Waterfall Development and Gorge Formation
As the formation of a waterfall progresses, several key processes contribute to its development and the creation of associated landforms.
The river continues to undercut the harder rock layer, leaving behind an increasingly unstable overhang. Eventually, this overhang becomes unsupported and collapses into the plunge pool below.
Definition: Plunge pool - A deep basin at the base of a waterfall, formed by the erosive action of falling water and swirling sediment.
When the overhang collapses, some of the fallen rocks are swirled around by the river in the plunge pool. This swirling action further deepens the plunge pool, enhancing the vertical drop of the waterfall.
Highlight: The depth of the plunge pool increases significantly during times of high discharge when hydraulic action is most powerful.
Vocabulary: Discharge - The volume of water in a river at a given point in time, measured in cumecs (cubic meters per second).
As this process continues, the waterfall gradually moves upstream. The ongoing erosion and collapse of rock layers create a steep-sided gorge that extends back into the hillside.
Example: The formation of Niagara Falls is a classic example of this process, with the falls having retreated upstream by about 11 kilometers over the past 12,000 years.
The formation of waterfalls in higher geography is thus a continuous cycle of erosion, undercutting, collapse, and retreat, shaping some of the most dramatic landscapes in river systems.
