1.5 - Geography Notes 37

Elaborate Notes

The Peninsular Block

The Peninsular Block, also known as the Peninsular Plateau, represents the oldest and most stable landmass of the Indian subcontinent. It is a vast tableland composed primarily of ancient crystalline, igneous, and metamorphic rocks.

• Geological History: It was a part of the Gondwana supercontinent, which began to break apart around 150 million years ago during the Jurassic period. As a rigid block, it has remained largely immune to the intense mountain-building forces that shaped the Himalayas, experiencing only block faulting and vertical movements. Geologists like D.N. Wadia, in his seminal work “Geology of India” (1919), described it as a ‘horst’ or a segment of the earth’s crust that has remained stable while adjacent areas have subsided.
• Boundaries and Extent: The block is roughly triangular. Its northern boundary is irregular, marked by the Aravalli Range, the Malwa and Chotanagpur plateaus, and extending up to the Ganga-Brahmaputra plains. In the northeast, it extends to the Meghalaya Plateau (Shillong Plateau) and the Karbi-Anglong Plateau. It is flanked by the Western Ghats on the west and the Eastern Ghats on the east.
• Malda Gap: The northeastern extension, the Meghalaya Plateau, is separated from the main peninsular block by a significant depression known as the Malda Gap or the Garo-Rajmahal Gap. This gap was formed by down-faulting (a normal fault) during the Himalayan orogeny. Later, it was filled by sediments deposited by the Ganga and Brahmaputra rivers, creating the fertile plains of present-day Bangladesh and West Bengal. This geological separation is a key reason why the Meghalaya plateau exhibits geological characteristics similar to the Chotanagpur Plateau rather than the Himalayas.
• Tectonic Episodes: Despite its overall stability, the block has undergone significant tectonic events:
  1. Submergence of the Western Flank: The western coast of India, particularly the part adjoining the Western Ghats, is believed to be a submerged coastline. This is evidenced by the straight coastline and the steep, fault-scarp face of the Western Ghats. This submergence is thought to have occurred during the early Tertiary period, separating the Laccadive Islands (Lakshadweep) from the mainland.
  2. Formation of Rift Valleys: The peninsular block is traversed by several rift valleys, which are elongated valleys formed by the sinking of a block of land between two faults. The most prominent examples are the Narmada and Tapi (or Tapti) rift valleys. These rivers flow westwards through these troughs, which is contrary to the general east-flowing drainage pattern of the peninsula.
  3. Deccan Traps Formation: During the late Cretaceous period, around 66 million years ago, as the Indian plate drifted northwards over the Réunion hotspot, massive fissures erupted, leading to extensive basaltic lava flows. This event, known as flood basalt eruption, covered a vast area of western and central India, forming the step-like topography of the Deccan Traps. The term ‘trap’ is derived from the Swedish word ‘trappa’, meaning stairs. Scholars like W. D. West have extensively studied the Deccan Traps, noting their thickness can exceed 2,000 meters in some areas.

Mountain Ranges in Peninsular Block

• Aravalli Range: Running from Delhi to Gujarat in a southwest direction, the Aravallis are one of the oldest fold mountain systems in the world, formed during the Proterozoic era. They are now considered relict mountains, heavily eroded and denuded over geological time, with peaks like Guru Shikhar (1,722 m) being their highest point.
• Vindhyas and Satpuras: These are not true fold mountains but are classified as block mountains. They were formed due to tensional forces leading to the subsidence of the land between them, creating the Narmada rift valley. The Vindhyan range acts as a major water divide between the Ganga river system to the north and the peninsular river systems to the south. The Satpura range runs parallel to the Vindhyas, south of the Narmada river. The correct North-to-South sequence is: Vindhya Range > Narmada River > Satpura Range > Tapi River.
• Western Ghats (Sahyadris): A continuous chain of mountains running parallel to the western coast. They are the faulted edge of the Deccan Plateau and are known for their steep western slopes and gentle eastern slopes.
• Eastern Ghats: A discontinuous series of eroded and broken hills running parallel to the eastern coast, dissected by major east-flowing peninsular rivers like the Mahanadi, Godavari, Krishna, and Kaveri.

