (नवीन वलित पर्वत).
- Formed by the tectonic collision of the Indian Plate with the Eurasian Plate.
- Still undergoing geological processes and prone to earthquakes.
Indo-Ganga-Brahmaputra Plain:
- A major geosynclinal depression (foredeep) formed in front of the Himalayas.
- Filled with sediments (alluvium) brought down by the rivers from the mountains over millions of years.

India is broadly divided into 6 major physiographic regions:

Structure: Parallel mountain ranges running from west-northwest to east-southeast direction (Arc shape, length ~2,400 km).
Major Ranges (North to South):
1. Greater Himalayas (Himadri): Continuous range, highest peaks (Mount Everest, Kanchenjunga), snow-covered throughout the year.
2. Lesser Himalayas (Himachal): Rugged terrain, famous hill stations (Shimla, Darjeeling), valleys like Kashmir and Kullu.
3. Outer Himalayas (Shivaliks): The southernmost foothill range, composed of unconsolidated sediments. Longitudinal valleys between Lesser Himalayas and Shivaliks are called Duns (e.g., Dehradun) and Duars in the east.
Regional Divisions (West to East): Kashmir Himalayas, Himachal Himalayas, Kumaon Himalayas, Darjeeling & Sikkim Himalayas, Arunachal Himalayas, and Eastern Hills/Purvanchal.

Formation: Formed by the depositional work of three major river systems: Indus, Ganga, and Brahmaputra.
Dimensions: ~3,200 km from east to west; average width 150–300 km; depth of alluvial deposits ranges from 1,000 to 2,000 m.
Relief / Belt-wise Division (North to South):
1. Bhabar: Narrow belt (8-16 km) parallel to the Shivalik foothills where rivers deposit heavy pebbles and boulders. Streams disappear underground.
2. Terai: Wet, swampy, and marshy region south of Bhabar where underground streams re-emerge. Rich in wildlife and dense forests.
3. Bhangar: Older alluvial plain forming terrace-like features above the flood plains. Often contains calcareous deposits locally known as Kankar.
4. Khadar: Newer, younger alluvial deposits of the flood plains. Flooded almost every year, making it extremely fertile for intensive agriculture.

Characteristics: Triangular in shape, composed of igneous and metamorphic rocks, highest elevation in the west sloping towards the east.
Major Sub-Divisions:
1. The Central Highlands: Bounded by the Aravalli range in the west and Satpura range in the south. Includes Malwa Plateau, Chotanagpur Plateau, and Bundelkhand/Baghelkhand.
2. The Deccan Plateau: Triangular landmass south of the Narmada river. Bordered by the Western Ghats (Sahyadri) in the west, Eastern Ghats in the east, and Satpura/Maikal ranges in the north.
3. The North-Eastern Plateau: An extension of the main peninsular plateau (Meghalaya Plateau and Karbi Anglong Plateau), separated by the Malda fault gap.

Location: Lies to the northwest of the Aravalli hills.
Features: An undulating sandy plain covered with sand dunes (Barchans), low rainfall (below 150 mm per year), arid climate, and sparse vegetation. Streams appear during the rainy season and disappear into the sand (Inland drainage). Luni is the only major river.

Divided into two parts based on the location relative to the Western and Eastern Ghats:

Western Coastal Plain: Narrow, rocky, and intervened by backwaters (Kayals in Kerala). Divided into Konkan (North), Kannada, and Malabar coast (South).
Eastern Coastal Plain: Broader and level plain formed by river deltas (Mahanadi, Godavari, Krishna, Kaveri). Divided into Northern Circars and Coromandel Coast (South).

India has two major island groups:

Andaman and Nicobar Islands: Located in the Bay of Bengal; volcanic and elevated portions of submarine mountains; separated by the Ten Degree Channel.
Lakshadweep Islands: Located in the Arabian Sea; entirely coral origin (Atolls); closest to the Malabar coast.

Talus / Scree: Rock debris accumulated at the foot of a mountain.
Dun: Longitudinal valleys found between the Lesser Himalayas and the Shivaliks.
Doab: The land lying between two converging rivers.
Kayals: Shallow lagoons or backwaters found on the Malabar coast used for fishing and inland navigation (e.g., Vembanad Lake).
Highest Peak in India: K2 (Godwin-Austen) in the Karakoram range (8,611 m) – Note: Kanchenjunga (8,586 m) is the highest peak in the Indian Himalayas.
Highest Peak of Peninsular India: Anamudi (2,695 m) in the Anaimalai Hills.