Welcome to the Dynamic Coastline!
Hello future Geographers! This chapter, Coastal Environments, is one of the most exciting parts of Physical Geography. We are going to explore how the powerful sea shapes the land, creating beautiful beaches, dramatic cliffs, and unique features.
Don't worry if this seems tricky at first—we will break down the forces of nature into simple steps. By the end, you will understand the constant battle between the sea and the land!
Quick Review: Why is studying coasts important?
Coasts are home to most of the world's population and are vital for trade and tourism. Understanding how they change helps us protect communities and manage precious land.
Section 1: The Engine of Change - Waves
1.1 How Waves are Formed
Waves are created when the wind blows over the surface of the water. The longer the distance the wind blows over (this is called the fetch), the bigger and more powerful the waves will be.
1.2 Constructive Waves (The Builders)
These waves are low frequency (arrive slowly, about 6-8 per minute) and are generally gentle. They are the "builders" of the coast.
- Swash: The water surging up the beach is stronger.
- Backwash: The water draining back down the beach is weaker.
1.3 Destructive Waves (The Destroyers)
These waves are high frequency (arrive quickly, about 10-14 per minute) and are powerful. They are the "destroyers" of the coast.
- Swash: The water surging up the beach is weaker.
- Backwash: The water draining back down the beach is stronger.
Key Takeaway:
Remember the job titles: Constructive waves (low frequency) build the beach. Destructive waves (high frequency) destroy the beach.
Section 2: Coastal Processes
2.1 Processes of Coastal Erosion
Erosion is the wearing away and breaking down of rock and sediment. The sea uses four main methods to attack the coast.
Memory Aid: Think H.A.A.S (sounds like 'haze') to remember the four types!
1. Hydraulic Action (The Pressure Cooker)
This is the most important process. It happens when waves hit the cliff face and force air into cracks. When the wave retreats, the pressure is released, causing the crack to expand. Over time, this pressure weakens the rock, causing bits to break off.
2. Abrasion (The Sandpaper Effect)
This occurs when the sea throws loose material (like pebbles and rocks) against the cliff face, chipping away at the rock like sandpaper.
3. Attrition (The Battering Ram)
This is when the stones and pebbles carried by the sea smash into each other, breaking them down into smaller, rounder pieces of sediment (sand).
4. Solution (The Dissolver)
This is the chemical process where weak acids in the seawater dissolve soluble rocks, such as limestone or chalk.
2.2 Transportation - Longshore Drift (LSD)
Transportation is the movement of eroded material along the coast. The most important movement is Longshore Drift (LSD).
Step-by-Step: How Longshore Drift Works
1. Waves approach the beach at an angle (usually determined by the prevailing wind).
2. The swash carries sediment up the beach at this angle.
3. The backwash, however, always drags the sediment straight back down the beach due to gravity.
4. This zig-zag movement (up at an angle, back straight down) slowly moves the material along the coast in one direction.
Analogy: Imagine carrying a bag of groceries (sediment). You walk diagonally up the road (swash) but then drop it straight down towards the gutter (backwash). You pick it up further along the road and repeat the diagonal walk. You are slowly moving the bag down the street.
2.3 Deposition
Deposition is simply when the sea drops the sediment it is carrying. This usually happens when the wave loses energy (e.g., in sheltered bays, or when the backwash of constructive waves is too weak to carry the material back out to sea). Deposition creates new landforms like beaches and spits.
Quick Review Box:
Erosion: Wearing away (H.A.A.S).
Transportation: Moving material (LSD).
Deposition: Dropping material (Loss of energy).
Section 3: Landforms of Coastal Erosion
Erosional landforms are created in areas where destructive waves dominate, often found along headlands (areas of hard rock that stick out into the sea).
3.1 Cliffs and Wave-Cut Platforms
Formation Process:
1. Destructive waves attack the base of the cliff through hydraulic action and abrasion.
2. This forms a notch (an undercut section) at the high-water mark.
3. As the notch deepens, the rock above it becomes unstable and eventually collapses, causing the cliff to retreat.
4. As the cliff retreats, a gently sloping area of rock is left behind at the base, visible at low tide. This is the wave-cut platform.
3.2 The Headland Sequence: Caves, Arches, Stacks, and Stumps
This sequence only occurs on headlands made of resistant rock.
1. Crack/Fault: The waves attack a weak line or fault in the headland.
2. Cave: Continued erosion (hydraulic action and abrasion) widens the crack into a deep hollow, forming a cave.
3. Arch: If the cave cuts all the way through the headland, or if two caves erode back-to-back, a hole is formed, creating an arch (like a bridge).
