Indo-Gangetic-Brahmaputra Plain etc : Formation, Topography, Geographical Regions, River Systems, Bhabhar, Tarai, Bangar, Khadar etc
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.
-
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.
