Let’s know how can a river grow old? We have explained how some of the rain which falls onto the land surface find its way into the rivers and how a river system is born, but now we have a chance to look at another one of these familiar geological cycles. This time it is the cycle of erosion.
This really means the way in which a river system works upon and molds the land forms. It has been suggested by an eminent scientist called W.M. Davis that there is a sequence of stages. He suggested that a river valley system can pass through three major stages provided that there is no interruption by further uplift of the land. He called these stages youth, maturity, and old age.
In practice, it is now thought not to b quite as simple as this, but you would still be able to recognize these stages if you saw them in the countryside. Davis suggested that in the youthful stage when the land has only just been uplifted the water rushes down the steep slopes carving deep, narrow valleys with many waterfalls.
Eventually, the rate at which these valleys are carved slows down and the river becomes wider, particularly where the rocks are less resistant to this wearing away. At this stage, the actions of the main rivers and their tributaries have begun to wear down and flatten the original surface. This is the mature stage.
At old age, the landscape has been worn to that of a flat or very gently sloped region called a peneplain. The main rivers wind their way slowly towards the sea in aeries of loops called meanders. Those hills which do survive are called monadnocks.
This time of old age, or the senile stage as it is sometimes called, may take a very long time to develop fully and in addition to the meanders you may be able to see that the river channel may eventually become raised above the level of the surrounding plain. The embankments holding back the waters are made up of fine salty or a sandy material called alluvium deposited there during times of flooding. They are called levees.
Sometimes, the meanders may curve around so far that the river finds it easier not to flow around the bend and the neck of the bend is cut off, leaving the remaining band as an ox-bow lake.
Finally, it may happen the sea-level may fall or the whole or part of the pen plan may be uplifted again and the river may be rejuvenated. That is, new rapids may be born, and the meander channels may be cut much more deeply by the fast flowing waters which then flow down to the sea.
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