Wave action is the work done by moving water on a coastline: waves wear rock away, move loose material and drop it again. In IGCSE Geography, a question about it often asks you to explain with a labelled diagram, so you need to turn each label into a reason.
This is the first skill in coasts and marine processes, and every later lesson builds on it.
How does a wave change a coast?
A wave moves up the beach as swash and drains back as backwash. What the coast looks like depends on which of the two is stronger.
- Constructive wave: low, long, arriving at a low rate. Strong swash, weak backwash, so material builds up.
- Destructive wave: high, steep, arriving at a high rate. Weak swash, strong backwash, so material is pulled out to sea.
Wave size depends on fetch, the distance of open water the wind blows across. A longer fetch gives more energy at the coast.
How do you build a wave-action diagram?
- Draw the land first: a cliff, a beach and the sea, as a simple side view.
- Add the waves as arrows, with the swash pointing up the beach and the backwash pointing down.
- Label each erosion process where it acts. Hydraulic action on the cracks in the cliff face, abrasion at the base where stones are thrown, attrition among the stones in the water, solution on rock that dissolves.
- Add a short note to each label saying what changes. “Air compressed in cracks, rock loosened” is better than “hydraulic action”.
- Finish with the result, such as a wave-cut notch and then a retreating cliff.
Worked example
All numbers below are invented for practice. Two wave types are recorded on a beach for one minute each.
Wave A has a time between crests of 10 seconds. Wave B has 5 seconds.
Step 1, frequency: waves per minute = 60 ÷ time between crests.
Wave A: 60 ÷ 10 = 6 waves per minute. Wave B: 60 ÷ 5 = 12 waves per minute.
Step 2, link to type: the lower rate fits a constructive wave, and the higher rate fits a destructive wave.
Step 3, link to the beach: with Wave A, the strong swash leaves sand and pebbles, so the beach builds up. With Wave B, there is little time for water to drain into the beach before the next wave arrives. The strong backwash removes material.
Step 4, check the rate: 6 × 10 = 60 and 12 × 5 = 60, so both agree with one minute.
A good diagram answer says all of this in labels and two or three short sentences.
The mistake to watch for
A common slip is to label a process but not say what it does.
Weak answer: “Hydraulic action and abrasion happen here.”
This names two processes and explains nothing.
Instead, tie each process to a thing and an effect: “Waves force air into cracks in the cliff (hydraulic action), which loosens blocks. Stones thrown at the base (abrasion) cut a notch.”
Another common slip is to mix up attrition and abrasion. Attrition wears the stones themselves, so they become smaller and rounder. Abrasion wears the cliff or bed.
Check yourself
1. A beach records a time between crests of 12 seconds. How many waves arrive per minute, and which wave type does that rate suggest?
Show answer
60 ÷ 12 = 5 waves per minute. This is a low rate, which suggests a constructive wave.
2. Four marker posts show cliff retreat in one year of 0.8 m, 1.2 m, 0.4 m and 0.6 m (invented figures). Find the mean retreat.
Show answer
0.8 + 1.2 + 0.4 + 0.6 = 3.0, and 3.0 ÷ 4 = 0.75 m.
3. Which process makes pebbles smaller and rounder?
Show answer
Attrition, because stones knock against each other as the water moves them.
Where this leads next
Once a wave diagram feels natural, follow the material along the shore in relating transport to a depositional feature. The statistics and distribution explorer helps with means and spread in field data.
Many students can draw the diagram and still struggle to explain it in a full paragraph. A teacher in online one-to-one Geography tuition can work on that link with your own sketches.