Coastal Landscapes Flashcards
Define a system
A set of interrelated objects comprising of components (stores) and processes (links) that are connected to form a working unit or unified whole
Name the energies present in a coastal landscape system
- Kinetic (energy from wind and waves)
- Thermal (energy from the sun)
- Potential (position of material on slopes, material from marine deposition, weathering and mass movement from cliffs)
What are the inputs in a coastal landscape?
- Kinetic energy from wind and waves
- Thermal energy from heat of the sun
- Potential energy from position of material on slopes, material from deposition, weathering and mass movement from cliffs.
Are coastal landscapes open or closed systems and why?
- Coasts, as a whole, are open systems.
- This is because energy AND matter can be transferred to neighbouring systems as inputs and transferred out in outputs.
Give examples of outputs in a coastal system
- Marine and wind erosion from beaches.
- Weathering from rock surface
- Evaporation
What do processes consist of (+give an example for each)
Stores and flows.
- Stores: beach and nearshore sediment accumulations
- Flows (transfers): movement of sediment along a beach by longshore drift.
Define sediment cell
- A stretch of coastline and it’s associated nearshore area within which the movement of coarse sediment, sand and shingle are largely self contained.
Are sediment cells considered open or closed systems?
- Closed system.
It is thought that no sediment is transferred from one cell to another.
How many large sediment cells are the around the coast of England and Wales
11
What are sediment boundaries determined by and give a geographical example.
- Sediment cell boundaries are determined by topography and shape of the coastline.
- Example: Lands end acts as a large barrier against sediment transfer.
Explain why it is unlikely that sediment cells are completely closed systems
It is unlikely to be completely closed due to variations in wind direction and the presence of tidal currents.
What are the 5 potential physical factor influences on coastal landscapes?
- Winds
- Waves
- Tides
- Geology
- Patterns of ocean currents
In what ways do winds influence coastal landscapes?
- Winds act as a source of energy for wave action - influencing erosion and transport.
For example, winds blowing at an oblique angle towards the coast makes the resultant waves obliquely approach too - generating longshore drift. - Can contribute to aeolian processes
How is wave energy generated?
Generated by the frictional drag of winds moving across the ocean surface
How does wind speed and fetch affect waves?
The higher the wind speed and longer the fetch, the longer the waves and higher the energy.
What energy do waves possess?
- Potential energy due to position above wave trough
- Kinetic energy caused by the motion of water molecules within the wave.
Waves move water forwards, true or false?
False!
Waves impart a circular motion to the individual water molecules.
What is the formula for wave energy?
- P = H²T
- P is the energy of the wavefront (kw/m)
- H is the wave height (m)
- T is the time interval between wave crests (s)
Outline how waves break
- Waves move into shallow water (depth of half the wavelength)
- The deepest circling molecules come into contact with the ocean floor
- Friction is produced which changes the speed, direction and strength. As a result, waves slow down as they drag - decreasing the wave length so successive waves begin to bunch up.
- The deepest part of the wave slows down more than the crest so it steepens, advances ahead of the base and topples over - breaking.
Outline the process of swash and backwash.
- As a wave breaks, there is a significant forward movement of water and energy.
- As the wave breaks, water moves up the beach as swash.
- The swash decreases in energy and speed as it advances up the beach due to friction and uphill gradient.
- When there is no more available energy to move forward, the water is drawn back down the beach as backwash. Energy for backwash comes from gravity.
- Backwash occurs perpendicular to the coastline, down the steepest slow angle.
List the features of a constructive wave
- Tend to be low in height
- Long wavelength
- Low frequency (6-8 p/m)
- Break by spilling forward
- Swash exceeds backwash
List the features of a destructive wave
- Greater height
- Shorter wavelength
- Higher frequency (12-14)
- Break by plunging downwards.
- Backwash exceeds swash
Why is swash energy exceeding backwash energy in constructive waves?
As they have long wavelengths, backwash returns to the sea before the next wave breaks.
From this, the next swash movement is uninterrupted and maintains energy.
Why does backwash exceed swash in destructive waves?
As waves plunge downwards, there is little forward transfer of energy to move water up steeply sloping beaches.
The steep beach slows down swash energy so it doesn’t travel far.
The short wavelength means the next swash is slowed by the returning backwash.
What is the relationship between gradient and wave type?
- High energy waves (winter months usually) tend to remove material from the top of the beach, transporting it to the offshore zone and reducing beach gradient.
- Low energy waves (typically summer months) steepens the beach profile .
Anatomy of a wave (bullet points)
- The highest surface part of a wave is the crest
- The lowest part is the trough
- The vertical distance between the crest and trough is wave height
- Horizontal distance between two adjacent crests is the wave length.
What are swell waves?
