Waterfalls

Waterfalls

1. A waterfall is a vertical drop in the upper course of a river, formed by river erosion.

2. Powerscourt Waterfall, Co. Wicklow

3. Waterfalls form where there is a band of hard rock and soft rock

   • Differential erosion occurs as the river erodes soft rock much faster than hard rock.
     • The hard rock is left elevated over the river as the soft rock beneath erodes away.
       • The process hydraulic action and abrasion lead to the erosion of the soft rock so the river falls down the cliff to the river bed, creating a plunge pool
         • At the base of the waterfall, a plunge pool forms.
           • This area was once made of soft rock but was eroded away by the force of the river moving downward.
             • As the river falls to the plunge pool it splashes back, eroding the back wall, made of soft rock, creating an overhang of hard rock and an undercut of soft rock created by solution.
               • The resistant rock eventually collapses into the bottom of the waterfall.
                 • The load material is transported down the river valley.
                   • As the cliff continues to break off in stages, it moves backward (headward erosion)

4. Hydraulic action, abrasion, solution, differential erosion, vertical erosion and headward erosion.

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