Unit 7: Coastal Environments Flashcards
what even is this bro
Coast
The part of the land adjoining or near the sea
Coastline
The boundary of a coast where land meets water
Coastal environments
The landforms and habitats that make up the area
Lithology
Hard rocks like granite and basalt give rugged landscapes (Northern Ireland) whereas soft rocks like sand and gravels produce low, flat landscape (Nile delta)
Geological structure
Concordant coastlines occur where the geological strata lie parallel to the coastline (South Ireland) whereas discordant coastlines occur where the geological strata ate at 90 degrees to the shoreline (South west Ireland)
Processes
Erosional landscapes contain rapidly retreating cliffs (East England) whereas areas of rapid deposition contain many sand dunes and coastal flats (Netherlands)
Human impacts
Some coasts are extensively modified (Florida) whereas others are more natural ( Iceland)
Ecosystem types
Mangrove, coral, sand dune, saltmarsh and rocky shore add further variety to the coastline
Coastal zones
Include a wider area than coasts or coastlines
Spread from 320 km offshore up to 60 km in land beyond political jurisdiction
These areas interact and influence each other through sediment supply, pollution, weather and climate
Dynamic and complex. Can experience rapid changes as inputs and processes on land, sea and the atmosphere mix
Wave generation
Waves result from friction between wind and sea surface
Waves of oscillation
Occurring in the deep ocean sea consisting of forward surges of energy but circulating water particles
Breaker waves
Waves that reach and then break onto the shore
Crest
Highest point on a wave
Trough
Lowest point on a wave
Height
Vertical distance between crest and trough
Wavelength
Horizontal distance between 2 identical points on a wave
Period
Time taken for a wave to travel 1 wavelength
Velocity
Speed of a wave
Frequency
Number of waves that break per second
Steepness
If greater than 1:7, it will break due to wave height / wavelength
Energy
Related to wave height
Small increase in height produces a large energy increase due to square relationship
Energy is released when the wave breaks
Orbit
The shape of a wave either circular or elliptical. Size of orbit decreases with depth
Base
The point at which water movement is no longer influenced by wind. Usually equal to the wavelength of the waves above
Wave height
Indicates the amount of energy a wave has
Determined by wind strength, fetch and depth of sea
Fetch is the distance of open water a wave travels over
The greater the fetch the larger the wave
Swell vs storm waves
Waves can be up to 15m high in the open ocean
When these aves travel long distances form where they were created (generation area) and reach far away shores they are swell waves. Have a lower height and longer wavelength. Will occur no matter what the local weather
Storm waves occur because of more local extreme weather conditions and are characterised by shorter wavelengths, greater heights and higher frequency
Wave shoaling
When wavelengths are reduced and wave height increases as a wave enters shallower water. At this point it is a breaker wave
Spilling breakers
Associated with gentle beach gradients and steep waves. Characterised by a gradual peaking of the wave until the crest becomes unstable causing a gentle spilling forward of the crest
Plunging breakers
Occur on steeper beaches with waves of intermediate steepness. Distinguished by the shoreward face of the wave becoming vertical, curling over and plunging forward and downward as an intact mass of water
Surging breakers
Found on steep beaches with low steepness waves. The front face and crest remain relatively smooth and the wave slides directly up the beach without breaking. A large proportion of the wave energy is reflected at the beach
Waves of translation
Once a wave breaks and travels onshore it is a wave of translation
-Constructive
-Destructive
Both have a swash and backwash
Constructive waves
Tend to occur when wave frequency is low (6-8) per minute especially when these waves advance over a gently shelving sea floor. Have been generated far offshore. The gentle offshore slope creates a gradual increase in friction which will cause a gradual steepening of the wave front. A spilling breaker is formed where water movement is elliptical. As the breaker collapses the powerful swash surges up the gentle gradient. Due to low frequency the backwash has time to return to he sea before the next wave breaks. The swash os not impeded and retains maximum energy
Destructive waves
Are the result of locally generated winds which create waves of high frequency (12-14 per minute). Rapid approach of waves especially if moving onshore up a steady shelving coastline creates a rapid increase in friction and a very steep, plunging breaker where water movement is circular. Due to rapid steepening and curling of wave breaker, the wave energy is transmitted down the beach on breaker collapse accelerated by the steeper gradient so the waves becomes destructive, breaking down beach material
Wave dominated processes and landforms
Shore platforms
Cliffs
Beaches
Splits, tombolos
Deltas
High energy
Tide dominated processes and landforms
Mudflats
Sandflats
Saltmarshes
Mangroves
Deltas
Low energy
Wind dominated processes and landforms
Sand dunes
High energy
Tides
Regular movements in the seas surface caused by the gravitational pull of the moon and sun on the oceans
The moon accounts for most of the pull
Low spring tide
Occur just after a new moon
High spring tide
Occur after a full moon when the sun and moon are aligned
Neap tides
Occurs when the sun and moon are at right angles to the earth
Influences on tide sizes
Size and shape of ocean basins
Characteristics of shoreline
Coriolis force caused by the spinning on the earth
Meteorological conditions
Tides are greatest in bays and funnel shaped coastlines
In the NH flows of water are directed to the right. In the SH to the left
During low pressure systems water will rise by 10 cm of every decrease of 10 millibars of pressure
Tidal range
The difference between high and low tide
This can vary
Classified as
-microtidal ( less than 2m)
-mesotidal (2-4m)
-macrotidal ( over 4m)
Amphidromic point
The place where there is no tidal range. Tides may increase with distance from the point