Waves formed in open oceans that travel huge distances from the place they were formed.
Compare a swell wave and storm wave
- Swell waves have a….
: Formed in open oceans
: Long wave length
: Wave period of 20 s - Storm waves
: Locally generated
: Short wavelength
: Greater height
: Shorter wave period
Define tides
Tides are the periodic rise and fall of the sea surface produced by the gravitational pull of the moon (and the sun).
How is high and low tide formed?
- The moon pulls water towards it, creating a high tide - and a compensatory bulge on the other side of the earth.
- In areas between these two bulges, there will be a low tide
Differentiate between a neap tide and spring tide
- A neap tide is where there is a low tidal range
- A spring tide is where there is a high tidal range
How often do neap or spring tides occur?
Twice monthly
How is a spring tide formed?
- When the moon, sun and earth are all aligned, gravitational pull is at it’s strongest and produces the highest tides (spring tides)
How is a neap tide formed?
- When the moon and sun are at right angles to each other, so the gravitational pull is therefore at it’s weakest - producing the lowest tides (neap tides)
How does tidal range influence landscapes?
- In enclosed areas (Mediterranean), tidal ranges are low so wave action is restricted to a narrow area of land.
- In areas where the coast is funneled (River Severn), tidal range is high.
THEREFORE.
Tidal range influences where wave action occurs, weathering processes on exposed land.
What are the two subsections of geology?
- Lithology
- Structure
Define lithology in relation to geology
Lithology describes the physical and chemical composition of rocks.
How does lithology of rocks influence coastal landscape?
- Rocks with weak lithology (clay) have little resistance to erosion, weathering and mass movements.
This is due to the bonds between particles being weak. - Rocks with strong lithology (basalt) are more resistant to erosion due to being formed of stronger bonds and dense interlocking crystals. They will form prominent coastal features such as headlands.
- Chalk is soluble in weak acids so is vulnerable to chemical weathering.
Define structure in relation to geology
Structure is the properties of individual rock types such as jointing, bedding and faulting - also including the permeability of the rock.
Differentiate between primary permeability and secondary permeability in structure (geology)
- Primary permeability:
Porous rocks (chalk) pores separate the mineral particles and absorb/store water. - Secondary permeability
Limestone is secondary permeable as water seeps into many joints and these are enlarged by solution.
How does rock structure influence coastal landscapes?
- Influence on a regional scale.
Uniform or parallel outcrops produce straight and concordant coastlines.
Rocks at right angles to the coast create discordant planforms.
Structure also alters cliff profiles.
Structure determines the angle of dip of rocks.
What are currents
A body of water moving in a definite direction
How are rip currents formed?
Formed by either tidal motion or waves breaking at right angles to the shore.
Cellular circulation is generated by differences in wave heights parallel to the shore - water from the top of breaking waves travel further up the shore and returns through the adjacent area where lower wave height shave broken.
In what ways do rip currents influence coastal landscapes?
- Affect sediment transport
- Modify the shore profile by creating cusps - perpetuating the rip current.
CURRENTS FLASGCARD
What are the three sources of sediment in coastal landscapes?
- Terrestrial
- Offshore
- Human
What is an example of a terrestrial sediment supply to the coast?
Rivers
Sediment delivery to the shoreline is intermittent, occurring mostly during river floods (terrestrial input), true or false?
True
What is the origin of terrestrial sediment?
The erosion of inland areas by water, wind, ice AND subaerial processes such as weathering and mass movement
Where can terrestrial sediment come from (list)
- River deposition
- Erosion by water, wind and ice
- Sub-aerial processes such as weathering and mass movement
- Wave erosion
- Longshore drift from one coastal area to another
What % does the erosion of weak cliffs in high energy environments contribute to sediment budget?
70%
How is coastal sediment supplied from offshore?
- Constructive waves bring sediment to the shore from offshore and deposit it (marine deposition)
- Tides and currents also contribute to marine deposition
- Winds blow sediment from exposed sand bars, sand dunes or other beaches
Why is sediment transported by wind usually fine sand?
Aeolian material is fine as wind has LESS energy than water so it cannot transport large particles
How does human sources of sediment contribute to the sediment budget?
- Management strategies such as beach renourishment includes bringing sediment from elsewhere to restore equilibrium when the sediment budget is in deficit.
What are two ways in which humans conduct beach nourishment?
- Sediment can be brought in by a lorry and dumped on the beach to be spread out by bulldozers
- Sand and water are pumped onshore by pipeline from offshore - low bunds hold the mixture in place as water drains away and leaves the sediment behind.
