A landform is erosional when waves have worn rock away to make it, and depositional when sediment has been laid down to build it. To classify, ask one question: was material removed or added?
This lesson is part of coastal processes and management. It builds on tracing sediment movement, because deposition needs a supply of moving sediment.
Which landforms belong to each group?
| Group | Clue in the description | Examples |
|---|---|---|
| Erosional | Bare rock, steep faces, gaps, isolated pillars | Cliff, wave-cut platform, cave, arch, stack, stump |
| Depositional | Sand, shingle or mud, ridges and bars that grow | Beach, spit, bar, tombolo |
The group depends on the process, not on the place. A feature at the foot of a cliff may still be depositional.
Worked example: one original headland and bay
An original headland has a steep rock face with a notch cut at its base. Beside it, a curved bay holds a beach of pale sand, and a narrow ridge of sand extends from the headland across part of the bay mouth.
Classify the features:
- The steep rock face and notch: waves have cut into the base, so this is erosional (cliff with a wave-cut notch).
- The pale sand beach in the bay: material has been dropped where wave energy is lower, so this is depositional.
- The ridge of sand across the bay mouth: a growing ridge of sediment is a spit, so this is depositional.
Notice that the cliff and the beach are neighbours but sit in opposite groups.
The mistake: sorting by location
A common slip is to label everything near a cliff as erosional, because “the coast is being eroded”. The working is neat, but the beach at the cliff foot is built from sediment.
| Feature | Wrong reasoning | Right reasoning |
|---|---|---|
| Beach below a cliff | Near the cliff, so erosional | Made of laid-down sand, so depositional |
| Isolated rock pillar | Standing alone, so depositional | Left by erosion of an arch, so erosional |
| Sand bar at a bay | Connected to rock, so erosional | Built by deposition, so depositional |
State the process in your answer: “rock worn away by wave action” or “sediment dropped where wave energy falls”.
Check yourself
Classify each feature and give the clue: (a) a flat rocky surface exposed at low tide at the base of a cliff, (b) a hooked ridge of sand growing from the land into a bay, (c) an isolated rock pillar 30 m offshore.
Answer
(a) Erosional: a wave-cut platform, left as the cliff wears back and only rock remains.
(b) Depositional: a spit, because sand is being added and the ridge is growing.
(c) Erosional: a stack, left when waves wore away the rock around it.
What to study next
Next, see how a built structure changes where sediment ends up in explaining how a structure may change sediment distribution. Then try the coastal practice set.
If you want a teacher to test your sorting on new descriptions, see online one-to-one Geography tuition.