Indo-Gangetic-Brahmaputra Plain

Indo-Gangetic-Brahmaputra Plain

• Contour Line: The 300m contour line divides the Himalayas and the Gangetic Basin.



• Southern Boundary: Demarcated by the edge of the peninsula coinciding with 75m contours for most of its length and 35m in the northeastern section, towards the delta.
• Topography: Extremely flat plains with a slope of nearly 1:1000 to 1:2000.
• Characteristics: The plains are flat, rolling, and have a monotonous character.

Formation of Indo-Gangetic-Brahmaputra Plain

• Himalayan Formation: The formation of the Indo-Gangetic plain is closely related to the formation of the Himalayas.
• Tethys Sea: Rivers previously flowed into the Tethys Sea before the Indian Plate collided with the Eurasian Plate.
• Deposition: These rivers deposited a large amount of sediments in the Tethys Geosyncline.



• Himalayas Formation: These sediments were uplifted, folded, and compressed, forming the Himalayas due to the northern movement of the Indian Plate.
• Trough Formation: The northern movement of the Indian Plate also created a trough to the south of the Himalayas.

Depositional Activity

• River Rejuvenation: The already existing rivers changed their course multiple times during the upliftment of the Himalayas, becoming rejuvenated (perpetual youth stage).
• Intense Erosion: Rejuvenation led to intense headward and vertical downcutting of soft strata overlying harder rock.
• Erosion Types: Headward erosion and vertical erosion in the early stages, lateral erosion in later stages contributed to huge amounts of conglomerates (detritus).
• Headward Erosion: Erosion at the origin of a stream channel, causing the stream channel to lengthen.
• Conglomerate Deposition: These conglomerates were deposited in the Indo-Gangetic Trough (syncline) between Peninsular India and the convergent boundary.

New Rivers and Alluvium

• Himalayan Upliftment: The upliftment of the Himalayas and glacier formation gave rise to new rivers.



• Glacial Erosion: These rivers, along with glacial erosion, supplied more alluvium, filling the depression further.
• Tethys Sea Receding: With the accumulation of sediments, the Tethys Sea began to recede.
• Aggradational Plain: Eventually, the depression was completely filled with alluvium, gravel, rock debris, forming a monotonous aggradational plain.
• Indo-Gangetic Plain: This is a monotonous aggradational plain formed due to fluvial depositions.
  • This arcuate (curved) plain is also known as the Indo-Gangetic-Brahmaputra Plain.

Contributions of Upper Peninsular Rivers

• The upper Peninsular rivers contributed to the formation of plains to a small extent.
• In recent times, the depositional work of three major river systems – the Indus, the Ganga, and the Brahmaputra – has become predominant.

Longitudinal Profile – Indo-Gangetic Plains

• Regions: Bhabhar, Tarai, Bangar, Khadar

Bhabhar Region

• Location: Adjacent to Shiwalik foothills.
• Composition: Coarse materials like cobbles, pebbles, gravels, boulders, and coarse sand.
• Characteristics: Narrow, porous stretch (8-16 km wide) running east-west, continuous from the Indus to the Tista.



• Unique Feature: High porosity due to the deposition of pebbles and rock debris.
• River Disappearance: Streams disappear once they reach the Bhabhar due to porosity, except during the rainy season.
• Agriculture: Unsuitable for agriculture; only trees with large roots thrive.
• Geographical Extent: Stretches from Punjab to Assam Himalayas.

Terai Plains

• Location: South of Bhabhar, parallel to the mountains from Punjab to Assam.



• Characteristics: Marshy, ill-drained, and thickly forested tract (15-30 km wide).
• Water Re-emergence: Underground streams of the Bhabhar re-emerge in the Terai, making it more prominent in the east due to higher rainfall.
• Soil Fertility: Nitrogen-rich soil with humus content, ideal for agriculture (sugarcane, rice, wheat).
• Widest Area: Widest along Bihar and eastern UP; narrowest in the east.

Bangar Region

• Location: Older alluvium along the river beds forming terraces higher than the flood plain.
• Notable Feature: Terraces impregnated with calcareous concretions known as ‘Kankar’.
• Regional Variations: The ‘Barind Plains’ in Bengal and the ‘Bhur formations’ in the Ganga-Yamuna Doab.
• Bhur Formations: Elevated pieces of land formed due to wind-blown sands during dry months.
• Fossils: Contains fossils of animals like rhinoceros, hippopotamus, elephants.
• Soil Degradation: Degraded in parts of UP due to salinization, leading to infertile Usar lands.

