🌊 Coastal Landscape Development: Your Study Guide 🌊

Hello Geographers! Welcome to one of the most dynamic and exciting units in physical geography: Coastal Systems and Landscapes.
Coasts are constantly changing—they are literally the meeting point of land, sea, and atmosphere, making them incredibly active environments.
This chapter will teach you how waves, winds, and currents work together to build stunning depositional landforms (like beaches) and carve dramatic erosional features (like cliffs and caves). Understanding these processes is crucial for tackling real-world challenges, such as coastal erosion and flood management. Let's dive in!

1. Coasts as Natural Systems (3.1.3.1)

In Geography, we view coasts using the Systems Approach. This means looking at the coast as a collection of parts (components) that interact with energy and material moving in and out.

Key System Concepts:
  • Inputs: Energy (solar, gravitational, wave/wind power) and materials (sediment from rivers, offshore, or eroded from cliffs).
  • Outputs: Sediment (e.g., being deposited far offshore) or energy leaving the system.
  • Stores/Components: Places where energy or material are held, such as beaches, sand dunes, or cliffs.
  • Flows/Transfers: The movement of energy or material, such as longshore drift or wave erosion.
Feedback and Equilibrium

Coastal systems are complex because they try to stay balanced:

  • Negative Feedback: This acts as a stabiliser. Example: If a beach starts to erode heavily (losing sediment), the sea deposits offshore bars. These bars reduce wave energy hitting the beach, allowing the beach to recover. (The system corrects itself).
  • Positive Feedback: This accelerates change. Example: If a sand dune loses vegetation (perhaps due to human trampling), the exposed sand is easily blown away, making the dune smaller and more vulnerable to further erosion. (The change gets worse).
  • Dynamic Equilibrium: This is the goal! The system is in a state of balance where inputs and outputs are equal, but the stores (the landforms) are constantly adjusting to minor shifts in conditions. It’s like a juggler—they stay balanced but are always moving.

Quick Review: Coasts are open systems. They need inputs (like energy and sediment) to maintain dynamic equilibrium.

2. Sources of Energy and Sediment (3.1.3.2)

The energy that drives change at the coast comes from several key sources.

Energy Sources:
  1. Winds: The primary driver of waves, transferring energy from the atmosphere to the hydrosphere.
  2. Waves: The most powerful force. We classify them into two main types:
    • Constructive Waves:
      These are typically low-energy, long wavelength waves. They have a stronger swash (movement up the beach) than backwash (movement down the beach). They deposit material, helping to build up beaches.
    • Destructive Waves:
      These are high-energy, steep waves. Their backwash is much stronger than their swash, meaning they erode material and carry it away. These are common during storms.
  3. Currents and Tides:
    • Tides (caused by the gravitational pull of the moon and sun) create tidal currents that move water and sediment.
    • Currents (longshore currents, rip currents) also distribute energy and material.

Did you know? The size of waves is largely determined by the fetch – the distance over which the wind has blown uninterrupted across the water surface.

Sediment: Sources, Cells, and Budgets

The sediment (sand, pebbles, mud) that forms coastal landforms comes from several sources:

  • Terrestrial Sources: Rivers (depositing eroded material), wind (blowing sand), and cliff erosion (mass movement/weathering).
  • Offshore Sources: Sediment carried onshore by waves or currents, or material dredged from the seabed.
  • Marine Organisms: Shells and coral fragments.

We manage sediment distribution using the concepts of Sediment Cells and Sediment Budgets.

Sediment Cells: These are largely self-contained areas along the coast where the movement of sediment is confined. There are 11 major sediment cells around England and Wales. They are "closed systems" in terms of sediment movement, meaning sediment is generally not transferred between them.

Sediment Budget: This tracks the inputs and outputs within a cell.

  • If Inputs > Outputs, the budget is positive (deposition is occurring, building up the coast).
  • If Outputs > Inputs, the budget is negative (erosion is occurring, coast retreats).

Key Takeaway: Energy creates the waves, and waves manage the sediment budget, determining whether the coast grows or shrinks.

3. Geomorphological Processes: The Distinctive Coastal Toolkit (3.1.3.2)

Coasts feature general geomorphological processes (weathering, mass movement, erosion, transportation, deposition) but also several unique marine processes.

