Coastal Processes

Compression : Air is trapped between the waves and a cliff. This is compressed & driven into cracks in the rocks causing great pressure. As the wave retreats it results in sudden decompression. This activity weakens the rocks.

Longshore drift: waves approach the beach at an angle, driven by the wind. Run up the beach at an angle and returns at a right angle… zig zag pattern. The swash carries sediment up the beach and the backwash carries it down the beach. This causes movement of sediment along the beach.

Abrasion: Boulders, pebbles and sand pounded against coast

Hydraulic Action: Impact of waves

Attrition: Stone rounded off by impact

Glacial Processes

Plucking: Meltwater penetrates cracks in the rock. This freezes & expands weakening and fracturing the rock. The galcier attaches itself to this rock and as it moves it pull or plucks the rock away. Assisted by freez thaw action.

Abrasion: Rocks attached to side & bed of the galcier scour, scrape & polish the surfaces they come in contact with. These cut scratches & grooves in the bedrock, called striae, which indicate the direction of movement of the galcier.

Basal slip: The sliding movement of a glacier over its rock flour. (rocks crushed by the glacier)

Freeze-thaw: Breaking of rock due to repeated freezing of water

Mass MovementMass Movement

Soil Creep:Soil Creep: Movement of soil down slope Movement of soil down slope GravityGravity Solifluction – swelling of soil, moves soil particlesSolifluction – swelling of soil, moves soil particles Frost heave – ice crystals move soilFrost heave – ice crystals move soil

Earth FlowsEarth Flows: Saturated Soil: Saturated Soil Lahars or Mud Flows:Lahars or Mud Flows: Large and Rapid, triggered by ice Large and Rapid, triggered by ice

melts by volcanic eruptionsmelts by volcanic eruptions SlumpingSlumping: Cliff edge collapses, rotational movement: Cliff edge collapses, rotational movement

Coastal ProcessesCoastal Processes

Coastline – line where sea and land meetCoastline – line where sea and land meet Shore – Area between low and high water markShore – Area between low and high water mark

Divided into foreshore and backshoreDivided into foreshore and backshore Waves – product of friction between wind and waterWaves – product of friction between wind and water Size and power of wave depends on the fetch(length of open Size and power of wave depends on the fetch(length of open

sea a wave travels over) and the power of the windsea a wave travels over) and the power of the wind Therefore waves stronger on Atlantic coast than Irish sea coastTherefore waves stronger on Atlantic coast than Irish sea coast

As waves approach shore it gets shallower so friction with the As waves approach shore it gets shallower so friction with the bottom increasesbottom increases

This slows the bottom so the top spills over breaking the waveThis slows the bottom so the top spills over breaking the wave Swash rushes up the beach away from the seaSwash rushes up the beach away from the sea Backwash comes back towards the seaBackwash comes back towards the sea

Wave typesWave types

Destructive – high energy, 10+ p/mDestructive – high energy, 10+ p/m Break rapidly, plunging vertically, capable of breaking of Break rapidly, plunging vertically, capable of breaking of

large amounts of rock, up to 25 tonnes of pressure per metre large amounts of rock, up to 25 tonnes of pressure per metre squared, erodes coastlinesquared, erodes coastline

Constructive – low waves that break gentler, -8 p/m, occur Constructive – low waves that break gentler, -8 p/m, occur on shore with gentle gradient, swash spread over large area so on shore with gentle gradient, swash spread over large area so backwash is weak, leads to more material being deposited than backwash is weak, leads to more material being deposited than erodederoded

Wave RefractionWave Refraction

This causes the waves to bend as they approach the shoreThis causes the waves to bend as they approach the shore Friction with the bottom near the coast causes the wave to Friction with the bottom near the coast causes the wave to

slow downslow down Wave in deep water stays at original speedWave in deep water stays at original speed This causes wave to bend or refract and hit the coast line at an This causes wave to bend or refract and hit the coast line at an

angleangle On headlands the wave slows down in front and waves swing On headlands the wave slows down in front and waves swing

around to attack the sides eroding themaround to attack the sides eroding them Little energy left for the bay so deposition occurs thereLittle energy left for the bay so deposition occurs there

