How waterfalls are formed?
Waterfalls form where soft rock erodes and a river cuts vertically to form a cliff. They usually appear in the upper course of a river, in the mountains or hills. Some waterfalls were formed by glaciers, which cut deep valleys into mountains as they formed and retreated. You can find more information here: http://www.kented.org.uk/ngfl/subjects/geography/rivers/river%20articles/waterfalls.