Edexcel GCSE Geography A (1GA0) — The Physical Environment
You can easily crumble a lump of clay in your hands, but you cannot do the same to a solid block of granite. The sea experiences this exact same difference when crashing against the coastline, shaping the land based on the rocks it hits.
The physical characteristics of these rocks are known as their lithology. Resistant rock (like granite, limestone, or chalk) forms steep, high, rugged cliffs and headlands because it withstands marine erosion. In contrast, less resistant rock (like clay, shale, or glacial till) forms lower, gentle slopes that are prone to slumping. Crucially, less resistant rocks do NOT form high, vertical faces because they lack the structural strength to support themselves.
Coastlines are classified by how these rock strata (layers) align with the sea. On a concordant coastline, rock strata run parallel to the sea, usually creating a relatively straight coastline. If the outer resistant layer is breached by the sea, a cove may form, such as Lulworth Cove in Dorset. On a discordant coastline, alternating bands of rock run perpendicular (at right angles) to the sea.
This alternating layout leads to differential erosion, where less resistant rocks erode much faster than resistant ones. This process creates headlands and bays, such as Swanage Bay (less resistant Wealden Clay) caught between Ballard Point (resistant chalk) and Peveril Point (resistant limestone). Once these are formed, wave refraction concentrates wave energy onto the headlands, increasing erosion there, while wave energy is dispersed in the bays, allowing the deposition of beaches.
To understand coastal forms, geographers use maps to identify structures and relate them back to the underlying geology. On British Geological Survey (BGS maps), resistant rocks are shown in bold or darker shades, while weak rocks are pale. Thick black lines represent faults, indicating areas of structural weakness where erosion will occur more rapidly.
When describing features on Ordnance Survey (OS maps), you must look for specific symbols and patterns. On 1:25,000 and 1:50,000 scale maps, follow these steps to identify coastal landforms:
Erosion is not constant; it experiences temporal variation depending on seasons and annual weather patterns. Coastal recession is much faster in winter due to a higher frequency of intense storms and a longer fetch (the distance wind blows over open water), which produces larger, destructive waves.
Different lithologies also retreat at vastly different speeds. Igneous rocks like granite might erode at just , while unconsolidated glacial till on the Holderness Coast can erode at an average of (fluctuating up to during sudden storm surges).
You can calculate the mean erosion rate using multi-year data. This provides an average figure that smooths out extreme anomalies.
Equation:
Worked Example:
Calculate the mean erosion rate for a cliff that has retreated 12.5 metres between 2013 and 2023.
Step 1: Write down the formula.
Step 2: Substitute the multi-year data. . .
Step 3: Calculate the final answer with units.
Students often use the terms 'hard' and 'soft' rock. While not entirely wrong, examiners prefer you to use the specific terms 'more resistant' and 'less resistant' to secure full marks.
When answering a 'Calculate' question, you must show every step of your working (formula and substitution) and always include the final units (e.g., m/year) to guarantee maximum marks, even if you make a calculator error.
In 'Analyse' questions using BGS maps, always explicitly link the rock type shown in the map's key to the physical shape of the coast (e.g., 'The headland protrudes because the BGS map indicates it is made of resistant limestone').
On OS maps, remember that 4-figure grid references are used for general areas like large bays, while 6-figure grid references are required to locate specific, small features like a single stack or groyne.
Lithology
The physical characteristics of rock, including its hardness, structure, and chemical composition.
Resistant rock
Hard rock (such as granite or limestone) that is tough and difficult for the sea to erode, typically forming headlands and steep cliffs.
Less resistant rock
Soft, often unconsolidated rock (such as clay or glacial till) that erodes quickly and typically forms bays or gently sloping cliffs.
Strata
Distinct layers of rock within the earth.
Concordant coastline
A coastline where bands of different rock types run parallel to the shore.
Discordant coastline
A coastline where bands of different rock types run perpendicular (at right angles) to the shore.
Differential erosion
The process where softer, less resistant rocks erode faster than harder, more resistant rocks, forming uneven coastlines like headlands and bays.
