Waves (Constructive & Destructive)

Types of Waves

Waves are the main agents shaping coastal landscapes in the UK. They are generated by wind blowing over the sea surface. Two main types of waves affect the coast differently:

• Constructive waves are low-energy waves with a long wavelength and low height. They have a low frequency, typically 6 6 waves per minute. Their swash (the movement of water up the beach) is stronger than their backwash (water returning to the sea), so they deposit more material than they erode.
• Destructive waves are high-energy waves with a short wavelength and greater height. They have a high frequency, around 10 14 waves per minute. Their backwash is stronger than their swash, which causes erosion of the coastline.

The difference in wave energy, frequency, and height determines whether a wave is constructive or destructive, impacting coastal processes.

For instance, on calm days with gentle winds, constructive waves build up beaches by depositing sand and pebbles. During storms, destructive waves erode cliffs and remove beach material.

Processes of Wave Action

Waves affect the coast mainly through two processes:

• Erosion 6 Mainly caused by destructive waves. These waves have powerful backwash that pulls sediment and rock away from the coast. The main types of coastal erosion caused by waves include:

• Hydraulic action: The force of water compresses air in cracks, weakening rock.
• Abrasion: Sediment and pebbles carried by waves grind against the cliff, wearing it down.
• Attrition: Rocks and pebbles collide and break into smaller pieces.

• Deposition 6 Mainly caused by constructive waves. When the wave energy is low, waves drop the sediment they carry, forming landforms like beaches.

The balance between erosion and deposition shapes the coastline. Destructive waves tend to dominate during stormy weather, eroding the coast. Constructive waves dominate in calmer conditions, building up beaches and other depositional features.

For example, at the Dorset coast, destructive waves erode the cliffs, while at nearby bays, constructive waves deposit sand to form wide beaches.

Effects on Coastal Landscapes

Waves play a vital role in shaping the UK's coastal landscapes by creating distinctive landforms through erosion and deposition.

• Beaches form mainly by deposition from constructive waves. Sand and shingle accumulate between headlands where wave energy is lower. Beaches provide natural protection against erosion and are common along many UK coastlines, such as Bournemouth and Scarborough.
• Cliffs and wave-cut platforms are formed by erosion from destructive waves. Cliffs are steep rock faces shaped by the constant pounding of waves. Over time, waves erode the base of cliffs, causing rock above to collapse. This process leaves a flat, rocky platform at the base called a wave-cut platform, visible at places like the Jurassic Coast.

The interaction of constructive and destructive waves creates a dynamic coastline. For example, headlands experience intense erosion by destructive waves, while bays between headlands often have beaches formed by deposition.

The constant action of waves shapes the UK coastline, influencing human activities such as tourism, settlement, and coastal management.

Learning example: Calculating wave frequency

If 12 waves hit the shore in 1 minute, the wave frequency is:

$\text{Frequency} = 12 \text{ waves per minute}$

This high frequency suggests these are likely destructive waves, as they typically have 10 14 waves per minute.