Western Ghats and Eastern Ghats Comparison

Feature	Western Ghats (Sahyadris)	Eastern Ghats (Purvanchal)
Extent	Run from the south of the Tapi river valley in Gujarat to Kanyakumari in Tamil Nadu, for about 1,600 km.	Run from the Mahanadi valley in Odisha to the Nilgiri Hills in Tamil Nadu.
Continuity	A near-continuous range, traversed only by a few passes like Thalghat, Bhorghat, and Palghat.	Highly discontinuous and fragmented, eroded by large east-flowing rivers originating in the Western Ghats.
Elevation & Slope	Higher in elevation (average 900-1600 m). Act as a true escarpment with a steep western face and a gentle eastern slope. Overall height increases from north to south.	Lower in elevation (average 600 m). They are a series of detached residual hills. The height generally increases from south to north, but the highest peaks are in the central part.
Highest Peak	Anaimudi (2,695 m) in the Anaimalai Hills, Kerala. It is the highest peak in Peninsular India.	The highest peak is a subject of debate. While Mahendragiri (1,501 m) in Odisha was traditionally considered the highest, recent data from the Andhra Pradesh government identifies Jindhagada Peak (1,690 m) in the Araku Valley as the highest.
Coastal Proximity	Very close to the coast, resulting in a narrow western coastal plain (except in Gujarat).	Located further from the coast, resulting in a wider eastern coastal plain.
Drainage	The origin of major peninsular rivers like the Godavari, Krishna, and Kaveri, which flow eastwards. Many short, swift rivers flow westwards into the Arabian Sea.	No major river originates here. They are primarily drained by rivers that have their source in the Western Ghats.
Precipitation	Receive heavy orographic rainfall (over 250 cm annually) from the Southwest Monsoon winds, making the windward side very wet.	Receive comparatively lower rainfall (around 100 cm annually) from both Southwest and retreating Northeast Monsoons. They lie in the rain-shadow zone of the Western Ghats for the SW Monsoon.
Vegetation	The high rainfall supports lush tropical evergreen and semi-evergreen forests on the windward slopes.	The lower rainfall supports tropical moist deciduous and dry deciduous forests.
Biodiversity	A UNESCO World Heritage Site and one of the world’s eight “hottest hotspots” of biological diversity, as identified by ecologist Norman Myers (1988).	Biodiversity is significant but lower compared to the Western Ghats due to fragmentation and lower rainfall.

Sub-divisions of Ghats

• Western Ghats:
  • Sahyadris: The northern section in Maharashtra and Karnataka.
  • Baba Budan Hills: Located in Karnataka, famous for being the site where coffee was first cultivated in India by the Sufi saint Baba Budan. It contains important iron ore deposits (Kemmangundi).
  • Nilgiri Hills (‘Blue Mountains’): A major junction where the Western and Eastern Ghats meet. They are named after the endemic Neelakurinji (Strobilanthes kunthiana) flower, which blooms once every 12 years, carpeting the hills in blue.
  • Anaimalai Hills (‘Elephant Mountains’): Located south of the Palghat Gap, containing Anaimudi peak.
  • Cardamom Hills (Elamalai): The southernmost part of the Western Ghats, known for the cultivation of cardamom, pepper, and coffee.
• Eastern Ghats:
  • Northern Section: Includes ranges like Mahendragiri in Odisha and the Madugula Konda range in Andhra Pradesh (where Jindhagada is located).
  • Central Section: Comprises prominent ranges like the Nallamala Hills and Palkonda Hills in Andhra Pradesh. The sacred Tirupati shrine is located in the Seshachalam Hills, an extension of the Palkonda range.
  • Southern Section: Includes the Javadi Hills and Shevaroy Hills in Tamil Nadu, which are composed of charnockites and gneisses.

