Revision: Unit I Physical Environment >> Relief Geography ISC (Arts) Class 12 CISCE

Key Points

Key Points: Western Himalayas VS Eastern Himalayas

Region / Plain	Key Points
Northern Plains	Formed by Indus, Ganga & Brahmaputra; very fertile
Punjab Plains	Indus tributaries; doabs; rich agriculture
Rajasthan Plains	Thar Desert; arid; Luni river; salt lakes
Ganga Plains	Highly fertile; dense population; bhabhar & terai
Brahmaputra Plains	Assam; marshy; floods; river islands

Key Points: Physical Divisions of India> The Peninsula

The Indian Peninsula lies south of the North Indian Plains and tapers toward the Indian Ocean.
It is the oldest and largest physiographic division of India, mostly made of stable tableland.
It is bounded by the Aravalli Range in the northwest and the Western and Eastern Ghats on the sides.
The region includes many hill ranges and plateaus, such as the Vindhyas, Satpuda, and Aravalis.
The Deccan Plateau is triangular and lies between the Western and Eastern Ghats, covering Maharashtra, Telangana, and Karnataka.
The plateau is divided into Central Plateaus, Eastern Plateaus, Deccan Plateau, Kathiawar–Kutch region, and North-Eastern Plateau.
This region is rich in minerals, has old rivers, and supports forests, farming, and mining.

Key Points: Western Ghats VS Eastern Ghats

Western Ghats	Eastern Ghats
High & steep	Low & gentle
Continuous	Discontinuous
Source of rivers	Rivers cut through
Heavy monsoon rain	Little monsoon rain
Anai Mudi (2695 m)	Mahendragiri (1500 m)

Key Points: Physical Divisions of India> The Peninsula

The Indian Peninsula lies south of the North Indian Plains and tapers toward the Indian Ocean.
It is the oldest and largest physiographic division of India, mostly made of stable tableland.
It is bounded by the Aravalli Range in the northwest and the Western and Eastern Ghats on the sides.
The region includes many hill ranges and plateaus, such as the Vindhyas, Satpuda, and Aravalis.
The Deccan Plateau is triangular and lies between the Western and Eastern Ghats, covering Maharashtra, Telangana, and Karnataka.
The plateau is divided into Central Plateaus, Eastern Plateaus, Deccan Plateau, Kathiawar–Kutch region, and North-Eastern Plateau.
This region is rich in minerals, has old rivers, and supports forests, farming, and mining.

Key Points: Physical Divisions of India> The Coastal Plains

India has a coastline of approximately 7,500 km, extending along the eastern (Bay of Bengal) and western (Arabian Sea) sides of the Peninsula, meeting at Cape Comorin.
The Western Coastal Plains are narrow, rocky, and indented, with short rivers forming estuaries; major ports include Mumbai and Kochi.
The Eastern Coastal Plains are broad and flat, formed by deposition from major rivers like the Mahanadi, Godavari, Krishna, and Kaveri, leading to fertile deltas.
Subdivisions: East coast – Northern Circars and Coromandel Coast; West coast – Gujarat, Konkan, Kanara, Malabar.
The coastal plains are important for ports, minerals (like salt and monazite), and fisheries.

Key Points: Physical Divisions of India> The Island Group

India has two major island groups: the Lakshadweep Islands in the Arabian Sea and the Andaman & Nicobar Islands in the Bay of Bengal.
The Lakshadweep Islands are mostly coral atoll islands, small, flat, and low in height, and lie off the Kerala coast.
The Andaman & Nicobar Islands consist of many islands (about 265–300), mostly forested and hilly, and are separated by the Ten Degree Channel.
Barren Island in the Andaman group has India’s only active volcano, and Indira Point in Great Nicobar is India’s southernmost point.
These island groups are important for strategic location, biodiversity, and are surrounded by coral reefs and rich marine life.