List geomorphic processes
- Weathering (mechanical, chemical and biological)
- Mass movement
- Wave processes (transportation types)
- Erosion
- Fluvial processes (including erosion)
- Deposition
- Aeolian processes
Define weathering
The in situ breakdown of rocks that are exposed at, or near, the land surface in chemical, biological and mechanical processes.
What is another name for mechanical processes?
Physical processes.
How does physical weathering generally break down rock?
- Smaller fragments are produced of the same rock WITHOUT chemical alteration.
- Physical weathering perpetuates itself by increasing the exposed surface area of the rock - allowing further weathering to occur.
List the processes of physical (mechanical) weathering
- Freeze-thaw weathering
- Pressure release weathering
- Thermal expansion
- Salt crystallization
What occurs in freeze-thaw weathering? (mechanical weathering)
- Water enters cracks/joints and freezes, expending nearly 10%.
- In confined spaces this exerts pressure, causing the rock to split or fragment.
What occurs in pressure release? (mechanical weathering)
- Overlying rocks are removed by weathering and erosion - leaving the underlying rock to expand and fracture parallel to the surface.
What occurs in thermal expansion? (mechanical weathering)
- Rocks expand when heated and contract when cooled.
- If there are frequent cycles of temperature fluctuation, outer layers of rock may crack and flake off (KNOWN AS INSOLATION)
What occurs in salt crystallization? (mechanical weathering)
- Salt solutions seep into porous rock spaces.
- Salts precipitate, forming crystals - the growth of these creates stress in the rock and cause it to disintegrate.
How does chemical weathering generally break down rock?
- Chemical weathering contributes to the decay of rock, this involves chemical reactions between moisture and minerals within the rock.
- Chemical weathering works by reducing the rock to its chemical constituents or altering the chemical/mineral composition.
- It results in the creation of weak residues of different material that is removed by erosion or transportation processes.
List the types of chemical weathering
- Oxidation
- Carbonation
- Solution
- Hydrolysis
- Hydration
What is the process of oxidation and what is an example? (chemical weathering)
- Minerals in rocks react with oxygen from the air or in water.
Minerals in the rock become soluble under extremely acidic conditions.
The original structure of the rock is destroyed. - An example is iron, iron-rich cements that bind sand grains together in sandstone are attacked by oxidation
What is the process of carbonation
- Rainwater combines with dissolved CO2 from the atmosphere to produce a carbonic acid.
Carbonic acid reacts with calcium carbonate in rocks such as limestone, forming calcium bicarbonate, which is extremely soluble.
What is the process of solution?
- Solution is any process by which a mineral dissolves in water.
What is the process of hydrolysis?
- Hydrolysis is the chemical reaction between rock minerals and water.
Silicates combine with water, leading to the production of secondary minerals such as clays.
What occurs during hydration?
- Water molecules added to rock minerals create new minerals of a larger volume.
- Hydration causes flaking in many rocks, due to the expansion of material during the chemical change of absorbing water.
List the flows of energy and materials that have impacts on geomorphic processes
- Weathering
- Mass movement
- Wave, fluvial and aeolian erosion
- Transportation and deposition
What is meant by a geomorphic process?
Natural mechanisms that shape the coastline.
What is meant by aeolian processes?
Geomorphic processes caused by the action of wind
Name aeolian processes
- Deflation: removal of fine particles
- Abrasion: sand grains transported by the wind wearing down surfaces.
- Suspension: transportation of fine particles over long distance
What are aeolian processes important for?
The accumulation of sediment in shaping sand dunes that act as coastal defences.
What is meant by a concordant coastline?
A coastline shape wherein rocks lie parallel to the coastline
What is meant by a discordant coastline?
A coastline shape where alternating bands of hard and softer rock lie at right angles to the coast
What landforms are associated with discordant coastlines?
Bays and headlands
Define wave refraction
The process by which waves break onto an irregularly shaped coastline (such as a headland separated by two bays).
Outline the process of wave refraction
- Waves approach an irregularly shaped coastline
- The waves drag by friction as they enter shallower water off the headland
- The wave crest in deeper water approaching the bay moves faster due to not being slowed by friction
- The wave bends and refracts around the headland and orthogonals converge.
- Wave energy is concentrated on the headland
What are the two biological weathering types?
- Role of tree roots and burrowing animals
- Role of organic acids in chelation
What does wave refraction do to bays and headlands?
- Wave refraction leads to wave energy being concentrated on the headland, so more erosion here
- For bays, orthogonals diverge and energy is dissipated leading to deposition.
What role does tidal range play in affecting the landscape?
Tidal ranges are significant in the development of coastlines as it influences where wave action will occur, the weathering processes and impacts of inter-tidal processes such as scouring.
How do tree roots contribute to biological weathering?
Tree roots grow into cracks or joints in rock which exerts outward pressure.
How do organic acids (chelation) contribute to biological weathering?
