Question #aebf7
1 Answer
Rivers pick up and move sediments in the river beds (erosion) and deposit them in the lower stretch of the river (deposition).
Explanation:
The very mobility of rivers makes them effective agents of erosion and deposition.
In the upper reaches of the river, where the gradient is steeper and the flow is faster, rivers erode the river bed and river banks in three different ways:
1. The sheer physical force of the water moves sediments.
2. The water corrodes sediments by chemically removing and dissolving ions.
3. The water contains suspended particles which physically strike the bed or banks and erode them.
This stage of the river creates, over time, V-shaped valleys, waterfalls, and gorges as the topography is changed by erosion.
In the middle stretch of the river, while erosion continues, especially of the banks, the sediments are mainly transported.
Towards the last stage of the river,, when the river is more sluggish, wider, on a level plain, and approaching its end (lake or sea), erosion of the bed is almost absent, while erosion of the banks continues. However, this stage is characterised more by deposition of the eroded sediments (also called silt) in the flood plain of the river. This can also lead to unique structures like deltaic islands, meanders, oxbow lakes, etc.
