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examBoard: Cambridge
examType: IGCSE
lessonTitle: Coastal Erosion Processes
Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage. It's a natural process that shapes our coastlines, creating dramatic landscapes like cliffs, caves and arches. However, it can also threaten coastal communities and infrastructure.
Key Definitions:
Hydraulic action occurs when air in cracks and crevices of cliff faces is compressed by the force of waves. As waves crash against the cliff, the air is forced into these gaps. When the wave retreats, the air rapidly expands, causing the surrounding rock to weaken and break apart. Think of it like repeatedly blowing up a balloon inside a crack until the pressure causes the rock to crumble!
Abrasion happens when waves throw rocks and pebbles against the cliff face. These act like sandpaper, wearing away the cliff surface over time. The more sediment in the water and the stronger the waves, the more powerful this erosional process becomes. It's like nature's own sandblasting machine!
Attrition is when rocks and pebbles carried by the sea collide with each other and break into smaller, smoother pieces. Next time you find a perfectly smooth pebble on the beach, you're holding evidence of attrition! This process doesn't directly erode the coastline but creates the tools (smaller, rounder pebbles) that make abrasion more effective.
Solution occurs when seawater dissolves certain types of rock. This is particularly effective on limestone and chalk coastlines, as these rocks contain calcium carbonate which reacts with acidic seawater. The slightly acidic nature of seawater (thanks to dissolved carbon dioxide) slowly dissolves these rocks, weakening the coastline.
The type of rock along a coastline significantly influences how quickly erosion occurs. Geologists classify rocks based on their resistance to erosion:
Examples: Granite, basalt, quartzite
These hard rocks erode slowly, often forming steep cliffs and headlands that jut out into the sea. They can withstand the constant battering of waves for millions of years.
Examples: Sandstone, some shales
These rocks erode at a moderate rate. They may form cliffs but will show more signs of erosion such as caves and arches over time.
Examples: Chalk, limestone, clay
These softer rocks erode quickly, often forming bays and gentler coastlines. Clay cliffs can experience rapid erosion, especially after heavy rainfall weakens them.
Several factors affect how quickly a coastline erodes:
The power of waves is a primary factor in coastal erosion. Destructive waves with strong backwash move material away from the coast, while constructive waves with stronger swash bring material onto the beach.
During storms, wave height and energy increase dramatically. A single severe storm can cause more erosion in a few hours than would normally occur over months. Storm surges can reach parts of the coast that are normally protected, causing rapid erosion.
The direction and strength of prevailing winds affect fetch (the distance wind travels over water). Longer fetch means bigger waves with more erosive power. In the UK, westerly winds create the largest fetch across the Atlantic Ocean, making western coasts particularly vulnerable.
Human activities can significantly alter natural erosion rates:
Coastal erosion creates distinctive landforms that form in a sequence as erosion progresses:
When a coastline has alternating bands of resistant and less resistant rock, the softer rock erodes faster, creating bays, while the harder rock forms headlands that jut out into the sea.
Waves attack weaknesses in headlands, first forming caves. When caves from opposite sides meet, they form arches. When an arch collapses, it leaves an isolated stack.
As waves erode the base of cliffs, they retreat landward, leaving a flat rocky platform at sea level that's exposed at low tide.
The Holderness Coast in East Yorkshire is Europe's fastest eroding coastline, retreating at an average rate of 1.5-2.5 metres per year!
Key Facts:
This case study perfectly demonstrates how different rock types erode at different rates and how human intervention can affect natural coastal processes.
The Jurassic Coast is a UNESCO World Heritage Site that showcases 185 million years of Earth's history through its spectacular erosional features.
Key Features:
The Jurassic Coast demonstrates the complete sequence of erosional landforms, from headlands and bays to caves, arches, stacks and stumps.
As coastal erosion threatens communities, various management strategies are employed:
These are physical structures built to protect the coastline:
These work with natural processes:
Coastal erosion is a complex natural process shaped by the interaction of waves, weather, rock type and human activities. Understanding these processes helps us predict how coastlines will change and develop appropriate management strategies. While erosion can threaten coastal communities, it also creates some of our most spectacular landscapes, from the white cliffs of Dover to the arches and stacks of the Jurassic Coast.
Remember that coastal landscapes are dynamic systems in constant change. What might seem like destruction is actually part of a natural cycle that has been occurring for millions of years, creating the diverse and beautiful coastlines we enjoy today.
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