Seljalandsfoss, Iceland and Niagara Falls, Canada
- Waterfalls can usually be found in the upper and middle course of a river.
- They are found when a river runs over alternating layers of hard and soft rock.
- As the water moves over the hard rock it will be able to erode any exposed softer rock.
- The erosion processes of hydraulic action, abrasion and attrition will work together to erode the rock – causing the waterfall to start to move backwards and leave a steep-sided gorge.