Coasts Flashcards
Two types of waves
Destructive
Storm conditions, 5-6m high. Weak swash and strong backwash. Lots of erosion, with high frequency.
Constructive
calm weather, 1m high, strong swash and weak backwash. Limited erosion, involved with the deposition and transporting of materials.
What determines wave size
Fetch, wind strength, how long the wind has blown for
How do waves shape the coastline
Erosion, transportation & deposition.
Name the four type of water erosion
Hydraulic action
Abrasion
Attrition
Corrosion
Hydraulic action
Water crashes against cliffs, air trapped and compressed in cracks. Air expands weakening the cracks and breaking pieces off
Abrasion
Process of waves hurling materials it is carrying, so the cliff face weakens and erodes
attrition
Rock fragments collide into smaller ones fo form smaller and smoother pebbles
Corrosion (solution)
Occurs when the wave develops a slight acidity so soft rocks, particularly CaCO3 rocks i.e limestone will dissolve in the water
Longshore drift
- Wave comes up to the shore at an angle, driven by the prevailing wind. The waves carry sediments
- Swash moves sediments up the beach at the angle of the prevailing wind
- Backwash is perpendicular to the shore
- Net result is that material is moved in the direction of the prevailing wind
Groynes
Wooden or concrete barriers at right angles to the beach to prevent excessive longshore drift
Sub-aerial processes
Land-based processes altering the shape of the coastline
Two main types of sub-aerial processes
Weathering and mass movements
Mechanical weathering
Fracture and breakdown of coastal rocks into fragments, either by:
Freeze-thaw
when temperature fluctuates above and below 0 then the water can go into the cracks, freeze, melt and break the rock. it keeps expanding and breaking the rock until the rock is destroyed
Hydration
Clay-rich rock will expand when wet and compress when dry. This causes cracks
Wetting and drying
The seawater hitting rocks in intertidal zones will slowly erode it
Biological weathering
Weathering caused by plants animals and microorganisms. Eg growing plant roots, which exert lots of pressure on the rock.
Chemical weathering
Weakening and decomposition of rocks, when they come into contact with chemicals. When water mixed with carbon it forms carbonic acid, and it causes carbonation. Also acid rain and oxidation
Mass movement
Large scale solar removal of material because of gravity and high water content. The main two are slumping and sliding
Slumping
Waves erode the base of the cliff surface, increasing the weight while reducing friction between material. So then it slumps vertically
Sliding
landslides often caused by lots of rain or extreme sea level rise
Geology
Collection of rock types
Lithology
The physical characteristics of particular rocks
Discordant geology
Alternating hard and soft rock perpendicular to the coast, leading to different levels of erosion
Hard rocks vs soft rocks comparison
Shape of cliffs:
Hard: high, steep
Soft: lower, less steep
Cliff faces:
Hard: bare rock, rugged
Soft: smooth (because of slumping)
Foot of cliff:
Hard: boulders, rocks
Soft: few rocks, sand and mud
Land uplift
Retreating sea levels, creates relict cliffs & raised beaches
How do headlands and bays form?
Discordant geology, soft rock erodes more. As waves approach the coastline they refract and converge onto the headlands causing intense erosion. The bays are therefore sheltered, and waves reaching them are low energy and sediments are deposited to form beaches.
Caves, arches, stacks and stumps formation
Waves force their way into cracks causing a cave to form by hydraulic action
once cave formed - further erosion into headland, eventually eroding all the way through- natural arch - eventually collapses under its own weight as arch gets widened by sea - forms stack
Stack is then further eroded at the base by the force of the waves and will eventually collapse to form a stump
Where is erosion mainly happening
at the base of the cliff, intertidal zone/wave attack zone, known as undercutting, forming an overhang which will eventually collapse.
Wave-cut platform characteristics
hard rock, gently sloping, base of the cliff.
How is a wave-cut platform formed
erosion, hydraulic action and abrasion, wave-cut notch is formed.
Through undercutting an overhang is formed. The cave-like feature at the bottom of the cliff is known as the wave-cut notch. It then collapses and over time the part of cliff below the wave attack zone which has less erosion stays as the cliff retreats inland so a gently sloping base of rock below sea is formed
Wave-cut notch
The cave-like feature at the bottom of the cliff
Beaches
Accumulation of sand and shingle, caused by deposition. Often formed in bays. Erosion is limited, and material is moved by longshore drift.