Barind Tract (Barind Plains)

• Location: A Pleistocene era unit in northwestern Bangladesh and north-central West Bengal, India.
• Border: Bordered by the floodplains of the Mahananda River to the west and the Karatoya River to the east.
• Soil Type: Characterized by reddish and yellowish clay soils, recognized as old alluvium.
• Elevation: A comparatively high, undulating region.

Khadar Region

• Composition: Newer alluvium forming flood plains along the river banks.
• Alluvial Deposition: New layers of alluvium deposited by river floods almost every year.
• Fertility: One of the most fertile regions along the Ganges.

Reh or Kollar

• Location: Saline efflorescences of drier areas in Haryana.
• Expansion: Reh areas have expanded with increased irrigation, where capillary action brings salts to the surface.

Rajasthan Plains

• Location: Ghaghar basin in North, Aravallis in East.
• Geology: Part of the Thar desert with alluvial deposits of Indus and its tributaries.
• Elevation: Average of 325 m above mean sea level.
• Rainfall: 25 cm isohyte divides the plain into Marusthali (west) and Rajasthan Bagar (east).
• Marusthali: Desert with shifting sand dunes called Dhrian.
• Vegetation: Khejri tree (associated with the Bishnoi tribe).



• Rajasthan Bagar: Semi-arid fertile tracts known as Rohi.
• Saline Lakes: Sambhar, Didwana, Degana, Kuchaman (largest is Sambhar lake near Jaipur).

Punjab Plains

• Formation: Formed by five rivers of the Indus system: Jhelum, Chenab, Ravi, Sutlej, Beas.
• Doabs: Chaj, Rechna, Bist, Bari, Sindsagar.

• 

• Elevation: Average of 250 m above mean sea level.
• Area: Total area is about 1.75 lakh sq km.
• Boundaries: Bounded by 291m contour line running parallel to Delhi–Ambala ridge; subsurface Delhi-Aravali ridge forms the eastern boundary.
• Regions: Malwa Plain (south of Sutlej), Haryana Tract (between Ghaggar and Yamuna rivers).
• Drainage Issues: Poor drainage, flood-prone areas.
• Ghaggar River: Present-day successor of the Saraswati River.

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Gangetic Plains

• Size: Largest unit of the Great Plain of India, covering about 3.75 lakh sq km from Delhi to Kolkata.
• Formation: Formed by the alluvial deposits of the Ganga and its tributaries, as well as rivers from the Peninsular Plateau.
• Landforms: Levees, bluffs, oxbow lakes, marshes, ravines.
• Floods: Frequent river course shifts, particularly Kosi river, known as the ‘Sorrow of Bihar’.
• Divisions: Upper Gangetic Plain, Middle Gangetic Plain, Lower Gangetic Plain.



• Upper Gangetic Plain: Includes Rohilkhand Plains, Ganga-Yamuna Doab, Yamuna-Chambal Basin.
• Middle Gangetic Plain: Includes Awadh Plain, Mithila Plain, and Magadh Plain.
• Lower Gangetic Plain: Includes Paradelta, Rarh Plains, and Delta Plains (Sunderbans).

Brahmaputra Plains

• Other Names: Also known as Assam Valley or Assam Plains.
• Formation: Formed by the depositional work of Brahmaputra and its tributaries.
• Features: Alluvial fans, river meandering, oxbow lakes, and large marshy tracts.
• Boundaries: Indo-Bangladesh border (west), Purvanchal Hills (east).
• Terai Conditions: Coarse alluvial debris from tributaries form semi-terai conditions.

Significance of the Plain

• Population: Hosts half of India’s population.
• Agriculture: Fertile alluvial soils, slow-moving perennial rivers, and favorable climate support intense agriculture.
• Regions: Punjab, Haryana, and Western Uttar Pradesh are the granary of India.
• Infrastructure: Extensive road and rail networks support industrialization and urbanization.
• Tourism: Religious and cultural sites along sacred rivers like Ganga and Yamuna.