Waterfalls & Gorges
· A band of hard rock meets softer rock, which is eroded more than the harder rock causing a step in the river bed. The water flowing over the step speeds up due to the lack of friction as it drops over the step, and the increase in speed gives the water greater erosive power. This causes a steep vertical drop in the river profile.
· This happens in the upper course of the river where it is more mountainous, where the riverbed is steeper and drops more.
· The cap rock (Hard Rock), is what the river flows on however beneath it is soft rock. As the water falls to a different level, it will erode the soft rock at the bottom, this is called undercutting. The water beneath is called a plunge pool.
· The plunge pool is carved out by abrasion as collapsed rocks are swirled round by turbulence.
· Over time, the rock is eroded away so that the hard rock on top is no longer supported. This overhang falls.
· This process happens continually, meaning the waterfall retreats upstream.