🌍 Class 11 Geography – Chapter 2
Structure and Geomorphology
🟢 Introduction (Earth)
- 🌎 The Earth is about 460 million years old.
- During this long span, many changes took place on the earth’s surface due to internal (endogenic) and external (exogenic) forces.
- The Indian subcontinent was once a part of Gondwana land.
- Millions of years ago, the Indian Plate was located south of the equator and was very large.
- Later, this plate broke into pieces:
- The Australian Plate moved towards the southeast.
- The Indian Plate moved towards the north.
🟠 Geological Divisions of India
On the basis of geological structure and rock groups, India is divided into three divisions:
- 🏞️ Peninsular Section
- 🏔️ Himalayas and other extra-peninsular mountain ranges
- 🌾 Indus–Ganga–Brahmaputra Plain
🔵 1. Peninsular Section
- The northern boundary of the Peninsular region runs:
- From Kutch → west of Aravalli Hills → Delhi → parallel to Yamuna & Ganga → Rajmahal Hills → Ganga delta.
- Composed mainly of ancient gneiss and granite.
- Has remained a rigid block since the Cambrian era.
✨ Features of the Peninsular Plateau
- Triangular-shaped plateau.
- Boundaries: Delhi–Cuttack (NW), Rajmahal Hills (East), Gir Hills (West), Cardamom Hills (South).
- Includes Shillong & Karbi-Anglong Plateau in the northeast.
- Oldest part of Earth’s crust.
- Average height: 600–900 m.
- Important hills:
- Aravalli (NW), Vindhya & Satpura (Central), Western Ghats & Eastern Ghats (Coastal).
- General slope: West → East.
- Northern slope: towards the north.
- Being the front of the Indo-Australian Plate, affected by vertical movements and faults.
- Examples: Fault valleys of Narmada, Tapi, Mahanadi and Block mountains of Satpura.
🔴 2. Himalayas and Other Extra-Peninsular Ranges
- Young, weak, and flexible compared to rigid Peninsular section.
- Still affected by endogenic and exogenic forces.
- Show features like:
- Folds, thrusts, faults.
- Gorges, V-shaped valleys, cliffs, waterfalls (due to river erosion).
- These mountains are still in their youthful stage.
Origin: Tectonic movements.
Structure and Geomorphology (Part – II)
🟢 3. Indus–Ganga–Brahmaputra Plain
- The third geological section of India is the plain of the Indus, Ganga, and Brahmaputra rivers.
- It is basically a geomorphic trough, formed during the third phase of Himalayan formation (~64 million years ago).
- Since then, it has been filled with sediments brought by:
- 🏔️ The Himalayas
- 🌄 Rivers originating from the Peninsular Plateau
- Average depth of alluvium: 1000 – 2000 m.
🟠 Important Physiographic Features
🌱 Karewa
- Glacial deposits found at 1000–1500 m altitude on the Pir Panjal range.
- Deposited by glaciers.
- Famous for Saffron (Zafran) cultivation.
🏔️ Greater Himalaya Range
- Also called: Central Axis Range or Great Himalayas.
- East–West length: ~2500 km.
- North–South width: 160 – 400 km.
⛰️ Bhabar
- Region from Indus River → Teesta River.
- Thin strip, 8–10 km wide.
- Not suitable for agriculture.
- Himalayan rivers deposit pebbles, stones, sand, gravel here.
🌳 Terai
- Lies south of Bhabar, parallel to it.
- Width: 10–20 km.
- Originally dense forest area, now converted into agricultural land.
- Made of fine alluvium soil.
🏞️ Bangar
- Old alluvial soil, higher than flood level.
- Less fertile, not much useful for agriculture.
- Sometimes contains lime-rich sandy soil.
- In Punjab, it is locally called Chhaya.
❄️ Cold Desert in India
- Located in north-eastern Kashmir Himalayas – Leh–Ladakh region.
- Situated between Greater Himalayas & Karakoram range.
