Explain why a waterfall is only a temporary feature on a rivers course. (4 marks)

Due to hydraulic action and abrasion, the soft rock is worn away, causing an overhang of heavy hard rock which will collapse on itself and fall into a deepening plunge pool. Waterfalls will continue to erode and flatten out until the river is completely smoothed out, and the hard resistant rock is removed, which is why it's temporary.