Key Points: Difference between Bhabar and Tarai

Bhabar	Tarai
Lies along the foot of the Shiwalik Hills from Indus to Tista	Lies south of Bhabar and runs parallel to it
8–16 km wide	20–30 km wide
Made of coarse, pebble-studded porous rocks	Made of fine alluvium
Streams disappear underground due to high porosity	Underground streams re-emerge, forming marshy land
Not suitable for agriculture	Reclaimed and fertile agricultural land

Key Points: Difference between Bhangar and Khadar

Bhangar	Khadar
Highland made of old alluvium	Lowland made of new alluvium
Lies above flood plains	Lies in flood plains and gets flooded yearly
Contains kankar (calcareous nodules)	Has clayey soil, very fertile
Less suitable for cultivation	Highly suitable for farming
Called ‘Dhaya’ in Punjab	Called ‘Bet’ in Punjab

Key Points: The Peninsular Plateau

Shape and Age: The Peninsular Plateau is the oldest landmass of India and forms an irregular triangular shape with apex at Kanniyakumari.
Extent and Height: It is about 1600 km long and 1400 km wide, with an average elevation of 600–900 metres.
Surrounding Hills: It is surrounded by hills—Aravalis, Vindhyas and Rajmahal hills in the north, Western Ghats in the west and Eastern Ghats in the east.
Main Divisions: The Narmada-Tapi trough divides the plateau into Malwa Plateau, Deccan Plateau and Chhotanagpur Plateau.
Malwa Plateau: Located north-west of Narmada-Tapi, made of hard rocks, slopes towards north-east, and rivers like Chambal and Betwa flow here (Chambal forms ravines called badlands).
Deccan Plateau: Lies south of Tapi, has average height around 600 m, slopes from west to east, so most rivers flow east (except Narmada and Tapi which flow west).
Chhotanagpur Plateau & Ghats: Chhotanagpur plateau is rich in coalfields (Damodar valley) and shows radial drainage. Western Ghats are higher and continuous with gaps like Thalghat and Palghat, while Eastern Ghats are lower and cut by rivers like Godavari and Krishna.

Key Points: Significance of the Peninsular Plateau

Oldest and Stable Landmass: The Peninsular Plateau is the oldest and most stable part of the Indian sub-continent.
Rich Mineral Resources: It has large deposits of iron, manganese, copper, bauxite, mica, gold, and about 98% of India’s Gondwana coal.
Fertile Soils and Agriculture: Large areas have black lava soil suitable for cotton, and other crops like millets, oilseeds, tea, coffee, rubber and rice.
Forest and Water Resources: The plateau has rich forests and rivers from the Western Ghats provide hydroelectric power and irrigation.
Tourism: The plateau is famous for hill stations such as Ooty, Kodaikanal, Mahabaleshwar, Mount Abu and Panchmarhi.

Key Points: The Islands

India has islands in both seas—Lakshadweep in the Arabian Sea and Andaman & Nicobar in the Bay of Bengal.
Lakshadweep Islands are small coral islands, and none is larger than a few square kilometres.
Andaman and Nicobar Islands form a long chain of islands stretched almost in a straight line.
There are about 572 islands in the Andaman-Nicobar group, covering a total area of 8249 sq. km.
Some Andaman-Nicobar islands are volcanic in origin; Barren Island is an active volcano, and Lakshadweep lies north of the Maldives.

Key Points: The Coastal Plains

Coastal Plains Location: India has two narrow coastal plains along the Peninsular Plateau—West Coastal Plain (Arabian Sea) and East Coastal Plain (Bay of Bengal).
West Coastal Plain: Lies between Western Ghats and Arabian Sea, extends from Gujarat to Kanniyakumari, and is narrow with average width about 64 km.
Divisions of West Coastal Plain:
i. Konkan (Mumbai to Goa) – 50–80 km wide, has estuaries
ii. Kannad Plain (middle part)
iii. Malabar Plain (south) – has lagoons and backwaters (example: Kochi)
East Coastal Plain: Lies along the Bay of Bengal from Odisha to Kanniyakumari, is wider than the west coast, and becomes broadest in Tamil Nadu (100–200 km).
Divisions and Features of East Coast:
a) North Circar Plain (Mahanadi to Krishna)
b) Coromandel/Carnatic Plain (Krishna to Cauvery)
Major rivers like the Mahanadi, Godavari, Krishna, and Cauvery form deltas and lagoons like Chilka and Pulicat.