Tidal range influences on coastal processes
Controls the vertical range of erosion and deposition
Weathering and biological activity is affected by the time between tides
Velocity of tidal currents impact levels of erosion
Tidal bores
A large wave or bore caused by the constriction of the spring tide as it enters a long, narrow, shallow inlet
Rip currents
An intermittent strong surface current flowing seaward from the shore
Can be caused by a combination of tides and the uneven breaking of waves along a shoreline
Once formed they modify the beach creating cusps which makes the current more likely to occur again in the future
Storm surges
An abnormal rise in sea level accompanying a hurricane or intense storm significantly above astronomical tide. Can cause extreme flooding in coasts
Causes of storm surges
Low atmospheric pressure
Strong winds
Wave action
Coastal topography
Tides
Impacts of storm surges
Loss of life
Property damage
Displacement
Environmental damage
Economic costs
Preparation and mitigation of storm surges
Early warning systems
Infrastructure improvements
Community preparedness
Environmental management
Hydraulic action
Occurs as waves break onto cliffs. As they break against the cliff face any air trapped in cracks, joints and bedding planes is put under great pressure. As the wave retreats the pressure is released with explosive force. This is cavitation. Stress weakens the coherence of the rock aiding erosion. Particularly obvious in well bedded and jointed rocks like limestones, sandstones, granite and chalk as well as rocks poorly consolidated like clay and glacial deposits. Also notable during storm wave activity
Abrasion
Where a breaking wave can hurl pebbles and shingle against a coast
Attrition
Occurs as other forms of erosion continue. The eroded material is worn down by attrition explaining the variety of sizes of beach material
Solution
Is a form of chemical erosion. With calcareous rock waves remove material by acidic water. The source of acidity is from organisms. These make the water more acidic especially in rock pools at low tide
Waves affecting rate of erosion (energy)
Wave steepness: Steep destructive waves formed locally have more erosive power than less steep constructive waves
Wave breaking point: Waves breaking at a cliff base cause maximum erosion whereas waves breaking off shore lose energy
Tides affecting rate of erosion (energy)
Neap and spring tides vary the zone of wave attack. Strong tidal currents can scaur estuary channels
Currents affecting rate of erosion (energy)
Longshore and rip currents can move large quantities of material
Winds affecting rate of erosion (energy)
Onshore winds erode rine beach sane to form dunes
Offshore winds may erode dunes and nourish the beach
The longer the fetch the greater the wave energy potential
Sediment supply affecting rate of erosion (material)
Continual supply is necessary for abrasion whereas an oversupply can protect the coast
Beach/rock platform width affecting rate of erosion (material)
Beaches/rock platforms influence wave energy by absorbing waves before they can attack cliffs
Rock resistance affecting rate of erosion (material)
Rock type influences the rate of erosion. Granites are very resistant whereas unconsolidated volcanic ash has little resistance to wave attack. Erosion is rapid where rocks of different resistance overlie one another
Rock structure and dip affecting rate of erosion (material)
Well jointed or faulted rocks are very susceptible to erosion
Horizontal or vertical structures produce steep cliffs
Rocks dipping away from the sea produce gentle cliffs
Offshore topography affecting rate of erosion (slope geometry)
A teep seabed creates higher and steeper waves than one with a gentle gradient
Longshore bars cause waves to break offshore and lose energy
Coastal orientation affecting rate of erosion (slope geometry)
Headlands with vertical cliffs tend to concentrate wave energy by refraction
Degree of exposure to waves influence erosion rates
Direction of fetch affecting rate of erosion (slope geometry)
The longer the fetch the greater the potential for erosion by waves
Formation of wave cut platforms
Wave action works between HWM and LWM so causes undercutting of a cliff face forming a notch and overhang. Breaking waves especially during storms and spring tides can erode the coast above HWM. As the undercutting continues the notch becomes deeper and the overhang more pronounced. The overhand will collapse causing the cliff line to retreat. The base of the cliff will be left behind as a broadening platform often covered with deposited material with the coarsest near the cliff base gradually becoming smaller towards the open sea
Weathering in sub ariel processes
Salt is where sodium and magnesium compounds expand in joints and cracks weakening rock structures
Freeze-thaw is where water freezes expands and degrades jointed rocks
Biological is carried out by molluscs, sponges and sea urchins
Solution is the chemical weathering of calcium by acidic water which occurs in rock pools due to the presence of organisms secreting organic acids
Slaking is where materials disintegrate when exposed to water by hydration cycles
Mass movements like slumping and rockfalls are also important in coasts
Marine transportation and deposition
Sediment sources vary. They include reworked beach deposits, offshore marine deposits, river deposits, glacial deposits, material from cliff mass movements, wind blown deposits and artificial beach nourishment. SOme beaches are formed of volcanic ash and others are formed of shingle. Shingle beaches are of glacial and periglacial deposits. Sandy beaches are the result of river sediment reworked by waves. Others are artificial and use sand from elsewhere
Bedload sediment transport
Grains transported by bedload are moved in continuous contact or discontinuous contact. In traction gains slide or roll. Weak currents may transport sand and strong currents transport pebbles and boulders. In saltation grains hop along the seabed. Moderate currents transport sand and strong transport pebbles
Suspended load sediment transport
