Structure and Physiography| Chapter 2 Class 11 Geography Notes

Class 11 Geography Ch 2 Structure and Physiography Notes: In Class 11 Geography Chapter 2, we learn about the different shapes and features of the Earth’s surface. This includes things like mountains, plateaus, plains, and valleys. We examine how these features are formed over a long time by various natural processes like movement of the Earth’s crust, erosion, and deposition. By studying this chapter, we get to understand more about how the Earth’s surface changes and how it’s connected to geological processes.

The Structure and Physiography notes cover all the necessary topics that are extremely important for the examination 2024. It can save you time and will positively affect your results.

Structure and Physiography| Chapter 2 Class 11 Geography Notes

Introduction

The Earth is approximately 460 million years old. Throughout this immense timespan, it has experienced numerous transformations driven by both internal (endogenic) and external (exogenic) forces. These forces have played a pivotal role in shaping various surface and subsurface features of the Earth.

Millions of years ago, the Indian plate was positioned to the south of the equator and was much larger, with the Australian plate being a part of it. Over time, this plate fragmented into several parts, with the Australian plate moving southeastward and the Indian plate shifting northward.

This ongoing northward movement of the Indian plate continues to have significant implications for the physical environment of the Indian subcontinent. The present geological structure and geomorphological processes in the Indian subcontinent are primarily shaped by the interaction of these endogenic and exogenic forces, along with the lateral movements of the plates.

Based on the variations in its geological structure and formations, India can be categorized into three main geological divisions. These geological regions broadly follow the physical features:

(i) The Penisular Block

(ii) The Himalayas and other Peninuslar Mountains

(iii) Indo-Ganga-Brahmaputra Plain.

The Peninsular Block

The northern boundary of the Peninsular Block can be traced along an irregular line from Kachchh, running along the western flank of the Aravali Range near Delhi, and then roughly parallel to the Yamuna and the Ganga rivers until reaching the Rajmahal Hills and the Ganga delta. Extensions of this block include the Karbi Anglong and the Meghalaya Plateau in the northeast, and Rajasthan in the west. In West Bengal, the northeastern parts are separated from the Chotanagpur Plateau by the Malda fault, while in Rajasthan, desert and desert-like features overlay this block.

Primarily composed of ancient gneisses and granites, the Peninsula has remained relatively stable since the Cambrian period, with exceptions such as parts of its western coast submerged beneath the sea and some regions altered due to tectonic activity. As a part of the Indo-Australian Plate, the Peninsula has experienced various vertical movements and block faulting, resulting in features like the rift valleys of the Narmada, Tapi, and Mahanadi rivers, and the Satpura block mountains. Relict and residual mountains, such as the Aravali hills, Nallamala hills, Javadi hills, Veliconda hills, Palkonda range, and Mahendragiri hills, characterize the Peninsula. River valleys here tend to be shallow with low gradients.

Many east-flowing rivers in the Peninsula form deltas before reaching the Bay of Bengal, with notable examples including the deltas of the Mahanadi, Krishna, Kaveri, and Godavari rivers.

The Himalayas and Other Peninsular Mountains

Unlike the stable and rigid Peninsular Block, the Himalayas and other Peninsular mountains possess a young, weak, and flexible geological structure. Consequently, they continue to undergo the interplay of exogenic and endogenic forces, leading to the formation of faults, folds, and thrust plains. Tectonic in origin, these mountains are characterized by fast-flowing rivers in their youthful stage, which dissect the terrain and carve out various landforms such as gorges, V-shaped valleys, rapids, and waterfalls. These features are indicative of the dynamic geological processes shaping the Himalayas and other mountainous regions.

Indo-Ganga-Brahmaputra Plain

The third geological division of India consists the plains formed by the rivers Indus, Ganga, and Brahmaputra. Initially, it was a geo-synclinal depression that reached its peak development during the third phase of Himalayan mountain formation around 64 million years ago. Since then, it has gradually been filled by sediments carried by the Himalayan and Peninsular rivers. The average depth of alluvial deposits in these plains ranges from 1,000 to 2,000 meters. The relief and physiography of India have been significantly shaped by the geological and geomorphological processes active in the Indian subcontinent.

