The SeaThe Sea

Creator and DestroyerCreator and Destroyer

The action of the seaThe action of the sea

• The sea is constantly changing the shape The sea is constantly changing the shape of our coastline.of our coastline.

• This is happening because waves, like This is happening because waves, like rivers, erode, transport, and deposit rivers, erode, transport, and deposit material.material.

• Waves move material along our Waves move material along our coastline.coastline.

Why do waves break on the Why do waves break on the Shoreline?Shoreline?

WavesWaves

• Waves are made because of friction Waves are made because of friction between the wind and the surface of the between the wind and the surface of the sea.sea.

• The size of the wave depends on 2 things.The size of the wave depends on 2 things.

1. The strength of the wind.1. The strength of the wind.2. The length of the sea (fetch).2. The length of the sea (fetch).

Waves – Swash & BackwashWaves – Swash & Backwash

• SwashSwash – As the wave reaches the – As the wave reaches the shore it breaks. The white foamy shore it breaks. The white foamy water that flows up the beach is water that flows up the beach is called the Swash.called the Swash.

• BackwashBackwash – When the water runs out – When the water runs out of speed it stops and it flows back of speed it stops and it flows back down the beach into the sea. This is down the beach into the sea. This is called the backwash.called the backwash.

Constructive wavesConstructive waves

• They have a strong Swash which transports They have a strong Swash which transports and deposits material on the beach. and deposits material on the beach.

• They have a weak Backwash which does not They have a weak Backwash which does not carry much material back to the sea.carry much material back to the sea.

• As a result they construct/add material to As a result they construct/add material to the beach. the beach.

Constructive WavesConstructive Waves

Destructive wavesDestructive waves

• They have a weak Swash.They have a weak Swash.

• They have a very strong Backwash They have a very strong Backwash which wears away and carries away which wears away and carries away material form the beach.material form the beach.

• Therefore, there is a lot of erosion and Therefore, there is a lot of erosion and they destroy/destruct the coastline.they destroy/destruct the coastline.

Destructive WavesDestructive Waves

Sea ErosionSea Erosion

• Sea erosion is caused by Destructive Sea erosion is caused by Destructive waves. They erode the coast in 4 waves. They erode the coast in 4 ways.ways.

1.1. Hydraulic ActionHydraulic Action

2.2. Air CompressionAir Compression

3.3. AbrasionAbrasion

4.4. Attrition Attrition

Sea ErosionSea Erosion

1.1. Hydraulic Action – this is the power Hydraulic Action – this is the power of the water hitting the coastline.of the water hitting the coastline.

2.2. Air Compression – The waves trap Air Compression – The waves trap air in crack in the rocks. As the air in crack in the rocks. As the waves retreat the trapped air waves retreat the trapped air expand quickly and can crack the expand quickly and can crack the rock.rock.

Sea ErosionSea Erosion

3. Abrasion – this is erosion caused by 3. Abrasion – this is erosion caused by small rocks carried in the sea water small rocks carried in the sea water hitting against the coastline.hitting against the coastline.

4. Attrition – this is erosion caused by 4. Attrition – this is erosion caused by the small stones hitting each other the small stones hitting each other breaking themselves into smaller breaking themselves into smaller pieces. pieces.

Landforms of Sea ErosionLandforms of Sea Erosion

• Like rivers, the sea creates many features Like rivers, the sea creates many features or landforms as a result of erosion. These or landforms as a result of erosion. These include,include,

1.1. CliffsCliffs

2.2. Bays and HeadlandsBays and Headlands

3.3. Sea caves, sea arch, sea stack, sea stumpSea caves, sea arch, sea stack, sea stump

4.4. Blowhole Blowhole

CliffsCliffs

• As the waves break onto the coast they As the waves break onto the coast they cut a notch into the rock. When the notch cut a notch into the rock. When the notch gets deeper the overhanging rock gets deeper the overhanging rock collapses. collapses.

• This process continues and the coastline This process continues and the coastline retreats inland.retreats inland.

• The material that falls into the sea form The material that falls into the sea form the cliff is called a wave cut platform.the cliff is called a wave cut platform.

• E.g. Cliffs of Moher, Co. Clare.E.g. Cliffs of Moher, Co. Clare.

Bays and HeadlandsBays and Headlands

• A bay is wide deep opening into the coastline.A bay is wide deep opening into the coastline.• A headland is a piece of land jutting out into the A headland is a piece of land jutting out into the

sea.sea.• Bays and headlands form when there are Bays and headlands form when there are

different types of rocks occur along the different types of rocks occur along the coastline.coastline.

• The softer rocks are eroded quickly creating a The softer rocks are eroded quickly creating a bay.bay.

• The harder rocks are eroded slowly and so they The harder rocks are eroded slowly and so they stick out into the seastick out into the sea

• E.g. Dublin Bay & Howth HeadE.g. Dublin Bay & Howth Head

Bays and HeadlandsBays and Headlands

Caves, Arches, Stacks & Caves, Arches, Stacks & BlowholesBlowholes

Sea CaveSea Cave

• A sea cave is a tunnel or passage at A sea cave is a tunnel or passage at the base of a cliff.the base of a cliff.

