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Describe and explain the formation of a gorge - 6 marks

Waterfalls often form when hard (e.g. granite) and soft (e.g. clay or chalk) rock are present , where water flows across the harder rock and drops onto softer rock. The falling water then starts to form a plunge pool due to different erosion such as hydraulic action and abrasion on the softer rock, as the plunge pool gets larger, the water becomes more turbulent and begins to undercut into the softer rock underneath the harder rock type. Due to the harder rock then becoming unstable and unsupported, the overhang then falls into the plunge pool which are eroded into smaller material by attrition and transported away.This continues to occur, causing the waterfall to retreat upstream, leaving harder rock debris behind. The continuous retreat of the waterfall forms a steep sided gorge as a result.