Physiography

The “physiography” of an area results from its structure, ongoing processes, and its stage of development. India’s landscape exhibits tremendous diversity in its physical features. The northern region encompasses extensive rugged terrain, featuring a series of mountain ranges with varying peaks, picturesque valleys, and deep gorges. the southern region is characterized by stable plateaus, highly dissected plateaus, weathered rocks, and prominent escarpments. Between these two regions lies the vast expanse of the North Indian Plain. Based on these broad variations, India can be divided into distinct physiographic divisions:

1. The Northern and North-eastern Mountains
2. The Northern Plain
3. The Peninsular Plateau
4. The Indian Desert
5. The Coastal Plains
6. The Islands.

The North and Northeastern Mountains

The North and Northeastern Mountains include the Himalayas and the Northeastern hills. Here are some key points about these regions:

• The Himalayas consist of several parallel mountain ranges, including the Greater Himalayas, Trans-Himalayan range, Middle Himalayas, and Shiwalik.
• These mountain ranges generally run from northwest to southeast, although their orientation varies in different regions.
• The Great Himalayan range, also known as the central axial range, spans approximately 2,500 km from east to west.
• The Himalayas act as a formidable barrier between the Indian subcontinent and Central and East Asian countries, influencing climate, drainage patterns, and cultural practices.
• The region can be divided into several sub-divisions, including Kashmir or Northwestern Himalayas, Himachal and Uttarakhand Himalayas, Darjiling and Sikkim Himalayas, Arunachal Himalayas, and Eastern Hills and Mountains.

Each sub-division has its own unique features, geological formations, and cultural significance. For example, the Kashmir Himalayas are known for their towering peaks, cold deserts, and famous valleys like Kashmir and Baltoro. The Himachal and Uttarakhand Himalayas feature prominent hill stations, while the Darjiling and Sikkim Himalayas are characterized by fast-flowing rivers and high mountain peaks like Kanchenjunga. The Arunachal Himalayas boast diverse ethnic tribal communities, rich biodiversity, and deep river gorges. Finally, the Eastern Hills and Mountains include low hills inhabited by various tribal groups practicing Jhum cultivation, with unique geographical features like Loktak Lake in Manipur and the soft unconsolidated rocks of Mizoram.

The Northern Plains

The northern plains of India are primarily formed by the vast deposits of alluvium brought by the rivers Indus, Ganga, and Brahmaputra. Here are some key characteristics of these plains:

• Stretching approximately 3,200 km from east to west, the northern plains have an average width ranging between 150-300 km.
• The depth of the alluvial deposits in these plains varies between 1,000-2,000 m.
• The northern plains can be divided into three major zones from north to south: the Bhabar, the Tarai, and the alluvial plains, further divided into the Khadar and the Bhangar.
• The Bhabar is a narrow belt parallel to the Shiwalik foothills, characterized by heavy deposits of rocks and boulders from mountain streams.
• South of the Bhabar lies the Tarai belt, where streams and rivers re-emerge, creating marshy and swampy conditions with lush vegetation and diverse wildlife.
• The alluvial plains consist of old and new alluvial deposits known as Bhangar and Khadar respectively, featuring mature stage fluvial erosional and depositional landforms.
• The Brahmaputra plains are marked by riverine islands, sand bars, and periodic floods, forming one of the largest deltas in the world, the Sunderbans delta.
• Despite being relatively flat with an elevation of 50-150 m above sea level, these plains support a large population due to their fertile alluvial soil, suitable for growing crops like wheat, rice, sugarcane, and jute.

