Edexcel A-level Geography - Coasts

Littoral Zone

Area of shoreline where land is subject to wave action

Littoral Zone Subdivisions

- Offshore
- Nearshore
- Foreshore
- Backshore
- Beach

Offshore

Where waves begin to break in the deeper water. Friction between the waves and the sea bed may cause some distortion of the wave shape.

Nearshore

Friction between the seabed and waves distorts the wave sufficiently to cause it to break.
Possible breakpoint bar formation.

Foreshore

The area between the high tide and the low tide mark.

Backshore

The area above the high tide mark, affected by wave action only during major storm events.

Why are Littoral zones dynamic zones of rapid change?

Short term - Changing inputs, through flows and outputs of energy and material. High and low tide variation, wave energy due to weather.
Long term - Sea level variation due to climate change

Classifying Coasts - Long Term Criteria (2)

- Geology
- Sea Level Change

Classifying Coasts - Geology

- Characteristics of land, including lithology (rock type) and structure (arrangement of rock units).
- Used to classify coasts as cliffed, sandy, estuarine, concordant and discordant

Cliffed /rocky Coastline (4)

- High energy environment
- Rate of Erosion exceeds Deposition.
- High relief varying from a few meters to hundreds of meters
- Resistant Geology

Sandy Coastline (5)

- Low Relief with Sand Dunes and Beaches
- Less Resistant Geology
- Low energy environment
- Rate of Deposition exceeds Erosion
- Constructive waves

Estuarine Coastline (5)

- Low Relief with Salt Marshes and Mudflats
- Form in River Mouths
- Low energy environment
- Rate of Deposition exceeds Erosion
- Less Resistant Geology

Classifying Coasts - Sea Level Change

- Used to Classify Coasts as Emergent or Submergent
- Caused by eustatic/isostatic changes
- Caused by climate change

Climate Change caused by Cycles

- Sea Levels rise and fall in 100,000 year cycles
- Due to Earths Orbit
- Falls for 90,000 years as ice sheets expand
- Rises for 10,000 years during interglacial periods
- Rises when all surface ice melts

Emergent Coastline

As Sea Levels fall, coastline land is exposed which was previously covered by the sea

Submergent Coastline

As Sea Levels rise, the land is covered

Concordant Coastline

- Alternating bands of rock that run parallel to the coastline
- Also called Dalmatian Coasts

Discordant Coastline

- Alternating bands of rock that run at 90 degrees to the coastline
- Also called Atlantic Coasts

Classifying Coasts - Short Term Criteria (3)

- Energy Inputs
- Sediment Inputs
- Advancing/Retreating

Classifying Coasts - Energy Inputs (5)

- Used to classify High/Low Energy Coastlines
- Waves (Main Input)
- Tides (Moon's Gravitational Pull)
- Currents
- Rivers

Classifying Coasts - Sediment Inputs

- Sediment is added through deposition and removed through erosion
- Sediment Inputs received by waves and wind, tides, currents, mass movement and tectonic processes

Classifying Coasts - Advancing/Retreating

- Classified as Advancing/Retreating due to processes
- Long Term Processes = Emergent/Submergent Coastline
- Short Term Processes = Eroding/Outbuilding Coastline

Outbuilding Coastline

- Erosion < Deposition
- Net gain of sediment
- Coastline advances

Eroding Coastline

- Erosion > Deposition
- Net loss of sediment
- Coastline retreats

Cliffed Coasts - UK

- Occupy 1,000km of UK coastline
- Mainly located in North and West
- High relief = 427m (Conachair Cliff, Isle of Hirtha)
- Low Relief = 3m (Chappel Porth, Cornwall)

Weathering

Breakdown of rock in situ, and may be a mechanical, biological or chemical process.

Erosion

Wearing away of land due to wave action

Mass movement

Downslope movement of material due to the force of gravity.