Coastal ErosionCoastal Erosion

Depends on the type of Rock – Hard or SoftDepends on the type of Rock – Hard or Soft Wave strength – destructive v constructiveWave strength – destructive v constructive Shape of the coastline- wave refraction focuses energy on Shape of the coastline- wave refraction focuses energy on

headlandsheadlands Slope of shore – gently sloping shores cause waves to break Slope of shore – gently sloping shores cause waves to break

further out so they lose energyfurther out so they lose energy Erosion greater when soft rock lies underneath hard rock, Erosion greater when soft rock lies underneath hard rock,

where rocks are well jointed or when strata dip towards the seawhere rocks are well jointed or when strata dip towards the sea Rising sea levels increase erosion – expected to rise by 20-25 Rising sea levels increase erosion – expected to rise by 20-25

cm in next 30 yrs in Irelandcm in next 30 yrs in Ireland

Cliffs and Wave Cut PlatformsCliffs and Wave Cut Platforms

Cliff is a vertical slope on the coastline as a result of erosionCliff is a vertical slope on the coastline as a result of erosion E.g. Cliffs of MoherE.g. Cliffs of Moher Wave energy aWave energy att its greatest when high steep d its greatest when high steep deestructive waves structive waves

hit the land and erode it through hydraulic action and abrasion hit the land and erode it through hydraulic action and abrasion and compressionand compression

A notch is cut at high water mark creating an overhangA notch is cut at high water mark creating an overhang When overhang develops it will eventually collapse and a When overhang develops it will eventually collapse and a

cliff is formedcliff is formed Cliff retreats inland and increases in height and material Cliff retreats inland and increases in height and material

collects at the foot of cliffcollects at the foot of cliff

This is worn down by attrition and some used to build a wave This is worn down by attrition and some used to build a wave built terracebuilt terrace

As the cliff retreats inland it exposes rock underneath with a As the cliff retreats inland it exposes rock underneath with a gentle seaward slope called a wave cut platformgentle seaward slope called a wave cut platform

If this platform gets too big the waves lose all there energy before If this platform gets too big the waves lose all there energy before reaching the cliff the cliff becomes inactive and erosion ceases reaching the cliff the cliff becomes inactive and erosion ceases to occurto occur

This can be seen by vegetation growing on the cliff and debris This can be seen by vegetation growing on the cliff and debris collecting at the bottomcollecting at the bottom

Vertical cliffs occur in areas of uniform rock or where strata dip Vertical cliffs occur in areas of uniform rock or where strata dip inlandinland

Bays and HeadlandsBays and Headlands

Coasts rarely worn back evenly due to differential erosion as a Coasts rarely worn back evenly due to differential erosion as a result to differing types of rock resistanceresult to differing types of rock resistance

Less resistant rock forms bays while resistant rock forms Less resistant rock forms bays while resistant rock forms headlandsheadlands

E.g. Galway Bay, Wicklow HeadE.g. Galway Bay, Wicklow Head Mostly caused by hydraulic action, particularly where the rock Mostly caused by hydraulic action, particularly where the rock

has joints and bedding planeshas joints and bedding planes Air compression also adds to the erosive power as does abrasion Air compression also adds to the erosive power as does abrasion

and solutionand solution Wave refraction erodes the headlands and makes them more Wave refraction erodes the headlands and makes them more

pronounced while bays are protected from high energy waves pronounced while bays are protected from high energy waves and are the scene of sea deposition forming beaches and are the scene of sea deposition forming beaches

Sea caves, Arches and StacksSea caves, Arches and Stacks

On headlands wave refraction opens up joints, faults or other On headlands wave refraction opens up joints, faults or other weaknesses to form sea caves mainly through abrasion, weaknesses to form sea caves mainly through abrasion, Hydraulic action and compressionHydraulic action and compression

If the cave is extended all the way through a headland a bridge If the cave is extended all the way through a headland a bridge like feature called a sea arch is formed – this can also happen like feature called a sea arch is formed – this can also happen from caves eroding back to backfrom caves eroding back to back

