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Waterfalls & Gorges

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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

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

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.
Diagram
Stage 3 & 4

Stage 3 & 4

  • 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.
Diagram
Jump to other topics
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Paper 1 - Changing River Environnments

2

Paper 1 - Changing Coastal Environments

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Paper 1 - Changing Ecosystems

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Paper 1 - Tectonic Hazards

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Paper 1 - Climate Change

6

Paper 2 - Changing Populations

7

Paper 2 - Changing Towns & Cities

8

Paper 2 - Development

9

Paper 2 - Changing Economies

10

Paper 2 - Resource Provision

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