Grains carried by turbulent flow and help up by water. Suspension occurs in moderate currents transporting silts or strong transporting sand. Grains transported as wash leads are always in suspension consisting of clay and dissolved material. Deposition is governed by sediment size and shape and may flocculate
Sediment cells
The coastal or littoral cell system examines coastal processes and patterns. It ranges from a single bay to regional. Each littoral cell is self contained where inputs and outputs are balanced. Dynamic equilibrium states that the littoral cell is the result of the inputs and processes operating in it. Change to 1 input has a knock on effect on processes and a change in landform. The balance changes so dynamic equilibrium
Longshore drift
Leads to sediment moving gradually along the shore. The swash moves sediment up the beach in direction of prevailing wind while backwash moves straight down the beach in direction of steepest gradient. Net movement is downdrift
Wave refraction
As a wave front approaches the shore, speed falls. Due to the interaction between onshore wind and direction and trend of coast wave fronts approach obliquely. This causes wavefront to bend and swing to break parallel to the shore. The speed and distortion change of the wavefront is wave refraction. If completed the fronts break parallel to the shore. Due to coastline shapes, refraction is not always totally achieved causing longshore drift which is a major transport of material. Refraction also distributes energy along a coast. Along a complex transverse coast with alternating headlands and bays, wave refraction concentrates wave energy and so erosional activity on headlands while energy is dispersed in bays as deposition. If refraction isn’t complete, longshore drift occurs
Formation of caves
Begins with the erosion of weak points in coastal cliffs often at the base where the sea exerts the most force. Marine erosion involves hydraulic action, abrasion and corrosion. Over time these processes enlarge cracks into small cavities. As erosion continues the cavities grow into substantial recesses or caves. The initial formation if heavily influenced by rock type and structure. Sedimentary rocks with bedding planes and joints are especially susceptible to cave formation
Formation of arches
As caves deepened they can penetrate through a headland. Happens when the sea erodes both sides of a headland where waves developed. Continuous wave action and sub aerial processes like weathering contribute to the enlargement and eventual meeting of opposite caves. Arches are further sculpted by marine and sub aerial erosion. The top of the arch is subjected to weathering like freeze-thaw and biological. This weakens the rock above the arch so is more susceptible to collapse
Formation of stacks
When the arch is too unstable to support its weight it collapses leaving an isolated pillar of rock. Characterised by vertical form, standing alone due to the seas erosive power. Erosion continues on the stack particularly at its base where most wave energy is concentrated. Abrasion and hydraulic action are key eroding the base. This leads to further weakening and collapse of the stack into a smaller more stable form
Formation of stumps
As the base of a stack is undercut by wave action the structure becomes unstable and collapses. The remaining base of the eroded stack only just visible at high tide is a stump. Stumps are the last remnants of the original cliff and are often submerged in high tide
Erosion mechanical
Loose material removed by waves. Energetic waves and microtidal range
Abrasion mechanical
Rock surfaces scoured by waves induced flow with water and sediment. Soft rocks, energetic waves and microtidal range
Hydraulic action mechanical
Wave induced pressure variations in the rock cause and widen cracks. Weak rocks, energetic waves and microtidal range
Physical weathering
Frost action and cycles of wetting and drying cause and widen cracks. Sedimentary rocks in cool regions
Salt weathering
Volumetric growth of crystals widens cracks. Sedimentary rocks in hot and dry regions
Chemical weathering
Removal of rock material through hydrolysis, oxidation, hydration and solution. Sedimentary rocks in hot and wet regions
Water-layer levelling
Physical, salt and chemical work along the edges of rock pools. Sedimentary rocks in areas with high evaporation
Biochemical erosion
Chemical weathering by metabolism products. Limestone in tropical regions
Biophysical erosion
Physical rock removal by animals grazing or boring. Limestone in tropical regions
Rockfalls and toppling
Rocks fall straight down cliff face. Well jointed rocks, undercutting by waves
Slides
Deep-seated failures. Deeply weathered rock, undercutting by rock
Flows
Flow of loose material down slope. Unconsolidated material, undercutting by waves
Types of rocky shore
Sloping shore platforms smoothly transition to seabed. Sub-horizontal shore platforms have larger drop offs with more potholes and pools. Plunging cliffs have no ramp of shore platform and drops straight into the sea. The dip of the bedding will create varying cliff profiles. If the bed dips vertically a sheer cliff face is formed. If the neds dip steeply seaward then steep, shelving cliffs with landslips form. Also takes into account weathering processes
Cliffs
Composite cliffs are made of more than one type of rock. Shape is determined by relative strength and structure of each rock, relative hardness and types of waves involved. Tidal range can also be significant
Geology and rates of erosion
Granite: <0.001m/year
Limestone: 0.01-0.1m/year
Shale: 0.01-0.1m/year
Chalk: 0.1-1m/year
Glacial till: 0.1-10m/year
Volcanic ash: >10m/year
Bevelled cliffs
A sea cliff whose upper part has been trimmed to a relatively low angle by quaternary periglacial processes while the lower part is still steep as a result of recent marine activity
Formation of bevelled cliffs
- Vertical cliff was formed due to marine processes in the last interglacial period when sea levels were higher than now
- During the glacial phase sea levels dropped and periglacial processes like solifluctuation and freeze-thaw affected the former sea cliff forming a bevelled edge
- When sea levels rose again during the interglacial there was renewed wave erosion which removes the debris and steepends the base leaving the upper part at a lower angle
