Waterfalls - Info sheet

Waterfalls are a captivating natural feature often found in upland regions where rivers traverse steep hillsides. The process of their formation is closely tied to the types of rocks present in these areas. As water flows rapidly downhill, it erodes the underlying rock layers. The rate of erosion varies depending on the rock's resistance; softer rocks such as shale are worn away more swiftly compared to harder rocks like sandstone or limestone. The latter types of rocks tend to form the capstones of waterfalls, dictating both the number of waterfalls along a river and the height of each individual waterfall. The thickness and resilience of these harder rock units are key factors in the development and characteristics of waterfalls.

The formation of a waterfall is a dynamic and ongoing process, as illustrated in a diagram provided by Focus Education (UK) Ltd. Initially, the water erodes softer rock layers, leading to the formation of an overhang composed of a tougher rock layer. As the river flows over this overhang, it creates a plunge pool in the softer rock below. Over time, the relentless erosion of the softer rock causes the overhanging harder rock to collapse. This event causes the waterfall to retreat upstream, resulting in the creation of a steep, gorge-like valley. This cycle of erosion and retreat continues, shaping the landscape and altering the course of the river over geological time scales.