Coastal Landscapes

What does the power of waves depend on

- Wind Speed

- Fetch

Fetch

The distance over which the wind blows

Swash

Water that moves up the shore

Backwash

Water that moves back down the shore, carries sediment back down the shore

Constructive Waves

- Strong Swash, weaker backwash

- Deposit sediment on the shore

When do constructive waves occur?

Calm weather and during summer months, when waves have less energy

Destructive waves

- Weak swash, stronger backwash

- Erode sediment from the shore

When do destructive waves occur?

Poor weather and during winter months, when waves have more energy

Erosion Processes

- Hydraulic Action

- Compressed Air

- Abrasion

- Attrition

- Solution

Hydraulic Action

The sheer force of waves pounding on the coast

Compressed air

- Air becomes trapped in cracks in the rock

- Incoming waves compress the air in the joints

- When the wave retreats, air expands

- Over time, this pressure breaks the rock

Abrasion

Pebbles, stones and rocks are dashed against the coast by waves

Attrition

Pebbles and stones that are carried by the sea rub against each other and become more rounded and worn down then eventually turn into sand

Solution

Salt in seawater gradually dissolves rock on the coastline

Longshore Drift

- Waves approach the shore at an angle then break

- Swash carries material at an angle

- Backwash carries some material at a right angle

- This zigzag movement causes sand and shingle to move along the length of the shore

What makes waves slow down and lose energy?

- Entering shallow water

- Entering a bay

- Crossing a wide beach

- Entering a shallow beach (one with an angle >9º)

Landforms of Coastal Erosion

- Cliffs and Wave-cut platforms

- Bays and headlands

- Sea caves, arches, stacks and stumps

Cliff

A vertical slope on the coast that can be composed of rock and/or soil.

Which waves form cliffs?

Destructive waves.

How is a wave-cut notch formed?

At high tide, Hydraulic Action, Compressed Air and Abrasion erode a wave-cut notch.

Where does a wave-cut platform form?

At the base of the cliff.

How is a wave-built terrace formed?

Sediment from the notch is transported and deposited below low tide

What happens to a wave-cut notch over time?

Erosion causes the notch to enlarge and the rocks above are undermined, collapse, and form a cliff

Cliff examples

- The Cliffs of Moher, Co. Clare

- Slieve League, Co. Donegal

Headland (Peninsula)

Area of hard rock that juts out into the sea

Bays

An inlet eroded between two headlands

Bay and Headland formation

Soft rock facing the sea gets eroded quickly by hydraulic action and abrasion leaving an ident (bay ) and hard rock jutting out into the sea (headland)

Bay and Headland examples

- Tralee Bay, Co. Kerryo

- Dingle Peninsula, Kerry Head

Sea caves, arches, stacks and stumps

Found on rocky coastlines where headlands have been eroded over a long period of time

Sea Cave

Compressed air, hydraulic action and abrasion wear away soft rock of a wave-cut notch at high tide

Sea Arch

Further erosion of a sea cave cuts through to the other side of a headland

Sea Stack

When the roof of a sea arch collapses

Sea stump

Eroded sea stack

Sea arch and stack example

- Great Pollet sea arch, Co. Donegal

- Dún Briste sea stack, Downpatrick Head, Co. Mayo

Blowhole

A shaft that goes through the roof of a sea cave to the land surface above, found on rocky coastlines

Blowhole formation

- Waves force air into the back of the cave

- The process of compressed air causes the rock to shatter

- Over time, a hole forms in the roof of the cave

When does seawater spray out of a blowhole?

During stormy weather

Blowhole examples

- McSwyne's Gun, Co. Donegal

- Downpatrick Head, north Co. Mayo

Landforms of Coastal Deposition

- Beaches

- Sand Dunes

-Sand Spits

- Tombolos

Beach

Gently sloping area of loose sand and shingle

What is the role of swash in the formation of beaches?

Carries sand and shingle up the shore and deposits the load as water soaks away

What is the role of backwash in the formation of beaches?

Weak, can only move finer material down the shore

What does this deposition do over time?

A beach forms

What material can be found at each shore sides

Coarse material found at the backshore, fine material at the foreshore

Storm Beach

Powerful waves throw boulders above the high tide mark

The backwash isn't strong enough to remove them.