How is a spit formed (and one example)
- Sudden change in coastline shape/direction
- longshore drift has momentum, so continues to transport and deposit material at sea
- over time sediments build up creating a sandy ridge outcrop (spit) on the coast
- salt marshes form behind spits as these waters are low energy and stagnant
5 spits often become curved due to secondary prevailing wind or the impact of cross-currents/storms
Spits at a river estuary never full cover the mouth of the river as the river flow erodes the material too fast
Example:
Spurn Head, Holderness Coast
how is a bar formed
- spits become bars when the sandy ridge outcrop fully blocks off a bay
- when a bar blocks off a bay, the body of water behind the bar is called a lagoon
how is a tombolo formed (and two examples)
- Tombolo forms when the spit link the mainland to a smaller land mass (a little bridge of sand)
Examples:
Trafalgar, Spain
Michael’s mount UK
berms
gentle ridges that form around the high tide mark where material has been deposited at the peak of a wave swash
cusps
sometimes form in the foreshore, semicircular ridges that form due to the combined impact of swash and backwash action, and when the beach possesses a range of coarser and finer material
ripples
Small ondulations on a beach caused by wave action
chemical weathering examples
rainwater is slightly acidic, so some rocks will dissolve in the water, if iron it will oxidise
biological weathering examples
plants and animals act on a cliff to break if down, e.g tree roots, bunny holes etc..
sediment cell
area of the coast where there is erosion and then deposition of the sediments from that erosion, and sediment stays in that area
sand dune example
Gibraltar point
halophyte
salt tolerant plant
xerophyte
drought resistant plant
How do sand dunes form
low tide the beach dries out, so onshore wind blows some sand and some obstacles will encourage sand deposition. Over time these sediments build up, and a small sand dune forms, the embryo dune
over time more layers of sand dunes are formed
embryo dune
first stage of a sand dune formation, small dune which has no stable soil and almost no plants rooted
Foredune
The first dune where sand really starts to build up and become larger, still no soil
yellow dune
higher sand dune, 10metres after the embryo dunes, marram grass.
A bit more biodiversity
grey dunes
maybe 50metres from the first embryo dune
not necessarily halophytes and xerophytes, real soil is now formed in mixture with sand, some more plants here e.g creeping willow and fescue
What increases and decreases as distance from the shore increases
salinity decreases
wind speed decreases
vegetation difference increases
hummus increases
vegetation height increases
dune heath
the climax of sand dunes
lots more hummus and organic matter in heathland, including trees and animals here, very sheltered by previous dunes, may even have some rivers flowing through after rain
sand dune succession (Psammosere succession)
Embryo dune - fore dune - yellow dune - grey dune - dune heath/ slacks
3 factors needed for sand dunes to form
wide beach and plentiful sediment supply
Strong onshore prevailing wind from the sea to the shore
an obstacle to encourage deposition
Salt marshes
coastal ecosystem found between land and open salt water or brackish water that is regularly flooded by the tides
Salt marshes formation
mud and silt are deposited along a sheltered part of the coastline e.g a spit. over time the mud breaks the surface to form mudflats. The first plant is usually cordgrass, aka pioneer plants
Due to sediment accumulation it gets covered less by the tide, and salt is also lower, so more plants can start growing, known as the second generation. more plants bigger and higher will grow, eventually forming trees (Carr woodland)
why are salt marshes important
they get rid of a lot of carbon which they can store, also shelter coastline from flooding etc.