- Major ranges:
- (a) Ladakh Range
- (b) Zaskar Series
- (c) Karakoram Range
🌄 Eastern Hills of the Himalayas
- Run in North → South direction.
- Known by different names:
- Patkai Bum
- Naga Hills
- Manipur Hills (North)
- Mizo or Lushai Hills (South)
- Low hills with many tribes practicing Jhum / shifting cultivation.
🌊 Islands of India
🟢 Islands of Arabian Sea
- Small and mostly uninhabited.
- No volcanoes.
- Total islands: 36 → Only 11 inhabited.
- Minicoy Island = largest island (part of Lakshadweep group).
- Separated by 11° channel.
- Formed by coral deposits.
🔵 Islands of Bay of Bengal
- Large and habitable.
- Barren Island → only active volcano in India.
- Total islands: ~572.
- Includes Andaman & Nicobar Islands.
- Separated by 10° channel.
- Volcanic origin.
Indian Physiography – Coastal Plains, Desert, Himalayas & Ghats
🟢 Western Coastal Plains of India
- Narrow in central part, widens in north & south.
- Average width 👉 64 km.
- Rivers are small & fast flowing, hence no deltas.
- More eroded surface → favorable for ports & harbors.
- Divisions –
- Goa Coast (North)
- Konkan Coast
- Malabar Coast (South, till Kerala)
🟠 Eastern Coastal Plains of India
- Wider than Western Coastal Plain (80–100 km).
- Rivers form long, wide deltas.
- Important river deltas 👉 Mahanadi, Godavari, Krishna, Kaveri.
- Raised coasts → few ports, difficult for harbors.
- Divisions –
- Northern Sarkar Coast (north of Godavari)
- Coromandel Coast (south of Godavari)
❓ Why no delta on the Western Coastal Plain?
- Western Coastal Plain lies along Arabian Sea.
- Rivers originate from Western Ghats, short & fast.
- Flow over hard rocks, so less sediment carried.
- Insufficient deposits 👉 no delta formation. ✅
🏜️ Indian Desert – Once Part of the Sea
- Located north-west of Aravalli Hills.
- Believed to be part of the sea in Mesozoic Era.
- Evidences –
- Wood Fossil Park (Akal)
- Marine deposits near Brahmasar (Jaisalmer)
🏞️ Tribes of Arunachal Pradesh
- Monpa, Dafla, Abor, Mishmi, Nishi, Naga tribes (from west to east).
🏔️ North & North-Eastern Ranges
- Include Himalayas & North-Eastern Hills.
- Origin 👉 Tectonic movements.
- Still young, eroded by fast rivers.
- Himalayas arc 👉 2500 km (Indus → Brahmaputra), width 160–400 km.
- NE Hills 👉 Patkoi Bum, Naga Hills, Manipur Hills, Mizo/Lusai Hills.
Parallel Himalayan Ranges:
- Greater Himalaya (Himadri) – Highest, snow-covered.
- Lesser Himalaya (Himachal) – Popular hill stations (Shimla, Mussoorie, Darjeeling etc.).
- Shivalik Range – Outermost, close to plains.
👉 Himalayas act as a natural wall, climate barrier & cultural divide.
⛰️ Difference: Western Ghats vs Eastern Ghats
🌄 Western Ghats
- Stretch 👉 Maharashtra → Kanyakumari.
- Known as – Sahyadri, Nilgiris, Anamalai, Cardamom Hills.
- Continuous range, only three passes (Thalghat, Bhorghat, Palghat).
- Avg. height 👉 1500 m (north → south increases).
- Anaimudi Peak (2695 m) – highest of Peninsular Plateau.
- Source of most peninsular rivers.
🌄 Eastern Ghats
- Stretch 👉 Mahanadi Valley → Nilgiris.
- Main ranges 👉 Javadi, Palkonda, Nallamala, Mahendragiri.
- Not continuous → cut by rivers.
- Avg. height 👉 600 m.
- Highly eroded → only residual ranges left.
- Meet Western Ghats at Nilgiris.
- No major rivers originate here.
