COASTAL

FEATURE PROCESS EXAMPLESBays and Headlands Erosion- hydraulic action,

abrasion, attrition & compressed air

Howth Head

Cliff Erosion Cliffs of Moher, Co. ClareCave Erosion Bruce’s Cave, Rathlin

IslandArch Erosion Old Head of KinsaleStack Erosion Cliffs of Moher, Co. ClareBlowhole Erosion Inishbofin, Co. MayoBeach Longshore drift and

depositionThe Warren

Sand spit Longshore drift and deposition

Rosses Point, Co.Sligo

Baymouth bar Longshore drift and deposition

Lady’s Island Lake, Co.Wexford

Tombolo Longshore drift and deposition

Sutton , Co. Dublin

Lagoon Longshore drift and deposition

Lady’s Island Lake, Co.Wexford

Sand dune Longshore drift and deposition

Brittas Bay, Co.Wicklow

Coastal Landforms

Landforms that develop along a coastline are shaped by the surface (exogenic) processes of erosion, transport and deposition.

Coastal Erosion The processes of erosion are very active along coastlines that have large,

destructive waves. The bigger the wave, the more energy it has to erode. The size of a wave is determined by the strength of the wind and the size of the area over which it blows (fetch). Waves erode coastlines using a number of methods or processes:

Hydraulic Action- Rocks along the coastline are worn down by the force of the water itself.

Compression- This is effective when water, hurled against the coastline, causes air in the cracks and pores to be compressed. When the wave retreats, the air expands. This constant compression and expansion of air causes the rocks to shatter.

Solution- When the minerals in some rocks mix with water, they dissolve and in time cause the rock to break up.

Abrasion- When boulders, pebbles and sand are thrown up against the base of the coastline, rocks of the coastline are worn down.

Coastal Erosion Landform – Cliff Cliffs are landforms of coastal erosion and provide

evidence that the coast is retreating. They are most common on high-energy coastlines

where destructive waves dominate. Cliffs can be classified as active or inactive. Active cliffs are free from vegetation and are vertical

or nearly vertical, they are usually found in areas where rocks have equal resistance and horizontal strata.

Inactive cliffs are vegetated and stable. The sea floor has a gentle gradient, which reduces wave action.

Cliffs are shaped by the processes of hydraulic action, abrasion and compressed air.

When destructive waves pound against the coastline, they widen weak points such as joints and bedding planes.

A notch then appears at the base of the coastline. Waves continue to widen this notch using small rocks and pebbles that

they carry. This is called abrasion. Air that is trapped in the pores of the coastline is compressed by the

incoming waves, only to expand as the waves retreat. This constant expansion and contraction causes the rock to shatter and break.

In time the cliff retreats, a wave-cut platform appears. This is a level stretch of rock often exposed at low tide. It can protect the

coastline, as it weakens wave power. Later, the waves drag some of the loose and abraded material further out

to sea to build an underwater ridge called a wave-built terrace. The Cliffs of Moher, Co. Clare, are a well-known example.

Coastal Deposition- Beach A beach is an area of sand and shingle found between the high and

low mark level of coastlines.

It is a landform of deposition and provides evidence that the coastline is advancing.

Beaches commonly form on low-energy coastlines that are sheltered, shallow or gently sloping.

In sheltered areas like bays, wave energy will be lower as it is concentrated at headlands in a process known as wave refraction. In shallow water, the waves lose energy by friction with sea bed and a low slope will allow material to build up.

Beaches are shaped by the swash and backwash motion of longshore drift and by constructive waves (waves that break at less than eight per minute).

Each wave approaches the beach area in the same direction as the prevailing wind. The incoming wave, the swash, will carry the wave load in the same direction as the wave movement. The backwash will flow back down at right angles to the coastline. If the swash is greater than the backwash, a beach will form.

Beaches are usually divided into 3 zones: a backshore, a mid-shore and a foreshore.

A standard beach will have a concave profile. Beach materials are the products of weathering and erosion carried

by wind and waves. Huge boulders can be worn down to tiny grains of sand by the processes of hydraulic action, abrasion and attrition.

The material is deposited by the waves only when certain conditions are met: a sheltered area to trap material, longshore drift and constructive waves.

Tides and ocean currents also play a role in their formation. They can carry sediments a few meters or hundreds of kilometers away, changing beaches every day by bringing in new materials and taking away others.

Beaches also change seasonally. During the winter, storm winds toss sand into the air. This can sometimes erode beaches and create sandbars. During the summer, waves retrieve sand from sandbars and build the beach back up again. These seasonal changes cause beaches to be wider and have a gentle slope in the summer, and be narrower and steeper in the winter.

Once formed, a beach may develop smaller landforms: berms, cusps, ridges and runnels.