Effect of relationship between resistance on morphology in cliffs
Strong rock of uniform resistance: Cliff retreat is determined by rock strength. Slow for granite. Fast for glacial till
Weaker rock strength and faster cliff retreat: Form of cliff depends on relative position of weaker rock. If at the base, undercutting and collapse may occur. If near the top, subject to sub-aerial processes and wave undercutting
The controlling factors in cliff stability
Strata dipping to inland: Sliding unlikely as movement is landwards
Strata dipping to sea: Movement is seawards and large potential for sliding. Seaward dipping rocks pose greater management challenges
Impermeable over permeable: Limited percolation and more stable cliff
Permeable over impermeable: Water may soak into cliff and slope failure is more likely where water builds up at the junction of 2 rock types
Cliffs at different latitudes
The tallest cliffs are often in temperate regions. This is due to the rapid removal of material at the base by high energy waves while the processes of undercutting actively develops new cliffs. In the tropics there is lower wave energy and the high rates of chemical weathering lends itself to more gentle slopes. In high latitudes there is a dominance of mechanical weathering resulting in a lot of material falling to the base of a cliff
Platform names
Traditionally called wave-cut or abrasion platforms. Now called coastal platforms because of role of other agents of weathering and erosion which is as significant as the wave
Relict platforms
Some marine geomorphologists believe coastal platforms are relict or ancient features. They argue they were created hundreds of thousands of years ago during periods when sea levels were more constant. Sea levels have risen and fallen but are now similar to the period when they were created so are visible during low tide
Associated mechanical and chemical weathering
Frost action: Could speed up weathering in high latitudes creating wider coastal platforms. Salt crystallisation: SOlution weathering could support wave action especially in tidal and splash zones
Associated biological weathering
Marine organisms can accelerate weathering during low tide at the point just above HWM. At night these organisms release more CO2 due to the lack of photosynthesis. The CO2 then combines with cold sea water to create an acidic environment and so increased chemical weathering. Some other organisms can also secrete acids that slowly rot the rock near HWM. Polychaetes and annelids, molluscs and sea urchins bore into the rock especially on chalk and limestone
Beach
An area of sand or small stones near the sea or another area of water. A beach is the accumulation of material deposited between LWM fro the lowest spring tides and the highest point storm waves reach during high tide
Backshore
A cliff or marked by a line of dunes. Above and at HWM there may be a berm or shingle ridge. This is coarse material pushed up the beach by spring tides and arises by storm waves that fling material above wave level. The seaward edge of the berm is scalloped and irregular due to beach cusps. These could be due to the edge of the swash which is often scalloped or due to the action of 2 sets of wavefront approaching the shore obliquely from opposite directions. Cusps are self perpetuating: swash is broken up by cusp projection concentrating energy onto it which removes material. Develop best in areas of high tidal range where waves approach at 90. Spacing is related to wave height and swash strength
Foreshore
Exposed at low tide. Beach material may be undercutting due to ridges (fulls) parallel to water line, pushed up by constructive waves at the height of tides. Separated by troughs (swales). Stretches of sand may compromise the foreshore. In complex coasts sand beaches may only be exposed as small bay head beaches in bays
Offshore
The first material is deposited. Waves touch the seabed so material is disturbed being pushed up as offshore bars when the offshore gradient is shallow
Nearshore development
God beach development is on a lowland coast with a sheltered aspect or trend made of soft rocks which are a good supply of material or where longshore drift supplies material. the closest area of water is nearshore
Littoral deposits
The larger/coarser material fallen from cliffs in the backshore
Neritic deposits
Finer material worn down by attrition usually in offshore
Beach profiles
Beach form is affected by the size, shape and composition of materials, tidal range and wave characteristics. As storm waves are more frequent in winter and swell waves in summer, beaches differ in winter and summer profiles. Constructive waves in summer may build up the beach but destructive waves in winter may change its size and shape. Steep destructive waves reduce beach angle whereas gentle constructive waves increase it. A low gradient produces shallow water which increases wave steepness. Plunging waves are on gentle beaches and surging waves on steeper beaches
Sediment size effect on beach profiles
Affects through percolation rate. Pebbles allow rapid infiltration and percolation so swash and backwash impact is reduced. The reduced backwash does not impede the next swash. If swash is stronger, deposition may occur. Sand produces a lower angle and less percolation. Backwash is greater on a gravel beach. Sediment size varies up a beach. The largest particles (cliff recession) are at the rear. Large, round material on upper beach is supplied during the highest spring tide only. On lower beach, wave action is more frequent, attrition is common and particle size is smaller
Swash aligned coasts
These are beaches and coasts that are oriented parallel to the crests of the prevailing wind. They are closed systems. There is very little longshore drift transportation. The net littoral drift rates are 0. There is little movement of the coarser material found in the backshore. Sediment moves up and down the beach with little lateral transfer
Drift aligned coasts
Coastlines and beaches that are oriented at an angle to the crest of the prevailing waves. Longshore drift is strong and are open systems. They result in the creation of spits, bars, tombolos and cuspate forelands. Sediment is transferred along the coast by longshore drift
Where do spits develop?
