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River Landforms: 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.

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.
Stage 3

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.
Diagram
Diagram
Jump to other topics
1

Physical Geography

1.1

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2

Human Geography

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Global Issues

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