Waterfalls

• Hydraulic action is when water forces air into rocks, dislodging them.
• Abrasion is when rocks in the water are dragged along the river bed, grinding it down.
• Solution is when salts and acids in the river dissolve minerals in the rock.
• Attrition is when rocks in the water hit off each other and break into smaller pieces.
• River flows over bands of less resistant (softer) and more resistant (harder) rock.
• Less resistant rock is quickly worn away due to the differential erosion.
• River undercuts harder rock leaving an overhang which becomes unsupported and collapses into plunge pool below.
• After the overhang falls, some of the rocks are swirled around by the river and this helps to form a deep plunge pool below the waterfall.
• The waterfall retreats upstream, the process continues, and a steep sided gorge is cut back into the hillside.