In this article, we will discuss The Great Plains of India. So, let’s get started.
The Great Plains Of India
The Great Plains of India lies to the south of the Shiwalik separated by the Himalayan Front
Fault (HFF). It is a transitional zone between the Himalaya of the north and Peninsular India
of the south. It is an aggradational plain formed by the alluvial deposits of the Indus, Ganga,
Brahmaputra and their tributaries. The plain stretches for about 2400 km from west to east. It has varying width; 90–100 km in Assam, 160 km near Rajmahal (Jharkhand), 200 km in Bihar, 280 km near Allahabad and 500 km in Punjab. In general, the width of the plain increases from east to west.
The Great Plains of India consist largely of alluvial deposits brought down by the rivers
originating in the Himalayan and the Peninsular region. The exact depth of alluvium has not yet
been fully determined. According to recent estimates, the average depth of alluvium in the
southern side of the plain (north of Bundelkhand) varies between 1300 to 1400 m, while towards the Shiwaliks, the depth of alluvium increases. The maximum depth of over 8000 m has been reached near Ambala, Yamunanagar, and Jagadhri (Haryana).
The Great Plains are remarkably homogeneous with little variation in relief features for hundreds of kilometers. The monotony of the physical landscape is broken at micro-level by the
river bluffs, Bhurs, levees, dead-arms of river channels, the ravines and khols. Changing river
courses in the areas of frequent floods is a unique geomorphic process in the plains. The frequent floods, although a cause of immense damage to life and property, lay down fresh layer of silts in the flood-plains every year, providing rich fertile soils.
Origin of the Great Plains of India
There is no unanimity amongst the geologists about the origin of the Great Plains of India. The puzzling questions are related to the enormous thickness of the alluvium, nature of the depression, mode of its formation, subterranean rock-beds and the underlying geological structure, Some of the important views about the origin of the Nirthern Plains of India have been presented briefly in the following section:
Alluviation of the Foredeep
According to Edward Suess, an eminent Austrian geologist, a “foredeep” was formed in front of the high crust-waves of the Himalayaas they were checked in their southward advance by the more rigid landmass of the Peninsula of India. This foredeep was like a large synclinorium (a large syncline with a number of small anticlines and synclines) owing to the unevenness of its bottom. According to Suess, the bed of this foredeep had a gentle slope towards north whereas the Peninsular side depicted a steep gradient. This bed rests on the basement of hard crystalline Peninsular rocks through which the region is connected to the Himalayan and the Peninsular blocks. The alluviation of this foredeep led to the formation of the Great Plains by the rivers, descending from the Himalayan region. One of the serious gaps in Suess’ theoryis related to his inability to give suitable explanation to the uneven slope of the bed of the plain. Moreover, no conclusive evidence is available through which it could be inferred that there exists crustal connection between the Himalayan region and the Peninsular block through the Great Plains.
Infilling of a Rift Valley
In the opinion of Sir G. Burrard, the Northern Plains of India are the result of infilling of a rift valley. Burrard opined that during the formation of the Himalaya a nft valley was created between the two parallel faults (one along the southem boundary of the Shiwaliks and the other along the northern boundary of the Peninsula) This rift valley was filled up by the detritus brought down by the Himalayan river. In order to support his argument Burrard has cited examples of the formation of similar rift valleys in the Himalaya and the Peninsular region especially the Narmada and Tapi rift valleys.
This concept, however, does not find approval of the modern geologists. The main criticism
raised against this concept is that nowhere in the world has such a giant rift valley with a length
of 2400 km and a width of over 500 km ever been formed by crustal downwarping. Also there is no geological evidence of the formation of such a rift valley in the northern part of the Peninsular foreland. The uneven bottom and the northward slope of the bottom of the Great Plains of India have also not been explained by this concept.
Recession of the Sea
In the opinion of Blandford, during the Eocene Period. Peninsular India was joined together with
Africa. During that period, there was one sea extending from Assam Valley to the Irrawaddy river (Myanmar) in the east and another from Iran and Baluchistan to Ladakh (Indus Valley) in the west. During the last part of the Eocene Period, arms of the Western Sea extended up to Punjab. Due to the rise of the Himalaya during the Miocene Period, these seas started receding by gradual deposits of sediments from the Himalayan rivers. After a prolonged period of sedimentation and subsidence, these gulfs (Gulf of Sind in the west and the Eastern Gulf up to the Shillong Plateau) were filled up, resulting in the formation of the Northern Plains of India.
The evidences cited in favour of the recession of the sea include: (i) the occurrence of limestone rocks in Kumaun-Garhwal region of Uttarakhand, (ii) the presence of saline water lakes in Rajasthan (Sambar, Rajsazmand. Pushkar, Pachpadra. Nakki, Fatehsagar Dheberr, Balasmand, etc.),(iii) the joining of the islands of the Gulf of Kachchh with the mainland, (iv) the seaward extension of the Sundarban Delta, (v) the emergence of new islands near Bangladesh coast, and (vi) the presence of marine fossils in the sediments of the Northern Plains of India. The theory, however, fails to give convincing arguments so far as the region of the central portion of the plain is concerned.
Remnant of the Tethys
Some of the geologists and geomorphologists opine that the Great Plains of India are a remnant of the Tethys Sea. According to them, after the upheaval of the Shiwaliks, the remaining part of the Tethys was left as a large trough which was joined to the Bay of Bengal in the east and the
Arabian Sea in the west. Rivers from the Himalaya deposited their load in the trough. Because the Himalaya were rising during that period, rivers experienced rejuvenation and greater quantity of eroded material which increased the thickness of the alluviums. Due to infilling of the central part of the trough the seas located in the east and the west started receding, and the Great Plains of India come into existence.
According to the recent views, the Northern Plains of India represent a sag in the crust formed between the northward drifting of the Indian Subcontinent and the comparatively soft sediments accumulated in the Tethyan basin when the latter were crumpled and lifted up into a mountain system. Subsequently, it was filled up by the river deposits.