Coastal Weathering and Erosion

Glossary:

acidic: of a pH level below 7, which can accelerate weathering processes when combined with rainwater.

beach: a landform along the shoreline of an ocean, sea, lake, or river, typically consisting of loose particles such as sand, gravel, or cobble.

carbon dioxide: A gas released during the process of respiration or burning of organic matter and absorbed by plants.

characteristic: a quality or trait or a unique feature.

Chemical weathering: The breakdown of rocks caused by a chemical change within the rock.

clay: A soft , sticky fine grained sedimentary rock.

cliff: A large rock face which raises, often vertically, along the coastlines, often formed by erosion.

coastal processes: actions that shape shorelines and coastal landforms. the process include erosion, sediment transport, and deposition.

Compression: the action of pressing or increasing the density of a matter within a space.

contract: the action of a material decreasing in size.

deposition: when a material is transported and dropped by an energy.

dissolve: when solid becomes liquid and becomes a solution.

erosion: the wearing away by the movement of natural forces.

expand: the action to make a material larger.

granite: hard light coloured ingenous rock.

lime stone: rocks formed due to volcanic or tectonic process.

mechanical weathering: the breakdown of rocks due to physical conditions.

metamorphic rock: when the rock’s structure is changed due to heat or pressure.

sedimentary rock: rocks formed by sediments and compression overtime due to pressure.

transportation: the movement of eroded materail.

Fetch

Fetch = the distance the wind blows over open water.

The longer the fetch:

The bigger the waves
The more powerful the erosion

Short fetch → small waves
Long fetch → strong destructive waves

1. Weathering (Breaking Rock Down)

Weathering happens in place. The rock stays where it is, but it gets broken into smaller pieces.

There are 3 main types:

A) Physical Weathering (Mechanical Weathering)

This breaks rock without changing what it’s made of.

1. Freeze–Thaw

Water goes into cracks in rocks.
It freezes.
When water freezes, it expands.
The expansion makes the crack bigger.
This repeats again and again until the rock breaks.

Think of it like water acting as a tiny wedge.

2. Wetting and Drying

Some rocks (like clay) absorb water.
When wet → they swell.
When dry → they shrink.
This constant swelling and shrinking makes the rock crack and crumble.

Common on cliffs with clay.

B) Chemical Weathering

This changes the chemistry of the rock.

Acidic (Carbonation)

Rainwater is slightly acidic because it mixes with carbon dioxide in the air.
This weak acid reacts with rocks like limestone.
The rock slowly dissolves.

So:

Physical weathering = breaks rock
Chemical weathering = dissolves or changes rock

🌊 2. Erosion (Moving Rock Away)

Erosion is when the sea removes and carries away rock.

There are 4 main types in coastal erosion:

1. Hydraulic Action

Waves crash against cliffs.
Air gets trapped in cracks.
The pressure of water + air weakens the rock.
Eventually pieces break off.

No rocks needed — just the force of water.

2. Abrasion (Corrasion)

These mean the same thing.

Waves throw sand, pebbles, and rocks against the cliff.
It’s like sandpaper scraping the rock.
The cliff gets worn away.

So:
Hydraulic action = force of water
Abrasion = rocks scraping the cliff

3. Attrition

This is different.

Rocks carried by waves hit each other.
They break into smaller pieces.
They become smoother and rounder.

That’s why beach pebbles are smooth.

Important:
Attrition = rocks hitting rocks
Abrasion = rocks hitting cliff

Quick Summary Table

Weathering = breaking rock
Erosion = moving rock

Physical weathering:

Freeze–thaw
Wetting and drying

Chemical weathering:

Acidic rain dissolving rock

Erosion:

Hydraulic action (water force)
Abrasion / Corrasion (rocks scrape cliff)
Attrition (rocks hit each other)
Solution (rock dissolves)

Destructive Waves = Beach Destroyers

Think: Strong, aggressive, storm waves

They:

Are tall and powerful
Have a strong backwash
Remove material from the beach

What’s Backwash?

After a wave crashes, water flows back down the beach.
That water flowing back = backwash.

In destructive waves:

Backwash is STRONGER than swash.
It drags sand and pebbles back into the sea.
The beach gets smaller.

👉 They cause erosion.

🌊 Constructive Waves = Beach Builders

Think: Gentle, calm waves

They:

Are lower and less powerful
Have a strong swash
Have weak backwash

What’s Swash?

Water moving UP the beach after a wave breaks.

In constructive waves:

Swash is stronger than backwash.
They bring sand onto the beach.
The beach gets bigger.

👉 They cause deposition (building up).

Remember fetch?

Long fetch → bigger waves → more destructive
Short fetch → smaller waves → more constructive

What is Longshore Drift?

Longshore drift is how sand and pebbles move along the coast.

Not into the sea.
Not up the beach.
But sideways along the shoreline.

Why does it happen?

Because waves don’t always hit the beach straight on.

They usually come in at an angle (because of the wind direction).

Step-by-Step Visual

Picture this clearly:

A wave comes in at an angle.
The swash carries sand up the beach at that angle.
Gravity pulls the water straight back down (backwash goes straight down).
Next wave comes at an angle again.
Sand slowly zig-zags down the beach.

Over time, sand moves sideways.

That zig-zag movement = longshore drift.

1. What would happen if sea level rises by 2 meters?

A 2-meter rise is huge.

Here’s what would happen:

Low-lying coastal areas would flood.
Beaches would shrink or disappear.
Cliffs would erode faster.
Storm surges would travel further inland.
Wetlands and habitats could be destroyed.

Basically: more flooding + more erosion.

Even small sea level rises increase wave attack on cliffs because water reaches higher up.

🏠 2. What would people living near the coast do?

People would have a few choices:

1⃣ Protect (Defend the coast)

Build sea walls
Use groynes
Add rock armour
Beach nourishment (adding sand)

This is expensive.

2⃣ Adapt

Raise houses on stilts
Improve drainage systems
Build flood barriers

3⃣ Retreat (Move Away)

Some areas may be too expensive to protect.
People might have to relocate inland.

Governments sometimes use “managed retreat.”

⚠ 3. Problems Created by Rising Sea Levels

Think in 3 categories: Environmental, Economic, Social.

🌍 Environmental

Loss of habitats (wetlands, mangroves)
Increased coastal erosion
Saltwater entering freshwater supplies

💰 Economic

Damage to homes and buildings
Loss of tourism
Expensive coastal defenses
Damage to ports and businesses

👥 Social

People losing homes
Communities forced to move
Increased risk to lives during storms