T2 - Coastal Landscapes and Change

Why is a coast an open system?

It receives inputs from outside and transfers outputs away from the coast into other systems like transferring water into the atmosphere

What is a sediment cell?

A self contained section of coastline where there are inputs, transfers and outputs

Give me examples of inputs, transfers and outputs in a sediment cell:

• Inputs - Cliffs, offshore bars

• Transfers - Longshore drift

• Outputs - Spits, beaches

What is a negative feedback loop?

A stabilizing mechanic that lessens any change

Example

• A storm erodes a lot of a beach

• This causes lots of sediment to be deposited as an offshore bar when the waves lose their energy

• This bar dissipates their wave energy which protects the beach from further erosion

• Over time the bar gets eroded as a buffer while sediment can be added from longshore drift or wind

• Then once the bar is gone dynamic equilibrium returns

What is a positive feedback loop?

A mechanic that exaggerates the change making it more unstable

Example

• People walking over a sand dune destroying vegetation & causing erosion

• The roots no longer hold sand together

• The sand dune will be completely eroded eventually leaving more of the beach open to erosion & further from dynamic equilibrium

What is the littoral zone?

The area of the coast where land is subject to wave action

What are the 4 subzones in the littoral zone?

• Backshore - The beach & parts that can be seen at low tide

• Foreshore - Where wave processes occur

• Nearshore - Where the water starts to get shallower from the sea

• Offshore - The open sea

What are the 6 erosional processes?

• Corrosion - Sand & pebbles are hurled against the cliff

• Abrasion - Sediment is ‘rubbed’ along the coastline to slowly erode it

• Attrition - Waves causing rocks and pebbles to hit each other & become rounder

• Hydraulic action - A wave hitting a cliff face causing air to be forced into cracks which widens them

• Solution - Mildly acidic seawater causing alkaline rock like limestone to be eroded

• Wave quarrying - Breaking waves hit the cliff face & exert pressure to pull away rocks

What are the 5 factors that lead to erosion rates increasing?

• High waves with a long fetch (distance wind has travelled over the wave)

• Waves approach the cliff perpendicular

• At high tide when they go further up the cliff

• Heavy rainfall as water trickles down through permeable rocks to weaken it

• If it is in winter as destructive waves are the largest & most powerful during winter

What are the 3 factors that can make rocks more vulnerable to erosion:

• Rock type (sedimentary is more vulnerable compared to igneous & metamorphic)

• Amount of cracks & fractures in the rock (leads to hydraulic action)

• Lithology of the rock (the minerals that make up a rock)

How are stumps formed?

• Caves are formed from widening faults in the base of a headland

• The cave widens eroding into the side of a headland to make an arch

• The arch will widen until it can’t support itself & leaves a stack on one side detached from the mainland

• Erosion attacks the base of the stack till it collapses into a stump

What is a wave-cut notch/platform?

• Erosion attack the base of a cliff to create a notch of eroded material between high & low tide

• As this notch becomes deeper from weathering weakening the cliff at the top

• The cliff becomes unstable and falls under its own weight

What is a blowhole?

• A pothole on the top of a cliff from chemical weathering

• And a cave at the bottom eroding deeper into the cliff face so the pothole deepens

• When they meet a vertical channel is created for waves to travel into and up the cliff face

Explain the process of longshore drift:

• Waves hit the beach at an angle determined by the direction of prevailing wind

• The waves push sediment in this direction up the beach in the swash

• Due to gravity the wave carries sediment back down the beach in backwash

• This moves sediment along the beach over time

What are the 4 processes of transportation other than longshore drift?

• Traction - Large sediment rolls along the sea bed & is pushed by currents

• Saltation - Smaller sediment bounces along the sea bed being pushed by currents

• Suspension - Small sediment is carried within the water

• Solution - Dissolved sediment is carried within the water

What is swash-aligned and drift-aligned?

• Swash-aligned is when waves approach parallel to the coast so there isn’t much longshore drift

• Drift-aligned is when waves approach at a significant angle so there is longshore drift

Why does deposition occur?

When waves lose energy and can’t carry the sediment anymore

• Gravity from the energy becoming low so heavy stuff is deposited first

• Flocculation where clay clumps together making it denser so it drops

What are 5 depositional landforms?

