Erosion and Deposition River Features
I am writing this essay to explain how the process of erosion and deposition are responsible for the creation of certain river features within the middle course. The Upper course displays the waterfall, the middle course exhibits features such as meanders and ox-bow lakes, and the lower course shows features such as which are both formed due to the processes of erosion and deposition.
Erosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river. It comes in four forms including: Hydraulic action, abrasion, solution and attrition. On the other hand, deposition occurs when the river loses velocity and in a river, eventually all particles will be deposited.
As the river begins at the source in the upper course of the river, features, such as waterfalls form. Waterfalls form when a sudden drop is met in the course of a river. This drop may be a result of a drop in sea level, erosion by ice or earth movements. But usually a waterfall is formed when a river meets a layer of harder rock, then flows over a layer of softer rock. The softer rock underneath is eroded more quickly than the more resistant hard rock, resulting in an undercutting below the harder rock. Over time, as the undercutting increases, an overhang of hard rock is formed, and is subsequently collapses under the force of its own weight. Over time, the break-offs from this collapse will form a deep plunge pool. This is because of the rocks being swirled around and colliding with the sides of the pool. These types of erosion are called hydraulic action and attrition. After these processes are repeated several times, a steep-sided gorge is formed as the waterfall retreats. Rapids occur where the layers of hard and soft rock are very thin, so no break in the slope occurs like in a water fall.
When a river is nearing its mouth, it is flowing over much flatter, with less of a gradient. At this point in the rivers profile, in the middle course, large bends often form known as meanders. These meanders form when a piece of hard rock lies on the bank on one side of a straight river. As the water flows past the hard rock, the soft rock past it is eroded. This directs the flow towards the outside of the river, causing lateral erosion on one side of the river, producing a slight bend in the path. The outside has a greater velocity and a higher energy than the inside, so as the river approaches the meander, the flow is directed toward the outside of the bend, causing erosion on one side of the meander. This causes a reduction in friction, increasing the velocity of the river at this point. This velocity enables the river to transport more material in suspension, with this material eroding in the form of hydraulic action and abrasion against the bank. This causes an undercutting of the bank, inducing it to collapse, and retreat backwards like a waterfall would. This undercutting is called a river cliff'.
In contrast, during this increase in velocity on the outside of the bend, the velocity decreases on the inside of the bend as it has a lower amount of energy. This is because there is less water on the inside because it has been thrown to the outside of the meander loop. Furthermore, the velocity decreases because there is more friction against the river bed and bank on the inside of the meander. Due to this loss in velocity and energy, the material in suspension is deposited. This deposition builds up to form a small beach of material known as a slip-off slope. As the river progresses through the channel, the water in a meander flows in a corkscrew like movement as it moves from the inside of the bend towards the outside of the bend.
As the outer banks of a meander continue to be eroded through processes such as hydraulic action, the neck of the meander becomes narrow and narrower. Eventually, due to the narrowing