Question

How does the indo ganga brahmaptura plain formed

Answer 1

Formation of Indo – Gangetic – Brahmaputra Plain

The formation of Indo-Gangetic plain is closely related to the formation of Himalayas


Formation of Indo – Gangetic – Brahmaputra trough
The rivers which were previously flowing into Tethys sea (Before Indian Plate collided with Eurasian Plate – continental drift, plate tectonics) deposited huge amount of sediments in the Tethys Geosyncline. [Geosyncline – a huge depression]

Himalayas are formed out of these sediments which were uplifted, folded and compressed due to northern movement of Indian Plate.

Northern movement of Indian Plate also created a trough to the south of Himalayas.

Depositional Activity

During the initial stages of upliftment of sediments, the already existing rivers changed their course several times and they were rejuvenated each time (perpetual youth stage of rivers {Fluvial Landforms}).

The rejuvenation is associated with intense headward and vertical downcutting of the soft strata overlying the harder rock stratum.

Headward erosion and vertical erosion of the river valley in the initial stages, lateral erosion in later stages contributed huge amount of conglomerates (detritus)(rock debris, silt, clay etc.) which were carried downslope.

[Head ward erosion == Erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, and so causes the stream channel to lengthen]

These conglomerates were deposited in the depression (Indo-Gangetic Trough or Indo-Gangetic syncline) (the base of the geosyncline is a hard crystalline rock) between peninsular India and the convergent boundary (the region of present day Himalayas).

New rivers and more alluvium

The raising of Himalayas and subsequent formation of glaciers gave rise to many new rivers. These rivers along with glacial erosion {Glacial Landforms}, supplied more alluvium which intensified the filling of the depression.

With the accumulation of more and more sediments (conglomerates), the Tethys sea started receding.

With passage of the time, the depression was completely filled with alluvium, gravel, rock debris (conglomerates) and the Tethys completely disappeared leaving behind a monotonous aggradational plain.

[monotonous == featureless topography; aggradational plain == plain formed due to depositional activity. Indo-Gangetic plain is a monotonous aggradational plain formed due to fluvial depositions].

Upper peninsular rivers have also contributed to the formation of plains, but to a very small extent.

During the recent times (since few million years), depositional work of three major river systems viz., the Indus, the Ganga and the Brahmaputra have become predominant.

Hence this arcuate (curved) plain is also known as Indo-Gangetic-Brahmaputra Plain.