COASTS

Why is the coast an open system?

• Because it receives inputs from the lithosphere, atmosphere, hydrosphere, biosphere and cryosphere

Why can the coast also be seen as a closed system?

• Due to the sediment cell process

What is a sediment cell?

• A self contained system along a stretch of coastline where sediment is moved and stored

What are examples of the inputs, stores, transfers and outputs of a sediment cell?

INPUTS

• Erosion

• Sediments carried by waves / rivers

• Wind generated waves

• Precipitation

STORES

• Beaches

• Cliffs

• Marsh environments

• Dunes

TRANSFERS

• Transportation processes

• Longshore drift

• Mass movement

• Wind blown sand

OUTPUTS

• Eroded material taken out to sea

• Ocean currents

• Evaporation

• Deposition

What is geomorphology?

• The study of landforms, the shapes of the earths surface, and the processes that create and change them overtime

What does terrestrial mean?

• Relating to the land

What is an example of positive feedback at the coast?

• As waves erode the cliff, material is released

• This material abrades the cliff which results in even more cliff erosion

What is an example of negative feedback at the coast?

• As the shore is eroded, the material makes the wave-cute platform wider

• This can absorb wave energy and reduce the impact at the base of the cliff

What is the littoral zone?

• The area of the coast that can be affected by wave action

• Is is a dynamic zone which means that it is constantly changing due to interaction between processes on land and in the sea

• These changes can be:

  • Long term due to climate or sea level change

  • Short term due to the tides, waves and storms

What human activities interfere with natural processes in the littoral zone?

• River dredging (making the river deeper) - interrupts ecosystems and sediment budgets

• Building of coastal defences - leads to down drift erosion

What are the four zones that the littoral zone is divided up into?

• BACKSHORE = Only affected by waves during very high storm events

• FORESHORE = The intertidal area between high and low tide

• NEARSHORE = The breaker zone - Friction between the seabed and the waves causes them to break

• OFFSHORE = The area outside the influence of waves

What is a concordant coast?

• Where different rock types run parallel to the coast

• Dalmatian and Haff coastlines are examples of concordant coastlines

What is a discordant coast?

• Where different rock types run perpendicular to the coast

• Alternating rock types lead to the formation of headland and bays

• Discordant coasts are also known as Atlantic coasts

• Example: Dorset, UK

How can sea level change occur?

• Global warming - natural and enhanced

• Tectonic activity - can lead to sections of land to rise or subside

• thermal expansion

What is thermal expansion and how does it occur?

• Thermal expansion is when water increases in volume as it warms up

  • The kinetic energy increases as the water molecules warm up, the molecules move faster and spread out, therefore increasing the volume

What are the types of longer term sea level changes?

• Eustatic = When the sea level itself changes e.g sea level rise as a result of ice caps melting

  • Causes coastal submergence

  • Creates submergent coastlines

  • e.g Norwegian Fjords

• Isostatic = When the land itself rises or falls relative to the sea e.g heavy glaciers and ice sheets weighed down the crust, so it recovered by rising sharply above sea level when glaciers melted and there was less weight

  • Creates emergent coastlines

  • e.g Raised beaches in Scotland / fossil cliffs

What are the characteristics of high and low energy coasts?

HIGH ENERGY COASTS

• Destructive waves

• Exposed to strong winds and long fetches

• Higher rates of erosion than deposition

• Tend to be rocky coasts

• Steep cliffs - marine cliff profile

• Less steep cliffs - subaerial cliff profile

• Headlands, wave cut platforms

LOW ENERGY COASTS

• Constructive waves

• Sheltered locations with short fetch

• Higher rates of deposition than erosion

• Sandy beaches, salt marshes, estuarine and tidal mud flats

• Gentle relief

• Sediment from land and sea

• Beaches, spits, coastal plains

When do rocky coasts form and what are its features?

• When there is more resistant geology - in the UK this is mainly in the north and west of the country

• Steep cliffs - found in high energy environments

• Cliffs with gentler slope tend to be found in low energy environments

• Erosion is more dominant than deposition

What are the two types of erosion that may dominate along rocky coastlines?