Abundant material is available especially shingle and sand
The coastline is irregular
Deposition is increasing by vegetation
There are estuaries and major rivers
Simple and compound spits
Common along indented coast where wave energy is reduced. The long narrow ridges of sand and shingle are joined at one end to the mainland. They become curved as waves undergo refraction. Cross-currents or storm waves may assist the hooked formation. If the curved end is pronounced it is a recurved spit. They grow in the direction of longshore drift and only exist through the continued supply of sediment. Within the curve, water is shallow and an area of mudflat and saltmarsh is exposed at low water. These grow as mud is trapped by marsh vegetation. The saltmarsh is intersected by channels or creeks which contain water even at low tide
The complex morphology of spits
A compound recurved spit has a narrow proximal end and a wide recurved distal end that can enclose a lagoon. The wide end usually consists of dune or beach ridges associated with older shorelines, demonstrating seaward migration
Bars
A bar is a ridge of material connected at both ends to the mainland. Above sea level. If a spit continues to grow lengthwise, it may link two headlands to form a bay bar. These can be composed of shingle or of sand. May also be formed by the onshore movement of material. Bay bars form across estuaries, blocking rivers formed from offshore material driven in by waves
Tombolos
If a ridge of material links an island with mainland the ridge is a tombolo. May also form in the shadow of wave refraction caused by an offshore island
Cuspate forelands
Consist of ridges deposited in a triangular shape and are the result of two spits joining or the combined effects of two sets of regular storm waves. Some are stabilised by vegetation while others migrate down the shoreline downdrift
Offshore bars
Usually composed of coarse sand or shingle. Develop as bars offshore on a gently shelving seabed. Waves feel bottom far offshore. This causes disturbance in the water which leads to deposition forming and offshore bar below sea level. Between the bar and shore, lagoons or sands develop. If the water in the lagoon is calm and fed by rivers, marshes and mudflats can develop. Bars can be moved onshore by storm winds and waves
Barrier beaches
Natural sandy breakwaters that form parallel to a flat coastline. They form only under certain conditions. A gently sloping and low-lying coast unprotected by cliffs faces an ocean. Over the land 15000 years the sea level has risen by 120m as glaciers and ice caps have melted. Wind and waves have formed sand dunes at the edge of a continental shelf. As the rising sea breaks over the dunes this forms lagoons behind the sandridge which divides into islands. Currents parallel to the coast scour sand form barrier beaches and deposit it further up or down the coast to form new islands
Coastal sand dunes
Coastal sand dunes are any accumulation of sand grains shaped into a mound of ridge by the wind under the influence of gravity near the sea
Requirements for sand dune formation
Coastal sand dunes form where a beach is big enough to allow the sand to completely dry out between high tides and where there are onshore winds to blow the dry sand landwards. The sand is then trapped by dune grasses which grow through the accumulating layers of hard, inorganic sand
Beaches at low tide
Sand accumulates on the beach from longshore drift
At low tide, the sand dries out allowing the prevailing winds to move the loose sand up the beach
If there is a large tidal range there is more time for the sand to dry out
Embryo dune
Sand needs and obstruction to accumulate around
Seaweed, dead seabirds, driftwood and other detritus may save this purpose
Fore dune
The first plants to colonise the foredunes are lyme grass, sea couch grass and marram grass
Yellow dunes
Being to show a greater diversity of plants as conditions become more favourable. As plants die and decay, a humus layer builds up and this traps water and nutrients
Mature dunes (grey dunes)
The most mature dunes are several hundred metres from the shore. Left undisturbed these develop a soil which can support shrubs and trees
Sand dune succession
pH decreases at surface of soil
Colour changes yellow to yellow and grey to grey to brown soil colour
Percentage of humus increases from <1% to >40%
Percentage of calcium carbonate decreases from 10% to <0.1%
Age of landform increases to 250+ years old
What is a saltmarsh?
Coastal wetlands that are flooded and drained by the tides. They are boggy and marshy as their soils are composed to deep mud and peat. They are areas of low, flat, poorly drained ground that is subject to daily or occasionally flooding by salt water, covered by a thick layer of grass
Where are saltmarshes found?
Low energy coastlines
Behind spits and barrier islands
In estuaries and harbours
Silt accumulates and on reaching sea level, forms mudbanks. In the tropics and subtropics, saltmarshes are replaced by mangroves
Formation of saltmarshes
A thin layer of mud forms over sand which is covered at each tide. Algae is the only plant growing on the mud
More mud is deposited and the first plants appear. The plants trap more mud and silt. The marsh is covered at each high tide and channels are cut as the water recedes
More plants appear higher up the marsh which accelerates mud accretion. Channels deepen as the marsh surface rises
More plants move into the higher zones and the mud deepend. High tides still flood the marsh but low tides are confined to the creeks which are further eroded as the water runs off
Species found in saltmarshes
Marshes in S England dominated by cordgrass. The first plants like green algase colonise the bare mudflat. Algae traps sediment and provides the conditions for the seeds of marsh samphire and eelgrass
Also provide nurseries for fish, mammals and birds. Glassworts and cordgrass are useful as they increase sediment deposition, provide food for fish and slow the movement of water. They are important for resident and migratory birds like egrets and spoonbills. These use the higher grasses as cover
Benefits of saltmarshes to humans
Acts as carbon sinks and can be very efficient at storing carbon. Carbon is brought in on the tide. When buried in the wet mud, decomposition is slows and the carbon is locked in. When plants die, rather than decomposing, the plants become buried instead of releasing carbon. As sea levels rise, more layers get buried and more blue carob gets locked beneath the surface
Protect shorelines and the people that live there from flooding. During heavy storms they provide a buffer. They reduce the strength of incoming water and preventing the worst of the storm from hitting populated areas further inland
They absorb and clean run off from farms. This filters herbicides, pesticides and heavy metals as well as excess sediment and nutrients
Threats saltmarshes are under
The need for productive farmland has seen them being reclaimed and drained. Also drained to expand cities and build new airports. Rising sea levels and frequent storms put them under pressure. Other human threats include contamination from sewers and runoff, overfishing, pollution and erosion. The interaction of saline water with a saltmarsh also causes the decay of some plants within them
What is a mangrove?
