why ganga is known as an antecedent river ? please answer the question in Bengali
Answers
rivers in their young age are with full of force and do not change their direction even when they are encountered with a barrier. They even cut the barrier with the great energy they possess, just like humans in their teen age.
Like wise Antecedent rivers do not change their course even if there is a change in underlying rock topography. Let us simplify this by an example. Rivers in the himalayan region do not change their course even during the upliftment of himalayas. These rivers cut across himalayas which come in their way as the rivers possess high energy and also because of the loose and easily erodable sediments of himalayas.
Eg. Sutlez river
Superimposed rivers are formed on a horizontal bed(made of sediments) which is formed over underlying rock structure. In the course of time the river creates it's own way and erodes the horizontal bed. After the horizontal bed is eroded, river comes into contact with underlying rock structure. Though the river comes into contact with underlying rock structure, the river does not deviate from its path and follows it's own path by imposing it's own course on underlying rock structures. Even though the course of river and that of underlying rock structure are completely opposite, the river follows it's own path without any deviation. Eg chambal river.
In antecedent rivers…. The rivers are formed even before their underlying rock topography
In superimposed rivers…. The rivers are formed over already present underlying rock structures.