• Marine erosion - The action of waves

• Sub-aerial erosion - Weathering and mass movement

What are the two different types of coastal plains and where does the sediment for deposition come from?

• Sandy coastlines

• Estuarine coastlines (where the river meets the sea)

• Both usually low energy coastal environments and tend to be low relief

• Sediment for deposition comes from:

  • Offshore sources (materials that come from the sea)

  • Terrestrial sources (materials that come from land)

Why do wetlands and marshes form?

• Due to poor drainage

How are Dalmatian coasts formed?

• As a result of tectonic forces and sea level rise

• Tectonic activity forms anticlines and synclines which run parallel to the sea

• e.g the Dalmatian coast in Croatia

How is a Haff coastline formed?

• Formed when a sandbar or spit grows across the mouth of the bay, partially cutting it off from open sea

• Example: the southern Baltic coastline

• These are low energy coastlines

What is wave refraction?

• Wave refraction changes the amount of energy reaching the shore on a small, local scale → headlands are experiencing higher erosion than bays

• Wave energy concentrates at the headland and increases the rate of erosion, therefore less energy reaches the bay

• Wave energy refracted towards the headland = increased erosion and landforms (caves, arches, stacks and stumps)

What are the characteristics that lithology can refer to?

• Strata - Layers of rock

• Bedding planes - Horizontal cracks created by pauses in rock formation

• Joints - Vertical cracks caused by tectonic movement or concentration

• Folds - The result of stress or pressure, causing it to fracture

• Dip - The angle of the rock strata

What is a cliff profile?

• Cliff profiles are the angle and height of the cliff face

• A profile also includes any features, such as wave cut notches

• Different lithology creates different cliff profiles

What is coastal recession and why does it happen?

• Coastal recession = The retreat of the coastline inland

• This may be due to:

  • Erosion

  • Sea level rise

  • Submergence

What types of lithology depend on how fast the coast is eroded?

• Mineral composition

• Rock classification

• Structure

LITHOLOGY DICTATES THE PACE OF RECESSION

How does mineral composition effect the rate of erosion?

• Some minerals are more reactive than others - This affects the rate of chemical weathering, for examples:

  • Calcite is reactive and so easily chemically weathered

  • Quartz is not reactive (inert) so chemical weathering is much slower

What is differential erosion?

• The changing rates of erosion of different rock types

What does differential erosion lead to?

• Complex cliff profiles

• Influences rates of recession

How does vegetation help to stabilise coastlines?

• The plant roots help to bind the soil / sand together - reducing the impact of erosion

• Wind speeds are reduced by vegetation which decreases erosion and increases deposition

• Dead plant material adds organic matter to the sand and eventually leads to the formation of soil

Why is vegetation often sparse in coastal environments?

• Exposure to salty / saline water

• Evaporation of water leads to increased salinity

• High wind speeds

• Lack of shade

• Lack of nutrients

• Free-draining sediment means water is not retained

What are pioneer species and how do they help to stabilise the environment?

• Pioneer species = the first plants to grow in the harsh coastal environment - help to build new ecosystems

• Pioneer species:

  • Help to stabilise the environment

  • Add organic matter

  • Increase shade

  • Trap more sediment

• Example: Sand dune succession

What is the formation of a sand dune?

1) Windblown sand is deposited against an obstruction: pebbles or driftwood

2) As more sand particles are caught, the dunes grow in size, forming rows perpendicular to the prevailing wind

3) Over time, the ridges of the dunes will be colonised and fixed by vegetation in a process called succession

What is the process of coastal dune succession?

