Structure and Physiography | CBSE Class 11 Geography Notes

This note covers India's geological structure, the Peninsular Block, the Northern and North-eastern Mountains, the Northern Plain, the Peninsular Plateau, the Indian Desert, the Coastal Plains and the Islands.

How do geological structure and processes shape India's physiography?

Definition: Physiography is the outcome of an area's structure, processes and stage of development. It describes the physical character of the land.

Structure concerns the rocks and their arrangement. Relief means differences in land height and form. India's contrasting mountains, plains and plateaus, or elevated tablelands, reflect a long history of changes within the Earth and at its surface.

The Earth is approximately 4,600 million years old. Endogenic forces originate within the Earth, while exogenic forces act at its surface. Their interaction, together with sideways movements of the Earth's plates, has shaped India's present geological structure and landforms.

How did the Indian plate move?

A plate is a large moving section of the Earth's rigid outer layer. Millions of years ago, the Indian plate lay south of the equator, the imaginary circle midway between the poles. It was much larger, and the Australian plate formed part of it.

Over millions of years, this plate broke into several parts. The Australian plate moved towards the southeast, while the Indian plate moved north. The Indian plate's northward movement continues and has significant consequences for the subcontinent's physical environment.

How do geological and physiographic divisions differ?

Geological divisions group regions by their structure and formations. The three broad divisions are the Peninsular Block, the Himalayas and other Peninsular Mountains and the Indo-Ganga-Brahmaputra Plain. These regions broadly follow the physical features.

The six physiographic divisions group the major surface landscapes: Northern and North-eastern Mountains, Northern Plain, Peninsular Plateau, Indian Desert, Coastal Plains and Islands. The north has rugged mountains, the south has stable elevated tableland, and the great northern plain lies between them.

The physical map labels the Himalayas, Northern Plain, Great Indian Desert and Peninsular ranges. Its key distinguishes height bands of 0 to 300, 300 to 600, 600 to 900 and above 900 metres above sea level.

See Fig. 2.2 in your NCERT textbook

What makes the Peninsular Block old and relatively stable?

The Peninsular Block forms an ancient geological foundation. Its northern boundary may be taken as an irregular line from Kachchh, along the western side of the Aravali Range near Delhi, then roughly parallel to the Yamuna and Ganga towards the Rajmahal Hills and Ganga delta. A delta is an accumulation of river deposits at a river mouth.

Rajasthan in the west and the Meghalaya Plateau and Karbi Anglong in the northeast are extensions of this block. The Malda fault in West Bengal separates its northeastern parts from the Chotanagpur Plateau. A fault is a fracture along which rocks have moved.

What do its rocks and movements show?

The peninsula consists essentially of very ancient gneisses, rocks changed by heat and pressure, and granites, rocks formed when molten material cools below the surface. These constitute a major part of the block.

Since the Cambrian period, a division of geological time, the peninsula has stood like a rigid block. Exceptions include some submerged parts of the western coast and other areas changed by movements of the Earth's crust, its outermost rocky layer, without affecting the original basement.

Block faulting means movement of crustal blocks along faults. Vertical movements and block faulting affected the peninsula as part of the Indo-Australian Plate.

A rift valley is a lowered area between faults; a block mountain is an elevated crustal block associated with faulting. The Narmada, Tapi and Mahanadi rift valleys and Satpura block mountains are examples. Relative stability therefore does not mean that the peninsula has remained entirely motionless.

How do mountains and rivers express this history?

The peninsula mostly contains relict and residual mountains, remnants left after extensive wearing down. Examples include the Aravali, Nallamala, Javadi, Veliconda and Mahendragiri hills and the Palkonda range. Its river valleys are shallow, with low gradients, meaning gentle slopes.

Most east-flowing rivers form deltas before entering the Bay of Bengal. The Mahanadi, Krishna, Kaveri and Godavari provide important examples.

How are the Northern and North-eastern Mountains arranged?

