Welcome to Coastal Systems and Processes!
Welcome to one of the most exciting parts of your AQA A Level Geography course. Have you ever stood on a beach and wondered why the sand is there, or why some cliffs look like they are crumbling? In this chapter, we are going to look at the coast not just as a pretty view, but as a dynamic system—a busy "machine" where energy and matter are constantly moving and changing. Don't worry if some of the terms seem technical at first; by the end of these notes, you’ll be seeing the coastline in a whole new way!
1. Coasts as Natural Systems
To understand the coast, geographers use a systems approach. Think of a coastal system like a bank account. You have money coming in (inputs), money sitting in the account (stores), and money being spent (outputs).
Key Components of the System
• Inputs: These are things that "enter" the system. The main inputs are energy (from waves, wind, tides, and currents) and sediment (from eroding cliffs or rivers).
• Outputs: These are things that "leave" the system. This could be sediment moving out to the deep ocean or energy dissipating (spreading out) as a wave breaks.
• Stores/Components: These are the physical features where sediment is kept for a while, like beaches, sand dunes, or spits.
• Flows/Transfers: These are the processes that move sediment from one store to another. A great example is Longshore Drift.
Balance and Feedback
Coastal systems like to be in dynamic equilibrium. This is a fancy way of saying the system is balanced, even though things are constantly moving. If something changes (like a huge storm), the system reacts to find a new balance.
• Negative Feedback: This is "good" for stability. It’s when the system acts to undo a change. Example: A storm erodes a beach, but the eroded sand forms an offshore bar. This bar then makes waves break further out, protecting the beach from more erosion. The system "fixed" itself!
• Positive Feedback: This is a "snowball effect" where a change leads to even more change. Example: If a small part of a sand dune is damaged by people walking on it, the wind can blow away the exposed sand, making a bigger hole (a blowout), which leads to even more erosion.
Quick Review: Landforms vs. Landscapes
A landform is an individual feature (like a single cliff or a beach). A landscape is the "big picture"—the whole area made up of many different landforms working together.
Key Takeaway: The coast is an "open system" where energy and matter flow in and out to create a balanced environment.
2. Sources of Energy
Every system needs "fuel" to work. On the coast, that fuel is energy.
Winds and Waves
The wind is the primary source of energy for the coast. Wind blowing over the ocean creates waves through friction. The amount of energy a wave has depends on the fetch (how far the wind has travelled over open water), wind strength, and how long the wind has been blowing.
There are two types of waves you must know:
1. Constructive Waves: These are "beach builders." They are low, flat, and have a strong swash (water moving up the beach) and a weak backwash (water moving back down). They deposit sediment.
2. Destructive Waves: These are "beach destroyers." They are high, steep, and have a weak swash but a very strong backwash. They scour the beach and carry sediment away.
Tides and Currents
• Tides: These are the daily rise and fall of the sea level caused by the moon’s gravity. They determine where the waves can "attack" the land.
• Currents: These are permanent or seasonal flows of water, like the Longshore Current, which helps move sediment along the coastline.
Did you know? High energy coasts (like the Atlantic coast of Scotland) have powerful waves and lots of erosion, while low energy coasts (like the Mediterranean) have gentle waves and more deposition.
3. Sediment Sources, Cells, and Budgets
Where does all the sand and shingle come from? It's not just there by magic!
Sediment Sources
Most coastal sediment comes from terrestrial sources (rivers and eroding cliffs). Some also comes from offshore (waves pushing sand from the seabed onto the land) or even human activity (beach nourishment, where humans pump sand onto a beach).
Sediment Cells
A sediment cell is a distinct area of the coastline that acts as a "closed system." This means sediment is recycled within the cell and very little leaves it. In England and Wales, there are 11 major sediment cells, usually separated by big headlands or estuaries.
The Sediment Budget
The sediment budget is the balance between the sediment entering and leaving a cell.
\( \text{Sediment Budget} = \text{Inputs} - \text{Outputs} \)
• If inputs are greater than outputs, the beach grows (a surplus).
• If outputs are greater than inputs, the beach shrinks (a deficit).
Key Takeaway: Managing the coast requires looking at the whole sediment cell, because stopping erosion in one place might starve a beach of sand further down the coast!
4. Geomorphological Processes
These are the processes that actually shape the land. We split them into "Marine" (sea-based) and "Sub-aerial" (land-based).
Marine Erosion (The Sea's Power)
• Hydraulic Action: The force of waves trapping air in cliff cracks. The pressure "explosively" expands, breaking the rock.
• Wave Quarrying: The weight of a massive wave hitting the cliff and simply pulling chunks of rock away.
• Corrasion/Abrasion: Waves hurl sand and pebbles against the cliff, acting like sandpaper.
• Cavitation: Air bubbles in the water implode under high pressure, sending tiny shockwaves into the rock.
• Solution (Corrosion): Saltwater dissolves certain types of rock, like limestone.
• Attrition: Not erosion of the cliff, but of the sediment itself! Pebbles hit each other in the waves, becoming smaller and rounder.
Transportation (Moving Material)
Material is moved in four main ways: Traction (rolling big rocks), Saltation (bouncing smaller stones), Suspension (carrying fine sand in the water), and Solution (dissolved minerals).
Longshore Drift (LSD): This is the most important movement. Waves approach the beach at an angle (driven by the wind). The swash carries sediment up at an angle, but the backwash pulls it straight back down. This creates a zig-zag movement along the shore.
Sub-aerial Processes (The Land's Role)
The sea isn't the only thing changing the coast!
• Weathering: Rocks breaking down in place due to rain, temperature changes, or plants.
• Mass Movement: When gravity pulls material down a cliff (like a landslide or mudflow), often after heavy rain has made the ground heavy and slippery.
• Runoff: Rainwater flowing over the surface and washing sediment into the sea.
Common Mistake to Avoid: Don't confuse weathering with erosion. Weathering happens to rock while it's sitting still. Erosion involves the rock being moved and broken by an external force like a wave.
Key Takeaway: Coastal landscapes are the result of a constant "war" between marine processes attacking from the sea and sub-aerial processes weakening the land from above.