1) Starts at the beach where wind deposits dry sand just above high tide line

2) This creates small embryo dunes colonised by pioneer species (Lyme grass, sea couch grass - adapted to survive in harsh, dry conditions)

3) Embryo dunes trap more sand and stabilise the dune. As more sand accumulates, larger yellow dunes form, dominated by marram grass which has deep roots and can tolerate burial by sand (yellow colour due to high sand content)

4) Further inland dunes become more stable and less salty (grey dunes) - more humus is added

5) Organic matter from plants begin to build up in soil improving fertility

6) Between dunes, dune slack (low lying area between dunes) collects water, making the soil more moist

7) Eventually, if conditions allow, you can find pine woodlands or climax vegetation (mature dunes) (fully developed plant community) - these are sheltered from sea spray so support more complex ecosystems

What is the process of salt marsh succession?

• 1) Sediment accumulates, sticks together (flocculation) and builds up to form mudflats

• 2) Pioneer plants begin to colonise the area (such as cord grass) - their long roots trap sediment, encourage deposition and stabilise the mudflat

• 3) The height of the sediment increases due to gentler conditions and more plants colonise (such as sea lavender) - Saline levels decrease due to rain washing out the salt meaning we get these “better” plants

• This continues until a climax community is achieved

What are the differences in wave height between constructive and destructive waves?

• CONSTRUCTIVE - Lower wave height

• DESTRUCTIVE - Higher wave height

What is Abrasion, Hydraulic action, Corrosion, Attrition?

• Abrasion (corrasion) = Sediment and stones are picked up by waves and wear away at the cliff / headland

• Hydraulic action = Shear force of the waves forcing air at high pressure into cracks in the cliff, over time this weakens the rock and causes the joint to widen

• Corrosion = Weak acids in seawater dissolve the rock particles

• Attrition = As rocks are moved around by the water, they knock into each other, gradually becoming smaller and rounder

What are the factors affecting erosion?

• Wave type

• Wave size

• Lithology

What is the formation of a wave cut platform?

• Powerful destructive waves attack the base of the cliff at high tide

• Hydraulic action and abrasion create a wave-cut notch which overtime increases in side (undercutting)

• Eventually, the overhang created by the undercutting collapses due to weathering and gravity

• The cliff retreats, leaving a wave cut platform that is exposed at low tide

What is the formation of caves, arches, stacks and stumps?

• Joints in the headland are susceptible to erosion by hydraulic action

• Over time, the joints widen, forming a cave that is enlarged by hydraulic action and abrasion

• Eventually, erosion cuts through the headland forming an arch

• The roof of the cave will eventually collapse due to gravity and the lack of support

• This leaves a stack that will overtime be eroded by weathering, abrasion and hydraulic action to form a stump

• Example: Durdle Door on the Dorset coast

What is wave refraction?

• The bending of waves as they approach the coast due to changes in water depth - happens on a small local scale

What sources cause material in the sea to arrive?

• Erosion from cliffs

• Transported by longshore drift along the coastline

• Brought inland from offshore by constructive waves

• Carried to the coastline by a river

What are the four ways material in moved in the water?

• TRACTION - large heavy material is dragged along the sea floor

• SALTATION - smaller material that can be lifted by water, bounces along the river bed

• SUSPENSION - Lighter material carried within the river flow

• SOLUTION - Lighter material carried within the river flow

What is the main factor affecting the direction of sediment transport?

• Direction of wave attack

What is the process of longshore drift?

1) Influenced by the prevailing wind, waves approach the beach at an angle

2) As the waves break, the swash carries material up the beach at the same angle

3) We the swash dies away, the backwash carries the material down the beach at right angles

4) The process repeats, transporting material along the beach in a zig zag movement

5) Offshore currents can contribute to the movement of sediment along or up the beach

What is current and the four types?

• Current = The flow of water in a specific direction which transports sediment

  • Surface currents = formed mainly by wind

  • Deep water currents (thermohaline circulation) = Caused by density differences

  • Tidal currents = Associated with rising and falling tides, the greater the tidal range the greater the strength of the currents

  • Rip currents = Under water currents that occur near the coastline and transport sediment a few metres out to sea

What is tidal range?

• The difference between high and low tide

  • Larger tidal ranges produce stronger tidal currents therefore transporting more sediment

What causes tides?

• The gravitational pull of the sun or moon

When does deposition occur?

