River Landforms: Waterfalls & Gorges
Geography: Edexcel IGCSE, topic 1.1.6
Waterfalls and Gorges
When a river flows over hard rock that overlays softer rock, a waterfall can form. Gorges are formed when waterfalls retreat over time.
Stage 1
- The less resistant (softer) rock begins to erode because of abrasion and hydraulic action.
- A step or notch forms in the softer rock, creating a river rapid.
Stage 2
- Over time, the softer rock gets more eroded. This leaves the hard rock sticking out above the soft rock.
- The height of the drop increases as the water pounds the less resistant rock at the base. Eventually a waterfall forms.
Stage 3
- The less resistant rock starts to be eroded underneath the hard rock. This process is called undercutting.
- The overhanging harder rock collapses because there is nothing underneath it to support it.
- The hard rock crumbles into the base and the abrasion between the hard rock and soft rock base creates a plunge pool.
- Hydraulic action keeps undercutting behind the waterfall.
- If the process repeats over a long time, a gorge may form.
Test yourself on River Landforms: Waterfalls & Gorges
What forms at the base of waterfalls over time?
What erosional process is predominantly responsible for the formation of plunge pools?
Formation of Waterfalls and Gorges