Welcome to Coastal Landscapes and Change!
Hello! Ready to explore the dynamic world of coasts? In this chapter, we are looking at the "meeting point" between the land and the sea. You’ll learn why some beaches are sandy while others are rocky, how the sea "eats" the land, and how humans try to stop it. Don't worry if this seems like a lot of information at first—we're going to break it down into bite-sized pieces that make sense!
1. The Littoral Zone and Coastal Classification
The littoral zone is just a fancy name for the wider coastal area. It is a zone of dynamic equilibrium, meaning it is constantly changing due to the battle between the land and the sea.
Breaking down the Littoral Zone
Think of the littoral zone as a series of steps moving from the land into the deep water:
1. Backshore: Usually dry; only affected by big storms.
2. Foreshore: This is where you walk at low tide; it's the area between the high and low tide marks.
3. Nearshore: Where waves start to break.
4. Offshore: Deep water where waves don't touch the seabed.
How do we classify coasts?
We can group coasts in different ways:
- By Geology: Rocky coasts (hard rock, high cliffs) vs. Coastal Plains (soft sediment, low-lying land).
- By Sea Level: Emergent (land is rising out of the sea) vs. Submergent (land is sinking or sea is rising).
- By Energy: High-energy (big waves, lots of erosion, e.g., Atlantic coast of Scotland) vs. Low-energy (calm waves, lots of deposition, e.g., Mediterranean).
Quick Review Box:
- Rocky coasts = High relief, resistant rock (like granite), high energy.
- Coastal plains = Low relief, weak "crumbs" of sediment, low energy.
Key Takeaway: The coast isn't just a line; it’s a wide zone that is always changing depending on the rocks, the waves, and the sea level.
2. Geological Structure and Rock Types
Why does the coastline wiggle? It usually comes down to geological structure (the way the rocks are arranged).
Concordant vs. Discordant Coasts
Imagine a sandwich.
- A Discordant Coast is like looking at the side of the sandwich where you see the bread, ham, and cheese all at once. The layers of rock run at right angles to the sea. This creates headlands (hard rock sticks out) and bays (soft rock is eaten away).
- A Concordant Coast is like looking at just the crust. The layers of rock run parallel to the sea.
Example: Dalmatian coasts (in Croatia) have long, narrow islands parallel to the shore. Haff coasts have long spits and lagoons.
Lithology: The "Ingredients" of the Coast
Lithology is just the type of rock.
- Igneous: Super tough rocks like Granite. They erode very slowly (less than 0.1cm a year!).
- Metamorphic: Also very tough, like Slate.
- Sedimentary: Often weaker, like Limestone or Sandstone.
- Unconsolidated: This isn't even "rock" yet! It’s just piles of clay or sand (like Boulder Clay). This can erode by meters every year!
Did you know? The cliffs at Happisburgh in Norfolk are made of unconsolidated sediment. They are disappearing so fast that people have lost their homes to the sea in just a few years!
Key Takeaway: Hard rock = slow erosion and steep cliffs. Soft "rock" = fast erosion and slumped, messy-looking cliffs.
3. Marine Processes: Waves and Erosion
Waves are the "engine" of the coast. They get their energy from the fetch (how far the wind has blown over the water).
Constructive vs. Destructive Waves
- Constructive Waves: They are "helpful." They are low, flat, and have a strong swash (water moving up the beach) that pushes sand up, building the beach.
- Destructive Waves: They are "mean." They are tall, steep, and have a strong backwash (water pulling back) that steals sand from the beach.
The 4 Types of Marine Erosion
Use the mnemonic H.A.C.A. to remember these:
1. Hydraulic Action: Air is trapped in cracks by a wave, then "explodes" out when the wave retreats, shattering the rock.
2. Abrasion: The sea throws pebbles at the cliff like sandpaper.
3. Corrosion (Solution): Weak acids in seawater dissolve certain rocks like Limestone.
4. Attrition: Pebbles in the sea crash into each other and become smaller, smoother, and rounder.
The Cave-Arch-Stack-Stump Sequence
This is a classic step-by-step process for headlands:
1. Caves: Erosion hits a fault or crack.
2. Arch: The cave erodes all the way through the headland.
3. Stack: The roof of the arch gets too heavy and collapses, leaving a pillar of rock in the sea.
4. Stump: The stack is eroded at the base until it falls over, leaving a small nub visible at low tide.
Key Takeaway: Destructive waves and the 4 types of erosion work together to turn solid headlands into tiny stumps over hundreds of years.
