Book: India: Physical Environment | Chapter 2
Structure and Physiography
1. Learning Objectives
After reading these notes, you will be able to:
1
Understand the geological history of India and how its landforms were formed over millions of years.2
Know the three geological divisions of India — Peninsular Block, Himalayas, and Indo-Ganga-Brahmaputra Plain.3
Describe the six physiographic divisions of India and their key features.4
Understand the Northern Plains, their zones (Bhabar, Tarai, Bhangar, Khadar), and the Peninsular Plateau divisions.5
Know about the Indian Desert, Coastal Plains, and the two island groups of India.2. Introduction
The earth and its landforms have evolved over a very long time. The earth is approximately 4,600 million years old. It has undergone many changes due to endogenic forces (forces from inside the earth) and exogenic forces (forces from outside). The Indian plate was once south of the equator and was much larger. Over millions of years it broke apart — the Australian plate moved southeast and the Indian plate moved northward. This northward movement is still continuing and has shaped India’s physical environment.
- The interplay of endogenic and exogenic forces + lateral plate movements gave India its present geological structure and geomorphological features.
- Based on geological structure, India is divided into three geological divisions:
→ (i) The Peninsular Block
→ (ii) The Himalayas and other Peninsular Mountains
→ (iii) Indo-Ganga-Brahmaputra Plain
3. Geological Divisions of India
🟤 The Peninsular Block
- Northern boundary: irregular line from Kachchh → Aravali range near Delhi → Yamuna → Ganga → Rajmahal Hills → Ganga delta.
- Extensions: Karbi Anglong and Meghalaya Plateau (northeast); Rajasthan (west).
- Formed by very ancient gneisses and granites — one of the oldest landmasses of India.
- Since the Cambrian period, it has stood like a rigid block. Part of the Indo-Australian Plate.
- Has undergone block faulting — rift valleys of Narmada, Tapi, Mahanadi and the Satpura block are examples.
- Mostly consists of relict and residual mountains: Aravali, Nallamala, Javadi, Veliconda, Palkonda, Mahendragiri hills.
- River valleys here are shallow with low gradients. East-flowing rivers form deltas — Mahanadi, Krishna, Kaveri, Godavari.
🏔️ The Himalayas and other Peninsular Mountains
- These are young, weak and flexible in geological structure — unlike the rigid Peninsular Block.
- Still subject to endogenic and exogenic forces → development of faults, folds and thrust plains.
- Tectonic in origin — dissected by fast-flowing rivers in their youthful stage.
- Landforms: gorges, V-shaped valleys, rapids, waterfalls — all indicate the youthful stage.
🌊 Indo-Ganga-Brahmaputra Plain
- Formed by the plains of rivers Indus, Ganga, and Brahmaputra.
- Was originally a geo-synclinal depression — developed maximum ~64 million years ago during third phase of Himalayan formation.
- Since then, gradually filled by sediments from Himalayan and Peninsular rivers.
- Average depth of alluvial deposits: 1,000–2,000 m.
4. Physiography
Physiography of an area is the outcome of structure, process, and the stage of development. India has great physical diversity — rugged mountains in the north, stable table land in the south, and vast plains in between.
🗺️ Mind Map — 6 Physiographic Divisions of India
Physiographic Divisions of India🏔️ 1. Northern & North-eastern MountainsHimalayas + NE Hills
🌾 2. The Northern PlainIndus-Ganga-Brahmaputra
🪨 3. Peninsular PlateauDeccan, Central Highlands, NE Plateau
🏜️ 4. The Indian DesertThar / Marusthali
🌊 5. The Coastal PlainsWestern & Eastern coast
🏝️ 6. The IslandsAndaman & Nicobar, Lakshadweep
5. The North and Northeastern Mountains
- Consists of the Himalayas and the Northeastern hills.
- Himalayas = series of parallel mountain ranges. Important ranges: Greater Himalayan range (includes Great Himalayas and Shiwalik).
- Length of Great Himalayan (central axial) range: ~2,500 km east to west. Width: 160–400 km north to south.
- Orientation varies by region:
→ NW India: northwest to southeast
→ Darjiling & Sikkim: east–west
→ Arunachal Pradesh: southwest to northwest
→ Nagaland, Manipur, Mizoram: north–south - Himalayas act as a climatic, drainage, and cultural divide — not just a physical barrier.
6. The Northern Plains
- Formed by alluvial deposits of Indus, Ganga, and Brahmaputra rivers.
- Length: ~3,200 km (east to west). Width: 150–300 km. Alluvium depth: 1,000–2,000 m.
- General elevation: 50–150 m above mean sea level.
- Fertile alluvial soil supports crops: wheat, rice, sugarcane, jute → densely populated region.
- Haryana and Delhi form a water divide between the Indus and the Ganga river systems.