• The waves erode a weak point (soft The waves erode a weak point (soft rock or an area with cracks/joints) in rock or an area with cracks/joints) in the cliffs. This forms a passage called the cliffs. This forms a passage called a cave.a cave.

Sea ArchSea Arch

• A sea arch is a passage that runs A sea arch is a passage that runs completely through the headland.completely through the headland.

• This can happen when a cave is This can happen when a cave is eroded deep into headland, or if two eroded deep into headland, or if two caves on either side of the headland caves on either side of the headland are eroded and join up to form a are eroded and join up to form a complete passage.complete passage.

Sea Stack and sea stumpsSea Stack and sea stumps

• A sea stack is a pillar of rock standing A sea stack is a pillar of rock standing in the water near the coast.in the water near the coast.

• When sea arches are eroded further When sea arches are eroded further they become wider.they become wider.

• Their roof collapses leaving a piece of Their roof collapses leaving a piece of land isolated from the coast.land isolated from the coast.

• This is a sea stack. It will be further This is a sea stack. It will be further eroded by the sea to form a sea eroded by the sea to form a sea stump.stump.

BlowholeBlowhole

• A blowhole is a passage from a cave up to A blowhole is a passage from a cave up to the surface of a cliff top.the surface of a cliff top.

• Compress air is trapped in the cave by Compress air is trapped in the cave by strong waves.strong waves.

• The pressure created cracks and loosens The pressure created cracks and loosens rock in the roof of the cave. This rock rock in the roof of the cave. This rock collapses over time forming a passageway collapses over time forming a passageway called a blowhole.called a blowhole.

• Sea spray spurts out of the opening during Sea spray spurts out of the opening during stormy weather.stormy weather.

• E.g. The Two Pistols, Co. Donegal. E.g. The Two Pistols, Co. Donegal.

Caves, Arches, Stacks & Caves, Arches, Stacks & BlowholesBlowholes

Transport by the SeaTransport by the Sea

• We have already learned that rivers We have already learned that rivers transport material (sand, silt, clay). transport material (sand, silt, clay). This is called the rivers load. This is called the rivers load.

• The sea also has a load which it The sea also has a load which it transports along. The load is made transports along. The load is made up of sand, pebbles, stones, and up of sand, pebbles, stones, and mud.mud.

Transport by the SeaTransport by the Sea

• Waves are responsible for transporting Waves are responsible for transporting the load. They do this in two ways.the load. They do this in two ways.

• 1. Up and down the shore by the 1. Up and down the shore by the Swash and the Backwash.Swash and the Backwash.

• 2. Along the shore by a process known 2. Along the shore by a process known as Longshore Drift. as Longshore Drift.

Swash and BackwashSwash and Backwash

• We have already looked at the We have already looked at the processes of swash and backwash.processes of swash and backwash.

• The swash will transport material up The swash will transport material up onto the beach.onto the beach.

• The backwash will transport material The backwash will transport material back down the beach towards the sea.back down the beach towards the sea.

Longshore DriftLongshore Drift

• Longshore drift moves material along the Longshore drift moves material along the beach.beach.

• This occurs when waves approach the This occurs when waves approach the beach at an angle.beach at an angle.

• The swash brings material up onto the The swash brings material up onto the beach, then the backwash brings it back beach, then the backwash brings it back down to the sea in a straight line. The down to the sea in a straight line. The swash, again moving in at an angle will swash, again moving in at an angle will move the material further across the beach. move the material further across the beach.

• This process continues and the load is This process continues and the load is moved along in a zig zag pattern.moved along in a zig zag pattern.

Deposition by the SeaDeposition by the Sea

• The sea deposits (drops off) some of The sea deposits (drops off) some of its load in sheltered places where the its load in sheltered places where the waves have less energy.waves have less energy.

• This may occur in a bay, or very This may occur in a bay, or very gently sloping shoreline.gently sloping shoreline.

• Like river deposition which we have Like river deposition which we have already studied, sea deposition also already studied, sea deposition also creates features or landforms. creates features or landforms.

Landforms of Sea Landforms of Sea DepositionDeposition• Sea deposition creates the following Sea deposition creates the following

features along our coastlines.features along our coastlines.

1.1. BeachesBeaches

2.2. Sand DunesSand Dunes

3.3. Sand spitsSand spits

4.4. TomboloTombolo

5.5. LagoonsLagoons

BeachesBeaches

BeachBeach• A beach is made of sand and shingle (small stones) A beach is made of sand and shingle (small stones)

which are deposited by the waves.which are deposited by the waves.• The swash carries material up onto the beach. The swash carries material up onto the beach.

