Geography (9230) | Coastal landscapes

🌊 Your Guide to Coastal Landscapes (9230) 🌊

Hello Geographers! Welcome to one of the most dynamic and exciting chapters: Coastal Landscapes. These notes are designed to break down the powerful processes that shape our shorelines—from massive cliffs to relaxing sandy beaches.

Don't worry if terms like "longshore drift" or "hydraulic action" seem complicated right now. We'll tackle them step-by-step, using simple analogies and clear explanations. Let's dive in!

1. Understanding the Energy Source: Waves

The coast is defined by energy, and most of that energy comes from waves. Waves are created by wind blowing over the sea surface.

Key Concept: Two Types of Waves

We classify waves based on what they do to the beach:

A) Constructive Waves (The Builders):

• Action: They construct (build up) the beach.
• Characteristics: Low frequency (happens less often), gentle slope.
• Swash vs. Backwash: The swash (water moving up the beach) is stronger than the backwash (water returning to the sea).
• Result: Net deposition (material is left behind).

B) Destructive Waves (The Wreckers):

• Action: They destroy or erode the beach.
• Characteristics: High frequency (happens often), steep profile (tall).
• Swash vs. Backwash: The backwash is stronger than the swash, pulling material back towards the sea.
• Result: Net erosion (material is removed).

🧠 Memory Aid: Think of 'C' for Constructive and Calm/Creating. Think of 'D' for Destructive and Dangerous/Deleting.

2. Coastal Processes: Shaping the Land

Waves and water act on the coast in four main ways, leading to erosion (the wearing away of rock).

The Four Types of Coastal Erosion (H.A.A.S.)

Understanding these processes is vital for the exam:

1. Hydraulic Action (H)

• The Process: The sheer power and pressure of the water and air hitting the cliff face. Waves compress air in cracks; when the wave retreats, the air expands violently, shattering the rock.
• Analogy: It’s like using a powerful water jet to break things apart.

2. Abrasion (A)

• The Process: Rock fragments (sediment) carried by the sea are thrown against the cliff face, wearing it away like sandpaper.
• Key Point: Abrasion requires tools (the rocks/sand).
• Analogy: Sandpapering a piece of wood. The sea is the hand, the sediment is the sandpaper.

3. Attrition (A)

• The Process: This is when the pebbles and sediment carried by the sea crash into each other, becoming smaller and more rounded over time.
• Key Point: This affects the material, not the cliff face itself.
• Analogy: Putting marbles in a washing machine—they constantly collide and wear down.

4. Solution (S) / Corrosion

• The Process: Mild acids in seawater dissolve soluble rocks, such as chalk and limestone.
• Key Point: This is a chemical process, especially effective in areas with limestone geology.

Takeaway: Erosion is powerful! Hydraulic Action and Abrasion are the main ways cliffs are destroyed.

3. Transportation and Deposition

Once rock material is eroded, it needs to be moved. The main way sediment moves along the coast is called Longshore Drift (LSD).

How Longshore Drift Works (Step-by-Step)

Longshore Drift is the zig-zag movement of sediment along the beach, following the direction of the prevailing wind and waves:

1. The swash (incoming wave) carries sediment up the beach, usually at an angle (driven by the prevailing wind).
2. The backwash (returning water) pulls the sediment back down the beach, straight down due to gravity (at a 90-degree angle to the coast).
3. This repeated process moves material gradually along the coast, resulting in a net movement (a zig-zag path).

Did you know? If there were no human structures (like groynes) stopping it, sediment could travel hundreds of miles over time!

Deposition

Deposition occurs when the energy of the waves and water decreases. This usually happens in sheltered areas, like bays, or where the water slows down (e.g., river mouths).

Key Takeaway: LSD is the essential process for moving sediment, leading to the formation of beaches and other depositional features.

4. Erosional Landforms: Cliffs, Caves, and Stacks

The constant attack by waves creates dramatic landforms. The type of rock (geology) greatly influences the shape of the coast.

A) Headlands and Bays

• Headland: An area of land that juts out into the sea. They are formed from resistant rock (hard rock) that erodes slowly.
• Bay: A wide, curved inlet between two headlands. They are formed where less resistant rock (soft rock, like clay) has been eroded rapidly.
• Analogy: Think of a wall: the brick (hard rock) stays up, but the mortar (soft rock) wears away quickly.