Key Points: Difference between West Coastal Plain and East Coastal Plain

West Coastal Plain	East Coastal Plain
Lies between Western Ghats and Arabian Sea	Lies between Eastern Ghats and Bay of Bengal
Narrow plain, average width about 64 km	Broader plain, average width about 80–100 km
Drained by short, fast rivers that do not form deltas	Large rivers form extensive deltas
Many lagoons, especially in the southern part	Fewer lagoons compared to west coast
Indented coastline, supports many natural ports	Straight coastline, fewer good ports

Key Points: Difference between Andaman and Nicobar and Lakshadweep Islands

Andaman & Nicobar Islands	Lakshadweep Islands
Located in the Bay of Bengal	Located in the Arabian Sea
About 572 islands (6°45'N–13°41'N)	Only 25 islands (8°N–12°20'N)
Large area: about 8249 sq. km	Very small islands (largest Minicoy only 4.53 sq. km)
Made of sandstone & limestone, some are volcanic	Made of coral origin, surrounded by fringing reefs
Mostly hilly, highest peak Saddle Peak (737 m)	Mostly low-lying, not more than 5 m above sea level

Key Points: The Indus-Ganga-Brahmaputra Plan

Formation: The Indus-Ganga-Brahmaputra Plain is formed by the depositional work of the Indus, Ganga and Brahmaputra rivers.
Extent: It stretches about 2400 km from Satluj to the Ganga delta along the foothills of the Himalayas.
Width: Its width varies from 150–300 km, but it is narrowest in Assam (90–100 km).
Depth: The plain was formed by continuous deposition filling an old depression, and its maximum depth is about 2000 metres.
Bhabar and Tarai belts:
a) Bhabar is a narrow pebble belt where streams disappear underground, not suitable for farming.
b) Tarai lies south of Bhabar, where streams re-emerge, and it is marshy but fertile.
Bhangar and Khadar:
a) Bhangar is made of old alluvium and contains kankar (lime nodules).
b) Khadar is the new alluvial floodplain, very fertile and good for agriculture.
Other features:
i. Bhur is an elevated sandy land near Ganga banks formed by wind-blown sand.
ii. Barind is an old alluvial terrace between Ganga and Brahmaputra-Jamuna, flood-prone.
iii. Barchan dunes are crescent-shaped sand dunes found in Rajasthan desert regions.

Key Points: Difference between Western Ghats and Eastern Ghats

Western Ghats	Eastern Ghats
Run north–south parallel to the western coast from Tapi to Kanniyakumari	Run north-east to south-west parallel to the eastern coast from Odisha to Nilgiris
Average height 900–1100 m	Average height about 600 m
Width 50–80 km	Wider, about 100–200 km
Form a continuous wall and can be crossed only through passes	Discontinuous, broken by river valleys
Have strong structural unity	Lack structural unity
Source of many rivers of Peninsular India	No major river originates here
Block south-west monsoon, causing heavy rainfall on west coast	Almost parallel to Bay of Bengal monsoon, so less rainfall

Key Points: The Himalayan Mountain Complex

India has great physiographic diversity including young fold mountains, plains, plateaus, coastal plains and islands.
Land area distribution (Census 1951):
10.7% mountainous (above 2135 m)
18.6% hilly (305–2135 m)
27.7% plateau (305–915 m)
43% plains
India is divided into 5 major relief divisions:
Himalayas, Indus-Ganga-Brahmaputra Plain, Peninsular Plateau, Coastal Plains, and Islands.
The Himalayan Mountain Complex stretches for about 2400 km from the Indus River (west) to the Brahmaputra River (east), with an average width of 160–400 km.
Himalayas have three parallel ranges:
i. Great Himalayas (Himadri) – highest, snow-covered, average height above 6000 m.
ii. Lesser Himalayas – 3700–4500 m, includes Pir Panjal and Dhaoladhar, hill stations located here.
iii. Shiwalik Range (Outer Himalayas) – 900–1200 m, lowest and southernmost.
Important valleys and duns:
a. Between Greater and Lesser Himalayas: Kashmir Valley and Kathmandu Valley
b. Between Lesser and Shiwalik: Duns (west) and Duars (east) like Dehra Dun.
Off-shoots and Karakoram Range:
Himalayas bend at Indus and Dihang gorges, forming NW and NE off-shoots.
The Karakoram Range (avg. 6000 m) has K2 (8611 m), the highest peak of India, and Karakoram Pass (5575 m).