The Northern and North-eastern Mountains consist of the Himalayas and the northeastern hills. The Himalayas comprise a series of parallel mountain ranges. Their geological structure is young, weak and flexible in contrast with the rigid and stable Peninsular Block.

These mountains have a tectonic origin, meaning an origin connected with movements and deformation of the Earth's crust. Internal and surface forces continue to act on them. Fast-flowing rivers cut through the mountains and display the characteristics of a youthful stage.

Here, youthful stage describes a stage of landform development. Features include gorges, or deep narrow valleys; valleys with V-shaped cross-sections; rapids, stretches of fast turbulent flow; and waterfalls, where water drops steeply.

Does every range run in the same direction?

The Great Himalayan range, also called the central axial range, is approximately 2,500 kilometres long from east to west. Its north-south width varies between 160 and 400 kilometres.

The Himalayas stand almost like a long, strong wall between the Indian subcontinent and Central and East Asian countries. They form a physical barrier and also a climatic, drainage and cultural divide, separating regions in these different respects.

Photographs: A Gorge and The Himalayas (NCERT Class 11 Figures 2.1 and 2.3). Figure 2.1 is a photograph showing a river between steep valley sides. Figure 2.3 is a photograph of a snow-covered mountain with sharply defined ridges and steep slopes.

How did the Northern Plain develop, and what are its main zones?

The Indo-Ganga-Brahmaputra Plain developed in a geo-synclinal depression, a large trough that received sediments. The depression reached its maximum development during the third phase of Himalayan mountain formation, approximately about 64 million years ago.

Himalayan and Peninsular rivers gradually filled this depression with sediments, materials transported and deposited by natural agents. The Northern Plain consists of alluvium, the material deposited by rivers, brought by the Indus, Ganga and Brahmaputra.

What are the important dimensions?

Mean sea level is the average sea-surface level used as a reference for height. The plains' length, width, height and deposit depth measure different aspects of the landscape.

What changes from the foothills towards the south?

1. At the change of slope beside the Shiwalik foothills, rivers deposit heavy rocks and boulders in the Bhabar, the narrow foothill belt.
2. Streams and rivers coming from the mountains, at times, disappear within this belt.
3. South of Bhabar, most streams and rivers re-emerge in the Tarai, the marshy belt, without properly demarcated channels. Swampy conditions support abundant natural vegetation and varied wildlife.
4. Farther south lie old and new alluvial deposits, called Bhangar and Khadar, respectively.

What features occur across the river plains?

River action, also called fluvial action, produces sand bars, or accumulations of sand; meanders, bends in a river; ox-bow lakes, curved lakes left by cut-off river bends; and braided channels, divided channels separated by deposits.

The Brahmaputra plains are known for riverine islands, islands within rivers, and sand bars. Most of these areas experience periodic floods and shifting river courses that form braided streams. River mouths form large deltas, including the Sunderbans delta.

Haryana and Delhi form a water divide, land separating drainage systems, between the Indus and Ganga systems. The Brahmaputra flows northeast to southwest, then turns almost 90 degrees southward at Dhubri before entering Bangladesh.

Fertile alluvial soils support wheat, rice, sugarcane and jute, helping the plains support a large population. Thus, the region's sediments, river landforms and agricultural importance are closely connected.

What gives the Peninsular Plateau its varied relief?

The Peninsular Plateau has the shape of an irregular triangle, rising from a height of 150 metres above the river plains to elevations of 600 to 900 metres. It is one of India's oldest and most stable landmasses.

Its outer extent includes the Delhi ridge, an Aravali extension, in the northwest; Rajmahal Hills in the east; Gir range in the west; and Cardamom Hills in the south. The Shillong and Karbi Anglong plateaus form a northeastern extension.

Which smaller plateaus and landforms occur here?

The region includes patland plateaus, plateaus with broad flat tops, such as the Hazaribagh, Palamu, Ranchi, Malwa, Coimbatore and Karnataka plateaus. Its general slope is from west to east, reflected in river flow. Black soil has an emphatic presence in the western and northwestern parts.