• When waves lose energy

• This happens when:

  • The wind slows or changes direction

  • The wave experiences friction, usually with the sea floor as the depth decreases

  • When the coastline changes direction such as a estuary or headland

Where do depositional landforms occur?

• At low energy coastline when the waves do not have enough energy carry large sediment load e.g a beach

How do beaches build up?

1) Beaches build up due to constructive waves

2) They form in sheltered areas such as bays

3) Beach formation is more common in summer when there are fewer destructive waves

How do drift aligned beaches form?

• Longshore drift moves sediment along the beach as waves approach at an angle

• This will often form a spit where the coastline changes direction

How do swash aligned beaches form?

• The energy must be low

• The waves are more parallel to the shore in swash aligned environments so there is little horizontal or lateral movement of sediment

What is the formation of a spit?

• Sediment is transported by waves along the coastline

• When the coastline changes direction, the waves no longer have the energy to carry the sediment and it is deposited

• The build-up of deposited sediment out to sea, often into an estuary, is called a spit

How is a tombolo formed?

• A tombolo is formed when a spit joins the mainland to an island

• Example: Chesil Beach, Dorset

What is a Barrier island?

• A barrier island is a ridge of shingle that runs parallel to the mainland coast

• It acts as a natural barrier, protecting the coastline - open at both ends

What is a sediment budget?

• The sediment budget is the balance between the inputs and outputs of sediment in the system

• Coastal systems should be in a state where the sediment budget is in a state of dynamic equilibrium

• However, human activity and natural changes like climate change can disturb the state of dynamic equilibrium

What are the types of weathering and their processes?

• Mechanical (physical) = When rocks break down, with no chemical changes (wetting and drying, freeze thaw)

• Biological = Rock breaks down due to organic activity (roots of plants, animals)

• Chemical = Rock breaks down due to a chemical reaction (acid rain, carbonation, oxidation)

What is wetting and drying (mechanical weathing)?

• Rocks expand when they are wet and then contract when they are dry

What is the process of salt crystallisation (mechanical weathering)?

1) Water collects in the cracks in the rock when it rains

2) When the sun shines the water evaporates, salt crystals are left behind in the cracks

3) Salt crystals grow over time and create stress on the rock causing it to break up

What is exfoliation / onion skin weathering (mechanical weathering)?

1) When rocks warm up in the day, the rock expands

2) At night, the rock cools and contracts

3) Over time, this causes very thin layers of rock to flake off

What are the different types of chemical weathering?

• Carbonation - As rain is slightly acidic, it reacts with carbonate rocks such as limestone, causing them to dissolve

• Oxidation - When iron minerals in the rock reacts with oxygen in the air to cause rust and breakdown the rock

• Solution - When other salt minerals in the rock are dissolved

What is mass movement?

• The downhill movement of material under the influence of gravity

  • Through flow and runoff caused by heavy rain can also make cliffs more unstable and increase the likelihood of mass movement

  • It includes landslides, slumping and rockfalls

What is the type of mass movement determined by?

• Angle of the slope (steeper slope, faster movement)

• Nature of regolith (weathered material)

• Amount and type of vegetation

• Water

• Type and structure of rock

• Human activity

• Climate

What is soil creep and its process (mass movement)?

• Common in humid climate

• Movement of < 1cm per year

• Process:

  • Soil expands when it freezes, gets wet or is heated by the sun

  • As the soil expands, it lifts at right angles to the slope

  • When the soil shrinks, it falls straight back down

• Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time

What is flow and its process (mass movement)?

• Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year

• Usually happens after the soil has become saturated with a flow of water across the surface

• Vegetation is flattened and carried away with the soil

What is a land slide and it’s process (mass movement)?

• A movement of material all together which remains together until hitting the bottom of a slope

What is a Rock-fall and its process (mass movement)?

• Slopes are steep and movement is rapid

• Rock falls in more resistant rock that has lines of weaknesses → weakened by subaerial processes → block / rock falling

• Happens in dry environments

• Caused by a number of reasons:

  • Extreme weathering

  • Rainfall - softening the surface

  • Earthquakes

  • Hot weather - can dry out soil causing it to shrink and allowing rocks to fall

What is slumping and it’s process (mass movement)?