Plateaus of Peninsular Block

• Malwa Plateau: Located in central India, bounded by the Aravallis to the west and the Bundelkhand region to the east. It is composed of basaltic lava from the Deccan Traps and is drained by rivers like Chambal and Betwa.
• Bundelkhand Plateau: An upland region south of the Yamuna river, spanning parts of Uttar Pradesh and Madhya Pradesh. It is known for its senile topography, composed of ancient ‘Bundelkhand gneiss’.
• Chotanagpur Plateau: Covers most of Jharkhand and adjacent parts of Odisha, West Bengal, and Chhattisgarh. It is a storehouse of minerals like coal, iron ore, mica, and bauxite. It consists of a series of plateaus at different elevations, such as the Patlands, Hazaribagh Plateau, and Ranchi Plateau.
• Meghalaya Plateau (Shillong Plateau): An eastward extension of the main Peninsular Block, separated by the Malda Gap. It includes the Garo, Khasi, and Jaintia hills, named after the local tribes. This region receives the highest rainfall in the world (e.g., Mawsynram).
• Deccan Plateau: The largest plateau in India, triangular in shape, lying south of the Satpura Range. It is bordered by the Western and Eastern Ghats. Its northern part is covered by the basaltic Deccan Traps.
• Telangana and Rayalaseema Plateaus: The Deccan plateau in Andhra Pradesh and Telangana is divided into two distinct regions by the Krishna River. The northern part is the Telangana Plateau, and the southern part is the Rayalaseema Plateau. The name ‘Rayalaseema’ is historical, derived from the ‘Rayas’ (kings) of the Vijayanagara Empire who ruled the region.
• Karnataka Plateau (Mysore Plateau): Located south of the Deccan Traps. Its western, hilly part, adjoining the Sahyadris, is known as Malnad (literally, ‘hill country’), characterized by dense forests. The eastern part is a rolling plain with lower elevation, known as the Maidan (‘plain country’).
• Dandakaranya Plateau: A physiographic region in east-central India, covering parts of Chhattisgarh, Odisha, and Andhra Pradesh. It is a rugged, forested upland and is historically significant as the place mentioned in the epic Ramayana.

The Plains of India

• Northern Plains:

  • Origin: Formed by the process of aggradation, which is the deposition of sediments. Geologically, they are the youngest physiographic feature of India. They occupy a foredeep or a depression that formed south of the Himalayas as they were uplifted. This depression was subsequently filled with alluvial deposits brought by the Himalayan rivers (Indus, Ganga, Brahmaputra) and their tributaries over millions of years. This theory was prominently explained by geologist Eduard Suess.
  • Extent: Stretching about 2,400 km in India (total 3,200 km including Pakistan) and varying in width from 240 to 320 km. It is the world’s largest expanse of uninterrupted alluvium.
  • Divisions:
    1. Rajasthan Plain: West of the Aravallis. The western part is a true desert known as Marusthali (Thar Desert). The eastern part is a semi-arid plain called Rajasthan Bagar, drained by the Luni river. Evidence of palaeo-channels suggests the presence of mighty rivers like the Saraswati in the past.
    2. Punjab-Haryana Plains: Formed by the Indus and its tributaries. The landscape is dominated by Doabs (land between two rivers).
    3. Ganga Plains: The largest unit, stretching from Delhi to Kolkata across UP, Bihar, and West Bengal. Sub-divided into Upper Ganga Plain (Doab, Rohilkhand), Middle Ganga Plain (Awadh), and Lower Ganga Plain.
    4. Brahmaputra Plains: Also known as the Assam Plains. A narrow plain extending from Sadiya in the east to Dhubri in the west, flanked by high mountains on all sides except the west. Prone to frequent flooding and river channel shifting.

• Types of Northern Plains (based on geomorphology, from north to south):

  • Bhabar: A narrow, porous belt (8-16 km wide) along the foothills of the Shiwaliks. It is composed of coarse gravel and boulders deposited by rivers descending from the mountains. Due to high porosity, smaller streams disappear underground in this zone. Not suitable for agriculture.
  • Terai: A marshy, damp, and thickly forested tract (15-30 km wide) south of the Bhabar. Here, the underground streams from the Bhabar re-emerge on the surface. The soil is fertile and rich in nitrogen. Much of the Terai has been cleared for agriculture, especially for cultivating rice, sugarcane, and wheat. The high humidity and stagnant water make it prone to mosquito-borne diseases like malaria.
  • Bangar: Composed of older alluvium, it forms the higher ground of the plains, located away from the river banks. This area is less prone to flooding. The soil contains calcareous concretions called ‘kankar’ and is less fertile than Khadar. It is where most of the population is settled.
  • Khadar: Composed of newer, finer alluvium, it forms the floodplains along the river banks. The soil is replenished by fresh silt deposits every year during floods, making it the most fertile tract of the Ganga plains. Ideal for intensive agriculture.