They are trees or shrubs that can survive in harsh conditions such as low oxygen, high salinity, poor nutrients, high winds, wave action and unstable sediment. Mangroves have many essential adaptations that allow them to survive in the conditions they are in
Formation of mangroves
The first trees grow with large pneumatophores are they are completely submerged underwater. The vertical roots begin to trap sediment and organic material from the water. There are more nutrients allowing the trees to grow bigger and they grow buttress roots to allow for more stability in the loose sediment. The larger root system traps more sediment allowing other plants to begin to grow as the sediment is above the HWM. Other coastal species will grow as a climate community behind the mangroves
Species found in mangroves
Birds such as herons, egrets, kingfishers. Many shrimp, molluscs, rabs, worms and bivalves. Juvenile and adult fish species including mudskippers and baby sharks. Mammals like bats, primates, fishing cats and more
Benefits of mangroves to humans
Major carbon stores, traps decaying material and the carbon dioxide it releases as it decays. Provides habitat for juvenile fish as well as many birds, insects and mammals. Act as coastal protection reducing coastal erosion. Protects coral reefs and seagrass from being smothered by sediment from rivers.
Threats mangroves are under
Pollution of coastal areas. Coastal development and over exploitation. Rising sea levels and climate change
Where are mangroves found?
Act as tidal forests between land and sea. Plants are so close to the shoreline that they are submerged in salt water when tides come in. Make up around 75% of tropical coastline. Temperature must be above 24C in the warmest month. Rainfall much be over 1250mm
What is an estuary?
Where one or more freshwater rivers or streams meet the salty ocean. The combination of this seawater and freshwater forms bracksing water. It is a partly enclosed protected coastal body of water. They are indentations in the coastline, often funnel shaped that are infilled with sediment
Formation of estuaries
Sea level rise at rapid pace, drowning river valleys and filling glacial troughs. They became traps for sediment due to the lack of strong waves. When the sea retreats, there is a lower volume of water so the river deposits silt to create mudflats. The intertidal zone undergoes environmental changes in salinity, tides and sediment composition.
Species found in estuaries
Yellowfin bream, sand whiting and various mullets. Crabs, shellfish and migratory birds are also found. Large numbers of wading birds are often attracted to estuaries due to the colonies of worms, molluscs and crustaceans.
Benefits of estuaries to humans
Provides nursing grounds for over 75% of the USAs commercial fish catch and 90% of its recreational fishing. 22/32 largest cities in the world are located on estuaries. Water draining carries sediment, nutrients and pollutants which is filtered out creating cleaner water. Estuarine plants help prevent erosion, floods and stabilise the shoreline
Threats estuaries are under
Urban coastal development, introduction of invasive species, recreation, structures, erosion and sediment build up, increased input from construction sites and dredging. Winds, tidal currents, waves and ice but many of the natural factors are also influenced by global warming
Types of estuary
Coastal plain
Bar-built
Complex
Ria
Tectonic
Fjord
Where are estuaries found?
Found at the mouths of freshwater rivers as this is where the freshwater can mix with the saltwater of the ocean. Shallow bays and inlets also form estuaries or in river delta systems. Common in temperate and tropical regions but not found far inland
Eustatic
Global scale sea level change caused by a change in the volume of water in the ocean store
Isostatic
Local scale sea level change caused by a change in the level of the land relative to the level of the sea
Emergence
The impact of a relative fall in sea level (marine regression)
Submergence
The impact of a rise in relative sea level (marine transgression)
Sea level change stage 1
Climate gets colder
Precipitation falls as snow
Turns to ice
Hydrological cycle slows
Water doesn’t return to sea
Global sea level fall
Eustatic sea level change
Sea level change stage 2
Ice grows
Weight causes land to sink
Affects some coastlines
Isostatic sea level change
Sea level change stage 3
Climate gets warmer
Ice begins to melt
Begins to replenish oceans
Sea level rise
Produces submergent features
Sea level change stage 4
Land areas adjusting to ice removing and melting
Isostatic change
If isostatic is greater than eustatic, emergent features form
Rias
Drowned river valley
Fjords
Created by the drowning of U shaped glacial valleys by the rising sea and/or sinking land
Fjards
A fjard is a large open space of water between groups of islands or mainland in archipelagos. Fjards can be found along sea coasts in freshwater lakes or in rivers
Fjords vs fjards
Fjords are characterised by steep high relief cliffs carved by glacial activity and often have split or branching channels
Fjards are glacial depressions or valleys that have much lower reliefs. They fill with eroded local materials which assist in filling along with rising sea levels since the ice age also contributing. Other low relief landforms like mudflats, saltmarshes and floodplains are only associated with fjards which further characterises the difference
Sea level processes
Initially sea level rise was faster than isostatic uplift. This led to the formation of marine erosion features and beaches which have been exposed by gradual uplift
Marine platforms
Exposed marine platforms are erosional
Fossil cliffs are erosional
Raised beaches are depositional
Main landforms by sea level change
High rock platforms
Older raised beaches
10m raised beach
Post glacial shorelines
Raised shoreline benefits
The land is relatively flat and gently sloping, ideal for building
The sites are close to the sea for fishing
They allow good communication via coastal roads
Raised shore lines and higher platforms are valuable for farming
Characteristics of coral reefs
Calcium carbonate structures made up of reef building stony corals. It is limited to the depth of light penetration so occur in shallow water to depths of 60m. They are also only found where the surrounding waters contain little suspended material. Reef building corals live only in tropical seas where theres temperature, salinity and less turbid water. Reefs occupy <0.25% of marine environments but shelter over 25% of marine life. There are 800 types of rock forming corals. Reefs have up to 2 million species
