© Boardworks Ltd 2009 1 of 35 Coastal Processes and Features Coasts

© Boardworks Ltd 20091 of 35

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Contents

Physical processes

Erosional landforms

Depositional landforms

Eustatic and isostatic change

Teacher’s notes included in the Notes Page

Flash activity (these activities are not editable) Web addresses Printable activity

Extension activity

Icons:


Key questions: Physical

processesPhysical processes

How do the processes of weathering and mass movement operate at the coast?

What are the main types of coastal erosion?

What is wave action and refraction?

How does longshore drift transport materials?

By the end of this chapter you should have considered these key themes and questions:


Processes of weathering

Weathering is the in situ breakdown of rocks. It occurs in place, without needing a transport medium.

Subaerial processes

Do you know what different processes of weathering operate at the coast?

Weathering is a subaerial process. This means it is land-based; it operates on the cliff face or land adjacent to the sea.


Chemical and biological weathering


Mechanical weathering


Mass movement

Mass movement describes the down-slope movement of weathered material under the influence of gravity

What factors aid mass movement?

sparse vegetation

undermining by wave action

heavy rain.

There are several different types of mass movement, including:

rotational slump

rock falls

How does each type occur?

mud slides.


Types of mass movement


Processes of erosion


The rate of erosion


Waves

When waves approach the shore, frictional resistance with the sea bed slows them down at their base. They get taller and their wavelength decreases. The top of the wave overtakes the bottom as the water gets shallower and they break.

The energy of waves determines whether they build up or degrade a beach. The former are called constructive waves and the latter destructive waves.

Height Wavelength Swash/backwash.

What determines whether waves are constructive or destructive?

Frequency


Wave refraction

Refraction is the ‘bending’ of wave fronts. When waves approach an irregular coastline, they refract and their energy is concentrated on the headland, increasing erosion here.

High energy waves – more

erosion

Low energy waves – less erosion and

more deposition

Low energy waves – less erosion and

more deposition


Transportation


Deposition

Sediment is deposited where waves and currents slow down or the supply of sediment exceeds the rate of removal.

Smaller particles, like sand, are only deposited when wave energy is low.

Pebbles are deposited when wave energy is high. Stormy seas are able to carry them and often throw them far up a beach.


Key questions: Erosional landforms

Erosional landforms

What erosional landforms are created by the operation of physical processes?

How are caves, arches, stacks and stumps formed?

What are concordant and discordant coasts and how do they vary?



Cliffs

Steep cliffs are often found at the coast in areas where the rocks are more resistant. Erosional processes, such as abrasion and quarrying, attack the base of the cliff.

Wave-cut notches and blow-holes are both temporary features of erosion caused by the sea eroding natural weaknesses in the rock structure – joints, bedding planes and cracks.

What temporary features are formed by erosion?


Wave-cut platforms

Erosion at the base of the cliff creates a wave-cut notch.

The cliff material above the notch is undermined.

The material becomes unstable and eventually collapses.

This repeats and the cliff retreats, leaving a rock platform.

What are the stages involved in their

formation?

Wave-cut platforms are flat areas found at the base of cliffs.


Do you know what landforms the pictures show?

Caves, arches, stacks and stumps

The most common types of landforms created in this way are caves, arches, stacks and stumps.

Some erosional landforms are created where wave action attacks weak points, such as joints in rocks and bedding planes between bands of rock.

Old Man of Hoy, Orkney

Durdle Door, Dorset


Creation of erosional landforms


Old Harry


Discordant coastlines


Concordant coastlines


Key questions:

Depositional Landforms

Depositional landforms

What depositional landforms are created by the operation of physical processes?

How are beaches formed and why do they vary in composition?

How are spits, bars and tombolos formed?



Beaches are composed of sediment that is small in size, like sand or shingle or a combination of the two.

Under what circumstances are beaches formed?

Beaches

Beaches are accumulations of deposited material between the reaches of low spring tides and the highest storm level.

When the rate of sediment deposition exceeds the rate of sediment removal

When rapid coastal erosion supplies abundant material

When wave energy is low.


Beach features


Shingle and sandy beaches


Spits, bars and tombolos


Formation of a spit


Key questions:



What is eustatic and isostatic change?

How do sea level changes affect the coast?

What are rias and fjords?

How are raised beaches created?





Submergent features are created as a result of rising sea levels drowning existing features. Emergent features are created by the land rising relative to the sea.

Submergent features:

What are submergent and emergent features?

Sea level change and landforms

Sea level changes can profoundly affect coastal scenery, and create both submergent and emergent features.

rias

fjords.

Emergent features:

raised beaches.


Rias and fjords

Rias are drowned river valleys. They occur at the sea end of steep sided valleys, which are flooded due to sea levels rise.

Fjords are drowned glacial troughs found where glaciated uplands of mid and high latitudes reached the sea. Many are found in Norway and Alaska.

What are some of the main features of fjords?

steep-sided cliffs

found in upland areas

deep water.


Raised beaches

In some places isostatic uplift has meant that the land rises relative to sea levels. This creates raised beaches, which are stranded above sea level.

On some parts of the Scottish coast, raised beaches have been identified at three levels: 8, 15 and 30m, indicating former sea levels. The former cliff lines, with notches and even caves, arches and stacks can be seen.

There are many raised beaches in the UK on west-facing Atlantic coasts in Cornwall, Wales and western Scotland.


Summary quiz


Glossary

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© Boardworks Ltd 2009 1 of 35 Coastal Processes and Features Coasts