• Spits, a long narrow strip of land formed by deposition

• Bars, a spit that crosses a bay and links up 2 sections of coast making a lagoon

• Tombolo, a bar that connects mainland to an offshore island, formed from wave refraction of the coastal island to reduce velocity increasing deposition

• Cuspate foreland, longshore drift along each side of a headland creating beaches which meet in the middle causing a triangle shape along the beach

• Offshore bars, a region where sand is deposited off shore as the wave breaks early

Explain Sand Dune & Plant succession:

Wind blows sand inland, plants stabilise them

Embryo dunes - Sand is trapped by debris & pioneer species begin to colonise, very fragile

Fore dunes - Embryo dunes give some protection, marram grass grows & has deep roots up to 3m, plants add organic matter to the dune making it more hospitable for plants

Yellow dunes - Marram grass dominates but more delicate flowers & insects are found, 20% of the dune is exposed

Grey dunes - Less than 10% of exposed sand, has more biodiversity, acidity and water is increased, shrubs appear

Mature dunes - The oldest and most stable dune found hundreds of metres from the shoreline

Explain Salt Marsh succession:

Low-energy environments where deposition occurs

They are behind spits & in estuaries where sediment settles & salt-tolerant plants colonise

Pioneer zone/mudflats - Low-lying muddy areas that are regularly flooded by the tide with little vegetation, salt-tolerant pioneer plants colonise

Lower salt marsh - Pioneer plants can survive with frequent flooding

Middle marsh - As the surface rises above the tide sea lavender colonises as the mud is deeper & there is more biodiversity

Upper marsh - Higher parts flood occasionally with grasses & shrubs colonising so more stable soils & less salty

What is mechanical weathering and 3 types of it:

Definition - The breakdown of rocks due to physical forces & no chemicals

• Freeze-thaw - Water enters cracks in rocks, freezes & expands by 10% which puts pressure on the rock

• Salt Crystallisation - As seawater evaporates, salt is left behind which grows into crystals over time which can corrode rocks from chemicals

• Wetting and Drying - Clay expands when wet and contracts when drying which can cause coasts to dry up

What is chemical weathering and 3 types of it:

Definition - The breakdown of rocks through chemical reactions

• Carbonation - Rainwater absorbing CO2 from the air to create a weak acid that reacts with calcium to be dissolved, acid rain reacts with limestone this way

• Oxidation - When minerals become exposed to the air from cracks the mineral will become oxidised and increase volume causing it to crumble (how iron rusts)

• Solution - When rock minerals like rock salt are dissolved

What is biological weathering and 5 types of it:

Definition - The breakdown of rocks due to the actions of plants, bacteria and animals

• Plant Roots - Roots growing into cracks exerting pressure & splitting them

• Birds - Puffins dig burrows into cliffs to weaken them

• Rock Boring - Clams secrete chemicals that dissolve rocks

• Seaweed acids - Some seaweeds contain acid which if hit against a rock will dissolve (kelp)

• Decaying vegetation - Water that flows through decaying vegetation and over coastal areas will be acidic

What does the type of mass movement depend on?

• The angle of the cliff

• The rocks lithology and geology

• The amount of vegetation on the cliff face

• The saturation of the ground

What are the 2 types of mass movement?

• Slides (sediment in the same place and the whole thing moves downhill)

• Flows (all the material mixes)

Give me 3 types of mass movement (flows):

• Soil creep - Movement of soil down hill

• Solifluction - Top layers thaw during summer but lower layers stay frozen & the surface layer flows over the frozen layers

• Mudflows - An increase in water content in soil can lead to mud flowing over rock

Give me 3 types of mass movement (slides):

• Rock falls - Rock falls

• Rock slides - Water between joints and bedding planes reduces friction and causes sliding

• Slumping - When soil is saturated with water soft materials fall forming rotational scars

What is a concordant coastline? and an example of one

Where the rock strata (layers) run parallel to the coast

Normally bands of more resistant and then less resistant rock so different landforms form

Example - Dalmatian coast where rise in sea level floods areas between resistant rock

What is a discordant coastline? and an example of one

Where rock strata (layers) run perpendicular to the sea creating headlands and bays where less resistant rock erodes faster than more resistant rock

Example - The Jurassic coast (Dorset)

What is wave refraction?

