Lithosphere - coasts

Coasts

These are areas where the sea meets the land

What are the two types of coastlines?

Coastlines of deposition and coastlines of erosion

How are coastlines shaped?

Waves are the main power force that changes coastlines

Formation of a wave

When wind blows across the surface of the water

What are the three things that influence the power and size of a wave?

• Distance travelled by the wave

• Duration of the wind

• Strength of the wind

Fetch

The distance travelled by a wave

Long fetch

Waves that travel a long distance produce powerful waves

Short fetch

Waves that travel a short distance produce smaller waves

How do waves shape a coastline?

When waves hit the coastline, they move water and material onto the coast, and also drag it backwards towards the sea

Swash

Movement of waves up the beach

Backwash

Movement of waves back down the beach

Wavelength

The distance between the crests (tops) of the waves

What are the two types of waves?

Constructive waves and destructive waves

What two things determine the type of wave?

The energy of the swash and backwash

Destructive waves

Powerful waves that are high in energy, often crashing down onto the beach and coastline that removes materials

Constructive waves

Gentle waves that are low in energy, often rolling up onto the beach and coastline that adds materials

Characteristics of destructive waves

• Strong backwash

• Tall waves, which break downwards with force

• Waves are steep and close together

• Weak swash

Characteristics of constructive waves

• Gentle waves roll onto the beach

• Strong swash

• Waves are low and far apart

• Weak backwash

Swash and backwash of destructive waves

The backwash is stronger than the swash

Swash and backwash of constructive waves

The swash is stronger than the backwash

Destructive waves

Constructive waves

What are the four processes of coastal erosion?

• Abrasion

• Attrition

• Hydraulic action

• Solution

Abrasion

Waves repeatedly throw loose rocks against the base of the cliff, causing more fragments to break off

Attrition

Loose rocks carried by the waves crash into each other, making them smaller and rounder

Hydraulic action

Waves crash against cliffs, forcing air and water into cracks, which creates pressure in the cracks causing them to explode open

Solution

Salts and acids in the seawater dissolve minerals in the rocks, leaving small hollows in the rocks

Processes of coastal erosion

Concordant coastline

Discordant coastline

What are the two factors that affect erosion?

Geology and wave fetch

Geology

Hard igneous and metamorphic rock is more difficult to erode than soft sedimentary rock

Wave fetch

The greater the fetch of a wave, the more power it has to erode

What are the two types of geology structures that affect the way a coastline erodes?

Concordant coastlines and discordant coastlines

Concordant coastlines

These occur when the geology of an area runs parallel to the coastline, only one type of rock is exposed to the processes of coastal erosion, which will erode at the same rate

Discordant coastlines

These occur when the geology of an area runs perpendicular to the coastline, multiple types of different rocks are exposed to the processes of coastal erosion, which will erode at different rates

Differential erosion

When some rocks erode more easily than others the rate of erosion will differ depending on the geology of the area

How are headlands and bays formed?

Differential erosion

Headland

An area of hard (resistant) rock that extends out into the sea

Bay

An inlet of the sea, surrounded by land

Formation of a headland and bay

• Bands of soft rock are weaker, therefore they erode more quickly, which forms bays

• Bands of hard rock are more resistant to erosion as they are stronger, which forms headlands

• Headlands protect the bays from destructive waves

• Beaches start to form in bays as waves deposit sediment

What geological structure is required for headlands and bays to form?

