This plain extends from west to east, between Himalayas in the north and Great Indian Plateau in the south. The plain extends from the arid and semi-arid areas of Rajasthan in the west to Brahmputra valley in the east.
The area of this plain is more than 7 lakh square km. This plain is very fertile and a very sizeable part of the Indian population lives in innumerable villages and several big cities in this region.
This plain is made up of the soils brought down and deposited by the rivers flowing from the Himalayas in the North and the Great Indian plateau in the South. The rivers have been depositing their sediments in this plain over millions of years. Therefore, the alluvium in this plain is quite a few hundred metres deep. In some of the parts, the depth of the sediments is as much as 2000 to 3000 metres.
This plain is almost dead flat. Its average height is 200 metres above the mean sea level. Due to a very gentle slope towards the sea, the rivers in this plain flow very leisurely and at times even sluggishly. The slope from Varanasi upto the mouth of Ganga is only 10 cm per km. The land around Ambala is a bit more elevated.
However, it acts as a water divide between the two major river basins - the Satluj in the west and the Ganga in the east. Rivers lying eastwards of this water divide flow into the Bay of Bengal while those west of it flow into the Arabian Sea.
The relatively higher part of the plain is called bangar. This area is never covered with flood water of the rivers. Contrary to this, the comparatively lower area is called the khadar. This area is flooded by streams almost every year. Khadar area is known as bet in Punjab.
There is a strip of plain about 10-15 km broad along the outer slopes of the Siwaliks in Punjab, Haryana and Uttar Pradesh. This region is known as bhabar. This strip of bhabar is made of gravel and coarse sand. The smaller streams disappear under ground in the bhabar region during the summer season and their water surfaces again after crossing the bhabar.
This water accumulates in the strip of plain about 15 to 30 km wide and extends to the south of bhabar. Accumulation of this water makes the land marshy. This marshy land is called the terai. Many parts of the terai have been reclaimed, for agricultural purposes.
The great Northern Plain can be divided into four parts:
This region includes the Rajasthan desert and bangar region lying to the west of Aravali ranges. The desert is partly rocky and partly sandy. In the ancient period, the perennial streams - Saraswati and Drishadvati - flowed through this region. This region includes the fertile area of Bikaner.
River Luni flows through this bangar region and falls into the Rann of Kutchchh. The famous salt water lake of Sambhar is situated in this part of the plain.
This plain extends over Punjab, Haryana and Uttar Pradesh. The part of this plain extending into Punjab and Haryana has been formed by the alluvium brought by rivers Satluj, Beas and Ravi. This is a very fertile area.
The part of this plain lying in Uttar Pradesh is made up of the deposits laid down, by the rivers like, Ganga, Yamuna, Ramganga, Gomati, Ghagra and Gandak. This part of plain is highly fertile and has been the cradle of Indian civilization and culture.
This part of the great plains covers the middle and the lower Ganga valley lying in the states of Bihar and West Bengal. Ganga flows through the middle of this plain in Bihar. Ghagra, Kosi and Gandak join Ganga from the north while Son joins from south.
On entering West Bengal the plain widens further extending from the foot hills of the Himalayas upto the Bay of Bengal. The southern part of the plain is delta region. Ganga is divided into several distributaries in the delta region. Hooghly is the best example of a distributary of Ganga. This part of the plain is very fertile and more rainy.
The northeastern part of the Great Indian Plain extends into Assam. This plain has been formed by deposition of alluvium brought down by river Brahmputra and its tributaries. Brahmputra is highly prone to devastating floods at regular intervals. After the floods, the river generally changes its course. This process has led to the formation of various islands in the river.
Majuli (1250 square kilometer) in the Brahmputra river is the world’s largest river island. This part is also very fertile. It is surrounded by hills from three sides. Bangladesh is situated on this plain and the delta jointly formed by Ganga and Brahmaputra and their distributaries.