- Created by: holly_u
- Created on: 04-04-18 15:55
The Littoral zone
Coast= an area where interaction of the sea and land processes occur. Between 60km on the land and 200 miles to sea
Factors affecting the coast: biological (plants), geological (rock type), meteoroligical (weather), hydrological (water), geomorphological (landforms) and human factors.
The Littoral Zone- area exposed between low and high tide mark
Backshore- only affected when very high tide
Foreshore- wave processes e.g longshore drift
Nearshore- human activities e.g fishing
Offshore- deepest water
3 types of coast:
Cliffed= abrupt transition from land to sea. At low tide wave-cut platforms exposed
Sandy= High tide beach is inundated (covered). Slow transition from land to sea
Estuarine= mouths of rivers. Mud flats and salt marshes. Gradual transition land to sea
Sea level change
Submergent- coasts are falling to sea level change
Emergent- coasts are rising to sea level change
High energy- exposed coasts, high wind speed and high fetch
Low energy- sheltered coasts, low wind speed and limited fetch
Primary- land based processes e.g deposition from land forms
Secondary- marine processes e.g marine deposition
Tidal range (distance between high and low tide)
High and Low Energy Coastlines
HIGH ENERGY- Atlantic Coast, Scotland
High wind speed
Erosion- wave-cut platforms
LOW ENERGY- East Anglian Coast
Low wind speed
Deposition- spits, bars
Lithology- Geological structure
Deformation (folding- anticline and sinclines)
Faulting (major fractures and weaknesses between the layers)
Strata (layers of rock)
Horizontal dip= layers horizontal (flat) to ground, easily eroded
Seaward dip, low angle= overhanging rock, vulnerable to rock falls
Seaward dip, high angle= one layer facing the sea, vulnerable to rock slides
Landward dip= dips towards land, very stable
Concordant and Discordant coasts
e.g Lulworth Cove, Dorset
Layers of rock are parallel to coastline. Hard rock is eroded first creating a small entrance then softer rock eroded quickly creating large 'body'.
e.g Swanage Bay, Dorset
Layers of rock are perpendicular to coastline. Soft rock erodes quicker than hard rock creating bays and hard rock is left as headlands. Creates an uneven coastline.
HAFF Coastline (type of concordant coastline)
e.g along the Baltic sea
Ridges of sediment run parallel to coast offshore creating lagoons.
Rates of Erosion
How fast a coastline moves inland is affected by lithology and rock type.
Most vulnerable rock at a coast is unconsolidated material (sand, gravel)
Igneous- formed by hardened volcanic lava. SLOW due to crystalline erosion rate e.g granite
Sedimentary- compressed layers of sediment under the sea. FAST erosion e.g limestone
Metamorphic- heat and pressure of rock causing to change form. SLOW heavily fractured erosion e.g slate
Permeable- water can flow through meaning more erosion e.g limestone
Impermable- water cannot flow through meaning less erosion e.g clay
HAPPISBURGH coastal erosion
Rock made of soft materials and horizontal strata. Layer cake sequence (which are permeable)
Cliffs 6-10m high
Over time erosion of cliffs has increased causing settlements close to cliff to be threatened
Coastal defences have been put in place but are not inh dis-repair
Vegetation stabilises sediment by:
Roots bind sediment together
Plants act as a protective layer so surface is not exposed
Protect sediment from wind erosion
Plants can be:
Halophytes- can tolerate high levels of salt water e.g on salt marshes
Xerophytes- can tolerate dry conditions e.g on sand dunes
Plant succession= the changing structure of a plant community over time
Pioneer species are the first stage
Climatic climax community is end result
Psammosere= sand dune ecosystem
Halosere= salt marsh ecosystem
Psammosere (Sand Dunes)
1) an obstacle such as a stick traps sand
2) Pioneer plants stabilise (Halophytes) the sand and create embryo dunes. Environment becomes less salty.
3) New plants grow forming Foredune. Then a yellow dune. Marram grass with 3m long roots (Xerophyte) and waxy leaves able to cope with being sand blasted.
4) More nutrients and humus (dead plants) create a grey dune, which has grown in size.
5) Eventually woodland grows on back .dunes
Dune slacks= dips in dunes where humus and water collects.
