Explain the processes involved in the formation of a waterfall.

Waterfalls are an erosive feature of the river system. Rivers erode their banks and bed through a variety of erosional processes, such as hydraulic action, corrosion, attrition and saltation. In the creation of waterfalls three of these processes are present; hydraulic action occurs where the force of the water can gradually wear away the banks and bed of the river by trapping air in its cracks and crevices. Corrosion uses suspended material in the river to wear down the banks of the river, while attrition involves suspended particles colliding and breaking down one another while in suspension. When you find a layer of softer, less resistant rock downstream of an area of harder, more resistant rock these erosional processes will wear away the softer rock faster than the harder rock. this downward erosion will start to create a step in the river between the band of hard and soft rock. Over time this step will increase in size until there is a significant enough drop for a plunge pool to be created. As the river flows over the lip of the hard rock into the plunge pool, where the soft rock has been eroded away, the force of the falling water will create a deepening pool, primarily through the process of hydraulic action. The falling water can often deflect upstream and undercut the harder, more resistant rock, creating an overhang. This overhang will eventually collapse over time as the pressure of gravity becomes too great and this causes the waterfall to retreat upstream. The material from the collapsed overhang can be used as tools for corrosion and attrition.As the waterfall retreats upstream it will leave behind a large gorge where the previous waterfalls used to be.