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Unlock This CourseUnderstanding how coastal landforms develop requires us to look beneath the surface at the underlying geology. Different rock types create dramatically different coastal landscapes - from towering cliffs to gentle beaches. By learning to read geological and Ordnance Survey maps, we can predict and explain why coastlines look the way they do.
Key Definitions:
Geological maps use different colours and patterns to show rock types. Hard rocks like granite appear in bold colours, whilst softer rocks like clay use lighter shades. The key or legend explains what each colour represents, along with the age of the rocks.
The type of rock along a coastline determines how quickly it will erode and what landforms will develop. Understanding rock resistance is crucial for predicting coastal change and managing coastal areas effectively.
Rocks can be classified by their resistance to erosion, which depends on their hardness, structure and how they were formed. This resistance directly influences coastal landform development.
Granite, limestone and sandstone resist erosion well. They form headlands, cliffs and rocky shores. These rocks often create dramatic coastal scenery with steep faces and minimal retreat.
Chalk and some sandstones erode at medium rates. They often form white cliffs with distinctive features like arches and stacks, as seen along parts of the English coast.
Clay, shale and soft sandstones erode quickly. They typically form bays, gentle slopes and areas prone to landslides. These areas often have beaches and mudflats.
The Dorset coast demonstrates how different rock types create varied landscapes. Hard Portland limestone forms headlands like Old Harry Rocks, whilst softer Kimmeridge clay creates Lulworth Cove's distinctive bay. The alternating bands of hard and soft rock, running parallel to the coast, create a classic discordant coastline pattern visible on both geological and OS maps.
Ordnance Survey maps provide detailed information about coastal features, elevation and human activities. When combined with geological knowledge, they become powerful tools for understanding coastal processes.
OS maps use specific symbols to represent coastal features. Learning these symbols helps you interpret the relationship between geology and landforms quickly and accurately.
Cliffs appear as thick black lines with small perpendicular marks. The closer these marks, the steeper the cliff. High cliffs often indicate resistant rock, whilst broken cliff lines suggest softer, more eroded coastlines.
Contour lines show elevation changes. Closely spaced contours near the coast indicate steep cliffs, whilst widely spaced lines suggest gentle slopes. V-shaped contours pointing inland often show valleys carved by rivers or erosion.
The way rocks are arranged and tilted affects how coasts develop. Understanding geological structure helps explain why some areas form bays whilst others become headlands.
The relationship between rock layers and the coastline creates two main types of coastal alignment, each producing distinctive landform patterns.
Rock layers run parallel to the coast. This creates relatively straight coastlines with similar rock types exposed along long stretches. The Dorset coast between Swanage and Weymouth shows this pattern, with limestone forming a continuous barrier.
Rock layers run at angles to the coast, creating alternating bands of hard and soft rock. This produces a headland and bay pattern, as seen along the Pembrokeshire coast in Wales, where resistant rocks form headlands and softer rocks create bays.
Flamborough Head demonstrates how chalk geology creates distinctive coastal features. The OS map shows steep cliffs marked by closely spaced contours, whilst the geological map reveals the chalk's resistance to erosion. The headland's shape reflects the chalk's jointing patterns, creating the famous white cliffs and sea stacks like Bempton Cliffs, important for seabird nesting.
Maps can reveal how coastlines change over time and help predict future changes. By comparing different map editions and understanding geological controls, we can assess coastal vulnerability.
Different rock types erode at different rates, creating predictable patterns visible on maps. Understanding these patterns helps coastal managers plan defences and predict future changes.
Soft cliffs like those at Holderness show rapid retreat rates. Maps reveal narrow coastal strips and frequent updates to cliff positions, indicating ongoing erosion problems.
Hard rock coastlines like Cornwall's granite cliffs show little change between map editions. Cliff positions remain constant, indicating geological resistance to erosion.
Sheltered bays and estuaries often show sediment accumulation. Maps reveal growing beaches, spits and mudflats where wave energy is reduced and deposition occurs.
Developing systematic approaches to map analysis helps you quickly identify geological controls on coastal landforms and make accurate interpretations.
Follow this systematic approach when analysing coastal maps to ensure you identify all important geological and geomorphological relationships.
Start by identifying the overall coastal pattern - is it straight, indented, or irregular? Look for headlands, bays and major coastal features. Note the scale and orientation of your map area.
Examine contour patterns, cliff symbols and elevation changes. Compare these with geological information to identify rock types and their influence on landform development. Look for evidence of erosion or deposition.
The Jurassic Coast stretches 95 miles from Exmouth to Studland Bay, showcasing 185 million years of geological history. Maps reveal how different rock formations create varied coastal landscapes - from the red sandstone cliffs of Exmouth to the white chalk stacks of Old Harry Rocks. The geological map shows clear bands of different aged rocks, each creating distinctive coastal features that can be identified on OS maps through cliff heights, beach types and erosion patterns.