Chapter 2. Structure and Physiography

Overview
• The Indian plate was to south of equator millions of years ago. It was much larger in size and Australian plate was a part of it.
• The northward movement of Indian plate is continuing and it has important consequences on physical environment of Indian subcontinent.
• Over these long years, these changes were brought primarily by endogenic and exogenic forces and lateral movements of plates.

The Peninsular Block
• The northern boundary of Peninsular Block may be taken as an irregular line and it roughly run parallel with Ganga.
• The Peninsula is formed by ancient gneisses and granites, which cover a major part of it.
• Karbi Anglong and Meghalaya Plateau are in Northeast and Rajasthan is in west.
• The northeastern parts are separated by Malda fault in West Bengal from Chotanagpur plateau and in Rajasthan, these blocks are covered with desert.
• The Peninsula mostly consists of relic and residual mountains like Aravali hills, Nallamala hills, Javadi hills, Velikonda hills, Palkonda range and Mahendragiri hills, etc.
• The river valleys are shallow with low gradients. Most of east flowing rivers forms delta before entering into Bay of Bengal.
• The deltas formed by Mahanadi, Krishna, & Godavari are important examples.

The Himalayas and Other Peninsular Mountains
• The Himalayas along with other peninsular mountains are young, weak & flexible in their geological structure unlike Peninsular block that is rigid and stable.
• They are affected by exogenic and endogenic forces resulting in development of faults, folds & thrust plains.
• The Himalayas are formed out of these sediments which were uplifted, folded & compressed due to northern movement of Indian Plate.

Indo-Ganga-Brahmaputra Plain
• The Northern Plains has been formed by interplay of 3 major river systems – Indus, Ganga & Brahmaputra along with their tributaries. It spread over an area of 7 lakh sq. km.
• The rivers which were flowing from Himalayan and Peninsular parts, deposit sediments. It was a huge Geo-synclinal depression.
• The average depth of alluvial deposits in these plains ranges from 1,000 to 2,000 m.

Physiography
• ‘Physiography’ of an area is result of structure, process & stage of development. India is divided into many physiographic divisions.
• The relief and physiography of India have been greatly influenced by geological and geomorphological processes active in Indian subcontinent with mountain ranges, peaks, valleys & gorges in Northern part.
• In Southern part, it consists of a stable table land with highly dissected plateaus, denuded rocks and developed a series of scarps. It is ancient landmass on earth’s surface.

The North and North-Eastern Mountains
• The Himalayas consist of a series of parallel mountain ranges.
• Some of important ranges are Greater Himalayan range, which includes Great Himalayas and Trans-Himalayan range, Middle Himalayas and Shiwalik.
• The general orientation of these ranges is from northwest to southeast direction in northwestern part of India.
• The Himalayas in Darjeeling and Sikkim regions lie in an east-west direction, while in Arunachal Pradesh they are from southwest to northwest direction. Nagaland, Manipur & Mizoram, are in north-south direction.
• The approximate length of Great Himalayan range, called central axial range, is 2,500 km from east to west, and its width varies between 160-400 km from north to south.
• The Himalayas stand almost like a strong and long wall between Indian subcontinent and Central and East Asian countries. Himalayas are not only a physical barrier, but they are a climatic, drainage & cultural divide.
• The Himalayas have been divided based on regions from west to east.
• The part of Himalayas lying between Indus and Satluj has been traditionally called Punjab Himalaya but it is known regionally as Kashmir and Himachal Himalaya from west to east respectively.
• The part of Himalayas lying between Satluj and Kali rivers is called Kumaon Himalayas.
• The Kali and Tista rivers divide Nepal Himalayas and part lying between Tista and Dihang rivers is called Assam Himalayas.
• The Brahmaputra marks easternmost boundary of Himalayas.
• Beyond Dihang gorge, Himalayas bend sharply to south and spread along eastern boundary of India, which is called Purvanchal or eastern hills and mountains. The Purvanchal comprises Patkai hills, Naga hills, Manipur hills and Mizo or Lushai hills.