The Peninsular Plateau

• The Peninsular plateau rises from approximately 150 meters above the river plains to an elevation of 600-900 meters.
• It forms an irregular triangle shape, extending from Delhi ridge in the northwest (an extension of the Aravalis) to the Rajmahal hills in the east, Gir range in the west, and the Cardamom hills in the south.
• Extensions in the northeast, such as the Shillong and Karbi-Anglong plateau, are also observed.
• The plateau comprises several patland plateaus like the Hazaribagh plateau, Palamu plateau, Ranchi plateau, Malwa plateau, Coimbatore plateau, and Karnataka plateau.
• It is one of India’s oldest and most stable landmasses, with a general elevation from west to east, as evidenced by the river flow patterns.
• Rivers like the Godavari, Krishna, and Mahanadi have their confluence in the Bay of Bengal, while the Narmada and Tapi flow into the Arabian Sea.
• Physiographic features include tors, block mountains, rift valleys, spurs, bare rocky structures, hummocky hills, and quartzite dykes.
• The western and northwestern parts are characterized by the presence of black soil.
• The plateau has experienced recurrent phases of upliftment and submergence, along with crustal faulting and fractures, including seismic activity along the Bhima fault.
• These variations result in diverse relief features, including ravines and gorges like those of Chambal, Bhind, and Morena.
• The Peninsular plateau can be categorized into three groups:

1. Deccan Plateau
2. Central Highlands
3. and Northeastern Plateau

The Deccan Plateau

• Bordered by the Western Ghats in the west, Eastern Ghats in the east, and the Satpura, Maikal range, and Mahadeo hills in the north.
• Western Ghats known locally as Sahyadri in Maharashtra, Nilgiri hills in Karnataka and Tamil Nadu, and Anaimalai hills and Cardamom hills in Kerala.
• Western Ghats are higher in elevation and more continuous than the Eastern Ghats, averaging about 1,500 m with increasing height from north to south.
• Anaimudi (2,695 m) on the Anaimalai hills and Dodabetta (2,637 m) on the Nilgiri hills are the highest peaks.
• Many Peninsular rivers originate in the Western Ghats. The Eastern Ghats are highly eroded by rivers like Mahanadi, Godavari, Krishna, and Kaveri.
• Important ranges include Javadi hills, Palkonda range, Nallamala hills, and Mahendragiri hills. The Nilgiri hills mark the meeting point of Eastern and Western Ghats.

The Central Highlands

• Bounded to the west by the Aravali range, with the Satpura range forming the northernmost boundary.
• Satpura range consists of scarped plateaus at an elevation of 600-900 m above sea level.
• Relict mountains with discontinuous ranges and metamorphic rocks like marble, slate, and gneiss.
• Elevation ranges between 700-1,000 m. Banas, a significant tributary of Chambal, originates from the Aravalli.
• The Rajmahal hills form an eastern extension, with abundant mineral resources in the Chotanagpur plateau.

The Northeastern Plateau

• An extension of the main Peninsular plateau, formed due to the northeastward movement of the Indian plate during the Himalayan origin.
• The Meghalaya plateau is further sub-divided into three:

1. (i) The Garo Hills
2. (ii) The Khasi Hills
3. (iii) The Jaintia Hills

• Meghalaya and Karbi Anglong plateau stand detached, with Meghalaya further divided into Garo Hills, Khasi Hills, and Jaintia Hills, named after tribal groups.
• Rich in mineral resources like coal, iron ore, limestone, and uranium, with highly eroded surfaces.
• Cherrapunji displays a bare rocky surface devoid of permanent vegetation cover.

The Indian Desert

To the northwest of the Aravali hills lies the Great Indian desert, characterized by undulating topography adorned with longitudinal dunes and barchans. With an annual rainfall of below 150 mm, this region experiences an arid climate with sparse vegetation, earning it the nickname “Marusthali.”

The Luni river, flowing in the southern part of the desert, holds some significance in this otherwise water-deficient region. Due to low precipitation and high evaporation rates, the area faces a scarcity of water. Several streams in the region disappear after flowing for some distance, showcasing a typical case of inland drainage, eventually joining a lake or playa. These lakes and playas contain brackish water, serving as the primary source of obtaining salt.

