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Unlock This CourseCliffs are some of the most dramatic coastal landforms on Earth. They're steep rock faces that drop straight down to the sea, created by the relentless power of waves attacking the coastline. Understanding how cliffs form helps us predict coastal change and manage coastal areas effectively.
Key Definitions:
Cliffs form when waves repeatedly attack the base of coastal slopes. This creates a wave-cut notch that gradually undermines the rock above. Eventually, the unsupported rock collapses, creating a steep cliff face. This process repeats, causing the cliff to retreat inland over time.
Several different processes work together to erode cliffs and create these impressive coastal features. Each process attacks the rock in a different way and their combined effect can be incredibly powerful.
Wave erosion works through four key processes that attack cliff faces in different ways. Understanding these helps explain why some cliffs erode faster than others.
Waves crash against the cliff, forcing air and water into cracks. When the wave retreats, the compressed air expands explosively, widening the cracks and breaking off rock fragments.
Waves pick up sand, pebbles and rocks, hurling them against the cliff face like a giant sandblaster. This grinding action wears away the rock surface and deepens the wave-cut notch.
Seawater contains weak acids that slowly dissolve certain types of rock, especially limestone and chalk. This chemical weathering weakens the rock structure over time.
Not all cliffs form in the same way or at the same speed. Several factors determine how quickly cliffs retreat and what shape they take. These factors work together to create the variety of cliff types we see around our coasts.
The type of rock and how it's arranged has a huge impact on cliff formation. Hard rocks like granite resist erosion and form tall, steep cliffs. Soft rocks like clay erode quickly, creating gentler slopes.
Granite, basalt and other hard rocks create vertical or near-vertical cliffs. These rocks resist erosion, so cliffs retreat slowly. The Old Man of Hoy in Scotland is a famous example of a hard rock cliff formation.
Clay, sand and other soft rocks erode quickly, creating gentler cliff profiles. These cliffs often have a curved shape and retreat rapidly. The Holderness coast in Yorkshire loses about 2 metres per year.
The Jurassic Coast stretches for 95 miles along Dorset and East Devon. It showcases different cliff types formed in rocks of varying ages and hardness. At Lulworth Cove, hard limestone forms steep cliffs, while softer clay behind creates gentler slopes. This demonstrates how rock type controls cliff profile perfectly.
Cliffs don't all look the same - they have different shapes and angles depending on the factors affecting their formation. Understanding these profiles helps us predict how cliffs will change over time.
Geographers classify cliffs based on their shape and angle. Each profile tells a story about the rock type, wave energy and erosion processes at work.
Found where very hard rocks meet high-energy waves. The rock is so resistant that it maintains a near-vertical face even under constant attack. Examples include parts of the Cornish coast where granite meets the Atlantic.
Formed in softer rocks or where wave energy is lower. The cliff face has a gentler angle, often with a curved profile. Mass movement processes like landslides are common on these cliffs.
While waves attack cliffs from below, weathering processes attack from above and within the rock. These processes work together with wave erosion to shape cliff formation and speed up retreat.
Several weathering processes work alongside wave erosion to break down cliff faces. These processes are particularly important at the top of cliffs where waves can't reach.
Water enters cracks in the rock and freezes. Ice expands by 9%, forcing the crack wider. Repeated freezing and thawing gradually splits the rock apart.
Salt spray from waves evaporates, leaving salt crystals in rock cracks. These crystals grow and expand, gradually widening the cracks and weakening the rock.
Plant roots grow in cracks, gradually forcing them apart. Burrowing animals and chemical processes from organic matter also help break down the rock.
Flamborough Head shows excellent examples of cliff formation in chalk. The white chalk cliffs rise up to 130 metres above sea level. Wave erosion has created a wave-cut platform at the base, while weathering processes attack the cliff top. The combination creates the classic vertical chalk cliff profile seen along much of eastern England.
Once wave erosion has undermined a cliff face, gravity takes over. Mass movement processes cause cliff collapse, which is often the most dramatic part of cliff retreat.
Different types of mass movement occur depending on the rock type, cliff angle and water content. Understanding these helps predict when and how cliffs might collapse.
Individual rocks or small groups of rocks fall from the cliff face. This happens when weathering has loosened rocks or when the wave-cut notch has removed support from below. Common on hard rock cliffs.
Large sections of cliff slide down slope surfaces. This often happens in soft rock cliffs, especially when the rock becomes saturated with water after heavy rainfall.
Human activities can speed up or slow down cliff formation and retreat. Understanding these impacts is crucial for coastal management and protecting coastal communities.
Some human activities make cliff erosion worse by removing natural protection or increasing the forces attacking the cliff.
The Holderness coast is Europe's fastest-eroding coastline, losing about 2 metres per year. The cliffs are made of soft boulder clay deposited during the Ice Age. Powerful North Sea waves attack the base while weathering weakens the cliff top. Sea defences at some locations have actually increased erosion elsewhere by redirecting wave energy down the coast.
Cliff formation is usually a slow process, but the speed varies enormously depending on local conditions. Some cliffs retreat centimetres per year, while others lose metres annually.
Scientists use various methods to measure how fast cliffs are retreating. This information helps with coastal management and predicting future changes.
Comparing old maps and photographs shows how cliff lines have changed over decades or centuries. This gives average retreat rates but can miss sudden collapse events.
GPS monitoring, laser scanning and satellite imagery provide precise measurements of cliff movement. These tools can detect even small changes and help predict future collapse.