GCSE Revision

River landforms of erosion

Interlocking spurs

In the upper course, the river is small and has a lot of energy from its steep gradient:

  1. The river erodes mainly downwards (vertical erosion), cutting a deep, V-shaped valley.
  2. It doesn't have the energy to erode sideways through the hard rock, so it winds around areas of harder rock in its way.
  3. These ridges of high land jut out from each side of the valley, fitting together like the teeth of a zip: .

From the valley floor, you can't see far up the valley, as each spur blocks the view.

Key terms

Waterfalls

hard rocksoft rockoverhangundercuttingplunge poolriver flows this way
  1. A waterfall forms where a band of hard rock lies on top of softer rock.
  2. The river erodes the soft rock faster, so a step forms in the river bed.
  3. Water falls over the step and erodes a deep at its foot, by hydraulic action and abrasion.
  4. The soft rock behind the falling water is undercut, leaving an overhang of hard rock.
  5. The overhang is no longer supported, and it collapses into the plunge pool.
  6. The process repeats, and the waterfall retreats upstream.

Key terms

Gorges

As a waterfall retreats upstream, collapse after collapse, it leaves a steep-sided, narrow valley below it: a .

  1. Water erodes the soft rock beneath the hard cap.
  2. The overhang collapses, and the waterfall moves back a little.
  3. Over thousands of years, the waterfall retreats a long way, cutting a gorge as long as the distance it has moved.

For example: below High Force, on the River Tees, is a gorge about 700 m long.

Exam tip

Explain a waterfall and gorge as one sequence: hard and soft rock, undercutting, collapse, retreat.

Key terms

Exam practice

Plan your own answer first, then open the model answers to see what each level looks like.

6 marks · about 6 minutes

Explain the formation of a waterfall and gorge.

Explain means: Give the reasons why something happens, developing each point with "because" or "so".

Link it

Use the facts from:

  • The River Tees (Teesdale and Teesside, north-east England, Present day)
Level 1 (Basic)· 2/6 marks (band 1–2)
A waterfall forms where there is hard rock and soft rock. The water erodes the soft rock and the waterfall moves back.

Why this level: Correct basic idea but no sequence or processes. To reach Level 2: explain the plunge pool, the undercutting, the overhang and the collapse in order.

Level 2 (Clear)· 4/6 marks (band 3–4)
A waterfall forms where hard rock lies on top of softer rock. The soft rock is eroded faster, making a step. The falling water erodes a plunge pool. The soft rock behind is undercut, leaving an overhang of hard rock, which eventually collapses. The waterfall then moves back.

Why this level: A clear sequence of the main stages. To reach Level 3: name the erosion processes, and explain how repeated retreat forms a gorge.

Level 3 (Detailed)· 6/6 marks (band 5–6)
A waterfall forms where a band of hard rock lies on top of softer rock. The river erodes the soft rock faster, so a step forms in the river bed. Water falling over the step erodes a deep plunge pool at its foot by hydraulic action and abrasion, as rocks are swirled around. Spray and swirling water undercut the soft rock behind the waterfall, leaving an overhang of hard rock with no support. Eventually the overhang collapses into the plunge pool, and the rocks help erode it further. As this repeats, the waterfall retreats upstream, leaving behind a steep-sided gorge, as at High Force on the River Tees.

Why this level: Detailed, ordered explanation with named processes, the cycle of retreat, the gorge and a named example. This is Level 3.

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