If a foredune grows enough it produces a dune ridge preventing further deposition of sand by blocking the wind. Also if strong wind blows away sediment until it reaches the water table (damp sand) it's less easily blown away.
Halosere (Salt Marshes)
Estuaries good for salt marshes:
- Rivers provide supply of sediment
Things affecting salt marshes:
- Sea level change
- Human activity e.g farming
1) mud and silt collect behind spits between low and high tide mark
2) Halophytes (salt tolerant) trap mud
3) Roots stabilise vegetation
4) Height of salt marsh increases so less erosion. Rarely sub-merged
Long wave length
6-8 per minute
Short wave length
10-14 per minute
Waves and Tides
Waves= caused by the wind blowing over the surface of the water creating ripples which grow in size
- strength of wind (stronger= bigger waves)
- duration wind flows for (longer= stronger)
- water depth (shallower= waves grow in height)
- water fetch (distance wind has blown over)
Tides= the alternate rise and fall of the sea due to gravitational pull of the moon and sun
The area of water in front of the moon and sun is gravitationally pulled creating higher tides. As the earth rotates this changes.
Spring tide= highest of both
Neap tide= lowest of both
Erosion generally occurs when:
Waves are largest, stormy conditions, high tides, waves approaching at 90 degrees
Hydraulic Action= air becomes trapped from the force of the waves crashing against the rock face which causes cracks, so more air is trapped. Heavily jointed sedimentary rocks affected.
Abrasion= Sediment in the waves is thrown against the cliff face chipping off material
Attrition= Already eroded sediment in the waves collides with itself, chipping away particles
Solution= alkaline rock e.g limestone is dissolved by slightly acidic water
Caves, Arches, Stacks and Stumps
A weakness in the rock causes a crack to form, hydraulic actions causes this to grow in size until a small cave forms. The force of the water and sediment in it (Abrasion) erodes the cave all the way through forming an arch. Sub-aerial processes such as weather erodes the unstable material above the arch and eventually it falls through creating a stack. The sub-aerial processes are continued until a stump is left.
Headlands and Bays
Soft rock is eroded quickly creating an inland called a bay and hard, more resistant rock erodes slower creating a headland.
Wave-cut notch and platform
At a steep rock face between the low and high tide mark a weakness in the rock grows due to erosion, this is a wave-cut notch. It erodes inland until the material above it becomes unstable and falls into the water creating a narrow flat area at the base of the cliff, wave-cut platform.
A joint between a sea cave and land allows air to pass through it when a wave occurs it creates an impressive spurt of water.
Sediment is transported along the coast by currents (flows of water in a direction driven by the wind, temperature of water salinity (salt content)
The movement is called longshore drift. A prevailing wind causes water to enter the beach at and angle, but it retreats at 90 degrees causing water & sediment to travel down current.
Traction- large boulders roll along the sea bed pushed by waves and currents
Saltation- smaller rocks bounce along the sea bed
Suspension- light material/ particles float in the current
Solution- alkaline material is dissolved in the water.
Longshore drift causes movement down a beach, however when there's a change in direction the movement carries on into the sea. It loses energy and deposits material creating a spit.
e.g SPURN HEAD, HOLDERNESS
The process of longshore drift continues after a change in direction of the coast connecting to areas of land.
Two areas of land are connected creating a lagoon.
Waves hit the sea bed in shallower water, therefore it loses energy and deposits its load away from the coastline.
A bar attaching the mainland to an island
Beach= accumulation of sand and shingle deposited by constructive waves in the nearshore, foreshore and backshore
Sandy beach- gentle gradient from land to sea due to sand being able to be carried further. Sand is compacted
Shingle beach- steep gradient as shingle is heavier and requires more energy to travel further
Waves break at a vertical angle (90 degrees) to coast so lack of longshore drift.
Waves break at an angle to the beach so longshore drift. Associated with spits and bars.
A sediment cell= A closed system with sources, transfers and sinks. It works through dynamic equilibrium as the sources and sinks are naturally balanced.
If equilibrium is disrupted e.g a storm, it returns back to normal over time through negative feedback (good) e.g major erosion during a storm may create an offshore bar reducing wave energy.
Positive feedback (bad) consists of sea level change and human interaction e.g coastal management. This dirsupts the long term dynamic equilibrium of the system.
