Welcome to Coastal Systems!

In this chapter, we are going to look at the coast in a whole new way. Instead of just thinking about a day at the beach, we are going to look at the coastline as a system. Think of it like a giant machine where energy (from the wind and waves) and material (like sand and pebbles) work together to create the amazing landscapes we see.

Don't worry if some of the terms sound a bit "sciencey" at first. We’ll break everything down into bite-sized pieces with plenty of everyday examples to help you along!

1. Coasts as Natural Systems

In Geography, a system is simply a set of objects that are linked together. Imagine a busy professional kitchen: ingredients come in (inputs), chefs cook them (processes), food is kept in the fridge (stores), and meals go out to customers (outputs). The coast works exactly like that!

The Ingredients of a Coastal System

  • Inputs: These are things that enter the system. The main inputs are energy (from waves, wind, tides, and currents) and matter (sediment like sand, silt, and shingle).
  • Outputs: These are things that leave the system, such as sediment being washed out to the deep ocean or energy being dissipated (lost) as heat or sound when a wave crashes.
  • Stores/Components: These are parts of the system where matter or energy stays for a while. A beach or a sand dune is a store of sediment.
  • Flows/Transfers: These are the "moving parts." For example, Longshore Drift is a flow that moves sand from one part of the coast to another.

Balance and Feedback

Nature usually tries to stay in a state of Dynamic Equilibrium. This is a fancy way of saying "a perfect balance." If something changes (like a massive storm), the system tries to correct itself to get back to that balance.

How does it correct itself? Through Feedback Loops:

  • Positive Feedback: This makes a change bigger. It’s like a snowball rolling down a hill. Example: If a beach starts to erode, it might allow bigger waves to hit the cliff, causing even more erosion.
  • Negative Feedback: This cancels out a change and brings things back to normal. It’s like a thermostat in your house. Example: A big storm erodes a beach and moves the sand into an offshore bar. This bar then forces waves to break further out at sea, protecting the beach from more erosion.

Quick Review:
System: A group of linked parts.
Input: Energy/Sediment coming in.
Output: Energy/Sediment leaving.
Dynamic Equilibrium: A state of balance.

Did you know? A landform is an individual feature (like a single cliff or a cave), while a landscape is the "big picture" made up of many landforms joined together!

Key Takeaway: The coast is a constantly changing "machine" that uses energy to move sediment around, always trying to find a perfect balance.

2. Sources of Energy

To move rocks and build beaches, the coast needs power. There are four main "batteries" that power the coast:

1. Wind

Wind is the primary source of energy. It creates waves through friction on the water's surface. The strength of the wave depends on the Fetch—this is the distance the wind has blown over the open water without being interrupted. The longer the fetch, the bigger the wave!

2. Waves

Waves are the "workers" of the coast. There are two main types you need to know:

  • Constructive Waves: These are "builders." They are low, infrequent, and have a strong swash (water moving up the beach) but a weak backwash (water moving back down). They deposit sediment and build up the beach.
  • Destructive Waves: These are "destroyers." They are high, frequent, and have a weak swash but a very strong backwash. They rip sediment away from the beach.

Memory Aid:
Constructive = Creates beach (Strong Swash).
Destructive = Destroys beach (Strong Backwash).

3. Tides and Currents

Tides are the periodic rise and fall of the sea level caused by the moon's gravity. They determine where the waves "work" on the cliff. Currents are the permanent or seasonal movement of water, like the Longshore Current, which helps transport sand along the coast.

High vs. Low Energy Coasts

  • High Energy Coasts: Think of stormy, rocky places like Cornwall or Western Scotland. Here, the waves are powerful, and erosion is faster than deposition. You'll see cliffs and sea stacks.
  • Low Energy Coasts: Think of calm, sheltered bays or estuaries. Here, the waves are gentle, and deposition is faster than erosion. You'll see big beaches and salt marshes.

Key Takeaway: Wind creates waves. Constructive waves build beaches; destructive waves take them away. High energy equals erosion; low energy equals deposition.

3. Sediment: Cells and Budgets

Sediment is the "currency" of the coast. It includes everything from tiny mud particles to giant boulders.

Where does the sediment come from? (Sources)

  1. Rivers: Most coastal sediment actually comes from rivers carrying it down from the land.
  2. Cliff Erosion: Rocks falling into the sea.
  3. Offshore: Sand pushed up from the sea floor by waves.

Sediment Cells

The UK coastline is divided into 11 Sediment Cells. These are basically "closed loops" where the sediment stays within that specific area. It’s like a self-contained ecosystem. If you take sand out of one end of a cell, it will eventually affect the other end, but it won't affect a different cell 200 miles away.

The Sediment Budget

This is like a bank account for sand. We use a simple formula to see if a beach is growing or shrinking:
\( \Delta S = I - O \)
(Change in Storage = Inputs minus Outputs)

  • If Inputs are higher than Outputs, you have a positive budget (the beach grows).
  • If Outputs are higher than Inputs, you have a negative budget (the beach shrinks/erodes).

Key Takeaway: Sediment moves within "cells." A positive sediment budget means the beach is getting bigger; a negative budget means it's disappearing.

4. Geomorphological Processes

This is just a fancy term for "how the land is shaped." These processes happen in two main areas: on the land (sub-aerial) and in the sea (marine).

Sub-Aerial Processes (Happening from the "Air")

These processes happen to the cliff face above the water line.

  • Weathering: Breaking rocks down where they sit. This can be Chemical (acid rain), Biological (tree roots), or Mechanical (like freeze-thaw where water freezes in cracks and splits the rock).
  • Mass Movement: When gravity pulls rocks or mud down the cliff. This includes Landslides, Rockfalls, and Slumping (common on clay cliffs).

Marine Erosion (The Power of the Sea)

This is how the sea attacks the land. Don't worry, these are easy to remember if you think of them as "actions":

  • Hydraulic Action: The sheer force of the water. Air gets trapped in cliff cracks, and the pressure causes the rock to explode outward.
  • Abrasion (or Corrasion): The "sandpaper" effect. The sea picks up rocks and flings them against the cliff.
  • Attrition: The "bumper cars" effect. Rocks in the sea hit each other and become smaller, smoother, and rounder.
  • Solution (or Corrosion): Seawater dissolves certain types of rock, like limestone.

Transportation and Deposition

Once the sea has eroded the rock, it has to move it (Transportation) and eventually drop it (Deposition).

  • Longshore Drift: This is the most important transportation process! Waves hit the beach at an angle (swash), but the water pulls back straight down (backwash). This moves sand in a "zigzag" pattern along the coast.
  • Traction: Large boulders rolling along the seabed.
  • Suspension: Tiny particles floating in the water.

Common Mistake to Avoid:
Students often confuse Abrasion (sea vs. cliff) with Attrition (rock vs. rock). Just remember: Attrition makes the rocks smaller; Abrasion makes the cliff smaller.

Key Takeaway: The coast is shaped by weathering from above and erosion from the waves. Longshore drift is the main way the sea "cleans up" and moves that material elsewhere.

Final Quick Summary

You've made it! Here is the "Golden Thread" of this chapter:

  1. The coast is a System of inputs, stores, and outputs.
  2. Wind and Waves provide the energy to make the system work.
  3. Sediment moves within Cells and its balance is called a Budget.
  4. Erosion and Weathering break land down, while Transportation and Deposition move and rebuild it.