explain why erosion changes from vertical erosion to morelatera erosion from the upper to middle course.
In the upper course of a river, vertical erosion is the dominant form of erosion as the river cuts down into the underlying rock to create a V-shaped valley. This is because the river is flowing down steep gradients and has a high energy level, allowing it to erode vertically.
As the river flows through the middle course, the gradient of the river decreases and the energy level decreases as well. This causes the river to meander more and flow more laterally across the landscape. With the decrease in energy, the river is less able to erode downwards and instead begins to erode sideways, shaping the landscape through lateral erosion.
Additionally, in the middle course of a river, the river channel is typically wider and deeper, allowing for more lateral erosion to occur as the river meanders and flows across the floodplain. This lateral erosion is responsible for the formation of features such as river bends, cut banks, and point bars.
Overall, erosion changes from vertical to lateral in the middle course of a river due to the decrease in energy and gradient of the river, as well as the wider and deeper channel that allows for more lateral erosion to shape the landscape.