Development of coral
All reefs begin as polyps which attach to a hard surface in shallow seas where there is enough light for growth. As they grow they exude calcium carbonate forming their skeleton. Then as they die they create reefs. Polyps have zooxanthellae, small algae inside them. There is a symbiotic relationship. The algae get shelter and food and the polyp gets food via photosynthesis
Rate of coral growth
Tropical reefs grow at <2.5-60cm per year making them the largest and oldest systems on earth
Temperature condition for coral growth
None develop where mean annual temperature is <20C. Optimal conditions are 23-25C
Depth condition for coral growth
Most grow in <25m of water so are found on margins of continents
Light condition for coral growth
The photosynthesis algae need light so live in shallow water and supply the coral with 98% of their food
Salinity condition for coral growth
Intolerant of water with salinity <32 psu but can tolerate >42 psu
Sediment condition for coral growth
Clogs feeding structures and cleansing systems and reduces available light
Wave action condition for coral growth
Prefer strong wave action which ensures oxygenated water, removes trapped sediment and supplies plankton. In storm conditions, waves may be too destructive
Air exposure condition for coral growth
Die is exposed for too long so found below low tide mark
Fringing reefs
Fringe the coastline of a landmass. Usually characterised by an outer reef edge capped by an agal ridge, a broad reef flat and a sand floored boat channel close to the shore. Many grow along shores protected by barrier reefs and so are characterised by organisms that are best adapted to low wave energy conditions
Barrier reefs
Occur at greater distances from the shore and are separated from the shore by a wide, deep lagoon. Tend to be broader, wider and more continuous than fringing reefs
Atoll reefs
Rise from submerged volcanic foundations and often support small islands of wave borne detritus. They are indistinguishable in form and species composition from barrier reefs except they are only on submerged oceanic islands
Patch reefs
Small, circular or irregular reefs that rise from the sea floor of lagoons behind barrier reefs or within atolls
Origin of reefs
Simply grow seaward from the land. Barrier reefs and atolls rise from a greater depth far below which coral can grow and many atolls are isolated in deep water. The lagoons between them and the coast are usually 45-100m deep and many km wide
Charles Darwin coral theory
In 1842 he explained the growth of barrier reefs and atolls as a gradual process due to subsidence. He outlines the way coral reefs could grow upwards from submerging fountains. This made it clear that fringing reefs might be succeeded by barrier and then atoll reefs. A fringing reef grows around an island and as the island subsides the coral continues to grow, keeping pace with the subsidence. Coral growth is more vigorous on the outer side of the reef so forms a higher rim whereas the inner part forms a wide and deep lagoon. The inner island becomes submerged. forming a ring of coral that is the atoll
John Murray coral theory
In 1872 he suggested that the base of the reef consisted of a submarine hill or plateau rising from the ocean floor. These reached within 60m of the sea surface and consisted of subsurface volcanic peaks to wave worn stumps. As a fringing reef grows, pounded by breaking waves, masses of coral fragments accumulate on the seaward side, washed there by waves and are cemented into a solid bank
Daly coral theory
Suggested that a rise in sea level may be responsible. A rise occurred in post glacial times due to melting ice sheets. He discovered traces of glaciation in Hawaii. It was much colder and lower in glacial times. All coral would have died and any surfaces would have been eroded. Once conditions warmed up and the sea levels rise, the previous reefs provided a base for the upward growth of coral. This accounts for the narrow, steep sided reefs that comprise most atolls, some with 75 degree slopes
Which coral theory was correct?
Darwin still receives considerable support. Daly was correct in principle but it is now believed that the erosion of old reefs was less rapid then he believed and the time in the glacial stages as not long enough for the formation of platforms. The erosional modification is now believed to be due to sub aerial limestone processes
Value of coral
Have 4000 species of fish and 800 species of reef building corals. They support rich communities through recycling processes and have high specie diversity rates
Seafood: 1/4 of fish catch in LICs providing foor for 1 billion in Asia. Can yield 15 tonnes of seafood/km^2 per year
Medicine: Use array of chemicals
Recreation:Major draw for tourism
Protection: Buffer adjacent shorelines through wave action
Threats to reefs
Global warming, sea level rise, overfishing, destruction of coasts and pollution endanger coral reefs. 58% are at high or medium risk of degradation
Coral bleaching
Reef building corals need warm, clear water. Pollution, sedimentation, climate change and other factors pressure this, halting photosynthesis resulting in the death of the living part of the reef. Zooxanthellae live in the tissue and carry out photosynthesis, providing energy. They give the coral its colour. When conditions are stressful it may leave, leaving the coral in an energy deficit without colour. If recolonised in a certain time ir may recover but if not it will die. Coral bleaching can be caused by 1-2C rises. The shallower the water the greater the potential for bleaching
2004 coral assessment
1/5 of reefs are beyond repair. The percentage of recovering reefs has risen but 70% are still threatened. The destruction is cause for economic and ecological concern especially for the communities that depend on their fish and revenue from tourism. The main causes are climate change, poor land management practices and coastal development
2010 coral assessment
Coral reefs were the first ecosystem to show damage from climate change. Climate change will cause irreversible damage due to
Increasing sea temperatures causing more bleaching. Some species may become extint
Bleaching will become a more frequent event
Increased acidification will reduce calcification causing slower growth, weaker skeletons and dissolution
Increase in storms will result in the destruction of reefs and erosion of coastline.