Where waves turn and lose energy around a headland on an uneven coastline

What is plant succession?

The long-term change in a plant community in an area

E.g a salt marsh forming

Why is marram grass a good pioneer plant?

• It is tough & flexible

• It has adapted to reduce water loss through transpiration

• Roots grow up to 3m deep and can tolerate up to 60°C

How can strength of a wave vary?

• In summer there are constructive waves compared to destructive winter waves

• Climate change means the UK can become stormier leading to an increase in destructive waves

• Human activity can affect the sediment supply across an area

What is isostatic change?

• Sea level change caused by post-glacial adjustments

• Since the Ice Age Southern England has been sinking around 1mm a year

What is eustatic change?

• The thermal expansion of water

• Water expands when it gets warmer so the volume increases & sea level increases

What is coastalisation?

The movement of people towards the coast

Why may coastalisation increase?

• Tourism

• High-yield agricultural land

• Housing pressure inland

Why does a storm surge occur?

When there is a short-term change in sea level due to low pressure during a tropical cyclone

What are the 3 factors affecting vulnerability to storm surges?

• Subsidence (sinking) of the land

• Removing natural vegetation like mangrove forests (Bay of Bengal)

• Global warming as increasing surface temperatures increases the frequency & intensity of storms

What are environmental refugees?

People who are displaced due to coastal flooding

What are the 4 different approaches to coastal management?

• Hold the line - Defenses are built to keep the shore where it is

• Managed retreat - Defenses are removed or changed to move land inward

• Advance the line - Defenses move the shore seawards

• Do nothing - No defenses are put in place so the coast can erode

What factors affect the coastal management technique?

• Economic value of the land & stuff being protected

• Technical feasibility of putting in hard engineering

• Ecological & cultural value of land like pre historic sites

What is the ICZM?

A holistic approach to a coastline as the entire sediment cell can be effected

• Recognizes peoples livelihoods & make sure coastal management is sustainable

• Must involve all stakeholders and working with natural processes

What is an SMP?

SMP - Shoreline management plan

Identifies all the activities that occur at the coastline

What is hard engineering?

• Man made structures to prevent erosion

• Effective at preventing erosion but at a high cost and with significant environmental impact

• Likely to exacerbate erosion elsewhere

What are 2 examples of hard engineering?

Rip Rap (Rock Armor)

• Large rocks that reduce wave energy while allowing water to flow through

• Cost effective

• Rocks are sourced from elsewhere so don’t fit in

• Pose a hazard to people

Revetments

• Wooden or concrete ramps that absorb wave energy

• Cost effective

• Ugly

• Constant maintenance needed

What is soft engineering?

Defenses that work with the physical environment by using natural methods

What are 4 examples of soft engineering?

Beach nourishment

• Sediment is taken from offshore sources to buildup the beach

• Protects from cliff erosion

• Increases tourist potential

• Needs constant maintenance

• Impacts on local coastal habitats

Cliff regrading & drainage

• Reduces the angle of the cliff to stabilize it from rotational slumping

• Cost effective

• Cliff can collapse suddenly as it is drier

• Can look unnatural

Dune stabilization

• Marram grass is planted to kickstart dune stabilization

• Cost effective & creates an environmnt

• Planting is time consuming

Marsh creation

• Managed retreat & allowing low-lying areas to flood

• Creates a wildlife environment

• No cost

• Farmers lose ladn

How can coastal management be more sustainable?

• Managing the natural resources already there

• Creating alternative livelihoods for people who lose land

• Educating communities on how to adapt

• Monitoring the coastal changes & then mitigating

• Managing flood risk/relocation

How can coastal management affect the sediment supply?

• Building a sea wall will reflect wave energy downdrift & increase erosion somewhere else

• Less erosion will occur in areas with a sea wall so there is less sediment in the area

• Less sediment on the beach will expose the cliff to erosion

• Groynes stop longshore drift so sediment isn’t moved away from one part of the coastline

What is terminal groyne syndrome?

• Groynes trap sediment from longshore drift

• Sediment builds up on one side of a beach

• This starves the other side of the groyne

• Without sand to protect it, wave energy hits the beach & erodes it