Marine Erosion Processes

These are the processes by which the sea attacks the coast. Don't worry if this seems tricky—just remember the HAWACS mnemonic for the six types listed in the syllabus!

  1. Hydraulic Action:
    This is purely the force of water and compressed air. Waves trap air in cracks and joints in the rock. As the wave retreats, the air expands suddenly, shattering the rock.
  2. Attrition:
    Material carried by the sea (like pebbles) smashes into each other, wearing them down into smaller, smoother, rounder fragments.
  3. Wave Quarrying (or Pounding):
    The sheer weight and velocity of large destructive waves hitting the cliff face can dislodge large blocks of rock, especially on jointed or highly fractured rock types.
  4. Abrasion/Corrasion:
    Sediment carried by the wave grinds, scrapes, and files away at the rock face, acting like sandpaper. This is most effective at the base of cliffs.
  5. Cavitation:
    A lesser-known process where rapid changes in water pressure cause the formation and immediate collapse of tiny air bubbles. This creates small shockwaves that erode the rock surface.
  6. Solution (or Corrosion):
    Rock minerals (especially limestone/chalk, which are calcium carbonate) are dissolved by weak acids in the seawater (carbonic acid).
Transportation and Deposition

Transportation is the movement of eroded material, primarily via Longshore/Littoral Drift.

Step-by-step Longshore Drift (LSD):

  1. Swash: Waves approach the shore at an angle (driven by prevailing winds). The swash carries sediment up the beach at this angle.
  2. Backwash: The water drains straight back down the steepest gradient, which is perpendicular (at 90 degrees) to the shoreline, under the force of gravity.
  3. Zig-Zag: The sediment is moved along the coast in a continuous zig-zag pattern.

Other Transport Methods:

  • Traction: Large pebbles/boulders rolled along the seabed.
  • Saltation: Smaller, lighter sediment bounced along the seabed.
  • Suspension: Fine material (silts and clays) carried within the water column.

Deposition: Occurs when energy levels drop (e.g., in sheltered bays or estuaries), allowing the water to no longer carry its sediment load. This builds depositional landforms like beaches and spits.

Sub-Aerial Processes (Weathering and Mass Movement)

These processes happen on the land above the tide line, attacking the cliff from the top down, weakening the rock and supplying sediment to the coast.

  • Weathering: Breakdown of rock in situ (in place).
    Types: Chemical (e.g., carbonation on chalk), Mechanical (e.g., freeze-thaw), Biological (e.g., root penetration).
  • Mass Movement: The downward movement of sediment due to gravity.
    Examples: Rockfall (fast, sudden collapse of vertical cliff face), Slides (rock moving along a planar surface), and Slumps (material rotating along a curved failure plane, common in weak, unconsolidated material like clay).
  • Runoff: Water flowing over the cliff face, eroding the surface and weakening the structure.

Key Takeaway: Marine erosion attacks the base of the cliff (the 'foot'), while sub-aerial processes attack the top, working together to make the cliff retreat.

4. Landforms of Coastal Erosion (3.1.3.3)

Erosional landforms develop primarily on High Energy Coasts where destructive waves dominate, often associated with resistant rock structures.

Cliffs and Wave Cut Platforms
  • Cliffs: Steep rock faces formed by erosion and sub-aerial processes. Their profile (shape) depends on the rock type (geology).
  • Wave Cut Platform: A flat area of rock left at the base of the cliff.
    Formation: Marine erosion (abrasion, hydraulic action) undercuts the cliff, creating a wave cut notch at high tide level. The notch enlarges until the rock above collapses (mass movement). This process repeats, and the cliff retreats, leaving a gently sloping platform behind.
Cliff Profile Features: Caves, Arches, Stacks

These features develop along coastlines where joints or weaknesses (faults) exist in resistant rock.

Step-by-step Formation of Cave, Arch, Stack, Stump:

  1. Weakness Attack: Waves target a major weakness (joint/fault) in a headland (a piece of land jutting into the sea).
  2. Cave Formation: Erosion widens the weakness into a cave.
  3. Arch Formation: Two caves on either side of the headland meet, or a single cave is enlarged, forming an arch that extends through the headland.
  4. Stack Formation: The arch is undercut by erosion, and its roof collapses due to gravity and weathering. A pillar of rock, called a stack, is left isolated from the headland.
  5. Stump Formation: The stack is eventually eroded down to a small, low-lying platform called a stump, which is only visible at low tide.