Beach examples

- Sand beach, Co. Kerry

- Shingle beach, Shanganagh, Shankill, Co. Dublin

Sand Dunes

Large mounds of sand deposited at the back of a beach, beyond the high tide mark.

How could sand on a beach be dried?

Onshore winds.

What sand blows inland?

Dry sand is lighter than wet sand and blows inland

Marram Grass

Thick, coarse grass that has deep roots and can tolerate the salty environment?

How does Marram Grass help Sand Dunes?

The roots help bind the grains of sand together and prevent them blowing further inland.

Sand Dunes examples

- Rosslare, Co. Wexford

- Tramore, Co. Waterford

Tombolos

A narrow ridge of sand or shingle that joins an island to the mainland.

How do tombolos form?

Waves approach an island from different directions.

What happens when these waves meet?

They cancel each other out and lose energy.

What does this loss of energy cause?

Deposition between the mainland and the island

What happens with further deposition over time?

A long, narrow sand bar builds up, connecting the island to the mainland

Tombolo examples

- Howth Head in Co. Dublin was once an island but is now connected by Sutton

Sand Spit

Long, narrow beach of sand/shingle, connected to the mainland at one end and extends across a bay at the other end.

How is a sand spit formed?

When longshore drift reaches a change in the direction of the coastline, e.g. a bay.

What does this change in coastline do?

Waves lose energy and deposit sediment on the seabed

What happens over time to the deposited material?

This material builds up and rises above sea level to form a sand spit.

What's the role of wind and wave action for a sand spit?

Causes the sand spit to lengthen and curve inwards

What will happen to the sand spit over time?

Longshore drift will continue to move sediment along the coast.

What will the spit eventually develop into?

A sand bar, seperating the bay from the sea

What is the salt lake left called?

A lagoon.

Groynes

Human-made concrete or wooden walls built at right angles to the sea

What are groynes used for?

Reduce the impact of longshore drift.

How do groynes work?

They trap sediment to help build up the beach on a coast

Groynes disadvantages

Areas further along the coast receive little or no sand from longshore drift -> coastal erosion

Groynes example

Rosslare, Co. Wexford

Rock armour / Boulders

Large boulders placed at the base of cliffs or sand dunes

How does rock armour work?

Reducing the erosive power of waves by absorbing it to protect coastlines made of sand and clay.

Sea walls

Built at the back of beaches to protect coastal towns that can be curved to turn the wave back on itself.

Gabions

Wired cages containing stones that absorb energy from incoming waves, placed in front of sand dunes or at the back of a beach

Rosslare Strand, south east of Co. Wexford

- Sunniest location in Ireland

- Location of the Rosslare ferry terminal that provides Roll-On-Roll-Off truck and car ferry services to Britain and Europe

Rosslare Pier / Sea Wall

- In 1867 a pier for ships was built at Rosslare Harbour

- The port became busier, and the pier was replaced with an impermeable sea wall

What impact did the sea wall have on the port of Rosslare?

It allowed the port of Rosslare to become busier over time.

How did road and rail connections affect the port of Rosslare?

They allowed the port to grow as a result of trade with Britain.

What effect did Brexit have on trade through Rosslare?

Brexit increased the amount of trade and transport through Rosslare from Europe.

What improvements are being made to transport links in the south-east and Dublin?

Motorway and rail links connecting through the south-east and Dublin are being modernised.

Social Impact of the Sea Wall

Tourism and the development of the port have attracted people to live and work in Rosslare.

How did the construction of the sea wall affect the sustainability of Rosslare Strand?

It negatively affected the sustainability of the beach along Rosslare Strand and sand spit.

What new geographical feature formed near the harbour after the sea wall construction?

A new beach formed near the harbour.

What was the impact of the new beach on sand transport along Rosslare Strand?

It decreased the transport of sand along Rosslare Strand.

What was the result of decreased sand transport on Rosslare sand spit?

It resulted in erosion of Rosslare sand spit.

What area experienced flooding due to the environmental impact of the sea wall?

A nearby golf course experienced flooding.

Coastal Defences at Rosslare

- Beginning 1974, gabions, rock armour and groynes

- Beach nourishment