Coastal Processes & Landforms Ms Carr 5 th year Geography.

Coastal Processes & Landforms

Ms Carr5th year Geography

Learning Intention

• Understand how coastal processes transform the landscape• Examine the landforms created by these coastal processes• FEEDs for these landforms• Feature• Explanation• Example• Diagram

• Identify coastal landforms on OS Maps and in Photographs

Today we will......

• Recall what we already know about coastal processes.

• Examine what influences coastal erosion.• Discuss two types of waves.• Recap on processes of coastal erosion.

• Textbook pages 122-124.

Mind Map..What I already know..

Chapter 12: Coastal Processes, Patterns & Associated Landforms, & 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- Highest energy at moment of collapse- If it hits a cliff before or after it breaks it won’t

erode as much

- Steepness of the wave- Formed nearer coast, steeper & stronger

- Rock resistance


Types of Waves1. Constructive waves

Deposit more than they erodeCarries material in Swash up the shoreMost common in summer

2. Destructive wavesErode more than they depositSteep wavesStrong BackwashMost common in winter


Wave Refraction Waves slow down as water

becomes shallow. This change in speed causes

the wave to bend and change their direction as they approach the shore, this is called Wave Refraction.

This causes waves to move towards the headland where their erosive force is released.

Erosion is stronger on the headland and deposition occurs in the bay.

Change of wave direction

Debris

Processes•Erosion•Transportation•Deposition


Processes of coastal erosion Hydraulic Action Compression Abrasion/Corrasion Attrition Solution/Corrosion

Erosion

• Hydraulic Action; direct force of the waves on the coast.• Abrasion; rock debris is hurled by the waves against the

coastline.• Attrition; fragments of stone are rounded and eroded by

hitting off each other.• Solution; minerals in certain rocks are dissolved by water.• Air Compression; breaking of rock as a result of being trapped

by waves in rocks.• Wave Refraction; bending of waves concentrates erosion at

headlands, this then leads to the formation of cliffs, caves, arches and stacks.


Longshore drift – a process of coastal transportation

The sea transports its load of sand and shingle in two main ways:

1. Up the shore in swash 2. Back down the shore in backwash

Transportation

• Longshore Drift–Movement of material along the coast–Zig zag path–Swash and Backwash

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Deposition occurs because the swash is more powerful than the backwash.

Erosion occurs because the backwash is more powerful than the swash

The movement of material along the coastline in a zig zag manner due to the angle of the approaching waves and the slope of the coastline.

The bending of waves due to a headland causing the waves to lose energy and deposition to occur.

Learning Intention

• Recap on coastal processes.• Examine landforms of coastal erosion.• Answer a FEED style question on one

landform.

Recap

• The return movement of water downshore is called _____________.

• ____________________ deposit more than they erode and are most common in summer.

• When a wave slows down, bends and changes direction it is called _________________.

• __________________ is the zig-zag movement of material along the coast.

• _____________ happens when fragments of rock are rounded and eroded by hitting off each other.

• When rock breaks as a result of being trapped by waves in rocks, it is called ____________________.

Landforms of Marine Erosion

• Cliffs• Wave-cut

Platform• Bay• Headland

• Cave• Blowholes• Sea Arches• Sea Stacks


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


Notch gets bigger, eventually the rocks above the notch (overhang) 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 rock

that are deposited below low-tide level

Cliffs

• Example; – Cliffs of Moher, Co Clare– Hook Head, Co Wexford

OS Map- Textbook page 125


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

Bays and Headlands

Bays and Headlands

Bays and Headlands

Malin Head, Donegal

Bays & Headlands

• Example;– Dublin Bay– Wicklow Head

• OS Map; Textbook page 126


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

Cave, arch, stack, stump

Cave, arch, stack, stump


A sea stack is a rock which is standing out in isolation in the sea away from the coastline

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

Cave, Arch, Stack, Stump

• Examples;– Hook Head, Co Wexford

– Caves; Ballybunion, Co Kerry– Arch; The Bridges of Ross, Co Clare– Sea Stack; Dun Briste, Co Mayo


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’. During stormy weather, sea spray blasts out through the

blowhole. Example; Hook Head, Co Wexford. Geo: a long narrow inlet that forms when the roof of a

cave, that was once connected to a blowhole collapses.

Landforms of Coastal Erosion on OS Maps

• Textbook- page 128.

Pairwork Quick Questions

• List 5 processes of coastal erosion.• List the 3 main landforms of coastal erosion.• Name an Irish example of each of the above

landforms.• What does a sea stack look like on an OS map?• Explain the term ‘differential erosion’.• What is a ‘geo’?

Caves, arches, stacks, stumps and blowholes are features of coastal erosion.

