Question

'the entire northern plains are made of alluvial soil' expain the reason

Answer 1

It is made up of the alluvium brought here and deposited by the rivers that have been eroding the Himalayas since ages.The same alluvium deposited in the trench like structure that was the earlier shape of norther region gave rise to the plains of northern India.The mains rivers that gave birth to these vast plains are The Indus ,The Ganga and The Brahmaputra .The eroded fine slit Alluvium was deposited at the foot–hills of the lofty Himalayas for millions and millions of years