- Brahmaputra flows NE to SW → takes a sharp 90° southward turn at Dhubri before entering Bangladesh.
- Famous delta: Sunderbans delta — one of the largest deltas in the world.
📌 Four Zones of the Northern Plains (North to South)
1. Bhabar
Narrow belt 8–10 km parallel to Shiwalik foothills. Rivers deposit boulders & disappear underground.
2. Tarai
Width 10–20 km. Streams re-emerge → marshy, swampy. Dense forest, varied wildlife.
3. Bhangar
Old alluvial deposits — older, higher areas. Mature fluvial landforms like meanders, ox-bow lakes.
4. Khadar
New alluvial deposits — younger, fertile. Renewed every year by flood deposition.
7. The Peninsular Plateau
- Elevation: 150 m above river plains to 600–900 m. Irregular triangle shape.
- Outer extent: Delhi ridge (NW), Rajmahal hills (east), Gir range (west), Cardamom hills (south).
- Extension in northeast: Shillong and Karbi-Anglong plateau.
- One of the oldest and most stable landmasses of India.
- General elevation: west to east (proved by river flow direction).
- Important features: tors, block mountains, rift valleys, spurs, quartzite dykes.
- NW part has black soil. Famous ravines: Chambal, Bhind, Morena.
📌 Three Divisions of the Peninsular Plateau
🟢 (i) The Deccan Plateau
- Bordered by Western Ghats (west), Eastern Ghats (east), Satpura + Maikal + Mahadeo hills (north)
- Western Ghats local names: Sahyadri (Maharashtra), Nilgiri hills (Karnataka/TN), Anaimalai & Cardamom hills (Kerala)
- Western Ghats avg elevation: ~1,500 m. Highest peak: Anaimudi (2,695 m) on Anaimalai hills
- Second highest: Dodabetta (2,637 m) on Nilgiri hills
- Eastern and Western Ghats meet at Nilgiri hills
- Eastern Ghats are discontinuous, low, and highly eroded
🟠 (ii) The Central Highlands
- Bounded by Aravali range in the west
- Elevation: 700–1,000 m; slopes towards north and northeast
- Satpura range — classic example of relict mountains (600–900 m)
- Most Yamuna tributaries originate from Vindhyan and Kaimur ranges
- Extension: Rajmahal hills (east); rich mineral region → Chotanagpur plateau
- Near Jaisalmer: covered by longitudinal sand ridges and barchans (crescent-shaped sand dunes)
🟣 (iii) The Northeastern Plateau
- Extension of the main Peninsular Block — separated due to fault between Rajmahal hills and Meghalaya plateau
- Meghalaya plateau sub-divided into: (i) Garo Hills (ii) Khasi Hills (iii) Jaintia Hills
- Extension also seen in Karbi Anglong hills, Assam
- Rich in minerals: coal, iron ore, sillimanite, limestone, uranium
- Receives heavy SW monsoon rainfall → highly eroded surface
- Cherrapunji — bare rocky surface, devoid of permanent vegetation
8. The Indian Desert
- Located to the northwest of the Aravali hills. Also called Marusthali or Thar Desert.
- Landforms: undulating topography, longitudinal dunes, barchans (crescent-shaped sand dunes).
- Rainfall: less than 150 mm/year → arid climate, sparse vegetation.
- Believed to have been under the sea during the Mesozoic era — evidence: wood fossils at Aakal, marine deposits near Brahmsar, Jaisalmer (wood-fossils ~180 million years old).
- Desert features: mushroom rocks, shifting dunes, oasis (mostly southern part).
- Orientation: northern part slopes towards Sindh, southern towards Rann of Kachchh.
- Most rivers are ephemeral. Luni river (in southern part) is significant.
- Low precipitation + high evaporation = water deficit region. Streams disappear → inland drainage, lakes and playas with brackish water (source of salt).