Discordant coastlines

Named example: headland and bay

Durdle Door, Dorset

Wave-cut platform

These are flat areas of rock which form at the base of a cliff

Formation of a wave-cut platform

• Overtime cliffs retreat backwards due to wave erosion

• Waves attack the base of the cliff, becoming unsupported

• The cliff will eventually collapse into the sea

Lines of weakness, blowhole, sea cave, arch, stack, and a stump

Erosion of headlands

Erosion of headlands

As headlands and bays form, headlands become more and more exposed to destructive waves, making them vulnerable to erosion

Named example: sea cave, arch, stack, and stump

Old Harry and his Wife

What are the five stages of coastal erosion (explain the stages in order)

• Lines of weakness

• Sea cave

• Arch

• Stack

• Stump

Stage one of coastal erosion: lines of weakness

Waves attack weaknesses in the headland through the processes of abrasion and hydraulic action, forming cracks in the base

Stage two of coastal erosion: formation of a sea cave

Cracks are eroded further through abrasion and hydraulic action, forming a sea cave

Stage three of coastal erosion: formation of an arch

The waves erode the sides and back of the sea cave until they break through to the other side of the headland, forming an arch

Stage four of coastal erosion: formation of a stack

Waves continue to erode the arch, widening it and weakening the top, the roof then becomes unsupported and collapses, leaving a free-standing piece of rock called a stack

Stage five of coastal erosion: formation of a stump

The stack is continually eroded at the base, becoming weaker until it eventually collapses and leaves a stump

Blowhole

This may form if the erosion at the back of a sea cave breaks through the top of the cliff as compressed air is pushed upwards by the power of the waves

Bay, cliff, and headland

Named example: wave-cut platform

Durlston cliffs

What are the three stages of coastal deposition (explain the stages in order)

• Sand spit

• Sand bar

• Tombolo

Named example: sand spit

Spurn Head, Yorkshire

Named example: sand bar

Chesil beach, Dorset

Named example: tombolo

St Ninian’s isle, Shetland

Sand spit, sand bar, and tombolo

Stage one of coastal deposition: formation of a sand spit

• Longshore drift moves the materials along the beach sideways

• Waves lose energy and start to deposit materials in calm and sheltered water, overtime the deposited material will begin to build up until it is above the sea level

• Deposition continues to occur until the beach extends into the sea, forming a spit

• Sand spits can develop a hooked or curved end, caused by a change in wind and wave direction

• Mud flats or salt marshes can develop in areas of calm water behind a spit

Stage two of coastal deposition: formation of a sand bar

• If a spit continues to grow out until it joins with the opposite side of a bay, a sand bar is formed

• This happens when there is no strong flow of water from a river into the sea, enclosing a sheltered lagoon behind it

Stage three of coastal deposition: formation of a tombolo

• When longshore drift deposits sediment and extends a spit out from the headland, connecting to an island

• This leaves a long, thin strip of beach

Wave-cut platform

Coastal deposition

This is when waves lose energy and deposit materials

Erosion

The wearing away and removal of materials such as rocks and soils

What are the four formations created through coastal erosion?

• Sea cave

• Arch

• Stack

• Stump

What three processes are waves capable of doing?

• Deposition

• Erosion

• Transportation

Coastal transportation

This is when waves transport materials

Longshore drift

This is a process where pebbles and other materials are moved sideways along a beach by the waves that are driven from the prevailing wind

What is the dominant processes of coastal transportation?

Longshore drift

Longshore drift

Process of longshore drift

• Waves approach the coast at an angle, due to the prevailing wind, carrying material with them

• When waves break, the swash carries water and material up the beach at the same angle

• Waves drag materials back out to sea in the backwash, the backwash travels at right angles to the beach due to gravity

• This results in the zig-zag movement of material along the coast

Prevailing wind

Winds that blow from a single directio nover an area of the Earth’s atmosphere

Sand spit

A long, narrow ridge of sand that extends out into the sea from one end of the mainland, caused by waves depositing materials

What two things are required for a sand spit to form?

The coastline must change direction and the water must be shallow and gentle

Sand bar

Stretches of sand formed across a bay through longshore drift

Tombolo

Stretches of deposited material that reaches out from the coastline to a small island

What are the three processes involved in the formation of a wave-cut platform?

• Abrasion

• Attrition

• Hydraulic action

What are the three processes involved in the formation of a headland and bay?

• Abrasion

• Attrition

• Hydraulic action

What are the three processes involved in the formation of a cave, arch, stack, and a stump?

• Abrasion

• Attrition

• Hydraulic action