Ans. The formation of the Himalayas due to upliftment of sediments out of the Tethys Sea
subsidence of the northern flank of the Peninsular Plateau resulted in the formation of a large basin.
Over millions of years this depression gradually got filled up with alluvium deposited by the three m
river systems – the Indus, the Ganga and the Brahmaputra flowing from the Himalayas in the no
Sediments were also deposited by the tributaries of these rivers rising from the mountains in the north
well as the Peninsular Plateau to its south. As a result, the fertile Indo-Gangetic or Northern Plains,
the Brahmaputra Plain in the northeast, were formed.
As the Himalayas gained in height, the rivers, glaciers and other agents of denudation beca
increasingly active in erosion. As a result, large amount of silt got deposited in the shrinking Tethys.