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Coastal processes, patterns and associated landforms

Coastal processes and the impact of recreational pressures,

coastal defence work, conservation and management measures

Coastal Processes, Patterns and

Associated Landforms, and

Human Interaction

• Waves

Responsible for erosion, transportation and deposition of material

along coastlines

Generated by wind passing over the surface of the sea

Fetch is the open area of the sea that a wave travels over

The longer the fetch, the stronger the wind speed, the stronger and

greater the waves generated

• Factors affecting the rate of coastal erosion

Where the breaking of a wave occurs

1. Steepness of the wave – greater erosion

2. Rock resistance – soft rock = greater erosion –

chalk - limestone

3. hard rock = less erosion - granite

• Types of waves

1. Constructive waves

2. Destructive waves

Constructive Waves – gentle wave

action – deposition of material –

features formed

Destructive wave action –

strong – storm waves –

destruction of coastal areas –

erosional features formed

Constructive waves

Destructive waves

• Wave refraction

Waves slow down as water becomes shallow

Waves bend and change their direction as they approach the shore

Causes waves to move towards the headland where their erosive force

is released

Coastal Erosion

• Processes of coastal erosion

Hydraulic action – force of the water

Air Compression – air in waves

Abrasion/corrosion – pebbles in waves act like

sandpaper

Attrition – pebbles hit off each other and

become rounded

Solution/corrosion- salt/ minerals in sea water

dissolve soft rock

DIAGRAM OF CLIFF FORMATION

The feature of

coastal erosion I

have studied is a

wave built terrace

– wave cut

platform

An example of this is found at

the Cliffs of Moher, Co. Clare

• Landforms of coastal erosion

1. Cliffs

Cliffs are vertical slopes on a coastline

Form as a result of a combination of coastal processes of

erosion, such as hydraulic action, compression, abrasion,

solution and attrition

Destructive waves attack an area of weakness in rocks

Crack/joint forms

Crack/joints are attacked by hydraulic force of the water and by

compression

Notch forms

• Landforms of coastal erosion

1. Cliffs (continued)

Notch gets bigger, eventually the rocks above the notch are unsupported and collapse to form a cliff

Shattered rock falls into the sea

Sea uses this shattered rock to further erode the cliff through abrasion

Solution also erodes the cliff face

These events continue over time and the cliff face retreats

Wave-cut platforms – surface of rock that remains in front of the retreating cliff

Wave-built terraces – deposited pieces of rockthat are deposited below low-tide level

• Landforms of coastal erosion

2. Bays and headlands

Differential erosion – rocks along coastlines

are eroded at differing rates depending on

whether they are soft or hard

Sections of coastline that are composed of

soft rock will erode faster than areas

composed of hard, more resistant rock

Stretches that are composed of soft rock will

form bays

Harder more resistant rock will take longer to

erode and will remain jutting out into the sea

as headlands

• Landforms of coastal erosion

3. Sea caves, sea arches, sea stacks and sea stumps

Caves form in an area of weakness on a cliff face or

headland

Processes of coastal erosion act on this area of

weakness and enlarge it to form caves

Caves are further eroded by abrasion, resulting in

them becoming larger

Sea arches form when continued erosion occurs in a

sea cave causing it to extend right through the

headland

A sea arch may also form when two sea caves form

back to back on the opposite sides of a headland

A sea stack is a rock which is standing out in

isolation in the sea away from the coastline

DIAGRAM OF CAVE, ARCH AND STACK FORMATION

Doolin, Co. Clare

Causeway coast,

Antrim

Sea Arches

3. Sea caves, sea arches, sea stacks and sea stumps

Sea stacks form when erosion continues on a sea

arch, widening the sea arch and causing the roof

of the sea arch to eventually collapse

When the roof of the sea arch collapses, it leaves

the former section of headland isolated or cut

away from the main headland/coast. What

remains standing out in the sea in isolation is called

a sea stack

A sea stump is the eroded remains of a sea stack

Landforms of coastal erosion

Coast of Victoria,

Australia

American

coast

Old Man of Hoy,

Orkney Islands

Downpatrick Head

Co. Mayo

• Landforms of coastal erosion

4. Blowholes

Blowholes form at areas of weakness, for example, where a hole

forms on the surface of a cliff top joins with a roof of a sea cave.

They are formed as a result of compression

Air may become trapped in a sea cave by waves

Results in a build up of pressure which leads to rock shattering the

rocks of the cave roof

Rock eventually collapses

creating a ‘blowhole’