Low marsh and mudflats features
permanently flooded or flooded twice per day
high salinity in water, soil
harsh conditions, always changing
only halophytic plant types can survive
High Marsh and upper marshes features
rarely flooded, only in storms
low salt content
more constant conditions
more vegetation variety and biodiversity, less resistant and less salt-tolerant
Carr woodland
salt marsh climax vegetation, trees e.g willow and alder
coral reef biodiversity
even though it covers less than 1% of ocean floor, roughly 25% of all marine biodiversity depends on it, up to 2mil species
What are coral reefs made up of
little animals called polyps, which secrete CaCO3 as its exoskeleton (limestone). They live in a symbiotic relationship with algae zooxanthellae
algae and polyps symbiotic relationship
Polyps:
give the algae somewhere to live, protection
Algae:
exchange inorganic nitrogen for amino acids, gives corals its colour because of the photosynthesis it carries out
Coral reef distribution limiting factors
- water must be warm (18-25C). shallow water therefore because it can’t be warm if the water is too deep
- shallow water, because water cannot be too cold and also because enough sunlight reaches the algae for photosynthesis
- salinity, only saltwater, so not found in areas with freshwater, e.g Amazon estuary
- clean water, without much sediment (would block sunlight too), so further away from industrialised places. areas with mangroves on the coast
- wave action, a bit is useful because it generates oxygen, but too much would damage
- air exposure, if exposed to the air for too long they would die
coral reefs economic successes for countries
feed 30-40mil people every year
more than 150mil people visit places with coral reefs
generate $30bln revenue per year
Threats to coral reefs
effect of tourism
effect of pollution
effect of deforestation and agriculture
Effect of overfishing
Effect of climate change (too hot)
Effect of tourism on coral reefs
corals easily stressed by human activities
any contact with humans would kill the coral immediately
if too many tourists there can be huge effects on the reefs
tourists try to illegally take corals and sell them, sometimes corals are used for sunscreen
effect of pollution on coral reefs
development leads to water pollution
air pollution increases temperature leading to coral bleaching. The symbiotic relationship between algae and coral ends so they both die
effect of deforestation and agriculture on coral reefs
deforestation makes soil less strong causing landslides
fertilisers cause eutrophication
Mangroves distribution
32N-38S, in sheltered, intertidal areas where there is lots of annual rainfall
mangrove ecosystem features
nursery space for fish and crustaceans, trap sediments, land builders. Mangrove timber provides fuel and materials
protection from tsunamis, storm-surges etc..
Mangrove 100m wide reduces destruction force by 90% Estimated 186$mil per year
why do coral reefs depend on mangrove forests
big carbon sequestration (taking from water)
mangroves filter the water for the reefs
Mangrove Forest Limiting Factors
- average temperature above 20C. seasonal temperature range under 5C. Not too good with the cold
- they need fine-grained substrate or sediment.
- the shores need to be free of strong wave action
- they need salt water
Different coastal stakeholders
Local residents
Farmers
Employers
Tourists
Environment Agency
Most common stakeholder debate
whether the coastline should be conserved or developed.
Coastal flooding causes
Storm surges – either due to an extreme high tide and low pressure system with an onshore wind, or due to a hurricane.
Tsunamis – as a result of an undersea earthquake
Climate change – isostatic readjustment, eustatic change, and thermal expansion.
4 types of coastal management
• Hold the line
• Advance the line
• Managed retreat
• Do nothing
Two types of hold/ advance the line methods are (+ examples)
• Hard engineering (groynes, revetments, sea walls, gabions, rip rap)
• Soft engineering (beach replenishment, cliff regrading, ecosystem rehabilitation and revegetation, managed retreat)
Factors which affect what coastal management type to choose
the economic value of the resources that would be protected, e.g. land, homes etc
engineering solutions - it might not be possible to ‘hold the line’ for moving landforms such as spits, or unstable cliffs
cultural and ecological value of land - historic sites and areas of unusual diversity
community pressure - local campaigns to protect the region
social value of communities - long-standing, historic communities
Case Study - The Holderness Coast key facts and processes occurring
It stretches from Flamborough Head in the north down to Spurn Head, where it meets the Humber Estuary in the south
It is the fastest-eroding coastline in Europe at 2 m per year
It is made of soft boulder clay and chalk
The coastline has naturally narrow beaches, which give less protection from erosion as wave power is not reduced
Longshore drift is the dominant process due to North Sea waves
Waves along the coastline have a long fetch (travel long distances), which increases wave energy
Case Study - The Holderness Coast management (remember for 3 important ones)
Bridlington is protected by a 4.7 km long sea wall
Withernsea has a sea wall, groynes, riprap and beach nourishment to widen the beach and reduce wave energy
Hornsea’s cliffs are formed from soft boulder clay
As a popular tourist destination, management is aimed at protecting hotels, and arcades and creating a sandy beach
Hornsea has spent money on repairing its wooden groynes at a cost of £5.2 million
It also has a concrete seawall
Approximately, 2.25% of all UK gas comes through the gas terminal at Easington and £4.5 million was spent on riprap, but the scheme protects the terminal and not the village
Case Study - The Holderness Coast conflicts
Due to the use of groynes at Mappleton, sediment has been prevented from moving south, which has increased erosion at Great Cowden
Erosion has destroyed farms, along with the loss of 100 chalets at the Golden Sands Holiday Park
Some sea defences negatively impact tourism and reduce the amount of money coming into the area
Overall, maintaining coastal defences is expensive and the cost may be too great to continue defending an area that is eroding quickly and will continue to erode
Barrier reef
Wide, deep lagoons below at depths at which polyps can live separate these, which are between 500 m and several kilometres from the coast