The landscape includes tors, exposed masses of rock, as well as bare rock, block mountains, rift valleys and spurs, ridges projecting from higher ground. There are also rounded or uneven small hills and wall-like quartzite dykes, ridges of hard quartz-rich rock, offering natural sites for water storage.

Upliftment is upward movement of land; submergence is its passage beneath water. Recurrent phases of upliftment and submergence, accompanied by crustal faults and fractures, have helped produce diversity in the plateau's relief.

The Bhima fault is notable for recurrent seismic activity, meaning earthquake activity. The northwestern plateau has complex relief with ravines, deeply eroded narrow channels, and gorges. Chambal, Bhind and Morena provide well-known examples of ravines.

What are its three broad subdivisions?

Prominent relief features distinguish the Deccan Plateau, Central Highlands and Northeastern Plateau. These are subdivisions of the Peninsular Plateau, rather than three additional major physiographic divisions of India.

Photograph: A Part of Peninsular Plateau (NCERT Class 11 Figure 2.5). The photograph shows steep exposed rock faces around a deep rocky cut, with a pale streak at upper left that may be falling water. The visible relief is uneven rather than uniformly flat.

How do the Western and Eastern Ghats differ around the Deccan Plateau?

The Deccan Plateau is bounded by the Western Ghats on the west and Eastern Ghats on the east. The Satpura and Maikal ranges and Mahadeo Hills form its northern boundary. The Ghats are hill and mountain ranges along the plateau's sides.

Which local names and heights distinguish the Western Ghats?

The Western Ghats have several local names: Sahyadri in Maharashtra, Nilgiri Hills in Karnataka and Tamil Nadu, and Anaimalai and Cardamom Hills in Kerala. They are comparatively higher and more continuous than the Eastern Ghats.

Most Peninsular rivers originate in the Western Ghats.

Why are the Eastern Ghats discontinuous?

The Eastern Ghats consist of low, discontinuous hills highly eroded by rivers such as the Mahanadi, Godavari, Krishna and Kaveri. Erosion is the wearing away and removal of material; here, river action has affected the hill ranges.

Important Eastern Ghat ranges include the Javadi Hills, Palconda range, Nallamala Hills and Mahendragiri Hills. The Eastern and Western Ghats meet at the Nilgiri Hills.

The useful comparison therefore concerns relative height, continuity and river action. The Western Ghats are higher and more continuous; the Eastern Ghats are lower, discontinuous and extensively eroded by the named rivers. The Nilgiris connect the two systems geographically.

How do the Central Highlands and Northeastern Plateau extend the peninsula?

What characterises the Central Highlands?

The Central Highlands are bounded by the Aravali Range on the west. Their general elevation is 700 to 1,000 metres above mean sea level, and they slope northward and northeastward.

To the south, the Satpura Range consists of a series of scarped plateaus, plateaus with steep edges, generally 600 to 900 metres above mean sea level. It forms the northernmost boundary of the Deccan Plateau and consists of highly worn-down, discontinuous relict ranges.

The Peninsular Plateau extends as far west as Jaisalmer, where elongated sand ridges and barchans, crescent-shaped accumulations of wind-blown sand, cover it. Such sand accumulations are called dunes. Surface desert features can therefore conceal an underlying plateau structure.

Metamorphic processes, which change existing rocks through heat and pressure, have affected this region. Marble, slate and gneiss are examples of the resulting rocks. Most Yamuna tributaries originate in the Vindhyan and Kaimur ranges. A tributary is a river joining another river.

The Banas is the only significant tributary of the Chambal originating in the Aravalli in the west. The Rajmahal Hills form an eastern extension of the Central Highlands. South of them, the Chotanagpur Plateau contains a large reserve of mineral resources.

Case study: How did the Meghalaya Plateau become detached?

The Northeastern Plateau is an extension of the main peninsula. It is believed that northeastward movement of the Indian plate during Himalayan formation created a huge fault between the Rajmahal Hills and Meghalaya Plateau.

Later, numerous rivers filled the depression through deposition, the laying down of transported material. Today, the Meghalaya and Karbi Anglong plateaus stand detached from the main Peninsular Block.

