Читать книгу Introducing Large Rivers - Avijit Gupta - Страница 19

The origin of a large river requires a suitable geological framework that creates (i) a large basin and (ii) a major river that slopes from elevated headwaters to the edge of the continent. Such developments happen primarily via plate tectonics although there could be other explanations. Sufficient precipitation needs to be accumulated in the basin to support and maintain the river. The basic form and function of the river that flows on the surface are spatially modified further by regional and local tectonics.

The size of the basin and the river is determined by plate tectonics and the amount of precipitation received by the area. The size of the river may change because of (i) plate movements which may lead to crustal spread or shortening and (ii) increase or decrease of precipitation. A large river therefore has a beginning and an end, and exists for a length of time. Several rivers such as the Mississippi or the Nile are very old and include parts of an earlier system. Many large rivers of the present are much younger, a number of them coming into existence or being drastically modified after the formation of the young fold mountains such as the Andes or the Himalaya.