Headlands
A section of mostly resistant land that protrudes outwards into the sea.
Bays
A curved indentation in the coastline, typically formed by the erosion of less resistant rock, often containing a beach.
Wave refraction
The bending of waves as they approach an uneven coastline, concentrating energy on headlands and dispersing it in bays.
BGS maps
British Geological Survey maps that show the underlying rock types, structures, and faults of an area using colours and symbols.
Faults
Cracks or areas of structural weakness in rock (shown as thick black lines on BGS maps) that can be easily exploited by marine erosion.
OS maps
Ordnance Survey maps that provide detailed representations of the physical landscape, including contour lines and specific symbols for features like cliffs and beaches.
Hachures
Short, perpendicular lines on a map used to indicate the direction and steepness of a slope, commonly used to represent cliffs on OS maps.
Contour lines
Lines on a map joining points of equal height; when placed very close together, they indicate steep slopes or vertical drops.
Intertidal zone
The area of the shoreline that is exposed at low tide and underwater at high tide, typically where beaches are found.
Shingle/pebbles
Small, rounded stones found on a beach, represented on OS maps by small black dots or stippling over a yellow background.
Temporal variation
Changes in the rate of a process (like coastal erosion) over different time periods, such as seasonal or annual fluctuations.
Coastal recession
The gradual landward retreat of the coastline over time due to marine erosion and mass movement.
Fetch
The maximum distance of open water over which the wind blows to generate waves; a longer fetch creates more powerful waves.
Mean erosion rate
The average distance a coastline retreats per year, calculated by dividing the total distance retreated by the number of years.
Put your knowledge into practice — try past paper questions for Geography A
Lithology
The physical characteristics of rock, including its hardness, structure, and chemical composition.
Resistant rock
Hard rock (such as granite or limestone) that is tough and difficult for the sea to erode, typically forming headlands and steep cliffs.
Less resistant rock
Soft, often unconsolidated rock (such as clay or glacial till) that erodes quickly and typically forms bays or gently sloping cliffs.
Strata
Distinct layers of rock within the earth.
Concordant coastline
A coastline where bands of different rock types run parallel to the shore.
Discordant coastline
A coastline where bands of different rock types run perpendicular (at right angles) to the shore.
Differential erosion
The process where softer, less resistant rocks erode faster than harder, more resistant rocks, forming uneven coastlines like headlands and bays.
Headlands
A section of mostly resistant land that protrudes outwards into the sea.
Bays
A curved indentation in the coastline, typically formed by the erosion of less resistant rock, often containing a beach.
Wave refraction
The bending of waves as they approach an uneven coastline, concentrating energy on headlands and dispersing it in bays.
BGS maps
British Geological Survey maps that show the underlying rock types, structures, and faults of an area using colours and symbols.
Faults
Cracks or areas of structural weakness in rock (shown as thick black lines on BGS maps) that can be easily exploited by marine erosion.
OS maps
Ordnance Survey maps that provide detailed representations of the physical landscape, including contour lines and specific symbols for features like cliffs and beaches.
Hachures
Short, perpendicular lines on a map used to indicate the direction and steepness of a slope, commonly used to represent cliffs on OS maps.
Contour lines
Lines on a map joining points of equal height; when placed very close together, they indicate steep slopes or vertical drops.
Intertidal zone
The area of the shoreline that is exposed at low tide and underwater at high tide, typically where beaches are found.
Shingle/pebbles
Small, rounded stones found on a beach, represented on OS maps by small black dots or stippling over a yellow background.
Temporal variation
Changes in the rate of a process (like coastal erosion) over different time periods, such as seasonal or annual fluctuations.
Coastal recession
The gradual landward retreat of the coastline over time due to marine erosion and mass movement.
Fetch
The maximum distance of open water over which the wind blows to generate waves; a longer fetch creates more powerful waves.
Mean erosion rate
The average distance a coastline retreats per year, calculated by dividing the total distance retreated by the number of years.