The Coastal Plains

On the basis of location and active geomorphological processes, India’s coastal plains can be broadly divided into two distinct regions:

(i) The Western Coastal Plains

• These plains represent a submerged coastal area, with historical evidence suggesting that parts of the Indian mainland, such as the city of Dwaraka, were once situated along this coast but are now underwater.
• Due to this submergence, the Western Coastal Plains form a narrow belt, providing ideal conditions for the development of ports and harbors. Notable natural ports along this coast include Kandla, Mazagaon, JLN port Navha Sheva, Marmagao, Mangalore, and Cochin.

The Western coast can be further divided into specific divisions:

(i) The Kachchh and Kathiawar coast in Gujarat,

(ii) Konkan coast in Maharashtra,

(iii) Goan coast, and

(iv) Malabar coast in Karnataka and Kerala respectively.

• Unlike the rivers on the Eastern coast, those flowing through the Western Coastal Plains do not form significant deltas.
• The Malabar coast is particularly notable for its “Kayals” or backwaters, utilized for fishing, inland navigation, and tourist attractions, including the renowned Nehru Trophy Vallamkali (boat race) held in Punnamada Kayal in Kerala.

(ii) The Eastern Coastal Plains

• These plains are broader and represent an emergent coast, characterized by well-developed deltas formed by rivers flowing eastward into the Bay of Bengal.
• Major deltas in this region include those of the Mahanadi, the Godavari, the Krishna, and the Kaveri rivers.
• Due to its emergent nature, the Eastern Coastal Plains have fewer ports and harbors compared to the Western coast.
• The continental shelf extending up to 500 km into the sea poses challenges for the development of ports and harbors along the Eastern coast.

The Islands

India has two major island groups, located in different parts of the country:

The Islands of the Bay of Bengal

• These island groups consist of approximately 572 islands and islets, situated roughly between 6°N-14°N and 92°E-94°E.
• The principal groups of islets include the Ritchie’s Archipelago and the Labrynth Island, categorized into the Andaman in the north and the Nicobar in the south.
• They are separated by the Ten Degree Channel, with the Andaman Islands being an elevated portion of submarine mountains, while some smaller islands have volcanic origins.
• Barren Island, the only active volcano in India, is situated in the Nicobar Islands.
• The coastal line of these islands features coral deposits and picturesque beaches. They experience convectional rainfall and boast an equatorial type of vegetation.

The Islands of the Arabian Sea

• This group includes Lakshadweep and Minicoy islands, scattered between 8°N-12°N and 71°E-74°E longitude.
• Located approximately 280 km-480 km off the Kerala coast, these islands are built of coral deposits.
• Among the approximately 36 islands, 11 are inhabited, with Minicoy being the largest island covering an area of 453 sq. km.
• The archipelago is broadly divided by the Eleventh Degree Channel, with Amini Island to the north and Canannore Island to the south.
• The islands in this group feature storm beaches characterized by unconsolidated pebbles, shingles, cobbles, and boulders on the eastern seaboard.

FAQs on Class 11 Geography Ch 2 Structure and Physiography

What is meant by physiography?

Physiography refers to the study and description of physical features and natural landscapes of the Earth’s surface, including landforms, terrain, and the underlying geological structures.

What are the major physiographic divisions of India?

India can be broadly divided into six major physiographic divisions:

• The Northern and Northeastern Mountains
• The Northern Plain
• The Peninsular Plateau
• The Indian Desert
• The Coastal Plains
• The Islands

What are some key features of the Northern and Northeastern Mountains?

The Northern and Northeastern Mountains comprise the Himalayas and the Northeastern hills. These mountains are characterized by their tectonic origin, with parallel mountain ranges, fast-flowing rivers, and various landforms such as gorges, valleys, rapids, and waterfalls.

What distinguishes the Peninsular Plateau from other physiographic divisions?

The Peninsular Plateau is a large triangular landmass bordered by mountain ranges and characterized by stable geological structures. It is one of the oldest and most stable landmasses in India, featuring plateaus, block mountains, rift valleys, and rocky structures.

What are the main characteristics of the Indian Desert?

The Indian Desert, located in the northwest, is characterized by undulating topography, longitudinal dunes, and arid climate with low vegetation cover. It receives minimal rainfall, resulting in water deficit conditions, and features streams that disappear into lakes or playas.