Formation of Coastal Plains

- Formed by Coastal Accretion (Continuous net deposition causes coastline to extend seawards)
- Can extend biologically if plants colonise shallow water, trapping sediment

Where does Coastal Accretion come from? (2)

- Offshore sources (transported by waves, currents and tides)
- Terrestrial sources (transported by rivers, glaciers, wind or mass movement)

Dynamic Equalibrium

- When Erosion = Deposition
- Continuous flows of energy and material through the coast but size of stores remains unchanged

Concordant coastline - Lulworth Cove

- Resistant Portland Limestone forms a protective stratum layer parallel to sea.
- Less Resistant Purbeck Limestone and Wealden Clay lie behind the Portland Limestone.
- Portland limestone erodes very slowly, retreating landwards by marine undercutting.
- At points where Portland Limestone is weaker, erosion managed to break through leading to the erosion of the less resistant Purback Limestone and Wealden Clay. This is done by lateral erosion.
- Destructive waves have a stronger backwash so material is dragged out the cove. This can cause small beaches.
- Waves continue to erode Portland Limestone. Attrition and abrasion are responsible for the erosion and the cove is widened more and more.

Concordant Coastline - Croatia

- Dalmatian coastline on the Adriatic Sea (Croatia in particular)
- Formed where the geological structure consists of folds parallel to the coastline
- Folded Ridges (Anticlines) and Down Folded Valleys (Synclines) are aligned parallel to the coast
- Sea Level rise at the end of the Devensian glacial period caused flooding of Synclines
- This produced narrow islands parallel to the coast that are seperated by narrow sea channels

Concordant Coastline - Haff Coastline

- Formed when deposition produced unconsolidated geological structures parallel to the coastline
- During Devesian Ice age, sea levels were 100m lower than today
- Thick layers of sand and gravel deposited by meltwater rivers
- Holocene interglacial constructive waves moved the deposited sediment landwards as sea levels rose
- Bars formed across bays and river mouthes, causing lagoons to be formed behind the bar (East of Gdansk)

Discordant coastline - Swanage Bay

- Isle of Purbeck in East Dorset
- The waves erode the less resistant Wealden Clay which eventually forms a bay, where wave energy is low.
- More resistant rock is resistant to erosion, so sticks out and forms a headland, where the wave energy is high.
- Jurassic Portland Limestone forms a headland extending 1km out into sea
- Resistant Cretaceous chalk forms another headland extending 2.5km out into the sea
- As the waves approach the headland, it absorbs wave power and refracts - meaning they change motion and direction around the headland.
- After the wave hits the headland, it is likely to become a constructive wave. These waves carry material and deposit it as swash is more powerful than backwash.
- The bay will eventually come forwards and become a beach, whilst the headlands are slowly eroded by hydraulic action.
- The coastline eventually becomes smooth until the process repeats.

Geological Structure

Characteristics and arrangement of rock units.

Strata

Different layers (or beds) of rock.

Bedding Plane

Surface separating layers of strata.

Deformation

Degree of tilting of folding of rock.

Dip

Angle of inclination of titled strata.

Fold

Tectonic forced that distort rock strata

Folding increases erosion rates

- Folded rock are heavily fissured and jointed, meaning they are more easily eroded.
- Rock is stretched along anticline crests and compressed in syncline troughs.

Fault

Fractured Rock that has moved from its original position.

Faulting increasing erosion rates

Due to huge forces being involved in faulting, they are often heavily fractured and broken. This can be easily exploited by marine erosion.

Joint

Fractured rock that hasn't moved from the original position.

Where do joints occur? (2)

- Igneous rocks = cooling joints form when magma contracts as it looses heat.
- Sedimentary rocks = joints form when rock is subject to compression or stretching by tectonic forces or weight of overlying rock.

Jointing increasing erosion rates

- Fissures can be exploited by marine erosion such as Hydraulic Action
Stair Hole = Purbeck Limestone is intensely folded. Folds have created joints causing the Purebeck Limestone to erode much more rapidly than adjacent Portland Limestone

Cliff profile

The height and angle of a cliff face as well as its features, such as wave-cut notches or changes in slope angle.

Longshore drift

The movement of water and sediment down a beach caused by waves coming in to shore at an angle

Micro Features

- Small scale coastal features such as caves and wave-cut notches
- Form in areas weakened by heavy jointing
- Have faster rates of erosion
- Enlarge the joint to form a cave

Rate of Recession

Speed at which the coastline is moving inland

Clastic rocks

Made of sediment particles cemented together

Crystalline rocks

Made of interlocking mineral crystals.

How does Lithology affect resistance? (3)

- Mineral Composition
- Rock Class
- Structure

Mineral Composition - Resistance

- Some rocks contain reactive minerals easily broken down by chemical weathering, e.g. calcite in limestone.
- Other minerals are more inert that chemically weather more slowly

Rock Class - Resistance

- Clastic Sedimentary rocks = limestone
- Cements that are reactive and easily chemically weathered = iron oxide
- Sedimentary rocks with weak cementation = boulder clay
- Crystalline and strong chemically bonded igneous rock = Granite

Structure - Resistance

- Rocks with fissures (faults and joints) or air spaces (porous) rocks, weather and erode rapidly.