4. Stack: Erosion continues to widen the arch until its roof collapses. This leaves a tall, isolated column of rock standing away from the headland, known as a stack.
5. Stump: The stack is attacked by weather and waves, eventually collapsing to form a small, often submerged, piece of rock called a stump.
Did you know? Famous examples of this sequence can be seen at Old Harry Rocks in Dorset, UK.
Section 4: Landforms of Coastal Deposition
Depositional landforms are created where constructive waves are dominant or in sheltered areas, like bays, where the wave energy is low.
4.1 Beaches
Beaches are the most common depositional feature.
- Sand Beaches: Found in sheltered bays; sand is fine and gently sloping. Built by constructive waves.
- Shingle/Pebble Beaches: Found where wave energy is higher; material is coarser and the beach slope is steeper.
4.2 Spits
A spit is an elongated ridge of sand or shingle that extends out from the land into the sea, usually across the mouth of a river or estuary.
Formation of a Spit:
1. Longshore Drift moves sediment along the coast.
2. The coast suddenly bends (e.g., at a river mouth) but the LSD process continues to move sediment in the same direction, depositing it into the sea.
3. The ridge of deposited material builds up and grows outwards.
4. A hooked or recurved end develops because the end of the spit is influenced by secondary winds or waves approaching from the opposite direction (or the shelter provided by the estuary).
5. The area behind the spit is sheltered from the waves, allowing fine sediment and silt to settle, often leading to the formation of a salt marsh.
4.3 Bars
A bar is similar to a spit, but it connects two headlands together, trapping a body of water behind it called a lagoon. Bars form when LSD operates across a bay.
4.4 Sand Dunes
These are mounds of sand found at the back of some beaches, developed by wind rather than water.
1. Sand dries out at high tide and is blown inland.
2. The wind meets an obstruction (like a piece of driftwood or grass) and deposits the sand.
3. Specialised, tough grasses (like marram grass) start to grow, binding the sand together and stabilising the dune.
Key Takeaway:
Deposition requires a loss of energy. Spits and Bars are key depositional landforms caused by Longshore Drift.
Section 5: Coastal Management
Coasts are often managed because they are vital areas for housing, infrastructure, and tourism. We separate management into two types: Hard Engineering (built structures) and Soft Engineering (working with nature).
5.1 Hard Engineering Strategies (Building Strong Defences)
1. Sea Walls
Description: Concrete walls built parallel to the coast, often curved to reflect wave energy back into the sea.
Pros: Highly effective at preventing erosion and flooding; provides promenades for people.
Cons: Very expensive to build and maintain; reflects energy, increasing erosion further down the coast (called terminal groyne syndrome).
2. Groynes
Description: Timber or rock barriers built at right angles to the sea, designed to trap sediment moved by Longshore Drift.
Pros: Creates a wider beach, which absorbs wave energy and attracts tourists; relatively cheap compared to sea walls.
Cons: Starves beaches further down the coast of sediment, leading to increased erosion in those areas.
3. Rock Armour (or Rip-Rap)
Description: Large piles of hard rocks placed at the foot of a cliff or behind a sea wall.
Pros: Absorbs wave energy (dissipates it in the gaps between the rocks); cheaper than a sea wall.
Cons: Looks unattractive and artificial; rocks may be sourced from distant quarries, increasing transport costs.
5.2 Soft Engineering Strategies (Working with Nature)
Soft engineering aims to mimic or enhance natural coastal defences, often being more sustainable.
1. Beach Nourishment (or Recharge)
Description: Sand or shingle is artificially added to the beach to make it wider and higher.
Pros: Looks natural; widens the beach, increasing its ability to absorb wave energy; popular with tourists.
Cons: Needs regular replacement (maintenance); can be very expensive to transport material.
2. Dune Stabilisation
Description: Planting grasses (like marram grass) and fencing off areas to protect fragile sand dunes.
Pros: Very natural and environmentally friendly; sand dunes are effective barriers against the sea.
Cons: Takes a long time for the ecosystem to establish; can be damaged easily if tourists ignore warnings.
Important Note for Exams:
When discussing coastal management, remember to always evaluate the environmental, economic, and social consequences of the chosen strategy. Most hard engineering solutions solve the problem locally but often create a new problem elsewhere!
Encouraging Thought: You’ve now mastered the major forces shaping our shores! Review the landforms by sketching them out—this helps lock the process sequence into your memory.