Theme B: Coastal Environments — Coastal Processes and Landforms
Welcome to your CCEA GCSE Geography revision notes for Coastal Processes and Landforms! This topic is a core part of Unit 1: Understanding Our Natural World. Whether you find coastal geography straightforward or a bit challenging, these notes break down every concept step-by-step with clear definitions, visual descriptions, and examiner warnings to help you succeed in your exam.
1. Wave Characteristics and Wave Types
Waves are created by wind blowing over the surface of the sea. The size and energy of a wave depend on how strong the wind is, how long it blows, and the fetch.
Key Definition:
Fetch: The maximum distance of open water over which the wind blows without interruption to generate waves.
Anatomy of a Wave
Understanding how a wave is measured is essential for diagrams and exam questions:
• Crest: The highest point of the wave.
• Trough: The lowest point between consecutive crests.
• Wave Height: The vertical distance between the trough and the crest.
• Wavelength: The horizontal distance between two consecutive crests (or troughs).
• Swash: The surge of water and sediment pushed up the beach face when a wave breaks. It travels up the beach at the angle of the prevailing wind.
• Backwash: The movement of water and sediment returning down the beach under gravity at a perpendicular right angle (\(90^\circ\)) to the shoreline.
Constructive vs. Destructive Waves
In the CCEA exam, you must be able to contrast the characteristics of constructive and destructive waves.
Constructive Waves (Beach Builders):
• Wave Profile: Low wave height in relation to their length (low, flat waves).
• Wave Frequency: Low frequency, typically breaking at a rate of \(6\text{–}9\) waves per minute.
• Energy Balance: Strong swash and weak backwash.
• Net Effect: Because the swash is stronger than the backwash, material is pushed up the beach and left behind, resulting in sediment deposition and a built-up beach profile.
Destructive Waves (Beach Destroyers):
• Wave Profile: Steep, tall wave profiles (high wave height relative to length).
• Wave Frequency: High frequency, typically breaking at a rate of \(10\text{–}15\) waves per minute.
• Energy Balance: Weak swash and a powerful backwash.
• Net Effect: Because the backwash is far more powerful than the swash, sediment is pulled away from the coast and dragged out to sea, causing coastal erosion.
Memory Trick: Constructive waves Create beaches (low frequency \(6\text{–}9\)/min, strong swash). Destructive waves Destroy beaches (high frequency \(10\text{–}15\)/min, strong backwash).
Key Takeaway for Section 1: Waves transfer energy to the coast. Constructive waves deposit sediment because their swash is stronger than their backwash, while destructive waves erode the coast because their backwash is far more powerful.
2. Coastal Processes
The coastline is shaped by three main coastal processes: Erosion, Transportation, and Deposition.
A. Coastal Erosion
Erosion is the wearing away and removal of rock along the coast. Seawater uses four distinct methods:
1. Hydraulic Action:
The sheer force of waves crashing against the cliff face. Water forces air into cracks, joints, and fissures in the rock, compressing the trapped air. When the wave recedes, the pressure is released explosively. Over time, repeated pressure changes widen the cracks and shatter the rock.
2. Abrasion (also known as Corrasion):
The sandpaper-like grinding action of waves hurling sand, shingle, and boulders against the cliff face and wave-cut platform. This mechanical scraping chips away rock particles.
3. Attrition:
Loose rock fragments and pebbles carried by waves continuously bump and collide into one another. Over time, these impacts break off sharp edges, making the sediment progressively smaller, smoother, and more rounded.
Examiner Warning: Attrition does NOT erode the cliff face! It only wears down the loose sediment carried by the water.
4. Solution (also known as Corrosion):
The chemical dissolving of soluble minerals in rocks (such as calcium carbonate in limestone or chalk) by weak acids found naturally in seawater.
B. Coastal Transportation & Longshore Drift (LSD)
Sediment moved along the coastline travels via a process called Longshore Drift (LSD). Here is the step-by-step sequence:
Step 1: The prevailing wind approaches the coastline at an oblique angle.
Step 2: Waves break at this same angle, causing the swash to push sand and pebbles diagonally up the beach.
Step 3: The backwash then pulls the sediment straight back down the beach slope under the pull of gravity at a right angle (\(90^\circ\)) to the shoreline.
Step 4: This continuous, repeating cycle creates a distinct zig-zag movement of sediment along the coast in the direction of the dominant drift.
C. Coastal Deposition
Deposition occurs when waves lose energy and velocity. When water slows down, it can no longer support its load, causing sand, shingle, and mud to settle. Deposition commonly happens in:
• Sheltered bays protected by headlands.
• Shallow water areas where friction with the seabed slows waves down.
• Areas sheltered behind coastal obstructions or spits.
Key Takeaway for Section 2: Hydraulic action and abrasion attack cliff faces, while attrition rounds moving pebbles. Longshore drift moves material in a zig-zag pattern along the coast because swash moves at an angle with the wind, but backwash pulls straight down at \(90^\circ\) due to gravity.
3. Landforms of Coastal Erosion
Destructive wave energy acting on varying rock types creates distinctive erosional landforms.
A. Headlands and Bays
Headlands and bays form along discordant coastlines, where alternating bands of resistant (hard) rock and less-resistant (soft) rock meet the sea at right angles (\(90^\circ\)).
1. Differential Erosion: Destructive waves attack the coastline. The less-resistant soft rock (e.g., clay or sands) erodes rapidly via hydraulic action and abrasion, curving inwards to form sheltered bays.
