Formation of waterfall: 4 mark Q

Question 1

Describe and explain the formation of a waterfall you have studied. i.e. River Severn Breaks It’s Neck

Answer 1

The River Severn Breaks Its Neck is a small waterfall around 3m high located in the Cambrian mountains in mid-Wales one mile south west of Plynlimon, the source of River Severn.

Here the River Severn flows over a hard layer of igneous rock which sits above a soft layer of sedimentary rock. The river has lots of gravitational potential energy as it is over 750m above sea level, so it flows quickly and is able to erode the softer rock through hydraulic action. An overhang of harder rock is created as the softer rock is undercut by hydraulic action and abrasion. The overhang becomes unstable because it is no longer supported by the sedimentary rock until it eventually collapses due to gravity. A deep plunge pool is created at the base of the waterfall by falling rocks (abrasion) and the weight of the water (hydraulic action). The process of undercutting and overhang collapse is repeated so that over many years the waterfall retreats back upstream leaving a steep sided gorge of retreat where the waterfall used to be.