The Meghalaya Plateau contains the Garo, Khasi and Jaintia Hills, named after the tribal groups inhabiting them. An extension occurs in Assam's Karbi Anglong Hills. Resources include coal, iron ore, sillimanite, limestone and uranium, all named mineral resources of this area.

The area receives maximum rainfall from the southwest monsoon, the seasonal rain-bearing wind system. Its surface is consequently highly eroded. Cherrapunji displays bare rock without permanent vegetation cover, as one place on this eroded plateau.

Why does the Indian Desert have distinctive landforms and drainage?

The Great Indian Desert lies northwest of the Aravali Hills. Its uneven surface contains longitudinal dunes, elongated sand ridges, and barchans. Rainfall is below 150 millimetres per year, producing an arid, or very dry, climate with little vegetation.

These characteristics give the region the name Marusthali. Although its underlying rock structure extends the Peninsular Plateau, extreme dryness has allowed physical weathering and wind action to shape its surface. Physical weathering means breakdown of rock without changing its chemical composition.

Case study: What evidence suggests a former sea near Jaisalmer?

It is believed that the desert region lay beneath the sea during the Mesozoic era, a division of geological time. Evidence includes the wood fossils park at Aakal and marine deposits around Brahmsar, near Jaisalmer.

Fossils are preserved remains or traces of past life; marine deposits are materials deposited in a sea. The approximate age of the wood fossils is estimated to be 180 million years.

How do dryness and slope affect drainage?

The northern desert slopes towards Sindh and the southern part towards the Rann of Kachchh. Most rivers are ephemeral, flowing only temporarily. The Luni, in the southern desert, is of some significance.

Low precipitation, meaning water received from the atmosphere, and high evaporation, the conversion of liquid water into vapour, create a water deficit. Some streams disappear after a short distance or join a lake or playa, a shallow desert basin that may hold water.

This is inland drainage, drainage ending within the land rather than reaching the sea. Lakes and playas contain brackish, or salty, water that provides a main source of salt. Other features include mushroom rocks, rocks shaped with a broad top and narrower base, and shifting dunes. Oases, watered desert spots, occur mostly in the southern part.

Photograph: The Indian Desert (NCERT Class 11 Figure 2.6). The photograph shows people riding camels across sand dunes. Curved dune crests and closely spaced ripples on the foreground sand are visible.

How do the western and eastern coastal plains compare?

The Coastal Plains are lowland belts beside the sea. Their division into western and eastern plains reflects both location and active landform-shaping processes. Submergence characterises the western coastal plain; emergence characterises the eastern coastal plain.

What distinguishes the western coastal plain?

A submerged coast has land that has passed beneath the sea. It is believed that Dwaraka, once part of the Indian mainland along the west coast, is submerged. The western plain is narrow because of submergence and offers natural conditions for ports and harbours.

The western coast extends from Gujarat to Kerala. Its divisions are the Kachchh and Kathiawar coast, Konkan coast, Goan coast and Malabar coast. It is narrower in the middle and broadens towards both north and south.

Important natural ports include Kandla, Mazagaon, Marmagao, Mangalore and Cochin. Rivers crossing this coastal plain do not form deltas. By contrast, most east-flowing Peninsular rivers form deltas before entering the Bay of Bengal.

The Malabar coast has kayals, or backwaters. They support fishing, inland navigation and tourism. The Nehru Trophy Vallamkali, a boat race, takes place every year in Kerala's Punnamada Kayal.

What distinguishes the eastern coastal plain?

An emergent coast has land exposed from beneath the sea. The eastern coastal plain is broader than the western plain. The Mahanadi, Godavari, Krishna and Kaveri form well-developed deltas as they enter the Bay of Bengal.

Its emergent nature is associated with fewer ports and harbours. The continental shelf, the submerged margin of a continent, extends up to 500 kilometres into the sea, making the development of good ports and harbours difficult.

The map labels the Western and Eastern Ghats along the peninsula, Lakshadweep in the Arabian Sea, and the Andaman and Nicobar Islands in the Bay of Bengal. The two island groups lie on opposite sides of the peninsula.