Igneous Rock

- Formed from solidified lava or magma
- Composed of interlocking crystals, forming hard, resistant rock
- Tend to have fewer joints and weaknesses, therefore being more resistant
- Erode at 0.1cm p.a.

Metamorphic Rock

- Formed by the recrystallisation of sedimentary and igneous rocks through heat and pressure
- Has a crystalline structure
- Less resistant than igneous rock due to crystals not being interlocked and the rock often containing folds and faults
- Erode at 0.1-0.3cm p.a.

Sedimentary Rock

- Formed by compaction and cementation of deposited sediment
- Contain weak bedding planes
- They are clastic
- Often heavily joined due to compaction
- Erode at 0.5cm-10cm p.a.

Unconsolidated Sediment

- Sediment that has not yet been cemented to form solid rock
- Example of this includes boulder clay
- Erode easily at 2-10m p.a.

Complex Cliff Profile

- Composed of strata of differing lithology
- Less resistant strata erode and weather quickly, being cut back rapidly. This can form wave cut notches
- Resistant strata erode and weather slowly, retreating less rapidly.
- Overhang eventually collapses due to gravitational forces

Permeable Rock

Allow water to flow through them.

Impermeable Rock

Do not allow water to flow through them.

Complex Cliff Profile (Permeable/Impermeable Strata)

Permeable rocks tend to be less resistant to weathering because water percolating comes into contact with a large surface area that can be chemically weathered.

Vegetation and Stabilisation

- Vegetation can stabilise unconsolidated sediment and protect it from erosion
- Plant roots bind sediment together, making it harder to erode
- Leaves covering the surface protect sediment from wave erosion and longshore drift
- Also protect sediment from wind erosion

Vegetation and sediment accumulation

- Vegetation can increase the rate of sediment accumulation
- Plant leaves interrupt flows of water and wind. This encourages deposition
- As vegetation dies, hummus is added to the soil

Why are coasts harsh environments for plants? (5)

- Exposed to high wind speeds during low tide
- Lack of shade produces high temperature range
- Vegetation submerged in salty water for half the day
- Evaporated sea spray makes sediment saline
- Sand lacks nutrients

Plant Succession

The changing structure of a plant community over time as an area of initially bare sediment is colonised

Pioneer plants

The first plants to colonise freshly deposited sediment.

How do Pioneer Plants modify the environment? (3)

- Stabilise sediment
- Add organic matter that retains moisture and provides nutrients
- Reduced evaporation in sand

Stages in Plant Succession

Each stage is called a Seral Stage

End result of Plant Succession

Climax community

Xerophytes

Plants adapted to dry conditions. They are able to colonise in bare sand.

Sand Dune Succession Order

- Embryo Dune
- Fore Dune
- Yellow Dune
- Grey Dune
- Climax Community

Sand Dune Succession - Embryo Dune

- Embryo Dune formed when sand accumulates around a small obstacle (e.g. driftwood)
- As Embryo Dune Grows, it is colonised by xerophytic pioneer plants (e.g. lyme grass)

Sand Dune Succession - Fore Dune

- Embryo Dunes alter the conditions allowing other plants to colonise thus forming fore dunes
- Pioneer plants stabilise sand allowing marram grass to colonise

Sand Dune Succession - Yellow Dune

- Marram grass allows dune to grow, leading to the formation of a yellow dune
- Marram grass has waxy leaves to limit water loss through transpiration and resist wind-blown sand abrasion
- Roots of Marram grass can grow 3m down the water table
- Stem of Marram grass can grow 1m per year to avoid burial by deposited sand

Sand Dune Succession - Grey Dune

- When Marram grass dies, it adds hummus to the sand, enabling the formation of soil.
- A grey dune develops with plants such as gorse
- This dune is now above the high tide mark so rainwater washes off salt away from the soil making it less saline

Sand Dune Succession - Climax Community

- Soil has improved nutrients and moisture retention.
- Non-xerophytic plants colonise the dunes until a climax plant community is reached, in equilibrium with the climate and soil conditions

Halophytes

Plants specifically adapted to saline conditions. They are able to colonise in mud and salt water.

