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Waterfalls are among the most dramatic features of river landscapes, with water plunging over cliffs and ledges. But have you ever wondered how they form and why they don’t stay in one place?
In Geography, learning about waterfalls goes beyond appreciating their beauty. Their formation and movement reveal how rivers shape the land through processes like erosion, undercutting, and rock collapse.
By understanding these processes, we can explore how landscapes evolve over time and what makes waterfalls a perfect example of the dynamic forces at work in the natural world.
Read on to discover the geological story behind how does a waterfall form.
A waterfall is a point in a river's course where water flows over a vertical drop or a series of steep drops. They occur in the upper course of a river, where the gradient is steepest, and the energy levels are high.
However, a waterfall is not a static landmark. Over thousands of years, they slowly move upstream, showing how rivers constantly reshape the landscape.
The formation of a waterfall starts with the right combination of rocks. For a dramatic drop to form, a river needs to flow over a band of hard, resistant rock, such as granite or limestone, sitting atop softer, weaker rock, such as sandstone or shale.
As the river moves across this boundary, the softer rock erodes more quickly than the hard rock above it. This erosion difference prepares the waterfall to develop and creates the steep drop we see.
As water falls over the edge, it hits the base with great force. Air trapped in rock cracks exerts pressure that helps break the rock apart. This process is called hydraulic action and gradually wears away the softer rock at the base.
Once water starts to drop vertically, it forms a deep basin at the base called a plunge pool. This is where the waterfall’s erosive power comes into play.
The water doesn't act alone. It carries a load of fallen rocks and pebbles, which act like natural sandpaper, gradually wearing away the softer rock.
As the plunge pool gets deeper, the soft rock behind the falling water is also worn away. This creates a hollow or notch beneath the harder rock above, setting the stage for the waterfall to slowly retreat upstream.
Over time, the hard top layer, or caprock, hangs over the hollow created by erosion. With nothing supporting it beneath, gravity takes over, and the ledge eventually collapses into the plunge pool. The broken pieces of rock then join the swirling water, helping to grind away the softer rock even faster and speeding up the waterfall’s retreat.
Waterfalls do not stay in one place forever. Each time the hard top layer, or caprock, collapses, the waterfall moves slightly upstream. This repeated movement is called retreat.
As the waterfall retreats over many years, it leaves behind a narrow, steep-sided valley known as a gorge. In diagrams, the gorge is usually shown downstream from the current waterfall, marking the path the water has carved through the landscape.
For a visual guide, HRB Education has created a step-by-step video on the formation of waterfalls to explain these stages for students preparing extended GCSE answers. The video also features several waterfall diagrams with terminology and logical sequencing.
Watch it to see how is a waterfall formed and shapes the landscape.
Waterfalls are more than just scenic features. Their formation and movement show how rivers shape the land over time. Erosion, undercutting, and collapse work together to form plunge pools, cause waterfalls to retreat, and eventually create gorges.
However, as understanding geography concepts such as “how are waterfalls formed” can require external support, HRB Education is here to help. Our specialised tutors guide GCSE students through well-structured explanations, curriculum-focused resources, and exam preparation that goes beyond memorisation.
Book a free consultation with us to plan your custom curriculum.
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