The big idea: A river is always doing three things: eroding (wearing away the channel), transporting (carrying the load), and depositing (dropping the load). Which one dominates depends on the river's energy — and energy depends mostly on velocity and discharge.
Fast, high-energy stretches erode; slow, low-energy stretches deposit. Every Option A landform is just one of these three processes winning in one place — so name the process first, then the landform it builds.
The four erosion processes
- Hydraulic action — the sheer force of moving water prises and pushes rock from the bed and banks.
- Abrasion (corrasion) — the river's load is scraped along the channel, sandpapering it wider and deeper.
- Attrition — load particles knock against each other and get smaller, rounder and smoother downstream.
- Solution (corrosion) — slightly acidic water dissolves soluble rock such as limestone.
The four transport processes
- Traction — the heaviest boulders are rolled along the bed.
- Saltation — pebbles are bounced along in a series of small hops.
- Suspension — fine silt and clay is held up within the flowing water (it looks muddy).
- Solution — dissolved minerals are carried along invisibly.
Deposition = the river runs out of energy: A river deposits its load when its velocity falls, so it can no longer carry the sediment — for example where the gradient flattens, where it meets the sea or a lake, on the inside of a meander bend, or in a flood. The heaviest load is dropped first, the finest last.
How this is tested: Paper 1 Option A opens with a data-response that often uses a table of landforms (e.g. the world's tallest waterfalls — name, country, height). You Identify a value that meets a stated band or State a mode/range, then later Explain how a named erosional landform forms or why erosion rates differ. Always read the exact column and quote the unit.
| Step | What happens | Process at work |
|---|---|---|
| 1. Hard over soft | A band of hard rock lies over softer rock in the bed. | Differential resistance |
| 2. Softer rock cut back | The softer rock is worn away faster, leaving the hard rock as a lip. | Hydraulic action + abrasion |
| 3. Plunge pool deepens | Falling water and swirling load drill a deep plunge pool at the base. | Abrasion + hydraulic action |
| 4. Overhang collapses | The unsupported hard-rock lip overhangs, then collapses into the pool. | Undercutting + gravity |
| 5. Waterfall retreats | Repeating this leaves the waterfall retreating upstream, cutting a gorge. | Headward retreat |
Other river-erosion landforms (not a waterfall)
- V-shaped valley — vertical erosion in the upper course cuts a steep, narrow valley.
- Gorge — a deep, near-vertical valley left where a waterfall has retreated upstream.
- Interlocking spurs — the young river winds around ridges of hard rock it cannot cut through.
- Rapids — broken, fast water over bands of harder rock that resist erosion.
- Potholes — circular hollows drilled into the bed where pebbles swirl in eddies (abrasion).
Why erosion rates differ between waterfalls: An Explain on erosion rate wants the controls: a greater drop gives faster, more erosive water; harder/softer rock contrasts speed undercutting; a bigger discharge (large drainage basin, wet climate) means more energy; and a coarser load abrades the bed harder. Pick two and develop each.
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In the lower course the river is wide, slow and full of load. Here deposition dominates, building the gentle landforms of the floodplain. The key idea is always the same: velocity falls, so the load is dropped — heaviest first, finest last.
| Step | What happens | Why |
|---|---|---|
| 1. River meets still water | The river reaches the sea or a lake and the current suddenly slows. | No gradient, no push |
| 2. Velocity falls | Slower water can no longer carry its sediment. | Energy drops |
| 3. Heaviest load first | Coarse sand and gravel are dropped close to the mouth. | Largest needs most energy |
| 4. Flocculation | Salt water makes fine clay clump and sink (flocculation). | Salt + clay react |
| 5. Delta builds up | Layers accumulate faster than waves remove them, building a delta. | Supply > removal |
Lowland depositional landforms
- Floodplain — the flat valley floor built of fine alluvium laid down when the river floods.
- Levees — raised banks of coarse sediment dropped first as a flood spills over the channel edge.
- Ox-bow lake — a cut-off meander loop left as a crescent lake after the river takes a shortcut.
- River terraces — old floodplain levels left as steps when the river later cuts down.
- Delta — a fan of deposited sediment where a sediment-rich river meets the sea or a lake.
Real rivers to name: Anchor answers with real places. The lower Mississippi has classic levees and a bird's-foot delta at the Gulf of Mexico. The Nile built a wide, fertile arcuate delta in Egypt. The Ganges-Brahmaputra forms one of the world's largest deltas in Bangladesh. For meanders, the lower Rio Grande swings across a broad floodplain leaving ox-bow lakes.
Meanders and floodplains use BOTH processes: A meander is the classic Option A landform because it shows erosion and deposition working together. On the outer bend the water is faster and deeper, so it erodes a steep river cliff. On the inner bend the water is slow and shallow, so it deposits a gentle slip-off slope (point bar).
Over time the meander migrates sideways and downstream, and this widening builds the flat floodplain. When two outer bends meet, the river takes a straight shortcut and the loop is cut off as an ox-bow lake.
| Part of the bend | Flow | Process | Landform |
|---|---|---|---|
| Outer bend | Fast, deep | Erosion (abrasion, hydraulic action) | River cliff |
| Inner bend | Slow, shallow | Deposition | Slip-off slope / point bar |
| Whole loop over time | Lateral migration | Erosion + deposition | Widening floodplain |
| Neck of the loop | Shortcut at a flood | Erosion then deposition | Cut-off -> ox-bow lake |
How this is tested — the [10] Examine essay: Paper 1 Option A ends with a 10-mark Examine essay, marked on markbands. The recurring version for this micro: how far do erosion and deposition each matter in forming meanders and floodplains, and how does their relative importance vary over time and along the river.
Top band needs: accurate process terms, both erosion and deposition developed with a named example, a weighing of their relative importance (which dominates where/when), and a clear conclusion.