Booklet 5- What are the key erosional processes at the coast? Flashcards
What is coastal erosion?
Plays a vital role in the coastal system, removing debris from the foot off cliffs and providing an input to the coastal sediment cell
-caused by the energy of the sea, converted by the power of the wind into waves, landforms and eroding sediment
Coastal process- Erosion
Hydraulic action, Attrition, Abrasion and Solution
Coastal process- Transport
Longshore drift, traction, saltation, suspension, solution
Coastal process-Deposition
Dropping sediment, gravity setting or floculation
Coastal process-Subariel weathering
Physical, chemical, biological
Coastal process- Mass movement
Creep, earth flow, rockfall, mudflow, landslide, rotational slip, slumping
Type of erosion-Hydraulic action
The force of waves hitting a cliff (or sea wall) compresses water and air into cracks and joints. This can be equivelant to 30,000 kg per square metre.
-This increase in pressure may lead to cracks widening and pieces of rock breaking off
Type of erosion-Corrosion/Solution
Salts and acids in the sea water can react with rocks, slowly dissolving them away.
- E.g this process on a cliff of Portland has been chemically attacked by carbonic acid and other chemicals in sea water
Type of erosion-Attrition
Rock fragments which have become detached by hydraulic action ad corrasion (abrasion) are worn down into smaller and more rounded pieces.
-Currents and tidal movements cause the fragments to be swirled around and to grind producing pebble beaches
Type of erosion-Abrasion/ Corrasion
Rock fragments may be picked up by waves and thrown against the rock face of cliffs by subsequent waves.
-The effectiveness of the corrasion depends on the strength of the wave, the nature of its ‘load’ and the resistance of the rock in the cliff face.
-Corrasion is the most effective at the base.
Type of erosion-Cavitation
Air bubbles in the water collapse, creating repeated shockwaves against the rocks.
-Waves scoop out the loose material in a similar way to the action of a giant digger in a quarry on land
What is the difference between cavitation, wave quarrying and hydraulic action?
-Wave quarrying occurs first as it is just reffering to the force of the waves creating cracks
-Hydraulic action occurs second as it is the compressing of water and air in these cracks
-Cavitation occurs last as it is the air bubbles in the water collapsing which leads to shockwaves
All the factors that effect erosion
-Rock type (mineral composition and permeability), Rock structure (bedding planes), Faults, Beach vs cliff morphology,Subarial processes,
-Coastal management,Wave Characteristic, Concordant vs Discordant Coastlines
Factor affecting erosion-Rock type;mineral composition and permeability
Rocks can be permeable or impermeable as if water can soak in they become saturated and more unstable
-mineral composition means some are harder e.g:
-hard rocks- granite and limestone
-soft rocks-boulder clay and sandstone
Very significant as erosion rates do change a lot like Cornwall and Hornsea are very different due to this.
Factor affecting erosion-Rock structure, bedding planes
Dip angle of layers within the rock
-Horizontal-are stable and less likely to collapse/ slide as they arent angled towards anywhere
-Vertical-unstable and means that after roads can slide down the cliff easily and therefore erosion happens easier
Not as significant as rock type as even if it was vertical but hard rock it would barely erode
Strata
Layers of the rock
Bedding planes
The planes between each layer of rock
Factor affecting erosion-Faults
Exist where there has been either compression or moving apart.
-can be seen in the Chalk cliffs at Flamborough Head.
-Cracks and faults create weaknesses that are exploited by erosion.
Rock type is more significant and waves are due to these are the factors that decide how many faults in the cliff face there will be
Factor affecting erosion-Beach vs cliff morphology
Beaches absorb wave energy and reduce the impact of waves on a cliff.
-If a beach is absent, this puts the cliffs much more at risk of erosion
-Quite significant as the beach can be extra source of management
Factor affecting erosion- Subariel processes
Weathering and mass movement will weaken cliffs and create piles of debris that are easily eroded by the sea.
Not as significant as rock type as that is what it depends on
Factor affecting erosion-Coastal management
Presence of external structures can impact sediment transfer.
-Terminal groyne syndrome may mean that beaches further down drift of sediment will face a larger impact
Factor affecting erosion-Wave characteristic
Inceased prevailing wind will increase erosion
-Destructive and constructive waves
-Wave steepness and breaking point
-Steeper waves that break close to the shore erode downwards on the sea bed causing creater erosion
Factor affecting erosion-Concordant vs Discordant
If the orientation of bands of the rocks is parallel then its concordant.
-If the bands are perdandicular to the coastline thats
discordant
-concordant have even rates of erosion whereas discordant have varied rates along the coast
What is a concordant coastline?
- Where the layers of rock are paralell to the coastline
-usually weakness like a fault
-so despite them being the same rock more erosion could occur in a certain area
-erodes into the layer of soft rock making a cove
-e.g Lulworth cove was created as a crack exposed the limestone layer to reach the The Wealden beds
What is a dicordant coastline?
- The layers of rock are perpandicular to the coastline as not all coastlines are perfect bands of alternating rock
-e.g the Holderness coast with chalk and glacier till cliffs
Sources of energy on the Holderness?
- Fetch, Coriolis Force, Storms, Air masses and tides
Sources of energy on the Holderness-Fetch
- Large uninterrupted areas of sea enables destructive waves to be driven by prevailing north-easterly winds across the North Sea
Sources of energy on the Holderness-Coriolis Force
- Directs the waves at the coastline from a north easterly direction
-force can result in successive days of powerful destructive waves along the coastline which can remove metres of land
Sources of energy on the Holderness coast-Storms
- Storm conditions within the North Sea, particularly during the winter months causes erosion
Sources of energy on the Holderness coast-Air masses
- Arctic maritime air pushes down towards the UK, creating bigger storm waves, which, further erodes the coastline due to the high energy they contain
-Waves can be up to 4 metres
Sources of energy on the Holderness coast-Tides
- There is a large tidal range along the coastline up to 7 metres at certain times of the year.
-Scouring and abrasion at the sub-tidal foreshores leads to basal cliffs erosion resulting in cliff retreat with an average of 1.5 metres per year.