• Duars Formation: The term ‘Duar’ means ‘door’ in local languages. These are alluvial floodplains in the eastern Himalayas’ foothills, particularly in West Bengal and Assam. Similar to the Terai, they are formed by coarse sediments deposited by swift-flowing Himalayan rivers. The fertile soil and sloping terrain are ideal for tea cultivation, making Darjeeling and Assam famous for their tea gardens.

• Coastal Plains:

  • These plains are located between the peninsular plateau and the coastline.
  • Western Coastal Plains: A narrow belt from the Rann of Kutch to Kanyakumari. It is a submerged coast, except for the Malabar coast which shows evidence of emergence (e.g., presence of lagoons and backwaters called ‘kayals’). This submergence is the reason for its narrowness and the presence of natural harbours.
    • Divisions: Kathiawar Coast (Gujarat), Konkan Coast (Maharashtra, Goa), and Malabar Coast (Karnataka, Kerala).
  • Eastern Coastal Plains: A wider and more level plain from the Sundarbans to Kanyakumari. It is an emergent coast, characterized by depositional features. The large east-flowing rivers have built extensive deltas (Mahanadi, Godavari, Krishna, Kaveri).
    • Divisions: Utkal Coast (Odisha), Northern Circars (Andhra Pradesh), and Coromandel Coast (Tamil Nadu).

Comparison of Coastal Plains

Feature	Western Coastal Plain	Eastern Coastal Plain
Origin	Submerged coastline (except Malabar). Tectonic uplift and submergence played a key role.	Emergent coastline, formed primarily by alluvial deposition by rivers.
Width	Narrower, with an average width of about 65 km.	Wider, with an average width of 120 km, reaching up to 200 km in deltaic regions.
River Mouths	Dominated by estuaries and lagoons. The short, swift rivers do not carry enough sediment to form deltas.	Dominated by well-developed deltas formed by the large, sediment-laden rivers.
Coastline	Indented or broken coastline, providing natural conditions for the development of ports and harbours (e.g., Mumbai, Kandla, Kochi).	Smooth, regular coastline, making natural harbour development difficult. Most ports are artificial (e.g., Chennai, Tuticorin), except for Visakhapatnam.
Depositional Features	Less prominent due to higher wave energy and steeper gradient.	Prominent depositional features like beaches, sandbars, spits, and lagoons (e.g., Chilika Lake, Pulicat Lake).
Continental Shelf	Wider continental shelf, especially off the coast of Mumbai, which is rich in petroleum and natural gas deposits (e.g., Mumbai High).	Narrower continental shelf.

Prelims Pointers

• Geological Feature: The Peninsular Block is a part of the ancient Gondwana landmass.
• Separation Gap: The Meghalaya Plateau is separated from the main peninsular block by the Malda Gap or Garo-Rajmahal Gap.
• Volcanic Formation: Deccan Traps were formed due to fissure eruption over the Réunion hotspot during the Cretaceous period.
• Mountain Types:
  • Aravallis are old fold mountains (relict mountains).
  • Vindhyas and Satpuras are block mountains.
• N-S Sequence: Vindhya Range → Narmada River → Satpura Range → Tapi River.
• Highest Peaks:
  • Peninsular India & Western Ghats: Anaimudi (2,695 m) in Anaimalai Hills.
  • Eastern Ghats: Jindhagada Peak (1,690 m) or Mahendragiri (1,501 m).
  • Aravalli Range: Guru Shikhar (1,722 m).
• Ghats Confluence: The Western Ghats and Eastern Ghats meet at the Nilgiri Hills.
• Specific Hills/Plateaus:
  • Coffee cultivation origin: Baba Budan Hills, Karnataka.
  • Neelakurinji flowers: Nilgiri Hills.
  • Tirupati shrine: Palkonda Range (Seshachalam Hills).
  • Karnataka Plateau Divisions: Hilly Malnad (west) and plain Maidan (east).
  • Chotanagpur Plateau: Known as the ‘storehouse of minerals’ in India.
• Northern Plains Terminology:
  • Doab: Land between two rivers.
  • Bhabar: Porous belt of boulders at the foothills where streams disappear.
  • Terai: Marshy region south of Bhabar where streams re-emerge.
  • Bangar: Older alluvium, found away from rivers. Contains ‘kankar’.
  • Khadar: Newer alluvium, found in floodplains. Most fertile.
• Punjab Doabs:
  1. Bist Doab: Between Beas and Sutlej.
  2. Bari Doab: Between Beas and Ravi.
  3. Rechna Doab: Between Ravi and Chenab.
  4. Chaj Doab: Between Chenab and Jhelum.
  5. Sind Sagar Doab: Between Jhelum-Chenab and Indus.
• Eastern Foothills: Alluvial plains in the eastern Himalayan foothills are called Duars (famous for tea).
• Coastal Plains:
  • Western Coast: Submerged coast, narrow, forms estuaries, has natural harbours.
  • Eastern Coast: Emergent coast, wide, forms deltas, has mostly artificial harbours.
• Coastal Names (North to South):
  • West Coast: Kathiawar → Konkan → Malabar.
  • East Coast: Utkal → Northern Circars → Coromandel.
• Backwaters: Lagoons on the Malabar Coast are called kayals (e.g., Vembanad Kayal).