19% have already been lost and 35% are seriously threatened
2011 coral assessment
60% were under threat from local sources
When thermal stress was added this rose to 75%
By 2050 over 90% will be affected by local and global threats
Coral and people
500 million depend on reefs for food, protection, materials and income. They provide 30 million with their livelihoods. Human will being will be reduced if corals are destroyed. 50% of the population lived on coasts in 2015 putting pressure on coastal resources
Evidence of climate change coral damage
First large scale bleaching was in 1983. The hottest years were 1997, 1998, 2003, 2004 and 2005. Any recovery was reversed by other human pressures
Temperatures have risen in all oceans in the last 40 years
Management coral strategies
Reduce greenhouse gas emissions and develop plants to sequester CO2
Limit damaging human activities to allow coral to recover
Provide assistance to LICs
Develop alternative livelihoods
Introduce local coastal management practices
Improve the management, monitoring and enforcement of regulations
Designate more reefs as marine protected areas to act as reservoirs of biodiversity
Reasons for coral management
Will become extinct if CO2 levels are above 450ppm
Low lying coastal communities will become more vulnerable
Why do coasts need managing?
Human pressure on the fragile coastal environment requires careful management. The management could be short term or long term and sustainable or unsustainable. Any management plan requires a detailed knowledge of coastal processes including sea level prediction, currents, tides and storm frequency. Many coasts are coming under increased human pressure due to population growth and urban development
Shoreline management plans
SMPs are designed to develop sustainable coastal defence schemes. Sections of the coast are divided into littoral cells and plans are drawn up for the use and protection of each zone
Defence options
Do nothing
Maintain existing levels of coastal defences
Improve the coastal defence
Allow the retreat of the coast in selected areas
Coastal management issues
Planning
Coastal protection
Cliff stabilisation and ground movement
Coastal infrastructure
Cost of beaches and public safety
Recreational activities and sport
Beach cleaning
Pollution and oil spills
Offshore dredging
Management of coastal land and property
Main types of coastal defences
Hard engineering
Soft engineering
Managed natural retreat
Hard engineering
When structures are built to either stop flooding, reduce erosion or both. These are expensive so are only used where the land is deemed economically valuable
Soft engineering
Does not involve building artificial structures but takes a more sustainable and natural approach. Less expensive and more long term, attractive and sustainable as they work with natural process
Managed retreat
Allows nature to take its course but still have some control. They allow the sea to break through sea defences and flood the land behind but the way this happens is managed
Costs of coastal management
Cost of building
Maintenance/repair
Increased erosion downdrift due to beach starvation or reduced longshore drift
Reduced access to beach during works
Reduced recreational value
Reduced accessibility
Smaller beach due to scour
Disruption of ecosystems
Visually unattractive
Works disrupt natural processes
Benefits of coastal management
Protected buildings, roads and infrastructure
Land prices rise
Peach of mind for residents
Employment on works
Urbanisation and coastal conflict
Land use and habitat destruction
Water pollution
Increased vulnerability to climate change
Transport and coastal conflict
Port development and habitat loss
Ship pollution
Coastal erosion
Agriculture and coastal conflict
Runoff and eutrophication
Wetland drainage
Conflicts over water use
Tourism and coastal conflict
Coastal development
Overcrowding and pollution
Conflicts with local communities
Hunting and fishing and coastal conflict
Overfishing
Bycatch and species loss
Conflicts with conservation efforts
Aquaculture and coastal conflict
Habitat destruction
Water pollution
Genetic pollution
Industry and coastal conflict
Coastal pollution
Habitat degradation
Social conflicts
Energy production and coastal conflict
Oil spills and marine pollution
Visual and noise pollution
Tourism and fishing conflict
Seawalls
Large scale concrete curved walls designed to reflect wave energy
Revetments
Porous designed to absorb wave energy
Gabions
Rocks held in wire cages, absorb wave energy
Groynes
To prevent longshore drift
Rock armour
Large rocks at base of cliff to absorb wave energy
Offshore breakwaters
Reduce wave power offshore
Rock strongpoints
To reduce longshore drift
Cliff drainage
Removal of water from rocks in the cliff
Cliff grading
Lowering of slope angle to make cliff safer
Offshore reefs
Waste materials to reduce speed of incoming wave
Beach nourishment
Sand pumped from seabed to replace eroded sand
Managed retreat
Coastline allowed to retreat in certain places
Do nothing
Accept that nature will win
Red lining
Planning permission withdrawn. New line of defences set back from existing coastline
Pros and cons of seawalls
Easily made
Good in areas of high density
Expensive
Lifespan about 30-40 years
Foundations may be undermined
Pros and cons of revetments
Easily made
Cheaper than seawalls
Lifespan limited
Pros and cons of gabions
Cheaper than seawalls and revetments
Small scale
Pros and cons of groynes
Relatively low cost
Easily repaired
Cause erosion on downdrift side
Interrupt sediment flow
Pros and cons of rock armour
Cheap
Unattractive
Small scale
May be removed in heavy storms
Pros and cons of offshore breakwaters
Cheap to build
Disrupt local ecology
Pros and cons of rock strongpoints
Relatively low cost
Easily repaired
Disrupt longshore drift
Erosion downdrift
Pros and cons of cliff drainage
Cost effective
Drains may become new lines of weakness
Dry cliffs may produce rockfalls
Pros and cons of cliff grading
Useful on clay
Uses large amounts of land
Impractical in heavily populated areas
Pros and cons of offshore reefs
Low technology and relatively cost effective
Long term impacts unknown
Pros and cons of beach nourishment
Looks natural
Expensive
Short term solution
Pros and cons of managed retreat
Cost effective
Maintains a natural coastline
Unpopular
Political implications
Pros and cons of do nothing
Cost effective
Unpopular
Political implications
Pros and cons of red lining
Cost effective
Unpopular
Political implications