See Fig. 2.2 in your NCERT textbook

How do India's two major island groups differ?

India's major island groups lie in the Bay of Bengal and the Arabian Sea. An island is land surrounded by water; an islet is a small island. An archipelago is a group of islands.

What characterises the Bay of Bengal islands?

This group has about 572 islands and islets, roughly between 6 and 14 degrees north latitude and 92 and 94 degrees east longitude. Latitude measures angular position north or south of the equator; longitude measures angular position east or west of the prime meridian, the reference line for zero longitude.

The principal groups of islets include Ritchie's archipelago and Labrynth island. The Andaman Islands lie in the north and the Nicobar Islands in the south. The Ten Degree Channel, a stretch of water between land areas, separates them.

It is believed that these islands are elevated portions of submarine mountains, mountains beneath the sea. Some smaller islands are volcanic, formed through eruptions of molten rock. A volcano is an opening through which molten rock and gases emerge. Barren Island, situated in the Andaman and Nicobar group, is India's only active volcano.

The coasts have some coral deposits, deposits built from the hard structures of small marine animals, and beaches. The islands receive convectional rainfall, caused by rising warm moist air, and have equatorial vegetation, vegetation characteristic of the region near the equator.

What characterises the Arabian Sea islands?

The Arabian Sea group includes Lakshadweep and Minicoy. It lies between 8 and 12 degrees north latitude and 71 and 74 degrees east longitude, at distances of 220 to 440 kilometres from the Kerala coast.

The entire group is built of coral deposits. There are approximately 36 islands, of which 11 are inhabited. The Nine Degree Channel broadly divides the group. Its eastern seaboard has storm beaches, beaches built up by storm action.

These beaches contain loose pebbles, shingles, cobbles and boulders, terms for stony beach material of differing sizes. The contrast in origin is central: coral deposits build the Arabian Sea group, while elevated submarine mountains are the believed origin of the Bay of Bengal group.

Photograph: An Island (NCERT Class 11 Figure 2.8). The photograph shows a wooded island surrounded by water, with a light-coloured strip around much of its edge.

Glossary

• Physiography — The physical character of an area resulting from structure, processes and stage of development.
• Peninsular Block — India's ancient, largely rigid geological block, extending into Rajasthan and parts of the northeast.
• Alluvium — Material deposited by rivers, forming the extensive deposits of the Northern Plain.
• Bhabar — Narrow belt beside the Shiwalik foothills where rivers deposit rocks and boulders and at times disappear.
• Tarai — Marshy belt south of Bhabar where most streams re-emerge without properly demarcated channels.
• Bhangar — Old alluvial deposits in the plains lying south of the Tarai belt.
• Khadar — New alluvial deposits in the plains lying south of the Tarai belt.
• Water divide — Land separating river drainage systems, exemplified by Haryana and Delhi between the Indus and Ganga systems.
• Barchans — Crescent-shaped sand dunes occurring among the characteristic surface features of the Indian Desert.
• Inland drainage — Drainage ending within the land, exemplified by desert streams joining lakes or playas.
• Kayals — Backwaters of the Malabar coast used for fishing, inland navigation and tourism.
• Ten Degree Channel — The waterbody separating the northern Andaman Islands from the southern Nicobar Islands.

Common errors and misconceptions

• Misconception: India has six geological divisions. Correct: Three broad geological divisions concern structure and formations; six physiographic divisions describe the major contrasts in surface landscapes.
• Misconception: Stability means that the Peninsular Block has experienced no movement. Correct: It has experienced vertical movements and block faulting, and some coastal parts have submerged.
• Misconception: Every Himalayan range runs in the same direction. Correct: Range direction varies across northwestern India, Darjiling and Sikkim, Arunachal Pradesh, and the northeastern hill states.
• Misconception: All streams disappear in Bhabar and all reappear in Tarai. Correct: Streams disappear at times in Bhabar; most re-emerge in Tarai.
• Misconception: Bhangar is new alluvium and Khadar is old alluvium. Correct: Bhangar consists of old deposits, while Khadar consists of new deposits.
• Misconception: The Eastern Ghats are higher and more continuous. Correct: The Western Ghats are comparatively higher and more continuous; rivers have highly eroded the Eastern Ghats.
• Misconception: The two major island groups have the same origin. Correct: The Arabian Sea group is built of coral deposits; the Bay of Bengal islands are believed to be elevated submarine mountains, with some smaller islands of volcanic origin.

