Wave Action & Erosion
- Coasts are the meeting point of land and sea and are an open system with inputs (sediment), transfers (longshore drift), stores (beach) and outputs (water).
- Coastal processes are divided into two parts:
- Marine processes: offshore (water-based)
- Terrestrial processes: onshore (land-based)
- These processes are then sub-divided into:
- Wave action
- Erosion
- Transportation
- Weathering
- Mass movement
- It is these activities that are responsible for producing distinctive landforms found on the coast
Wave Action
- Waves are marine processes. They erode, transport and deposit material
- Waves are formed by winds blowing over the surface of the sea
- The height and strength of a wave is dependent on 3 factors:
- The fetch
- The amount of time the wind blows
- The strength of the wind
- The greater the strength, time and fetch of the wind, the larger the wave
- As a wave approaches the coast and enters shallower water, friction from the sea bed causes the wave to lean forward and eventually crest and break onto the beach
- The movement of water up the beach is called the swash, and the return movement is the backwash
Types of Waves
- There are two types of waves:
- Destructive waves erode the beach
- Constructive waves are beach builders
Comparison of Wave Type
|
Constructive Wave |
Destructive Wave |
Swash | Strong | Weak |
Backwash | Weak | Strong |
Wavelength | Long with low height | Short with high height |
Frequency | Low (6–8 per minute) | High (10–12 per minute) |
Type of beach | Sandy: depositional | Shingle: erosional |
Exam Tip
Make sure you are familiar with the way waves are formed and their different characteristics. Don't be surprised if you are asked to identify the type of wave from a list of identifiers.
Worked example
Which statement below, best describes the characteristics of a destructive wave? (1)
A | long wavelength & weak backwash |
B | short wavelength & weak backwash |
C | short wavelength & strong backwash |
D | long wavelength & strong backwash |
Answer
- The answer is C (1):
- A destructive wave has a short wavelength, high frequency rate, steep wave gradient & a strong backwash
Erosion
- Destructive waves erode the coastline in four ways:
- Hydraulic Action
- Attrition
- Corrosion
- Abrasion
Exam Tip
Make sure you know the difference between the four types of erosion, particularly between abrasion (corrasion) and attrition. So many students confuse these two terms. A tip for you, is to think of abrasion as rubbing with sandpaper or maybe you have grazed your knees or elbows when you fell off your bike/skateboard? Those grazes were abrasions on your knees/elbows etc.