Some of this material, especially the heavier Some of this material, especially the heavier material, stays on the beach because the weak material, stays on the beach because the weak backwash cannot carry it back to the sea. The backwash cannot carry it back to the sea. The backwash carries only lighter sand particles back backwash carries only lighter sand particles back down towards the beach.down towards the beach.

• For this reason we say that beach material is For this reason we say that beach material is sorted, with the heavier materials furthest from the sorted, with the heavier materials furthest from the water, and the lighter sand close to the water.water, and the lighter sand close to the water.

• During storms, when the swash is very powerful, it During storms, when the swash is very powerful, it can force heavy stones high up onto the beach can force heavy stones high up onto the beach where they remain to form a storm beach.where they remain to form a storm beach.

• E.g. sandy beach, Curracloe, Co. Wexford.E.g. sandy beach, Curracloe, Co. Wexford.

Sand DunesSand Dunes

• Sand dunes are hills of sand which Sand dunes are hills of sand which form above the high tide level.form above the high tide level.

• Wind dries sand on the beach making Wind dries sand on the beach making it lighter. The sand is then blown it lighter. The sand is then blown inland until it is trapped by a wall or inland until it is trapped by a wall or vegetation.vegetation.

• The sand builds up to form hills of The sand builds up to form hills of sand which are sand dunes.sand which are sand dunes.

• E.g. Portmarnock, Co. Dublin.E.g. Portmarnock, Co. Dublin.

Spits, Bars, Tombolo, Spits, Bars, Tombolo, LagoonLagoon

Sand SpitSand Spit

• A sand spit is a ridge of sand or shingle A sand spit is a ridge of sand or shingle which extends out into the sea. It is which extends out into the sea. It is connected to the land at one end.connected to the land at one end.

• Longshore drift moves material along the Longshore drift moves material along the beach. When it reaches a shallow bay the beach. When it reaches a shallow bay the waves have less energy and they deposit waves have less energy and they deposit some of the load on the sea bed.some of the load on the sea bed.

• This material builds up over time and rise This material builds up over time and rise above the sea water.above the sea water.

• E.g. Tramore, Co. Waterford. E.g. Tramore, Co. Waterford.

TomboloTombolo

• A tombolo is a ridge of sand or A tombolo is a ridge of sand or shingle which connects an island to shingle which connects an island to the coastline.the coastline.

• A tombolo is formed when a sand A tombolo is formed when a sand spit occurs linking an island to the spit occurs linking an island to the coastline rather than stretching coastline rather than stretching across a bay.across a bay.

• E.g. At Howth, Co. Dublin.E.g. At Howth, Co. Dublin.

LagoonLagoon

• A lagoon is a body of water cut off from A lagoon is a body of water cut off from the sea by a sand spit.the sea by a sand spit.

• When a sand spit is formed it stretches out When a sand spit is formed it stretches out across a bay. It may eventually reach the across a bay. It may eventually reach the other side of the bay closing off the water other side of the bay closing off the water behind it.behind it.

• This water forms a saltwater lake called a This water forms a saltwater lake called a lagoon.lagoon.

• E.g. Lough Gill, Co. Kerry. E.g. Lough Gill, Co. Kerry.

Spits, Bars, Tombolo, Spits, Bars, Tombolo, LagoonLagoon

People and CoastlinesPeople and Coastlines

• The sea plays an important part in The sea plays an important part in our lives. Many people live by the our lives. Many people live by the coast, and most of the worlds largest coast, and most of the worlds largest cities are in coastal regions.cities are in coastal regions.

• The sea provides us with energy (oil, The sea provides us with energy (oil, gas, wave power) as well as leisure gas, wave power) as well as leisure activities, transport routes, and food.activities, transport routes, and food.

People and CoastlinesPeople and Coastlines

• However, the sea can also be However, the sea can also be destructive. People have tried to destructive. People have tried to control this destructive power of the control this destructive power of the sea using,sea using,

• 1. Sea Walls1. Sea Walls

• 2. Boulders2. Boulders

• 3. Groynes3. Groynes

People and CoastlinesPeople and Coastlines• Sea WallsSea Walls – Sea walls are concrete walls with – Sea walls are concrete walls with

a curved top on them which helps to deflect a curved top on them which helps to deflect the waves back out to sea.the waves back out to sea.

• BouldersBoulders – Large rocks are placed at the – Large rocks are placed at the base of cliffs or in front of sand dunes. It base of cliffs or in front of sand dunes. It prevents erosion by reducing the power of the prevents erosion by reducing the power of the waves.waves.

• GroynesGroynes – Groynes are low walls built of – Groynes are low walls built of wood. They are built at right angles to the wood. They are built at right angles to the shore to help prevent sand being moved shore to help prevent sand being moved along the beach by Longshore Drift.along the beach by Longshore Drift.

Protecting the Coastline using Protecting the Coastline using GroynesGroynes

Protecting the Coastline using Protecting the Coastline using BouldersBoulders

Tourism and our CoastlineTourism and our Coastline