Exam-style questions with model answers

Q1. Given that the alluvial plains south of Tarai contain old deposits called Bhangar and new deposits called Khadar, define Bhangar and Khadar in one point each. [2 marks]

1. Bhangar consists of the old alluvial deposits found in the plains south of the Tarai belt.
2. Khadar consists of the new alluvial deposits found in the plains south of the Tarai belt.

Q2. Given these observations, explain the Bhabar-Tarai sequence in three points: mountain rivers deposit heavy rocks and boulders in an 8 to 10 kilometre belt parallel to the Shiwalik foothills; streams at times disappear there; southward, most re-emerge without properly demarcated channels in a marshy belt approximately 10 to 20 kilometres wide. [3 marks]

1. The Bhabar is the 8 to 10 kilometre belt parallel to the Shiwalik foothills where rivers coming from the mountains deposit heavy rocks and boulders.
2. Streams and rivers at times disappear in Bhabar.
3. The Tarai lies farther south, approximately 10 to 20 kilometres wide. Most streams re-emerge without properly demarcated channels, producing marshy conditions.

Q3. Use the following information to compare the Ghats in four points: the Western Ghats are comparatively higher and more continuous, averaging about 1,500 metres; their height increases southward. The Eastern Ghats are low, discontinuous hills, highly eroded by the Mahanadi, Godavari, Krishna and Kaveri. Most Peninsular rivers originate in the Western Ghats. Both ranges meet at the Nilgiri Hills. [4 marks]

1. The Western Ghats are comparatively higher, with an average elevation of about 1,500 metres and increasing height from north to south; the Eastern Ghats are lower.
2. The Western Ghats are more continuous, whereas the Eastern Ghats consist of discontinuous hills.
3. River relationships differ: most Peninsular rivers originate in the Western Ghats, while the Mahanadi, Godavari, Krishna and Kaveri have highly eroded the Eastern Ghats.
4. The two hill systems meet at the Nilgiri Hills, where the Western Ghats join the Eastern Ghats.

Q4. Compare the coastal plains under four headings and state two uses of the Malabar kayals, using only these facts: the western plain is submerged and narrow, provides natural conditions for ports and harbours, and has rivers that do not form deltas; Malabar kayals support fishing and inland navigation. The eastern plain is emergent and broader, has fewer ports and harbours, and has deltas of the Mahanadi, Godavari, Krishna and Kaveri; its continental shelf extends up to 500 kilometres, making good harbour development difficult. [5 marks]

1. Coastal character: The western coastal plain is an example of a submerged coast, whereas the eastern coastal plain is an example of an emergent coast.
2. Width: The western coastal plain forms a narrow belt; the eastern coastal plain is broader in comparison with the western plain.
3. Deltas: Rivers crossing the western plain do not form deltas. The eastern plain has deltas formed by the Mahanadi, Godavari, Krishna and Kaveri.
4. Harbour conditions: The west provides favourable natural conditions. The east has fewer ports and harbours, and its shelf extends up to 500 kilometres, creating difficulty.
5. Backwater uses: The given western example is the Malabar kayals, used for fishing and inland navigation. These are distinct from the eastern delta examples.

