Class 11 Geography Notes Chapter 2 (Structure and physiography) – India Physical Environment Book

Detailed Notes with MCQs of Chapter 2: 'Structure and Physiography' from your 'India Physical Environment' textbook. This is a foundational chapter, crucial for understanding the physical landscape of India, and frequently tested in government exams. We need to grasp both the underlying geological structure and the resulting landforms.

Chapter 2: Structure and Physiography - Detailed Notes

Introduction:
India exhibits remarkable physical diversity owing to its varied geological structure and complex geomorphic processes operating over millions of years. The present structure and relief are a result of endogenic (internal) and exogenic (external) forces acting upon the landmass.

Part 1: Geological Structure

India's geological history is complex, involving the formation, drifting, and collision of tectonic plates. Based on geological history and structure, India can be broadly divided into three geological divisions:

1. The Peninsular Block:

   • Formation: Part of the ancient Gondwanaland. Formed primarily from Archaean gneisses and schists. It has remained a relatively stable block since the Cambrian period, experiencing block faulting and vertical movements, but largely unaffected by mountain-building folding like the Himalayas.
   • Extent: Roughly triangular shape, extending from the Aravalis in the northwest, Kutch in the west, Rajmahal hills in the east, and Kanyakumari in the south. Includes the Karbi-Anglong plateau and Meghalaya plateau (separated from the main block by the Malda fault).
   • Characteristics: Oldest and most stable landmass of India. Composed of ancient crystalline, igneous, and metamorphic rocks. Features include relict and residual mountains (Aravalis, Nallamala hills, Javadi hills, Velikonda hills, Palkonda range, Mahendragiri hills), broad and shallow valleys, and rounded hills. The Narmada and Tapi rivers flow through rift valleys, indicating faulting.
   • Significance: Rich in metallic minerals (iron ore, manganese, copper, bauxite) and non-metallic minerals (mica, limestone). Black soil (regur) formed from weathering of Deccan Traps lava is crucial for cotton cultivation.

2. The Himalayas and other Extra-Peninsular Mountains:

   • Formation: Geologically young, weak, and flexible structures formed due to the collision of the Indian Plate with the Eurasian Plate, starting around 40-50 million years ago (Tertiary period). The Tethys Sea sediments between the two plates were folded and uplifted.
   • Characteristics: Represent the loftiest and most rugged mountain barriers of the world. Tectonically active zone, prone to earthquakes and landslides. Composed mainly of sedimentary and metamorphic rocks. Features include high peaks, deep gorges, V-shaped valleys, rapids, waterfalls, and glaciers. Still rising in elevation.
   • Significance: Climatic barrier (monsoon, cold winds), source of perennial rivers (Indus, Ganga, Brahmaputra), rich biodiversity, potential for hydroelectric power, tourism.

3. Indo-Ganga-Brahmaputra Plain:

   • Formation: A large geosynclinal depression formed between the rising Himalayas in the north and the stable Peninsular Block in the south. Gradually filled with sediments (alluvium) brought down by the Indus, Ganga, Brahmaputra, and their tributaries. Deposition started after the Himalayan uplift.
   • Characteristics: Geologically the youngest unit. Featureless plain (monotonous relief) with very low gradient. Deep alluvial deposits (thickness varies, exceeding 1000-2000m in places). Fertile alluvial soils.
   • Significance: Agriculturally the most productive region of India (food basket). Densely populated. Supports a vast network of transportation and communication.

Major Rock Systems of India (Chronological Order - Important for Exams):

