1.1.4 Factors affecting coastal processes and landforms

What is meant by structure in coastal geology?

The way rocks are arranged or disposed geologically

What is meant by lithology?

The physical and chemical make-up of a rock

How do structure and lithology influence coasts?

They control erosion rates, landform development, and coastline shape

What aspects of the coast do structure and lithology affect?

Plan view, profile (cliffs), and micro-features like caves and stacks

Why are igneous and metamorphic rocks more resistant?

They are harder due to heat and compression during formation

Why are southern and eastern UK coasts more erodible?

They are made of soft rocks like clay, sand, and glacial till

How does permeability influence erosion?

Permeable rocks allow water infiltration, sometimes increasing stability but also enabling mass movement

Why does chalk form steep cliffs?

It is permeable and relatively strong, resisting erosion

What happens when permeable rock overlies impermeable rock?

A lubrication layer forms, increasing risk of slumping

How do joints and bedding planes affect erosion?

They weaken rock and provide lines of weakness for weathering and erosion

How do faults influence coastal landforms?

They create weak zones that can be exploited to form bays, caves, and inlets

Why are silica-rich rocks resistant?

They are chemically inert and resist weathering

How does limestone weather chemically?

Through carbonation, especially rapidly in saltwater

What is differential erosion?

The process where rocks of different resistance erode at different rates

What is a concordant coastline?

Rock layers run parallel to the coastline

What landform can form on concordant coasts?

Coves (e.g. Lulworth Cove)

What is a discordant coastline?

Rock layers run perpendicular to the coastline

What landforms form on discordant coasts?

Headlands and bays

How does Durdle Door form?

Marine erosion exploits weaknesses in limestone to form an arch

What processes form Durdle Door?

Hydraulic action, abrasion, carbonation, and weathering

What is Selwicks Bay an example of?

A bay formed by structural weakness in resistant chalk

Why did Selwicks Bay form?

Faulting, jointing, and weaker chalk increased erosion

Why is Holderness rapidly eroding?

It is made of weak, unconsolidated boulder clay

What is boulder clay?

An unsorted mix of clay, sand, gravel, and boulders from glaciation

Why is boulder clay unstable?

It becomes weak when saturated and prone to slumping

What is rotational slumping?

Mass movement along curved slip planes in saturated material

How does marine erosion increase instability?

It undercuts the base of cliffs, removing support

What controls cliff profiles?

Rock type, wave energy, structure, and subaerial processes

What is toe armour?

Debris at the base of cliffs that temporarily protects against erosion

What is the clapotis effect?

Wave reflection from steep cliffs reducing direct erosion

What conditions are needed for micro-features?

Thick, resistant rock with joints and weaknesses

What is a blowhole?

A vertical shaft formed when waves force air and water upward through a cave

What is a geo?

A steep-sided inlet formed by erosion along a weakness

How does an arch form?

When two caves erode through a headland and meet

What happens when an arch collapses?

It forms a stack

What happens to stacks over time?

They erode into stumps

What is fetch?

The distance wind blows over water

How does fetch affect waves?

Longer fetch produces larger, more powerful waves

What is wave refraction?

Waves bending in shallow water, focusing energy on headlands

What is wave reflection?

Waves bouncing off cliffs, reducing erosion but creating turbulence

What is longshore drift?

Sediment transport along the coast due to angled wave approach

How do waves affect erosion patterns?

Angle, type, and energy determine erosion and deposition

What is the wave climate at Holderness?

Moderate-high energy with frequent storms

What is the wave climate at Portland Bill?

High energy with larger waves and strong tidal currents

Why does Holderness erode faster than Portland Bill?

It has weaker rock despite slightly lower wave energy

Key principle about erosion rates?

Rock type is as important as wave energy