Q5. Organise these island facts into five paired comparisons: the Bay of Bengal group has about 572 islands and islets; its Andaman and Nicobar divisions are separated by the Ten Degree Channel. It is believed to consist of elevated submarine mountains, with some smaller volcanic islands, and includes India's only active volcano, Barren Island. The Arabian Sea group includes Lakshadweep and Minicoy, has approximately 36 islands with 11 inhabited, is built entirely of coral deposits, lies 220 to 440 kilometres off Kerala, and is broadly divided by the Nine Degree Channel. [5 marks]

1. Location: One group lies in the Bay of Bengal. The other lies in the Arabian Sea, at a distance of 220 to 440 kilometres from Kerala.
2. Number: The Bay of Bengal group contains about 572 islands and islets. The Arabian Sea group contains approximately 36 islands, of which 11 are inhabited.
3. Named divisions: Andaman and Nicobar form the Bay of Bengal divisions. Lakshadweep and Minicoy are included in the Arabian Sea group.
4. Origin: The Bay group is believed to represent elevated submarine mountains, with some smaller volcanic islands, including Barren Island, India's only active volcano. The Arabian Sea group is built entirely of coral deposits.
5. Channels: The Ten Degree Channel separates Andaman and Nicobar. The Nine Degree Channel broadly divides the Arabian Sea island group.

Q6. Explain the desert's environment and drainage in four points from these data: rainfall is below 150 millimetres per year, vegetation is sparse, evaporation is high, most rivers are ephemeral, the Luni flows in the southern part, and some streams disappear after a distance or join lakes and playas containing brackish water used to obtain salt. Here, ephemeral means temporary, playa means a shallow desert basin, and brackish means salty. [4 marks]

1. Aridity: Rainfall below 150 millimetres per year is associated with a dry environment and sparse vegetation in the desert.
2. Water deficit: Low rainfall together with high evaporation creates a shortage of available water in this region.
3. River flow: Most rivers are ephemeral, so their flow is temporary. The Luni is a river flowing in the southern part of the desert.
4. Inland drainage: Some streams disappear or enter lakes and playas. These waterbodies contain brackish water used for obtaining salt.

Key takeaways

• India's physiography reflects geological structure, landform-shaping processes and stage of development, with three broad geological divisions and six major physiographic divisions.
• The Peninsular Block is ancient and relatively stable, but vertical movements, block faulting and partial coastal submergence have affected it.
• The Himalayan region has young, weak and flexible geological structure, with fast-flowing rivers and landforms associated with a youthful stage.
• Across the Northern Plain, Bhabar lies beside the foothills, Tarai occurs farther south, and Bhangar and Khadar represent old and new alluvium.
• The Peninsular Plateau comprises the Deccan Plateau, Central Highlands and Northeastern Plateau; the Western Ghats are comparatively higher and more continuous than the Eastern Ghats.
• Low rainfall and high evaporation create desert water deficits; most desert rivers are ephemeral, and some streams end in lakes or playas.
• The western coastal plain is submerged and narrow, while the eastern plain is emergent, broader and marked by well-developed river deltas.
• The Arabian Sea islands are built of coral deposits; the Bay of Bengal islands are believed to represent elevated submarine mountains, with some smaller volcanic islands.

Test yourself

What three factors determine an area's physiography?

Its structure, the processes acting upon it, and its stage of development together determine its physiography.

Why does describing the peninsula as stable not mean that it has never moved?

The Peninsular Block has experienced vertical movements and block faulting, while some parts of its western coast are submerged.

Where do the Western and Eastern Ghats meet?

The Western and Eastern Ghats meet at the Nilgiri Hills, where Dodabetta is also located.

Which three hill divisions make up the Meghalaya Plateau?

The Garo, Khasi and Jaintia Hills form its three subdivisions, named after the tribal groups inhabiting the region.

What evidence supports the belief that the desert region was once under the sea?

The wood fossils park at Aakal and marine deposits around Brahmsar, near Jaisalmer, provide evidence supporting this belief.

What are kayals, and how are they used?

Kayals are Malabar coast backwaters used for fishing, inland navigation and tourism.

Which channel separates the Andaman Islands from the Nicobar Islands?

The Ten Degree Channel separates the Andaman Islands in the north from the Nicobar Islands in the south.

Where is India's only active volcano situated?

Barren Island, India's only active volcano, lies in the Andaman and Nicobar island group.