9. The Coastal Plains
🔵 Western Coastal Plains
- Example of submerged coastal plain → narrow belt
- Extends from Gujarat coast (north) to Kerala coast (south)
- Divisions: Kachchh & Kathiawar (Gujarat) · Konkan (Maharashtra) · Goan coast · Malabar coast (Karnataka & Kerala)
- Narrow in middle, broader towards north and south
- No delta formation — rivers flow directly into sea
- Malabar coast: Kayals (backwaters) — used for fishing, inland navigation, tourism
- Famous: Nehru Trophy Vallamkali (boat race) at Punnamada Kayal, Kerala
- Important ports: Kandla, Mazagaon, JLN Port Navha Sheva, Marmagao, Mangalore, Cochin
🟢 Eastern Coastal Plains
- Example of emergent coast → broader than western coast
- Well-developed deltas formed by Mahanadi, Godavari, Krishna, Kaveri
- Emergent nature → fewer ports and harbours
- Continental shelf extends up to 500 km into the sea → difficult to develop ports
⚖️ Key Difference: Western vs Eastern Coast
Western coast = Submerged → Narrow → Natural ports · No deltasEastern coast = Emergent → Broader → Deltas formed · Fewer ports
10. The Islands
🔵 Andaman & Nicobar Islands (Bay of Bengal)
- About 572 islands/islets
- Located between 6°N–14°N and 92°E–94°E
- Two principal groups: Ritchie’s archipelago and Labrynth island
- Divided into: Andaman (north) and Nicobar (south)
- Separated by Ten Degree Channel
- Believed to be elevated submarine mountains; some smaller islands are volcanic in origin
- Barren Island — only active volcano in India
- Important peaks: Saddle Peak (738 m), Mt. Diavolo (515 m), Mt. Koyob (460 m), Mt. Thuiller (642 m)
- Coral deposits, beautiful beaches; equatorial type vegetation
- Receive convectional rainfall
🟢 Lakshadweep Islands (Arabian Sea)
- Include Lakshadweep and Minicoy
- Located between 8°N–12°N and 71°E–74°E
- Distance: 220–440 km off Kerala coast
- Entire group built of coral deposits
- ~36 islands, of which 11 are inhabited
- Largest island: Minicoy (453 sq. km)
- Divided by Nine Degree Channel — Amini Island (north) and Canannore Island (south)
- Storm beaches on eastern seaboard: pebbles, shingles, cobbles, boulders
📌 Key Fact
On 26 December 2004, the Andaman and Nicobar Islands were devastated by a Tsunami (triggered by a massive undersea earthquake in the Indian Ocean).Summary — Quick Revision
1
Earth = ~4,600 million years old. Indian plate moved northward → still moving → shapes India’s landforms.
2
Three geological divisions: Peninsular Block (oldest, rigid), Himalayas (young, flexible), Indo-Ganga-Brahmaputra Plain (alluvial).
3
Six physiographic divisions: Northern Mountains · Northern Plains · Peninsular Plateau · Indian Desert · Coastal Plains · Islands.
4
Himalayas: length ~2,500 km, width 160–400 km. Act as physical, climatic, drainage and cultural divide.
5
Northern Plains: 3,200 km long, 4 zones — Bhabar → Tarai → Bhangar → Khadar from north to south.
6
Peninsular Plateau has 3 divisions: Deccan Plateau (Anaimudi 2,695 m is highest peak), Central Highlands, Northeastern Plateau (Meghalaya, Karbi Anglong).
7
Indian Desert (Marusthali): rainfall < 150 mm/year. Features: barchans, mushroom rocks, shifting dunes. Luni is the significant river here.
8
Western coast = submerged, narrow, natural ports, Kayals. Eastern coast = emergent, broader, large deltas.
9
Andaman & Nicobar (~572 islands, Bay of Bengal) separated by Ten Degree Channel. Barren Island = only active volcano in India.
10
Lakshadweep (~36 islands, Arabian Sea) = entirely coral deposits. Largest island = Minicoy (453 sq. km). Divided by Nine Degree Channel.
Important Terms to Remember
- Endogenic Forces: Forces originating from inside the earth (e.g., earthquakes, volcanic activity, plate movement).
- Exogenic Forces: Forces originating from outside the earth (e.g., weathering, erosion by rivers, wind, ice).
- Physiography: The study of the physical features (landforms) of an area — outcome of structure, process and stage of development.
- Geo-synclinal Depression: A long, narrow depression in the earth’s crust where sediments accumulate over millions of years. The Indo-Gangetic Plain was originally this.
- Bhabar: Narrow 8–10 km belt below Shiwalik foothills where rivers deposit boulders and disappear underground.
- Tarai: 10–20 km belt south of Bhabar where rivers re-emerge, creating marshy swampy conditions with dense forest and wildlife.
- Bhangar: Old alluvial deposits in the Northern Plains — older, higher areas.
- Khadar: New alluvial deposits in the Northern Plains — younger, more fertile areas near rivers.
- Barchan: A crescent-shaped sand dune found in deserts.
- Marusthali: Another name for the Thar Desert (Great Indian Desert).
- Kayals: Backwaters (lagoons) along the Malabar coast of Kerala, used for fishing, inland navigation and tourism.
- Ten Degree Channel: Water body separating the Andaman Islands from the Nicobar Islands.
- Nine Degree Channel: Water body dividing the Lakshadweep island group into Amini Island (north) and Canannore Island (south).
- Barren Island: Located in Andaman & Nicobar Islands — the only active volcano in India.
- Anaimudi: Highest peak (2,695 m) of the Peninsular Plateau — located on Anaimalai hills (Western Ghats).