• Archaean System: Oldest rocks, form the basement complex. Gneisses (Bundelkhand Gneiss) and Schists. Devoid of fossils. Rich in metallic minerals (iron, manganese, copper, gold). Found extensively in the Peninsula.
• Dharwar System: Oldest metamorphosed sedimentary rocks. Formed by erosion and sedimentation of Archaean rocks. Named after the Dharwar district of Karnataka. Highly metalliferous (iron ore, manganese, gold, copper, lead, zinc). Found in Karnataka, Chotanagpur, Aravalis.
• Cuddapah System: Unfossiliferous sedimentary rocks (shales, limestones, quartzites). Named after the Cuddapah district of Andhra Pradesh. Rich in building materials (limestone, sandstone) and some low-grade iron and manganese ores. Found in Andhra Pradesh, Chhattisgarh, Rajasthan.
• Vindhyan System: Largely unfossiliferous sedimentary rocks overlying the Cuddapah system. Famous for building materials like red sandstone, limestone, diamonds (Panna mines). Found in the Vindhyan range area (MP, UP, Bihar, Rajasthan). Separates North India from South India geologically.
• Gondwana System: Formed during the Carboniferous period. Sedimentary rocks containing fossils (flora and fauna). Crucially important as they contain nearly 98% of India's coal reserves (bituminous coal). Found mainly in river valleys (Damodar, Mahanadi, Godavari).
• Deccan Traps: Volcanic basaltic lava flows during the Cretaceous period, covering a vast area of the Peninsular plateau (Maharashtra, Gujarat, MP). Weathering leads to fertile black soil (regur).
• Tertiary System: Rocks formed during the Himalayan uplift (Eocene to Pliocene). Important for petroleum reserves (Assam, Gujarat, Mumbai High). Lignite coal found in Tamil Nadu, Rajasthan.
• Quaternary System: Recent deposits. Pleistocene (older alluvium - Bhangar, Karewas of Kashmir) and Holocene (newer alluvium - Khadar, deltaic deposits, coastal sediments). Most fertile soils.

Part 2: Physiography

Based on structure, relief, and geomorphic processes, India is divided into the following physiographic divisions:

1. The Northern and North-eastern Mountains (The Himalayas):

   • Orientation: Arc shape, running West-East from Indus to Brahmaputra. Also North-South alignment in Arunachal Pradesh and North-eastern states.
   • Sub-divisions (North to South):
     • Trans-Himalayas: (Mainly in Tibet/POK) Karakoram, Ladakh, Zanskar ranges. K2 (Godwin Austen) is in Karakoram.
     • Greater Himalayas (Himadri): Highest and most continuous range. Average height ~6000m. Core composed of granite. Contains highest peaks (Everest, Kanchenjunga, Nanga Parbat, Nanda Devi). Source of glaciers (Gangotri, Yamunotri). Asymmetrical folds.
     • Lesser Himalayas (Himachal): South of Himadri. Average height 3700-4500m. Width ~50km. Composed of highly compressed and altered rocks. Important ranges: Pir Panjal (longest), Dhaula Dhar, Mahabharat. Famous valleys: Kashmir, Kangra, Kullu. Known for hill stations (Shimla, Mussoorie, Nainital).
     • Outer Himalayas (Shiwaliks): Outermost range. Average height 900-1100m. Width 10-50km. Composed of unconsolidated sediments brought by rivers from Himadri/Himachal. Prone to erosion and landslides. Longitudinal valleys between Himachal and Shiwaliks are called 'Duns' (e.g., Dehra Dun, Kotli Dun, Patli Dun).
   • Longitudinal Divisions (West to East - based on river valleys):
     • Punjab Himalayas: Between Indus and Satluj rivers. (Includes Kashmir and Himachal Himalayas).
     • Kumaon Himalayas: Between Satluj and Kali rivers. Nanda Devi is the highest peak.
     • Nepal Himalayas: Between Kali and Tista rivers. Tallest section, includes Mt. Everest.
     • Assam Himalayas: Between Tista and Dihang (Brahmaputra) rivers.
   • The Eastern Hills (Purvanchal): Southward extension of Himalayas beyond the Dihang gorge. Run North-South along India's eastern boundary. Composed mainly of strong sandstones (sedimentary). Covered with dense forests. Include Patkai Bum, Naga Hills, Manipur Hills, Mizo (Lushai) Hills.

