Name and explain the formation of the river landform labelled A in Resource 1. (Waterfall Formation - 6 marks)

A waterfall, labelled A in resource 1, normally forms in the upper valley of rivers where alternating bands of hard and soft rock occur along the river bed. The bands of softer rock are eroded at a faster rate, causing the formation of a step. Hydraulic pressure and abrasion are concentrated at the base of step, further eroding the soft rock to undercut the hard rock. Over time the step further erodes, widening into a plunge pool. The undercut hard rock forms an overhang above which eventually becomes unstable and collapses. The waterfall then retreats backward upstream, forming a gorge.