Example: The Twelve Apostles on the coast of Victoria, Australia, are famous stacks.

Key Takeaway: The process of cliff retreat and the sequence of caves, arches, and stacks demonstrate the power of marine erosion over time.

5. Landforms of Coastal Deposition (3.1.3.3)

Depositional landforms form on Low Energy Coasts, often where there are shallow waters or sheltered areas like bays, allowing constructive waves to dominate and drop their sediment load.

Beaches

Accumulations of sand or pebbles between high and low tide marks.

  • Sand Beaches: Usually gentler slopes. Sand is fine and compacts when wet, reducing the effect of backwash.
  • Shingle/Pebble Beaches: Steeper slopes. Water rapidly drains through the large air gaps, meaning the backwash is weak compared to the swash, resulting in material piling up steeply.
Spits and Tombolos
  • Spit: A long, narrow ridge of sand or shingle attached to the land at one end, extending out into the sea or across an estuary mouth. They form where Longshore Drift continues across an indentation (like a river mouth) but the sudden drop in energy (due to deep water or opposing currents) causes deposition.
  • Simple Spit: A straight extension of the coastline.
  • Compound Spit: Has recurrent depositional features on its landward side (often curved ends, called recurved laterals, caused by changes in prevailing wind/wave direction).
  • Tombolo: A beach or bar that connects an island to the mainland (or to another island). Example: Chesil Beach in the UK is sometimes considered a tombolo connecting the Isle of Portland.
Offshore Bars, Barrier Beaches, and Islands

These are large ridges of sediment built parallel to the coast, usually due to rising sea levels or the transportation of sediment from the beach face during storms.

  • Offshore Bars: Submerged ridges of sand or shingle built in the nearshore zone.
  • Barrier Beaches/Islands: Sand or shingle ridges that stand above high tide, lying parallel to the coast. These are separated from the mainland by a lagoon or marsh. They act as important natural coastal defences.
Sand Dunes

Sand dunes form at the back of wide, sandy beaches where the prevailing onshore wind is strong enough to blow dry sand inland.

Dune Succession (Psammosere): The process of landform development is governed by vegetation succession:

  1. Sand is trapped by pioneer plants (like Marram Grass).
  2. The plants bind the sand, forming embryo dunes, which are highly mobile.
  3. As soil forms and organic matter increases, these grow into fore dunes and then yellow dunes (where vegetation coverage increases).
  4. Finally, they stabilise into grey dunes and eventually, a climax community (often woodland) may develop if conditions allow.

Common Mistake: Remember that dunes are stabilised by Marram Grass, which is specifically adapted to the harsh, salty environment (it is a halophyte).

6. Estuarine Environments: Mudflats and Saltmarshes (3.1.3.3)

Estuaries are sheltered, low-energy coastal areas where freshwater rivers meet the saltwater sea. The calm conditions, often protected from high wave energy, favour deposition.

Mudflats and Saltmarshes
  • Mudflats: Formed by the deposition of fine sediment (silt and clay) carried by rivers and tides. They are exposed at low tide.
  • Saltmarshes: Develop when mudflats rise high enough to be covered only by the highest tides. Pioneer salt-tolerant vegetation (like Glasswort) colonises the mud, trapping more sediment, raising the surface, and creating a marsh environment.

Factors in Development:

  • Low energy environment (sheltered location).
  • High sediment supply (from the river and sea).
  • Salt-tolerant vegetation to trap and stabilise the accumulating mud.

Key Takeaway: Estuarine environments are critical buffers for the coastline, protecting inland areas from storm surges.

7. Sea Level Change and Coastline Types (3.1.3.3)

Coastal landscapes are fundamentally shaped by changes in the relative level of the sea and land over geological time.

Types of Sea Level Change
  • Eustatic Change: Global changes in the volume of water in the ocean, typically due to climate change.
    Example: During Ice Ages, water is locked up in ice sheets, causing sea level to drop (a global fall). When ice melts, sea level rises (a global rise).
  • Isostatic Change: Local changes in the height of the land surface, often caused by the weight of ice or sediment.
    Example: During the last Ice Age, Scotland was pressed down by ice (it is still rising today, called isostatic recovery), while the South of England experienced land fall (it is still sinking today).
  • Tectonic Change: Local or regional changes in land height due to tectonic forces (e.g., earthquakes lifting or dropping the coastline).