Key Points: Regional Divisions of the Himalayas

Sir S. Burrard divided the Himalayas into 4 main regional sections, separated by deep river gorges.
Punjab (Kashmir) Himalayas lie between the Indus and Satluj rivers, are about 560 km long, and include ranges like Ladakh, Pir Panjal, Dhaoladhar and Zaskar.
Zoji La Pass (3444 m) is an important pass located in the Punjab Himalayas.
Kumaon (Himachal/Uttarakhand) Himalayas extend between the Satluj and Kali rivers (about 320 km) and are the source region of the Ganga and Yamuna.
Nepal Himalayas (Kali to Tista, 800 km) are the highest part with peaks like Everest, Kanchenjunga, Dhaulagiri, Annapurna, Makalu, and contain the Kathmandu Valley; Assam Himalayas lie between Tista and Dihang rivers (about 720 km).

Key Points: Significance of the Himalayas

Climatic Influence: The Himalayas stop cold winds from Central Asia and force monsoon winds to cause rainfall and snowfall in India.
Natural Defence Barrier: They act as a protective wall against foreign invasions, though modern warfare has reduced this importance.
Source of Perennial Rivers: Most major rivers like the Ganga, Indus and Brahmaputra originate here and get water from snow and glaciers.
Formation of Fertile Plains: Himalayan rivers bring large amounts of alluvium which forms fertile soil in the Northern Plains, called the “Gift of the Himalayas”.
Hydroelectric Power: Fast-flowing Himalayan rivers provide great potential for producing hydroelectricity through dams and waterfalls.
Forest and Agricultural Resources: Himalayas have rich forests, medicinal plants, grazing lands, and terrace farming of crops like rice, wheat, maize and tea.
Tourism, Pilgrimage and Minerals: The region attracts tourists and pilgrims due to scenic beauty and holy shrines, and also contains valuable minerals like coal, oil and metals.

Key Points: Difference between Western Himalayas and Eastern Himalayas

Basis	Western Himalayas	Eastern Himalayas
Location	West of 86°E, between Indus and Kali rivers	East of 88°E, between Tista and Brahmaputra rivers
Relief/Structure	Rise gradually in a series of ranges	Rise abruptly from plains of Bihar and West Bengal
Major Ranges/Peaks	Includes Dhaoladhar, Pir Panjal, Zaskar, Ladakh, Karakoram	Includes high peaks like Everest and Kanchenjunga close together
Rainfall	Less than 100 cm annually	More than 200 cm annually
Vegetation	Mainly alpine and coniferous forests	Dense evergreen forests

Key Points: Regional Divisions and Significance of the Plain

The Great Northern Plain is not completely flat; it has local relief variations from the Thar Desert to Assam, so it is divided into regional parts.
Rajasthan Plain (Thar Desert): Lies between Aravali Hills and Indus Plain, has sand dunes, very low rainfall (below 25 cm), almost no vegetation, and includes saline lakes like Sambhar.
Punjab-Haryana Plain: Formed by alluvium of five rivers (Satluj, Beas, Ravi, Chenab, Jhelum) and is famous for doabs (land between two rivers).
Khadar belt (Bet lands) in Punjab is flood-prone but highly fertile; erosion by streams called Chos causes deep gullies in Shiwalik region.
Ganga Plain: Located in U.P., Bihar and West Bengal, formed by Ganga and tributaries; divided into Upper, Middle and Lower Ganga Plains and includes the important Ganga-Yamuna Doab.
Brahmaputra Plain (Assam Plain): Formed by Brahmaputra and tributaries, extends about 640 km, and is narrow (about 90–100 km wide).
Significance: Due to fertile soil, irrigation and rivers, this plain supports about half of India’s population, is called the granary of India, has good transport networks, industries, and is also important for religious and cultural development.

Geological Evolution and Structure Drainage

Revision: Unit I Physical Environment >> Relief Geography ISC (Arts) Class 12 CISCE

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