11 sediment cells along English and Welsh coastline.
Sub-aerial processes- Weathering
weathering is not the same as erosion. weathering is in-situ (no movement)
Types of Weathering:
MECHANICAL- break down of rocks due to an exertion of physical force. dominates cold climates.
e.g Freeze-thaw. Water gets in cracks of rocks and expands when frozen opening the crack
BIOLOGICAL- actions of plants and animals.
e.g Rock boring. Clams/ molluscs bore into rock and secrete chemicals which dissolve it.
CHEMICAL- chemical reaction and generation of new chemical compounds. dominates hot climates
e.g Carbonation. Slow dissolving of Limestone due to acidic rainfall produced a calicum bicarbonate solution
Sub-aerial processes- Mass movement
Mass movement= the downward slope of rock and soil.
Rotational slumping- rain saturates cracks and the base of the cliff gets eroded creating a curved surface. Permeable strata (chalk) sits on top of impermeable (clay). Seaward dip.
Landforms: Terraced cliff profile and rotational scars (unvegetated part of cliff face where rock used to be)
Rock fall- rocks become dislodged by mechanical weathering/ hydraulic action. Very rapid
Landforms: Talus scree slope, which is excess product from cliffs after rock fall at the base of a cliff
Earth/ mud flow- Saturated material flows downwards
Mudslide- Soft rock slides on mass
Rock topple- A steep seaward dip topple the top rock over the rest
Burton Bradstock- rock fall
In 2012 on the Jurassic Coast
Causes: wet weather, erosion at the base of the cliff and sub-aerial processes e.g weathering
Effects: 400 tonnes of material fell in 20 minutes
A 22 year old woman was killed
Sea level change
Short term (day to day change):
- atmospheric pressure. low= increased height
- high and low tides
Long term change:
ISOSTATIC- local rise/fall in land levels
EUSTATIC- global rise/fall in sea levels
Emergent coast (sea level drops)
Isostatic= ice sheets locked on land causing global sea levels to fall
Eustatic= ice sheets melt and land slowly rebounds (post glacial isostatic adjustment) Scotland
Submergent coast (sea level rises)
Isostatic= land sinks due to accretion (deposition of sediment)
Eustatic= ice melts causing sea levels to rise globally
Emergent & Submergent coasts
Raised beach- tectonic uplift causes the beach to be above sea level. erosion is not occurring
Fossil cliff- heavily vegetated slope often above a raised beach. no erosion
Fjord- U-shaped cross profile. Very deep flooded glacial valleys
Dalmatian coast- Valleys are flooded by rise in sea levels so tops remain e.g Dalmatia coasta, Croatia
Ria- River valley tree like structure flooded by rise in sea levels
Contemporary Sea Level Change
- Currently rising at 2mm per year
- 60% people are within 60km of the coast
- Effects: Cliff and beach erosion, storm surges, salinisation (salt contamination) of farmland, salinisation of water cupplies, destruction of habitats
- Environmental refugees e.g in the Maldives
- Coastal cities e.g Miami under threat
- Major roads and rail links affecting in UK
Sea Level change is difficult to predict:
- Thermal expansion depends on global temperatures
- Melting of glaciers and ice sheets will increase levels but unsure when
Coastal Retreat (erosion)
Factors increasing erosion: long fetch, high energy waves, stormy conditions, weak cliffs, soft geology, longshore drift, removal of sediment, coastal management
-soft geology- layer cake sequence
-coastal defences, now decaying (introduced after 1953 floods which killed 307). Happisburgh between two hard sea defences.
- destructive waves, especially in bad weather
- coastal defences in some areas e.g Mappleton
- mass movement
- variations in cliff height
- boulder clay cliffs
Causes of coastal flooding: Storm surges, Rising sea levels (human contriubutions) rising 2mm per year, Tsunamis e.g Tohoku 2011, Stormy weather conditions in combination with river estuaries joining.
HIC UK, 2013 Storm Surge:
Causes= wind and water funnelled from the North Sea, high air pressure, bad weather conditions.
Social- 2 deaths, 100,000 people in Scotland left with no electricity
Economic- £100 million insurance, 2500 homes flooded
Environmental- coastal erosion
LIC Bangladesh Storm Surge, 2007
Causes: Cyclone Sidr and intense rainfall, low lying land, large population, deforestation of mangroves, running water from Ganges
Effects: 3000 deaths, 7 million homeless, paddy fields destroyed, disease e.g cholera, traumatised people.