If arch walls widen and roof is weathered it can collapse If arch walls widen and roof is weathered it can collapse forming a sea stackforming a sea stack

If stack is eroded down to sea level its known as a sea stumpIf stack is eroded down to sea level its known as a sea stump

TransportationTransportation

Materials broken down by erosion are reduced in size by Materials broken down by erosion are reduced in size by attrition until able to be transportedattrition until able to be transported

Sediments moved up and down beaches by breaking wavesSediments moved up and down beaches by breaking waves The water that rushes up a beach is known as the swash and The water that rushes up a beach is known as the swash and

the water returning to the sea is known as the backwashthe water returning to the sea is known as the backwash Sediments moved by process known as longshore driftSediments moved by process known as longshore drift Waves reach beach at an angle and so swash is at an angle but Waves reach beach at an angle and so swash is at an angle but

backwash returns at right angles backwash returns at right angles This process is repeated.This process is repeated.

BeachesBeaches

Result of low energy constructive wavesResult of low energy constructive waves Created when amount of material deposited is greater then Created when amount of material deposited is greater then

material erodedmaterial eroded Beaches consist of boulders, pebbles, sand, shingle, mud etcBeaches consist of boulders, pebbles, sand, shingle, mud etc Some comes from sea erosion but most transported by streamsSome comes from sea erosion but most transported by streams Beaches are gently sloping between LWM and HWM and can Beaches are gently sloping between LWM and HWM and can

vary in lengthvary in length Most beaches have a foreshore and backshoreMost beaches have a foreshore and backshore Backshore has steeper slope, coarser material and is only Backshore has steeper slope, coarser material and is only

reached in highest tides or storm conditionsreached in highest tides or storm conditions

The foreshore is lower, gentle gradient and consists of sand, The foreshore is lower, gentle gradient and consists of sand, mud and shell particlesmud and shell particles

Storm beaches are ridges of large stones thrown up by strong Storm beaches are ridges of large stones thrown up by strong waves back beyond reach of normal waveswaves back beyond reach of normal waves

Berms – ridges of coarse material that indicate the high tide Berms – ridges of coarse material that indicate the high tide level of constructive waveslevel of constructive waves

Ridges and runnels develop on seaward edge of foreshore and Ridges and runnels develop on seaward edge of foreshore and run parallel to sea where the waves breakrun parallel to sea where the waves break

Sand dunes develop inland where there is plenty of sand and Sand dunes develop inland where there is plenty of sand and prevailing wind comes from the seaprevailing wind comes from the sea

Sand blown inland and is trapped to form beginning of sand Sand blown inland and is trapped to form beginning of sand dunedune

Dunes unstable and will continually migrate unless Dunes unstable and will continually migrate unless consolidated by marram grass e.g. Youghal, Ventryconsolidated by marram grass e.g. Youghal, Ventry

Sandspits and Tombolos Sandspits are long narrow ridges of sand and shingle that are attached to

land on one side Formed by longshore drift when coast changes direction sharply Sediments carried off shore and deposited on sea bed building up to form

spit Continues to grow as long as deposition is greater than erosion Sand dunes may from on sheltered landward side and beach formed on

seaward side End can often be recurved due to change in wave direction Salt marsh can also develop on the landward side E.g. Strandhill co sligo Tombolo is a spit that connects an island to the shore e.g. Howth linked to

Sutton Island

Lagoons and Salt Marshes Lagoon is small body of water cut off or almost cut off from

open sea Land cutting it off known as a bay mouth bar Can be created by sandspit sealing off a entire bay or offshore

bar migrating towards land Offshore bar in parallel ridge of sand that forms off shore Occurs on shallow gently sloping coasts so waves break

further out and deposit material It is increase in height by constructive waves and longshore

drift Can be moved forwards by waves breaking over it to form a

lagoon E.g.Our Lady’s Island Lake, Wexford

Salt marshes often develop in these lagoons Mud and sand deposited by the sea and alluvium deposited by

rivers result in infilling and lagoon becomes shallower Area becomes colonised by salt loving plants This increased rate of deposition and builds up to form marsh

that is exposed permanently above normal tide E.g. Backstrand in Tramore, and Bull Island in Dublin