The area above the water, including the intertidal zone, is known as the beach berm. Beach berm can include vegetation, such as trees, shrubs and grasses. The most familiar characteristics of a beach berm is its type of sand or rock.

Beaches serve a useful purpose in the struggle against coastal erosion by reducing the impact of waves on the coastline.

Beaches may be sandy, e.g. Lahinch, Co. Clare.

Sample Answer- Cliffs and Wave-cut Platforms (Erosion)Cliffs of Moher, Co. Clare & Downpatrick Head, Co. Mayo

Exposesd land along the coast becomes eroded at high tide level by destructive wave action. As the water lashes the coastline (hydraulic action), breaking waves compress air in the cracks and crevices in the rock (compression).

As the waves retreat, this air expands explosively and shatters the rock. As the cracks and lines develop even more, a notch is formed. Abrasion now increases in importance as the sea’s land increases in amount and sand, pebbles and boulders crash against the coastline. Dependant on the resistance of the rock (differential erosion), the notch becomes eroded even more and more and eventually the notch increases in height, width and depth. Over time, the unsupported rock material above it gives way and collapses to form a cliff.

The continuous formation of notches and under-cutting leads to a retreat of the cliff and the formation of a wave-cut platform at its base. The type of cliff slope largely relates to the rock type and how it is laid down. If the

strata are vertical or horizontal, steep cliffs will develop, while if the strata dip landward or seaward, gently sloping cliffs will develop. C

liff formation is also influenced by non-marine factors, for example surface run-off, wind and frost. Soil creep or landslides can occur if there is a very steep slope.

Sample Answer- Sand Bar & Sand Spit (Deposition) A sand bar is a sand spit that has extended out across a bay. It is formed

by the processes of deposition, long shore drift, constructive waves and wave refraction. A sand spit develops where a coastline changes suddenly and the long-shore drift cannot keep moving in a zigzag movement of sediment along the sea shore.

Sand, shingle, gravel and stones are deposited in the slow water in the changing coastline by the process of deposition. Over time it builds up until it reaches the sea surface and becomes a base for the finer material to be deposited on top by the process of longshore drift in the bay mouth.

As the spit continues to grow, the constructive waves deposit their load as they pass over the deposits. Fine sand is added to the spit by the large powerful winds that blow in from the beaches. This creates sand dunes on the land side of the spit. Marram grass begins to grow to keep the sand dunes stable with their deep, deep roots.

The spit develops a curved end at the end. This is due to the process of wave refraction where the strong waves bend around the edge of the spit, creating a curved shape.

Over time, the spit extends to the whole length of the mouth of the bay. There must be no river estuary or rivers flowing into the bay as they wash away all the deposits, preventing spit bars

As the sand bar has blocked the mouth of a bay, the trapped sea water becomes a lagoon of seawater. During storms huge waves may wash over the sandbar, throwing deposits into the lagoon with them.

The lagoon eventually becomes a salty marsh as the water evaporates. Vegetation such as reeds, bulrushes and coarse vegetation may grow in the sediment.

The two types of sand bars are known as Baymouth sand bars and Offshore sand bars. Baymouth sand bars form across bays whereas an offshore sand bar forms out at sea. These sand bars may be pushed by the waves to the mouth of a bar to form a Baymouth sand bar.

In conclusion, this is the formation of a sand bar. A sand spit forms due to the processes of deposition, constructive waves, wave refraction and long-shore driftShort Questions:

Beach nourishment is the supply of sand to the shore to increase the recreational value and/or to secure the beach against shore erosion by

feeding sand on the beach. It is an example of a soft structure in coastal defence. It is rare due to its expensive nature.

A: Rock FallB: JointC: Wave-cut PlatformD: Bedding planesE: HeadlandF: Sea Cave

Rock structures such as joints and bedding planes are most associated with sedimentary rock.

A: Offshore bar (natural)B: Groyne (human)C: Cliff (natural)D: Rock armour (human)

Groynes are placed at 90’ degrees to the shoreline in order to effectively combat longshore drift.( The groynes then interrupt the process of deposition leading to a build-up of sediments in one area on a beach, but consequently can starve another area.)

A: Sea stumpB: C: Sea archD:

A: TomboloB: Sand spitC: Lagoon

A: BlowholeB: Sea ArchC: Sea stackD: Bay

Long Questions 2019 2.C – The impact of human

activity on coastal processes.

2017 1.C – The impact of coastal defence measures on coastal processes. 2017 3.B- Examine the impact of processes of erosion on the formation of

one coastal landform. 2016 2.B- Examine the role of the processes of deposition on the

formation of any one landform. 2015 1.B- Examine the impact of the processes of erosion on the

formation of one coastal landform. 2014 1.C- The impact of coastal defence work on coastal processes. 2014 2.B- The formation of one landform of erosion or deposition. 2013 2.A- Explain with diagram formation of one landform of erosion.