Mains Insights

GS Paper I: Geography

1. Interrelation between Physiography and Economy:

   • Peninsular Plateau: The ancient geological structure makes the Chotanagpur and Dandakaranya plateaus rich in metallic minerals (iron, manganese) and coal, forming the industrial heartland of India. However, the plateau’s undulating terrain and non-perennial rivers pose challenges for irrigation.
   • Northern Plains: The fertile alluvial soils deposited by Himalayan rivers have made this region the “Granary of India,” supporting high population density and intensive agriculture. This has socio-economic implications, including issues of land fragmentation and the need for sustainable agricultural practices (e.g., post-Green Revolution challenges).
   • Coastal Plains: The contrasting nature of the western and eastern coasts directly impacts economic activities. The indented west coast fosters natural harbours, boosting trade (e.g., Mumbai Port). The wider continental shelf here is crucial for oil and gas exploration (Mumbai High). The deltas on the east coast form fertile ‘rice bowls’ (e.g., Krishna-Godavari delta).

2. Impact of Tectonics on Indian Physiography:

   • Cause-Effect: The northward movement of the Indian plate not only caused the Himalayan orogeny but also secondary tectonic events in the “stable” peninsular block. The formation of the Narmada-Tapi rift valleys is a direct consequence of these tensional forces. This has created a unique westward drainage pattern for these two rivers, unlike the general eastward slope of the peninsula.
   • Deccan Traps: The passage over the Réunion hotspot led to the formation of the Deccan Traps. This has resulted in black soil (regur), which is ideal for cotton cultivation, shaping the agrarian economy of Maharashtra and surrounding regions. It also provides a unique geological landscape to study flood basalt volcanism.

3. The Western Ghats: A Case Study in Bio-Geographical Significance:

   • Ecological Importance: The continuous nature of the Western Ghats creates a significant orographic barrier, profoundly influencing the monsoonal climate of the entire Indian peninsula. It is a UNESCO World Heritage site and a global biodiversity hotspot, hosting a large number of endemic species.
   • Debate & Conservation: The ecological sensitivity of the Ghats is a subject of intense debate, as highlighted by the reports of the Madhav Gadgil Committee (Western Ghats Ecology Expert Panel, 2011) and the K. Kasturirangan Committee (2013). The debate revolves around balancing conservation with developmental needs (mining, infrastructure, agriculture), a classic environment vs. development dilemma relevant for GS Paper III as well.

4. River Systems and Human Settlements:

   • The formation of Bangar and Khadar plains has historically influenced settlement patterns. The older, safer Bangar plains have been home to dense, ancient settlements, while the fertile but flood-prone Khadar plains were used primarily for seasonal agriculture. This dynamic relationship between rivers and human life is a central theme in Indian geography and history.
   • The dissection of the Eastern Ghats by rivers has created fertile basins and deltas, supporting large agricultural populations. However, it has also made the mountain range ecologically fragmented and more vulnerable to environmental degradation compared to the more contiguous Western Ghats.