B) The Cliff Erosion Sequence

Hard rock headlands are attacked by waves, leading to a predictable sequence of landforms:

1. Crack/Fault: Destructive waves exploit weaknesses (cracks) in the rock.
2. Cave: Erosion (mainly Hydraulic Action and Abrasion) widens the crack into a cave.
3. Arch: If the cave is eroded right through the headland, an arch is formed. (e.g., Durdle Door, Dorset, UK).
4. Stack: Continuous erosion at the base of the arch weakens its roof. Eventually, the roof collapses, leaving an isolated pillar of rock called a stack. (e.g., The Old Man of Hoy, Scotland).
5. Stump: The stack is eroded at the base, collapsing to form a small platform visible at low tide, known as a stump.

Key Term: Wave-Cut Platform: Continuous erosion at the base of the cliff creates a wave-cut notch (an undercut). Over time, the notch collapses, and the cliff retreats, leaving a flat, rocky area at the foot of the cliff known as a wave-cut platform.

5. Depositional Landforms: Beaches, Spits, and Bars

Where energy is low, deposition occurs, leading to features that are generally made of loose sediment (sand or shingle).

A) Beaches

• Accumulations of sand, shingle, or pebbles found between the low and high water marks.
• Sand beaches are usually found in sheltered bays where Constructive waves are dominant.
• Shingle/pebble beaches are steeper and are often found where Destructive waves have pulled away the finer sand.

B) Spits

A spit is a long, narrow ridge of sand or shingle attached to the land at one end and extending out into the sea or across a river estuary.

• Formation: Longshore Drift carries sediment past a bend in the coastline (or across a river mouth).
• As the water loses energy in the deeper, calmer water, the sediment is deposited.
• The end facing the sea often develops a recurved end or hook because of opposing winds or wave refraction.
• The sheltered area behind the spit often becomes a salt marsh (a muddy, vegetated area).
• Example: Spurn Head, UK.

C) Bars

• A bar forms if a spit grows long enough to connect two headlands across a bay.
• The bar traps water behind it, creating a freshwater or brackish (mixed salt/fresh) lake called a lagoon.

Quick Review: Spits stick out; Bars block off the bay completely.

6. Coastal Management: Protecting the Coastline

Coasts are highly valued but also vulnerable. Management strategies are used to protect people, property, and businesses from erosion and flooding.

Two Main Types of Management Strategy

Coastal management is usually divided into Hard Engineering (using artificial structures) and Soft Engineering (working with nature).

A) Hard Engineering (Building Things)

These methods are expensive, effective in the short term, but often unsustainable and visually intrusive.

1. Sea Walls: Large concrete barriers built along the base of the cliff or promenade.
• Benefit: Excellent protection against erosion and flooding.
• Cost/Drawback: Very expensive; reflects wave energy causing erosion at the base.
2. Groynes: Timber or rock structures built at 90 degrees to the beach, trapping sediment moved by Longshore Drift.
• Benefit: Creates a wider, higher beach (natural defence).
• Cost/Drawback: Starves beaches further down the coast of sediment, increasing erosion there (the 'knock-on' effect).
3. Rock Armour (Rip-Rap): Large boulders placed at the base of a cliff.
• Benefit: Absorbs wave energy effectively.
• Cost/Drawback: Expensive to transport; looks very unnatural.

B) Soft Engineering (Working with Nature)

These methods are cheaper, more environmentally friendly, and often blend better with the natural landscape.

1. Beach Nourishment (Replenishment): Sand and shingle are added to the beach (often dredged from the seabed).
• Benefit: Creates a wider beach, which absorbs wave energy naturally. Looks natural.
• Cost/Drawback: Requires constant repetition; sand source must be found.
2. Dune Stabilisation: Planting vegetation (like Marram Grass) to stabilise sand dunes, which act as natural barriers.
• Benefit: Very cheap, highly sustainable, and natural-looking.
• Cost/Drawback: Takes time for vegetation to establish; dunes are sensitive to human access.
3. Managed Retreat: Allowing the sea to flood low-value land (e.g., farmland) where the costs of defence outweigh the benefits.
• Benefit: Cheaper than building defences; creates new habitats (salt marshes).
• Cost/Drawback: Compensation must be paid to landowners; unpopular with locals who lose land.

🔥 Final Thought: Coastal management is always a balance between cost, effectiveness, and environmental impact. There is no perfect solution!

You have now covered the core processes and landforms of coastal geography. Take a deep breath—you are well on your way to mastering this topic!