Caves: what are they? Type of rock they are formed in Why hard rock? Hydraulic Action (P) Compressed Air (P) Weakness in the roof of the cave Formation of a blowhole Continued erosion on roof and back wall Formation of an arch Weathering and erosion of the roof of arch Creation of a stack Erosion of stack Abrasion (P) of stack – why Creation of a stump

Exam Question; FEED

Caves are open hollows usually found near the base of a headland on the cliff face. They tend to form in areas of hard rock along the coastline. Soft rock erodes too quickly for a cave to maintain its shape therefore they tend to form slowly in hard rock and can be deep and large. Caves occur due to the main marine processes of erosion such as hydraulic action (the power and the force of the seas waves pounding the coastline) and Compressed air (where air is trapped between the cliff face and the wave and causes the air to expand. This in turn causes the cracks to enlarge and the coastline to erode). Over time the sea will continue to erode the back wall of the cave and in stormy times cracks in the roof of the cave will be further eroded by solution and compressed air. This creates an area of weakness such as a tunnel or vent in the roof all the way to the surface of the headland. If a vent opens from the roof of the cave to the top of a headland a blowhole is now formed. During times of high tide or storms water will force its way up the vent and spray out on the surface. As this feature is formed the cave continues to erode backwards through the headland. Sometimes one cave will erode the whole way through or sometimes two caves will meet from either side of the headland. As this happens an arch is formed. However, the roof of the arch (with the blowhole) is weakened and continuous erosion will cause the roof to collapse. Once an arch collapse the headland appears smaller and the remaining outer wall is called a stack. However there is an increase of broken rocks and debris in the area and the processes of abrasion (the scraping of the seas load against the coastline) will continue to erode the stack. Over time it is eroded down to a stump. This is an area of rock barely visible over the waves and dangerous for incoming boats.The creation of these features are responsible for the coastline appearing to ‘retreat’ and appear smaller on maps/photographs.E: Examples x 3D: Diagram (frame, title, details, colour, labels)

DEPOSITIONCoastal Landforms

Learning Intention

• Examine landforms of coastal deposition.• Review a sample answer on one landform.• Answer a FEED style question on another

landform.


• Textbook page 129-132

Deposition

Coastal deposition occurs when waves lose energy and therefore their ability to carry material

Sea deposits its load on the coastal area Constructive waves have an ability to move the

load inland Wave refraction in bays result in wave energy

decreasing and this results in deposition occurring Deposited material may include shingle, sand and

sediment

Landforms of Marine Deposition

• Beach• Storm Beach• Sand Spit

• Sand Bar• Lagoon• Tombolo


Beach A beach is an area of sand, shingle or gravel Beaches are created by the processes of longshore

drift, constructive waves and wave refraction, Located in an area between low tide mark and

where the highest storm waves can reach Constructive waves swash is powerful Waves move up the sea shore, slow down and their

load of sand and rocks is deposited Heavier load of rock and shingle is deposited on the

backshore Finer, lighter material such as sand is deposited on

the foreshore Over time a beach is formed

A storm beach is made of pebbles and stones It forms when waves are strong enough to push large

rocks and boulders above the high tide mark A storm beach is usually steeper than a regular beach.

Sand Dunes

– Hills of sand– Sand is dried and blown inland– Vegetation can trap the sand– Marram grass is sometimes planted to prevent it

blowing further inland– Eg; Curracloe, Co Wexford

• Berms– Ridges, like steps or terraces– Gentle constructive waves push sediment into long low

ridges– Mark the junction between foreshore and backshore

Runnels & RidgesRunnels-depressions on the sand on the foreshoreRidges-the gentle rises between the runnelsFormed by the action of constructive waves

CuspsCresent shaped hollows where shingle changes to sandResult of complex wave actions on pebble beaches

Beach

•Feature•Explain •Examples•Diagram


Sand Spit A sand spit is a long narrow ridge of deposited sand and

shingle It is connected to the coast at one end Sand spits develop due to longshore drift and deposition Sand spits form where the process of longshore drift is

interrupted Waves lose energy and slow down Location of estuary or change in wind direction Sediment is deposited in sheltered and shallow water Over time this sediment builds up and becomes visible

above the level of the sea


On the seaward side of the sand spit constructive waves deposit fine sediment such as sand and form a beach

Over time the sand spit gets wider As sand spits grow the area of water behind it is

often then sheltered by waves and wind This often leads to the formation of a salt marsh Wave refraction may occur at the end of a sand spit

which results in the sediment being carried around the end of the sand spit to form a recurved spit, this looks like a hook.

Spit

• Example; Inch Strand, Dingle, Co Kerry

Pairwork Recap

• Beaches are created by the processes of;1.2.3.

• Three beach features are;1.2.3.

• A sand spit is a _______, _________ ____________of deposited _________ and ___________.

• Sand spits develop due to _______________________and __________________.


Sand Bar & Lagoon A sand bar forms when a sand spit extends across a

bay Sand bars will eventually seal off an area of coastline The water directly behind the sand bar will then be

called a lagoon

Two Types of Sand Bar

Offshore Bar Located away from the

coastline Parallel to the coastline Generally only exposed at

times of low tide Breaking waves deposit sand

on the offshore bar Size of the offshore bar

increases over time May eventually block or close

off the bay creating a lagoon

Baymouth bar Sand spit extends from one

side of a landmass across a bay and reaches the other landmass

Blocks/closes off the bay

Example Our Lady’s Island, Co.

Wexford.

Baymouth Bar

Classwork

• Quick Questions–Page 132

Tombolo

Tombolos are formed due to wave refraction and longshore drift

Result from a sand spit extending out to an island and connecting the island to the mainland

Waves approach the island, wave refraction occurs Sediment is deposited Results in the spit connecting the island to the

mainland and – a tombolo is formed

Tombolo

Tombolo

• Example;– Howth, Co Dublin- Sutton is built on the tombolo.

Coastal Landforms on OS Maps

• Textbook page 133

Exam Questions

Coastal Processes, Patterns & Landforms

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Coastal Processes & Landforms Ms Carr 5 th year Geography.

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