2. The Northern Plain:

   • Formation: Alluvial deposits of Indus, Ganga, and Brahmaputra rivers.
   • Extent: Spreads over 7 lakh sq. km. Length ~2400 km, Width 240-320 km.
   • Sub-divisions (based on relief features - North to South):
     • Bhabar: Narrow belt (8-16 km) parallel to Shiwalik foothills. Porous zone with pebbles and boulders where streams disappear underground. Not suitable for agriculture.
     • Terai: South of Bhabar (15-30 km wide). Streams re-emerge here. Marshy, swampy region with thick forests and wildlife. Being reclaimed for agriculture. Dudhwa National Park is here.
     • Bhangar: Largest part of the plain. Composed of older alluvium. Lies above flood levels. Less fertile than Khadar. Contains calcareous concretions called 'Kankar'.
     • Khadar: Newer, younger floodplain deposits. Renewed annually by floods. Very fertile, ideal for intensive agriculture.
   • Regional Divisions (West to East):
     • Punjab Plains: Formed by Indus and its tributaries (Jhelum, Chenab, Ravi, Beas, Satluj). Dominated by 'Doabs' (land between two rivers). Mostly in Pakistan now.
     • Ganga Plains: Extends between Ghaggar and Tista rivers. Covers Haryana, Delhi, UP, Bihar, parts of Jharkhand, West Bengal. Sub-divided into Upper, Middle, and Lower Ganga Plains.
     • Brahmaputra Plains: Mainly in Assam. Known for riverine islands (Majuli - largest inhabited riverine island) and braided river channels. Prone to floods.

3. The Peninsular Plateau:

   • Formation: Oldest landmass, part of Gondwanaland. Composed of old crystalline, igneous, and metamorphic rocks.
   • Features: Tableland, broad shallow valleys, rounded hills. Tilted generally towards the east.
   • Major Divisions:
     • The Central Highlands: North of Narmada river. Bounded by Aravalis (NW), Vindhyan range (S), Satpura range (S). Includes:
       • Malwa Plateau: West-central part, drained by Chambal, Sind, Betwa, Ken (flow SW to NE, indicating slope).
       • Bundelkhand & Baghelkhand: Eastward extensions.
       • Chotanagpur Plateau: Further east, drained by Damodar river. Rich mineral resource base ('Ruhr of India'). Includes Ranchi, Hazaribagh, Kodarma plateaus. Rajmahal hills form the eastern edge.
     • The Deccan Plateau: Triangular landmass south of Narmada river. Bounded by Satpura range (N), Western Ghats (W), Eastern Ghats (E). Includes:
       • Deccan Traps: NW part, black soil region.
       • Western Ghats (Sahyadris): Continuous range parallel to the west coast. Higher than Eastern Ghats (Avg. 900-1600m). Orographic rainfall source. Highest peaks: Anai Mudi (2695m, Anaimalai Hills), Doda Betta (2637m, Nilgiri Hills). Important passes: Thal Ghat, Bhor Ghat, Pal Ghat.
       • Eastern Ghats: Discontinuous and lower range (Avg. 600m) parallel to the east coast. Eroded by rivers like Mahanadi, Godavari, Krishna, Kaveri. Highest peak: Mahendragiri (1501m), though some sources cite Jindhagada Peak as higher. Nilgiri Hills mark the junction of Western and Eastern Ghats.
       • North-East Extension: Meghalaya Plateau (Shillong Plateau) and Karbi-Anglong Plateau. Separated by Malda Fault. Rich in coal, iron ore, limestone. Garo, Khasi, Jaintia hills are part of Meghalaya Plateau (named after tribes).

4. The Indian Desert (Thar Desert):

   • Location: Northwest India, west of Aravali Hills. Mostly in Rajasthan, extends into Pakistan.
   • Features: Arid climate (rainfall < 150mm/year). Sandy plain with dunes. Vegetation is scarce (xerophytic). Streams appear only during rainy season and disappear into sand. Luni is the only large river. Saline lakes (Sambhar, Didwana). Barchans (crescent-shaped dunes) are prominent, longitudinal dunes common near Indo-Pak border. Believed to be submerged under sea during Mesozoic era.

