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Unlock This CourseWaves are one of the most powerful forces shaping our coastlines. Every day, millions of waves crash against shores around the world, constantly changing the landscape through erosion, transport and deposition. Understanding how waves work is essential for explaining why some coastlines are rocky and dramatic whilst others are sandy and gentle.
Wave action is responsible for creating many of the coastal landforms we see today, from towering cliffs to sweeping beaches. The power of waves can move enormous boulders, carve sea caves and transport sand hundreds of kilometres along a coast.
Key Definitions:
Waves are created when wind blows across the sea surface, transferring energy to the water. The stronger the wind, the longer it blows and the greater the fetch, the larger the waves become. As waves travel towards the shore, they carry this energy with them, ready to release it when they break on the coastline.
Not all waves are the same. Their size, shape and behaviour depend on the conditions that created them and how they interact with the seabed as they approach the shore.
Geographers measure waves using several key features. Wave height is the vertical distance between the crest (top) and trough (bottom). Wavelength is the horizontal distance between two wave crests. Wave frequency tells us how many waves pass a point in a given time, usually measured in waves per minute.
Measured from trough to crest. Storm waves can reach over 10 metres high, whilst normal waves are typically 1-3 metres.
The distance between wave crests. Can range from a few metres to several hundred metres in deep ocean swells.
How often waves arrive. Destructive waves have high frequency (10-14 per minute), constructive waves have low frequency (6-8 per minute).
Waves can be classified into two main types based on their effect on the coastline. This classification is crucial for understanding how different coastal landforms develop.
These waves build up beaches by depositing sediment. They have a low height, long wavelength and low frequency. Their swash is stronger than their backwash, so they carry more material up the beach than they take away. Constructive waves are common in summer when weather conditions are calmer.
These waves erode coastlines by removing sediment. They have a high height, short wavelength and high frequency. Their backwash is stronger than their swash, so they drag more material back into the sea. Destructive waves are common during storms and in winter months.
As waves approach the shore, they don't always hit the coastline straight on. Wave refraction occurs when waves bend as they enter shallow water and this process has a huge impact on coastal erosion patterns.
When waves approach a coastline with headlands and bays, they slow down in shallow water but continue at normal speed in deeper water. This causes the wave to bend, concentrating wave energy on headlands whilst reducing it in bays. This is why headlands are often eroded to form cliffs, whilst bays tend to be areas of deposition where beaches form.
Flamborough Head demonstrates wave refraction perfectly. The chalk headland juts out into the North Sea, causing waves to refract around it. This concentrates wave energy on the headland, creating dramatic white cliffs up to 130 metres high. Meanwhile, the nearby bays at Bridlington and Filey have sandy beaches where wave energy is reduced and deposition occurs.
Waves erode coastlines through several different processes, each working in its own way to break down rock and transport the resulting sediment.
Understanding these processes helps explain how different coastal landforms are created and why some rocks are more resistant to erosion than others.
The sheer force of waves hitting the coast. Water gets forced into cracks in rocks, compressing air inside. When the wave retreats, the compressed air expands explosively, widening the cracks.
Waves pick up stones, pebbles and sand, hurling them against the coast like a giant piece of sandpaper. This grinding action wears away the rock face and creates a wave-cut notch.
Rocks and pebbles carried by waves knock against each other, gradually becoming smaller and more rounded. This process creates the smooth pebbles found on many beaches.
One of the most important processes in coastal geography is longshore drift - the movement of sediment along a coastline. This process is responsible for creating many coastal features and can cause serious problems for coastal management.
When waves approach a beach at an angle, they carry sediment up the beach at the same angle during swash. However, backwash always flows straight back down the beach due to gravity. This creates a zigzag movement of sediment along the coast. The direction of longshore drift depends on the prevailing wind direction.
Longshore drift can transport millions of tonnes of sediment each year. On the UK's east coast, drift generally moves sediment from north to south, whilst on the west coast it typically moves from south to north.
Spurn Head is a 5.5km long spit created by longshore drift along the Yorkshire coast. Sediment eroded from the Holderness coast is transported southwards by longshore drift and deposited where the coastline changes direction at the mouth of the Humber Estuary. The spit continues to grow and change shape as more sediment is added each year.
Understanding wave processes is essential for effective coastal management. Engineers and planners need to know how waves behave to design sea defences that will protect coastal communities.
Scientists use computer models to predict wave conditions and their effects on coastlines. These models consider factors like wind speed, fetch, water depth and coastal shape to forecast wave heights and erosion rates. This information helps coastal managers plan defences and evacuation procedures.
Wave conditions change dramatically with the seasons. Winter storms bring destructive waves that erode beaches and damage sea defences. Summer conditions are generally calmer, allowing constructive waves to rebuild beaches naturally.
Human activities can significantly affect how waves behave and impact coastlines. Coastal development, sea defences and offshore activities all influence wave action.
Sea walls, groynes and breakwaters are designed to absorb or redirect wave energy. However, these structures can have unintended consequences, sometimes increasing erosion in other areas or disrupting natural sediment transport processes.
Happisburgh demonstrates the power of wave action and the challenges of coastal defence. The village has lost over 35 houses to coastal erosion since 1990. Waves here can be over 4 metres high during storms and the soft clay cliffs retreat by up to 10 metres per year. The decision to stop maintaining sea defences has allowed natural processes to continue, but at great cost to the local community.