• Moderate to rapid speed

• A large area of land moves down the slope in one piece

• Because of the way it slumps, it leaves behind a curved indented surface

• top layer gets saturated by rain and therefore moves down the cliff

What distinctive landforms do mass movement create?

• Rotational scar

  • Curved

  • Un-weathered

  • In-vegetated

  • Forms as a result of rotational slumping

• Talus scree slope

  • Fan-shaped mound of material

  • Made of block fall debris which has accumulated at the foot of a cliff

  • Concave profile

• Terraced cliff profile

  • The profile of the cliff is stepped

  • As a result of the lithology or fractures in the rock

What are the causes of eustatic change?

• Changing amounts of ice

  • At end of last ice age (10,000 years ago) global sea levels rose rapidly due to melting ice, creating well known water ways like the English Channel

  • Sea levels may also decrease when ice forms, locking water away in the ice sheets and glaciers

• Thermal expansion

  • Occurs as warm water expands

• Tectonics

  • Magma rising to the surface lifts the crust and reduces the capacity of the oceans, causing sea levels to rise

What are the causes of isostatic change?

• Post-glacial adjustment

  • During a period of glaciation, extremely heavy ice sheets weigh land down

  • When the glacial period ends and the ice melts, the land will rebound to a high level, lowering the sea level

  • This is a process known as isostatic readjustment / recovery

• Accretion

  • Within the sediment cell, there are areas of net deposition causing land to build up

• Subsidence

  • Caused by the lowering of the water table or increased deposition weighing down the sediment

• Tectonics

  • The folding of sedimentary rock

  • Lava and ash from volcanos increase the height of the land relative to the sea level

How much have global sea levels risen since the Industrial Revolution?

• About 235mm

How much does the IPCC predict that sea levels will rise by 2100?

• Between 0.26 and 0.77mm higher than they are now

How many people live on high-risk coasts and what % of the world’s cities are coastal?

• More than 1 billion people live on high risk coasts

• 75% of the worlds cities are coastal

What are the human factors affecting coastal recession?

• DREDGING

  • The removal of sediment from rivers or the sea

  • This impacts the amount of sediment being deposited at the coast

• DAMS

  • The construction of dams, traps river sediment behind the dam wall

  • Like dredging, this starves the coast of sediment

  • The reduction of sediment supplied to the coast due to dams and dreading leads to greater coastal erosion because:

    • Beaches decrease in size as they are not supplied with sediment

    • Destructive waves have more impact by increasing the rate of coastal erosion

What is onshore and offshore wind?

• Onshore = Wind which is blowing from over the sea / water towards the land

• Offshore = Wind blowing from the land out to sea - leads to calm conditions

What is prevailing wind?

• Wind that comes from one direction - in most directions

Examples of low and high energy coastlines?

• High = Atlantic coasts of Norway

• Low = Venice lagoon

What is tidal range?

• The difference in height between high and low tide

What are anticyclones and depressions?

• Anticyclones = High pressure weather system

• Depression = Low pressure weather system

What are the local factors increasing coastal flood risk?

• Height of land

  • Low lying areas are more vulnerable to rising sea levels and storm surges

  • Storm surges and spring tides lead to water flooding areas of the back-shore and beyond

• Degree of subsistence

  • When the ground sinks - This may be due to over abstraction of water and the ground therefore sinking to fill the gap of the water removed

  • Clearing land for agriculture and ground water abstraction increases the risk of subsidence

  • Building of settlements, along with the weight of the buildings increases the risk of subsidence

• Vegetation removal

  • Vegetation traps sediment which helps to increase the land height - The higher the land, the lower the chance of floods

  • Vegetation also reduces the impact of waves and erosion because it absorbs energy - therefore less vegetation increases the risk of flood

What is a storm surge?

• Storm surge = A temporary rise in sea level caused by a storm / tropical cyclone, primarily driven by strong winds, pushing water towards the coastline

What are storm surges caused by?