Major Changes in the last 10,000 years: The end of the last glacial period caused massive eustatic rise (melting ice) and ongoing isostatic adjustments (land bouncing back). The overall trend has been rising sea levels.

Coastlines of Emergence and Submergence

These are the outcomes of relative sea level changes:

Coastlines of Emergence (The land rises relative to the sea):

  • Raised Beaches: Former beaches and wave cut platforms left stranded above the current sea level.
  • Marine Platforms: Extensive flat areas created by wave erosion, now visible inland.

Coastlines of Submergence (The sea rises relative to the land):

  • Rias: Submerged river valleys (estuaries). The lower course of the river valley is flooded by the sea. They have winding shorelines and are widest at the mouth. Example: Cork Harbour, Ireland.
  • Fjords: Submerged glacial valleys. They are deep, steep-sided, and U-shaped, often having a shallow entrance known as a threshold. Example: Western Norway.
  • Dalmatian Coasts: Formed when river valleys parallel to the coast are submerged. Only the tops of the former hills remain above the water as a chain of islands parallel to the coast. Example: The Dalmatian Coast, Croatia.

Key Takeaway: Eustatic change is global (think bathtub filling up), while Isostatic change is local (think person standing up in the bathtub).

8. Coastal Management (3.1.3.4)

Human activities have major impacts on coastal systems (e.g., building defences, damming rivers which reduces sediment input). Management is necessary to protect homes and infrastructure from erosion and flooding.

Traditional Approaches (Hard Engineering)

These methods are visible, often expensive, and aim to stop the natural processes completely.

  • Sea Walls: Concrete barriers reflecting wave energy back out to sea. (Effective but expensive and can increase erosion elsewhere.)
  • Groynes: Timber or rock barriers built perpendicular to the shore to trap sediment moving via longshore drift. (Builds a beach for protection, but causes erosion down-drift—the 'terminal groyne syndrome'.)
  • Rock Armour (Rip-Rap): Large boulders placed at the foot of a cliff to absorb wave energy. (Effective and cheap to maintain, but visually intrusive.)
  • Gabions: Wire cages filled with rocks, often placed at the base of cliffs. (Cheaper than rock armour, but eventually rust and break down.)
Sustainable Approaches (Soft Engineering)

These methods are less intrusive, cheaper, and work with natural processes, often enhancing natural defences.

  • Beach Nourishment/Replenishment: Sand or shingle is added to an existing beach to make it wider, which absorbs wave energy. (Aesthetically pleasing, but needs constant maintenance and sediment source.)
  • Dune Stabilisation: Planting vegetation (like Marram Grass) or fencing to help repair and conserve natural sand dunes, which act as a flexible barrier.
  • Managed Retreat (Coastal Realignment): Allowing the sea to flood low-lying land in selected areas. This creates new inter-tidal habitats (like saltmarshes) which then act as natural flood buffers for the land further inland.
Shoreline Management and ICZM

Modern management requires an approach that considers the entire system (the sediment cell) rather than just a single point.

  • Shoreline Management Plans (SMPs): Detailed documents specific to sediment cells. They usually adopt one of four policies:
    1. Hold the Line: Maintain existing defence structures.
    2. Advance the Line: Build new defences seawards.
    3. Do Nothing: Allow nature to take its course (often used in remote areas).
    4. Managed Realignment: Allow the coast to retreat naturally, but in a controlled manner.
  • Integrated Coastal Zone Management (ICZM): This is the most comprehensive approach. It considers not just physical processes but also the human activities (economic, social, political) that affect the coastal zone. It aims to achieve sustainability across the entire coastal region, involving all stakeholders.

Key Takeaway: Hard engineering provides immediate protection but often has negative impacts elsewhere. Soft engineering and ICZM focus on long-term, sustainable solutions based on the systems approach.

Case Study Reminder (3.1.3.6)

Remember, you must be able to illustrate and analyse these concepts using Case Studies. Ensure you have detailed knowledge of:

  • A local coastal environment to illustrate processes and outcomes.
  • A contrasting coastal landscape (e.g., comparing a high-energy erosional coast like Dorset, UK, with a low-energy depositional coast or an ICZM project like Vietnam's Mangrove Protection) to evaluate risks, opportunities, and human responses.