Book 5, Question 65
Backward Bound! Why Do Waterfalls Move Backward?
Falling water can wear away the softer rock under a waterfall's edge. When the rock above loses support, it breaks off. Little by little, the waterfall moves upstream.
From the book
Page from A Million Whys Book 5
More fun facts
- Many waterfalls form where a river flows over hard rock lying on top of softer rock.
- The water wears away the soft rock faster than the hard rock.
- This leaves a ledge of hard rock hanging out over nothing, called an overhang.
- Without support, the overhang breaks off and falls into the pool below.
- The pool at the bottom of a waterfall is called a plunge pool, and falling rocks swirl around and deepen it.
- Each time this happens, the waterfall moves back upstream.
- As the waterfall keeps moving back, it cuts a steep-sided valley called a gorge.
Questions kids ask
What is a gorge?
A gorge is a steep, narrow valley left behind as a waterfall slowly moves upstream.