• Depression (low pressure) leading to storm events

• Tropical cyclones

What is a tropical cyclone, how is it formed, where, and what weather do they bring?

• A tropical cyclone is an area of very low air pressure

• Formed by warm, moist air rising from the ocean surface, forming cumulonimbus clouds, which rotate around a central eye

• They form in the zone between 5 - 30° north and south of the equator, in areas where sea temperatures are 27°C or above

• Tropical cyclones bring heavy rain and strong winds

• When wind speeds reach 39mph, it is categorised as a tropical storm, when they reach 74mph it is a tropical cyclone

What are the short term impacts of storm surges?

• Deaths and injuries

• Homes destroyed leading to homelessness

• Increase in water borne diseases

• Destruction of infrastructure

• Businesses destroyed - leading to loss of employment and decrease in GDP

• Loss of power

• Loss of agricultural land

• Destruction of crops and livestock

What are the two main factors increasing flood risk?

• Global sea level rise - due to warming oceans and melting ice sheets and glaciers

• Increased frequency and magnitude of storms

How would a 50cm sea level rise effect the world?

• Impact 800 million people in the world

• In the UK, 200km of coastal flood defences would be vulnerable; leaving £120 billion worth of infrastructure and resources at risk of flooding

• Coastal flooding events would become more frequent

What are the economic impacts of coastal recession and flooding?

HOUSING

• Cost of land

• Repairing / rebuilding homes

BUSINESSES

• Destruction and damage to businesses leads to the loss of $billions in profits

• The cost of rebuilding businesses

AGRICULTURAL LAND

• Loss of productive land can lead to food shortages and loss of income from crop and livestock sales

INFRASTRUCTURE, ROADS, POWER, WATER, COMMUNICATION

• Roads, power stations, power lines, water and energy are all costly to rebuild and repair after flooding

What are the social impacts of coastal recession and flooding?

RELOCATION

• Increasing numbers of properties will be at risk forcing people to relocate their homes

LOSS OF LIVELIHOOD

• Income for farmers lost due to loss of livestock and flooding of crops

• Loss of jobs when businesses are affected

AMENITY VALUE (something that has worth due to people’s appreciation)

• Large areas of land with amenity value are coastal and at risk from coastal flooding

How much does an acre of farmland cost?

• Between £12,000 and £50,000

What is an environmental refugee?

• A person forced to move by environmental changes e.g coastal flooding

• Environmental refugees will be a global problem in all countries regardless of levels of development

What is hard and soft engineering?

• Hard engineering - The construction of structures designed to absorb the energy of the waves, usually made out of concrete

• Soft engineering - Works with natural processes and material

What is cost benefit analysis (CBA)?

• A report that is used to evaluate whether an engineering project is worth undertaking by comparing its total costs with its expected benefits

  • Some areas are left with no protection because the costs are deemed to outweigh the benefits

Who is at the most risk from sea level rise?

• Low lying island nations / small island nations

• Such as Tuvalu, the Marshall Islands and Seyshells

What issues do small / low lying island nations face due to sea level rise?

The issues they face include:

• Loss of land and lack of money for coastal defences

• Coral reef bleaching which reduces the natural defences against storm surges

• Salt water encroachment reduces freshwater supply

• Loss of tourism

• Limited space for relocation - in the Maldives they are building an artificial island for relocating some of the population

How do conflicts occur as a result of sustainable management?

• Farmers may lose productive land due to managed retreat or do-nothing policies because their land has less value than that in towns

• People may lose their homes and have to relocate in areas where the cost-benefit analysis decides the areas cannot be protected

What is the Integrated coastal zone management (ICZM)?

• The coordinated planning and management of coastal areas to ensure their long term sustainability

• The shoreline management plans in the UK are a form of ICZM

• should consider all stakeholders of the coastline when making management decisions → e.g. residents, local council / government, farmers (agriculture)

• e.g. the manhood peninsula → includes managed realignment, coastal defences at west wittering beach / east head spit