Halosere

Plant Succession in salty water

Why are Estuarine areas ideal for salt marshes? (2)

- Sheltered from strong waves (enables deposition)
- Rivers transport sediment to the river mouth which can add to deposition

Salt Marsh Succession

1) Flocculation = Mixing of sea water and fresh water causing clay particles to stick together and sink
2) Blue-green algae colonise mud, exposed at low tide for only a few hours.
3) Algae binds mud, adds organic matter, and traps sediment.
4) Sediment thickens, water depth reduces so mud is covered by tide for less time
5) Halophytic cord grass colonises. The marsh is still low and covered by high tide each day
6) Accumulation of organic matter rises the height of the marsh
7) Salt marsh becomes colonised by plants such as scurvy grass
8) Rainwater washes salt out of the high marsh soil
9) Land plants continue to colonise until a climax community is reached

What does wave size depend on? (4)

- Strength of wind
- Duration for which the wind blows
- Water depth
- Wave fetch

Constructive Waves

- Low energy waves
- Low, flat wave height (<1m)
- Long wavelength (up to 100 m)
- Low wave frequency (about 6-9 per minute)
- Strong swash that pushes sediment up the beach. Weak backwash means that a lot of material is deposited

Destructive Waves

- High energy waves
- Large wave height (>1 m)
- Short wavelength (about 20 m)
- High wave frequency (13-15 per minute)
- Weak Swash and strong backwash. Causes sediment to get eroded from the beach

Beach Morphology

Shape of the Beach

Beach sediment profile

Pattern of distribution of different sized or shaped deposited material.

How do constructive waves alter beach morphology and beach sediment profiles?

- Net movement of sediment up the beach causing a steeper beach profile
- Berms (Ridge of Material) can be created at the point where the swash reaches at high tide
- Sorting of material due to swash/backwash energy. Sand closer to water and heavy sediment towards back of beach
- Coarse sand deposited in the middle of the beach whereas only fine sand makes it down to the water

How do destructive waves alter beach morphology and beach sediment profiles?

- Reduced beach gradient due to net transport of sediment down the beach (weak swash and strong backwash)
- Sediment thrown from waves can accumulate as a storm ridge
- Large sediment particles dragged to the water and deposited below low tide mark

Decadal Variation of Beach Morphology and Beach Sediment Profiles

- Climate change is expected to bring more extreme weather events to the UK
- Winter profiles may be present for longer time over course of year
- More frequent and powerful destructive waves could decrease beach size and increase rates of erosion

Seasonal Variation (Winter - UK) of Beach Morphology and Beach Sediment Profiles

- Destructive, high-energy waves dominate
- Lowers angle of beach profile
- Shingle spread over the whole beach
- Offshore bars formed causing deposition of sediment offshore

Seasonal Variation (Summer - UK) of Beach Morphology and Beach Sediment Profiles

- Constructive, low-energy waves dominate
- Beach angle steepens
- Particles sorted by size along the beach (larger shingle towards back of beach)
- Berm ridges constructed at high tide mark

Monthly Variation of Beach Morphology and Beach Sediment Profiles

- Tide height varies over course of lunar month.
- Highest tide twice a month (spring tide). Lowest tide twice a month (neap tide)
- Spring -> Neap tide = berms formed at lower points down the beach
- Neap -> Spring tide = berms destroyed as sediment pushed up beach due to rising swash reach

Daily Variation of Beach Morphology and Beach Sediment Profiles

- Storms can change the shape of the beach within a few hours
- Destructive waves change to constructive waves as wind slows
- Calm anticyclonic conditions in winter can produce constructive waves that begin to rebuild beach, steepening profile a few days before storm.

Wave Erosion Processes (4)

- Hydraulic Action
- Corrosion
- Abrasion
- Attrition

Hydraulic Action

- Water causes pressure on the rock causing it to erode.
- High energy waves are most effective at Hydraulic action due to targeting all weaknesses
- Resistant rock may only be eroded by Hydraulic action (joints within rock)

Corrosion

- Rock being dissolved in water due to minerals
- Constructive waves most effective due to longer time for chemical reaction to occur
- Carbonated rock such as limestone are most quickly eroded by corrosion

Abrasion

- Sediment within wave is thrown against rock. This is repeated and rock is chipped away.
- High energy waves with a larger height have more energy so increase rates of erosion through abrasion
- Sedimentary rock eroded most quickly by abrasion