4. Moving and Dropping Sediment
Once the sea has eroded the rock, it has to put it somewhere!
Longshore Drift (LSD)
This is how the beach "walks" down the coast.
- Waves hit the beach at an angle (determined by the wind).
- Swash carries sand up at an angle.
- Backwash pulls it straight back down due to gravity.
- Repeat this 1,000 times, and the sand moves in a zigzag pattern along the coast.
Depositional Landforms
When the coast changes shape or the water slows down, it drops its load:
- Spits: A long "finger" of sand sticking out into the sea (e.g., Spurn Head).
- Tombolos: A spit that connects an island to the mainland (e.g., Chesil Beach).
- Bars: A spit that grows all the way across a bay, creating a lagoon behind it.
The Sediment Cell Concept
Think of a sediment cell like a bank account for sand.
- Sources (Inputs): Erosion of cliffs or sand brought in by rivers.
- Transfers: Longshore drift moving the "money" (sand) around.
- Sinks (Outputs): Where sand is deposited and stays, like in dunes or deep sea.
The system tries to stay in dynamic equilibrium (balance).
Key Takeaway: Longshore drift is a zigzag movement that builds landforms like spits and bars by moving sediment from one place to another.
5. Sea Level Change
Sea levels aren't fixed. They change over thousands of years.
Eustatic vs. Isostatic (The tricky part!)
Eustatic Change = Global. Think of the water. If the ice caps melt, the sea level rises everywhere.
Isostatic Change = Local. Think of the land. During the Ice Age, the weight of the ice pushed the land down. Now the ice is gone, the land is slowly "springing" back up (like a sponge).
Resulting Landscapes
- Emergent (Sea level fell/Land rose): You see Raised Beaches and "fossil cliffs" high above the current sea level.
- Submergent (Sea level rose/Land fell):
- Rias: Drowned river valleys (wide and shallow).
- Fjords: Drowned glacial valleys (deep, U-shaped, and very steep).
Quick Review Box:
- Eustatic = Water volume change (Global).
- Isostatic = Land height change (Local).
- Rias = V-shaped valley + Sea.
- Fjords = U-shaped valley + Sea.
Key Takeaway: Our coastlines today are heavily shaped by what happened during and after the last Ice Age.
6. Managing the Coast
As sea levels rise and erosion gets faster, we have to decide how to protect people and the economy.
Hard Engineering (Fighting Nature)
These are man-made, "solid" structures. They are expensive and often look ugly.
- Sea Walls: Concrete walls that reflect wave energy. Very expensive.
- Groynes: Timber fences built at right angles to stop Longshore Drift. They keep the beach big, but "starve" the coast further down of sand!
- Rip Rap: Big boulders that absorb wave energy.
Soft Engineering (Working with Nature)
These are cheaper and more natural-looking.
- Beach Nourishment: Pumping fresh sand onto a beach.
- Dune Stabilisation: Planting Marram Grass to stop sand dunes from blowing away.
Sustainable Management: ICZM and SMPs
We can't protect every inch of the coast—it's too expensive. We use Integrated Coastal Zone Management (ICZM) to look at the whole coast, not just one village.
Shoreline Management Plans (SMPs) have 4 choices for any area:
1. Hold the Line: Keep the coast exactly where it is using defenses.
2. Advance the Line: Build new land out into the sea (very rare).
3. Managed Realignment (Retreat): Let the sea flood certain areas to create new salt marshes.
4. No Active Intervention: Do nothing and let nature take its course.
Common Mistake to Avoid: Don't assume "Do Nothing" is just being lazy! Sometimes it's the most sustainable choice because the cost of building a sea wall is much higher than the value of the empty fields it would protect.
Key Takeaway: Coastal management is a balancing act between money, people's homes, and the environment. There are always "winners" and "losers."
Final Encouragement
You've made it through the core of Coastal Landscapes! Remember: geography is all about connections. The type of rock determines the erosion, which determines the sediment, which determines the management. Keep looking for those links, and you'll do great!