5. The Coastal Plains:

   • Location: Flanking the Peninsular Plateau on the west and east.
   • Western Coastal Plain: Between Western Ghats and Arabian Sea. Narrow plain. Submerged coast (except south). Good natural harbours (Mumbai, Marmagao). Sub-divisions (North to South):
     • Kachchh & Kathiawar Coast (Gujarat)
     • Konkan Coast (Maharashtra, Goa)
     • Kannada/Kanara Coast (Karnataka)
     • Malabar Coast (Kerala) - known for 'Kayals' (lagoons/backwaters, e.g., Vembanad lake). Estuaries common.
   • Eastern Coastal Plain: Between Eastern Ghats and Bay of Bengal. Wider and more level than western plain. Emergent coast. Less natural harbours. Large deltas formed by Mahanadi, Godavari, Krishna, Kaveri. Sub-divisions (North to South):
     • Utkal Coast (Odisha) - Chilika Lake (largest saltwater lagoon in India) is located here.
     • Andhra Coast/Northern Circars (Andhra Pradesh) - Kolleru Lake.
     • Coromandel Coast (Tamil Nadu). Deltas are prominent.

6. The Islands:

   • Lakshadweep Islands: In the Arabian Sea. Group of 36 islands (approx.). Close to Malabar coast. Composed of coral deposits (atolls). Kavaratti is the administrative headquarters. Pitti island has a bird sanctuary (uninhabited). Total area ~32 sq km.
   • Andaman and Nicobar Islands: In the Bay of Bengal. Larger group, more numerous and scattered. Believed to be an elevated portion of submarine mountains (extension of Arakan Yoma). Divided by Ten Degree Channel (Andaman-N, Nicobar-S). Port Blair is the capital (South Andaman). Barren Island (India's only active volcano) is here. Narcondam is a dormant volcanic island. Important peaks: Saddle Peak (North Andaman), Mount Thuillier (Great Nicobar). Close to the equator, experience equatorial climate, thick forest cover. Strategic importance.

Practice MCQs for Exam Preparation:

1. Which of the following geological divisions of India is considered the oldest and most stable landmass?
   (a) The Himalayas
   (b) The Indo-Ganga-Brahmaputra Plain
   (c) The Peninsular Block
   (d) The Coastal Plains

2. The famous valleys of Kashmir, Kangra, and Kullu are located in which part of the Himalayas?
   (a) Greater Himalayas (Himadri)
   (b) Lesser Himalayas (Himachal)
   (c) Outer Himalayas (Shiwaliks)
   (d) Trans-Himalayas

3. 'Karewas', known for saffron cultivation, are glacial deposits found in:
   (a) Kumaon Himalayas
   (b) Assam Himalayas
   (c) Kashmir Himalayas
   (d) Nepal Himalayas

4. The Malda Fault separates the Meghalaya Plateau from which larger physiographic unit?
   (a) The Northern Plains
   (b) The Chotanagpur Plateau (part of Peninsular Block)
   (c) The Eastern Ghats
   (d) The Purvanchal Hills

5. Which soil type, ideal for cotton cultivation, is predominantly found in the Deccan Traps region?
   (a) Alluvial Soil
   (b) Laterite Soil
   (c) Red Soil
   (d) Black Soil (Regur)

6. The longitudinal valleys lying between the Lesser Himalayas and the Shiwaliks are known as:
   (a) Duns
   (b) Duars
   (c) Kayals
   (d) Bhabar

7. Which of the following rock systems contains almost 98% of India's coal reserves?
   (a) Dharwar System
   (b) Cuddapah System
   (c) Vindhyan System
   (d) Gondwana System

8. Anai Mudi, the highest peak of Peninsular India, is located in the:
   (a) Nilgiri Hills
   (b) Cardamom Hills
   (c) Anaimalai Hills
   (d) Palani Hills

9. The Lakshadweep Islands are primarily of which origin?
   (a) Volcanic Origin
   (b) Tectonic Uplift
   (c) Coral Origin
   (d) Depositional Landforms

10. Which of the following represents the correct sequence of the Northern Plain belts from North to South, parallel to the Himalayan foothills?
    (a) Terai, Bhabar, Khadar, Bhangar
    (b) Bhabar, Terai, Bhangar, Khadar
    (c) Bhangar, Khadar, Bhabar, Terai
    (d) Khadar, Bhangar, Terai, Bhabar

Answer Key:

1. (c)
2. (b)
3. (c)
4. (b)
5. (d)
6. (a)
7. (d)
8. (c)
9. (c)
10. (b)

Make sure you revise these notes thoroughly. Pay attention to the specific terminology, locations, formation processes, and significance of each feature. Understanding the link between the geological structure and the resulting landforms is key. Good luck with your preparation!