The Northern Plains
• The Western part of Northern Plain is referred to as Punjab Plains. This plain is formed by Indus and its tributaries – Jhelum, Chenab, Ravi, Beas & Satluj.
• The Ganga plain extends between Ghaggar and Tista rivers. It is spread over states of Nothern India, Haryana, Delhi, U.P., Bihar, partly Jharkhand and West Bengal.
• Brahmaputra plain lies in state of Assam.
• From north to south, these can be divided into 3 major zones: Bhabar, Terai & Alluvial plains.

The Peninsular Plateau
• The Peninsular Plateau is a tableland composed of old crystalline, igneous & metamorphic rocks.
• It was formed due to breaking and drifting of Gondwana land.
• The Peninsular plateau is black soil area called Deccan Trap.
• At height of 150 m above river plains up to an elevation of 600-900 m is irregular triangle shape called peninsular plateau.
• The Deccan Plateau – It is a triangular landmass that lies to South of river Narmada.
• An extension of plateau is visible in northeast which is called Meghalaya, KarbhiAnglong Plateau and North Cachar Hills.
• The Western Ghats and Eastern Ghats mark western and eastern edges of Deccan Plateau.

Western Ghats:
• They lies parallel to western coast.
• They are more continuous than Eastern Ghats and can be crossed through passes only.
• They are higher than Eastern Ghats. Their average elevation is 900-1600 meters.
• Anaimudi (2,695 m) is highest peak.

Eastern Ghats:
• They stretches from Mahanadi valley to Nilgiris in south.
• They are discontinuous and irregular. They are dissected by rivers draining into Bay of Bengal.
• Their average elevation is 600 meters.
• Mahendragiri (1,501 metres) is highest peak.
• The Central Highlands: The Part of Peninsular plateau lying to north of Narmada River, covering a major area of Malwa plateau, is called Central Highlands.
• The eastward extensions of this plateau are locally called Bundelkhand and Baghelkhand.
• The extension of Peninsular plateau has been covered by longitudinal sand ridges and crescentshaped dunes known as barchans.
• The Northeastern Plateau: It is believed, that due to force exerted by north-eastward movement of Indian plate at time of Himalayan origin, a huge fault was created between Rajmahal hills and Meghalaya plateau.

The Indian Desert
• The Indian desert lies towards western margins of Aravali Hills. It is a sandy plain covered with dunes.
• This region receives very low rainfall below 150 mm per year. It has a dry climate with low vegetation cover. It is called Marusthal.
• Based on orientation, desert can be divided into two parts: northern part is sloping towards Sindh and southern towards Rann of Kutch. Most of rivers in this region, are ephemeral.

The Coastal Plains
• A Coastal Plain is a flat, low-lying piece of land next to ocean.
• To east and west of Peninsular plateau, 2 narrow strips of plain lands are found, which are respectively known as Eastern Coastal Plain and Western Coastal Plain.
• Eastern Coastal Plains – It is a wide stretch of landmass lying between Eastern Ghats and Bay of Bengal.
• In northern part, it is referred to as Northern Circars, while Southern part is referred to as Coromandel Coast.
• Large rivers such as Mahanadi, Godavari, Krishna, & Kaveri have formed extensive delta on this coast. Lake Chilka is an important feature along eastern coast.
• Western Coastal Plains – It lies between Western Ghats and Arabian Sea.
• It is a narrow plain and consists of 3 sections as mentioned below: 1. The Northern part of coast is known as Konkan (Mumbai, Goa). 2. The Central part stretch is known as Kannad Plain. 3. The Southern stretch is referred to as Malabar Coast.

The Islands
• An Island is a piece of sub-continental land that is surrounded by water. Lakshadweep Islands group is composed of small coral islands.
• These Islands lie close to equator. These islands receive convectional rainfall and have an equatorial type of vegetation.
• The entire group of islands is divided into two broad categories, The Andaman in North and The Nicobar in South. These are separated by a water body which is known as Ten Degree Channel.

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