2. Headland Formation: The more resistant hard rock (e.g., limestone, chalk, or granite) erodes much more slowly and is left jutting out into the sea as prominent headlands.
B. Cliffs and Wave-Cut Platforms
Over time, cliff erosion leads to the retreat of the coastline and leaves behind a flat rock platform:
1. Undercutting: Destructive waves concentrate their erosive power (hydraulic action and abrasion) at the base of the cliff between the high and low water marks, carving out a hollow known as a wave-cut notch.
2. Overhang Formation: Continued undercutting deepens the notch, leaving the cliff above unsupported as an overhang.
3. Collapse: Eventually, the unsupported overhang can no longer bear its own weight and collapses into the sea under the pull of gravity.
4. Cliff Retreat: As this cycle of undercutting and collapse repeats over many years, the cliff face steadily retreats inland.
5. Wave-Cut Platform: In front of the retreating cliff, a gently sloping, smoothed, rocky ledge is left behind at the base. This is the wave-cut platform, which is exposed at low tide and submerged at high tide.
C. The Headland Sequence: Cave, Arch, Stack, and Stump
Headlands are exposed to severe wave attack from multiple sides. They erode through a strict sequential order:
1. Crack / Fault: Marine processes (hydraulic action and abrasion) exploit lines of natural weakness, joints, or faults in the resistant headland rock.
2. Cave: Persistent hydraulic pressure and abrasive grinding widen and deepen these cracks into a hollow opening called a cave.
3. Arch: Erosion continues until the cave breaks all the way through the headland, or two caves eroding back-to-back meet in the middle, creating an open bridge of rock known as an arch.
4. Stack: Marine undercutting widens the arch base, while sub-aerial weathering (e.g., freeze-thaw weathering) weakens the arch roof. Eventually, the heavy roof collapses under gravity into the sea, leaving an isolated vertical pillar of rock standing out in the sea called a stack.
5. Stump: Destructive waves continue to undercut the base of the stack while weathering attacks the top. Eventually, the pillar collapses to form a low-lying rocky base called a stump, which is usually only visible at low tide.
Sequence Checklist: Crack \(\rightarrow\) Cave \(\rightarrow\) Arch \(\rightarrow\) Stack \(\rightarrow\) Stump.
Key Takeaway for Section 3: Discordant coastlines produce headlands and bays due to differential erosion. Undercut cliffs collapse and retreat to leave wave-cut platforms. Headlands break down systematically from cracks to caves, arches, stacks, and finally stumps.
4. Landforms of Coastal Deposition
Where constructive waves dominate and wave energy drops, sediment accumulates into depositional landforms.
A. Beaches
Beaches are accumulations of sand and shingle deposited by constructive waves between the low water mark and the highest storm tide line.
• Sandy Beaches: Generally have a very gentle, flat gradient because fine sand particles wash back easily down the slope.
• Shingle Beaches: Have steep gradients because coarse, large pebbles allow water to percolate through quickly, preventing backwash from dragging all the material back down.
B. Sand Spits and Hooked Spits
A spit is an extended ridge of sand or shingle projecting out from the mainland across an estuary or bay.
How a Spit Forms (Step-by-Step):
1. Longshore Drift: Sediment is transported along the coast in a zig-zag pattern driven by the prevailing wind.
2. Coastline Change: When the coastline suddenly changes direction (for example, at a river estuary or bay entrance), longshore drift does not turn the corner.
3. Deposition into Open Water: As waves reach the deeper, sheltered water at the bend, they lose energy and deposit their sediment load out into the sea.
4. Spit Growth: Continued deposition builds up a long, narrow finger or ridge of sand and shingle extending outwards from the land.
5. Hooked / Recurved End: Changes in the dominant wind direction or secondary wave refraction bend the end of the spit back towards the land, forming a hooked spit (or recurved end).
6. Salt Marsh Formation: In the low-energy, sheltered water behind the spit, river silt and fine marine sediments accumulate to form a salt marsh.
Examiner Note: A spit cannot grow completely across a river estuary because the strong flow of river water moving out to sea washes the sediment away, keeping the channel open.
Key Takeaway for Section 4: Spits form where longshore drift carries sediment past a sudden change in coastal direction. Deposition builds a ridge into open water, secondary winds create hooked ends, and sheltered salt marshes develop behind.
5. Quick Summary & Common Exam Mistakes Checklist
Before your exam, double-check that you avoid these common student pitfalls:
Mistake 1: Confusing Attrition with Cliff Erosion.
Correction: Attrition is strictly sediment colliding with sediment (making pebbles smaller and rounder). It does NOT erode the cliff face.
Mistake 2: Confusing Abrasion (Corrasion) with Solution (Corrosion).
Correction: Abrasion is mechanical scraping with rock fragments (like sandpaper). Solution is chemical dissolving of rock by weak acids in seawater.
Mistake 3: Forgetting the Angle of Backwash.
Correction: Swash moves up the beach at an oblique angle (following the prevailing wind), but backwash ALWAYS pulls straight down at a \(90^\circ\) right angle due to gravity.
Mistake 4: Missing the Mechanism of Stack Formation.
Correction: A stack is NOT formed because waves slice it off the mainland. A stack forms because an arch roof collapses under gravity after being weakened by weathering and marine undercutting.
Mistake 5: Mixing up Wave Rates.
Correction: Constructive waves break slowly (\(6\text{–}9\) per minute); destructive waves break quickly (\(10\text{–}15\) per minute).