Islands at risk- environmental refugees
If 50cm rise, 77% of the land would be inundated. Environmental refugees, no homes. Water supplies contaminated, livelihoods ruined, tourist industry destroyed.
- Capital- Male has a 3m Sea Wall
- New island contructed built from sediment dredged from sea bed. 1m higher than Male
Management Approaches- Hard
Do Nothing- no interference
Hold the line- keep the same
Extend the line- more techniques to reduce
Retreat the line- surrender. Ask people to move away
HARD ENGINEERING stopping physical processes such as erosion
+ people feel protected, it lasts a long time
- costs are high, eye-sores, has affects in other places, prone to failure
Sea Wall- phsyical barrier dissipating wave energy. + effective - eye-sore
Rip-rap- large rocks dissipating wave energy + gives confidence - eye sore
Revetments- large interlocking permable structures + cheap - not as effective
Groynes- wooden barriers on beaches to stop longshore drift + effective - stops supply of sediment down coast
Management Approaches- Soft
works with natural processes to reduce coastal erosion and flood threat.
Beach nourishment- replenishing sediment lost by erosion and to enlarge beaches for tourism. Normally trucks deposit the sediment. + expensive £2 million per km - it's ongoing as longshore drift continues naturally.
Dune stabilisation- processes to reduce erosion as dunes act as barriers too erosion and habitats to plants and animals. Techniques include: dune fencing, marram grass replanting, wooden boards to walk on. + low costs especially long-ter,
Cliff stabilisation- cliffs covered in vegetation to protect from erosion and drainage system to reduce waterlogging. + cheap - not effective long-term
Managed retreat- areas along the coast allowed to erode and flood naturally to re-build ecosystems + cheap - people have to be recompensated if they have to move
Hard and soft case studies
HARD - Deltawerken, Netherlands
Built after 1953 North Sea Floods.
Needed because: low-lying land, to maintain safe access to North Sea from Dutch Ports
Flood defences were built. Dams and Sluice gates like Thames Estuary between islands.
+ confidence to residents, shuts sea out
- expensive ($5 billion)
SOFT Essex marshes, Abbotts Hall farm
Allowed to flood naturally
+ allows habitats to grow, improves water quality and cheap
- no confidence for people
Communities have to adapt within the wider coastal zone.
Ways: education on why we need to adapt, managing natural resources e.g fish, creating alternative livelihoods than the sea, adapting to rising sea levels by relocating.
e.g in the Maldives. Education on importance of mangroves and small grants given to islanders to develop sustainble farming as alternative food.
Integrated Coastal Zone Management
The entire coast is managed holistically (whole) including rivers.
Recognises that it must be sustainable.
All stakeholders must work together a Shoreline Management Plans extend across boundaries.
Options: No active intervention, Hold the line, Managed retreat, advance the line.
Considerations: technical feasability, economic value of what to protect, cultural value of land and pressure from communities.
Holderness, East Yorkshire
Hornsea= hold the line. Important historic sites, large habitats for birds, population of 8500
Spurn head= no active intervention. Abandonment of the spit, no longer afford to repair
- families had to move
Mappleton= hold the line. in 1990s sea defences e.g rock groynes and cliff regrading, so in future will be protected.
Cost Benefit Analyis helps decide whether defending coast is worth it.
Controversial because human costs are hard to quantify e.g stress and the value of houses depends on the risk.
Holderness- CBA decided that on undefended areas to have 'no active intervention' and on defended e.g Mappleton and Hornsea to 'hold the line'. Benefits outweigh costs.
Environmental Impact Assessment looks at short-term impacts on environment and long-term impacts of building defences. Using: water quality, water movement, changes to marine plants and animals, air quality etc
Holderness= current protection scheme works well
Winners and Losers
Winners- people who have property saved e.g in Mappleton, habitats conserved
Losers- property lost, business owners where no management taking place, people in LIC cannot afford to claim compensation especially as more vulnerable coastlines in Bangladesh.
Case study: Essex Marshes. No conflict as owners recieved money, water quality improved, income from eco-tourism and habitats enhanced.