Waterfalls & Gorges
Geography: Cambridge International GCSE (2027 Exams), topic 1.2.1
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.
Diagram
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.
- The softer rock leaves the hard rock sticking out above the soft rock.
Waterfall Forms
- The water pounds the less resistant rock at the base.
- So the height of the drop increases.
- Eventually a waterfall forms.
Diagram
Stage 3 & 4
- The softer rock begins to erode underneath the hard rock.
- Erosion underneath the hard rock is called undercutting.
Plunge Pool Forms
- The overhanging harder rock collapses because nothing supports it underneath.
- The hard rock crumbles into the base.
- The abrasion between the hard rock and soft rock creates a plunge pool.
Gorge Forms
- Hydraulic action keeps undercutting behind the waterfall.
- If the process repeats over a long time, a gorge may form.
Labelled Diagram
Test yourself on 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