- Organic acids are produced during decomposition which causes soil to become more acidic and react with rock minerals in chelation
- In addition, molluscs on shore platforms can secrete acids that c
produce small hollows in rock, making it more porous
List effects of wind energy on coastlines
- Energy of waves are dependent on the strength, duration and length of fetch from the wind.
- Wind creates waves due to frictional drag
- Length of fetch determines the size of waves and energy.
- Creates spatial variations in energy due to varying wind strength and direction.
What is a counterpoint to weathering being the most significant geomorphic process?
In many coastal landscapes, such as Western Europe, sea presence moderates temperatures so air temperature rarely drops below 0.
This reduces the extent of fluctuations which renders many weathering processes ineffective
What are 3 types of ocean currents?
- Longshore currents
- Rip currents
- Upwelling
What effect does ocean currents have on coastal landscape development?
- Warm ocean currents transfer heat from low latitudes to high latitudes, and vice versa with cold currents.
- This transfer of heat energy is significant as it affects air temperature, and sub-aerial processes
What is meant by sub-aerial processes?
A collective term for weathering and mass movement processes.
What is important to consider in arguing the most significant geomorphic processes?
- Different locations have different dominant processes
- For example, estuarine environments has tidal energy that dominates it - such as the Rhone Delta
- In dune environments, wind / aeolian processes dominate.
What occurs when there is a positive sediment budget?
More material is added than removed (accretion of material) so the shoreline builds to the sea
What occurs when there is a negative sediment budget?
More material is removed than added so the shoreline recedes inward.
Define mass movement (a sub-aerial process)
The movement of regolith (material) down a slope
Name 4 examples of mass movement
- Landslides
- Rockfalls
- Mudflow
- Rotational slip / slumping
What occurs during a landslide?
Cliffs made of softer rocks slip when lubricated / saturated by rainfall
What occurs during rockfall?
Rocks undercut by sea or slopes are affected by chemical weathering
What occurs during mudflows?
Heavy rain saturates fine material and it moves downhill
What occurs during rotational slip / slumping?
Soft material overlying resistant material is exposed to excessive lubrication and ‘slips’ in a rotational manner
Weak rocks such as clay are more susceptible to slumps, true or false?
True.
They become heavier when wet, adding to downslope force
State 5 erosional wave processes.
- Abrasion
- Attrition
- Pounding
- Hydraulic action
- Solution
What is abrasion? (or corrasion)
When waves armed with rock particles scour the coastline - essentially rock rubbing against rock
What is attrition?
- A process where rock particles, transported by wave action, collide with each other and coastal rocks - eventually becoming more worn away.
- The rocks become smoother and rounded as well as smaller, producing sand.
What is hydraulic action?
- When waves break against rock, and air and water trapped in crevices becomes compressed.
- As the wave recedes the pressure is released, air and water expand and widen cracks.
What is pounding?
- Where a breaking wave exerts pressure on the rock causing it to weaken.
What is solution (corrosion)?
A process which involves dissolving minerals such as magnesium carbonate in coastal rocks
What is a limitation to the process of solution (corrasion)
- Solution is of limited significance as the pH of seawater is usually around 7 or 8.
- Even if pollution changes pH, only coastal rocks containing significant amounts of soluble material are likely to be effected.
What are the 4 different types of transportation?
- Solution
- Suspension
- Saltation
- Traction
- Can also include longshore drift!
What is solution, as a type of transportation?
- A way material is transported in which minerals are dissolved into a mass of moving water.
- This load is invisible and the minerals remain in solution until water is evaporated and they precipitate out of solution.
What is suspension?
- A type of transportation in which small particles of sand, silt and clay are carried by currents.
What is saltation?
- A type of transportation in which small stones ‘bounce’ along the seabed.
- This is where turbulent flow may enable heavier particles to be picked up (entrained) and carried for a short distance only to drop again.
What is traction?
- A type of transportation where the largest particles in the load are pushed along the sea floor by force of the flow.
What occurs to create longshore drift?
- Waves approach the coast at an angle due to the direction of the dominant wind.
- The waves break and swash carried particles diagonally up the beach, and backwash moves them perpendicularly back down the beach under the influence of gravity.
How does longshore drift effect sediment size down the beach?
Longshore drift leads to attrition of beach sediment so particles tend to become smaller and more rounded with increasing distance along the beach.
When does deposition occur?
When velocity and/or volume of water decreases and energy is reduced?
What features of a coastal environments can promote deposition?
- When rate of sediment accumulation exceeds removal
- When waves slow after breaking
- Where backwash water percolates into beach material
- In low energy environments that are sheltered from wind and waves such as estuaries.
Define ‘settling velocity’ (part of deposition) and what is does
- The velocity at which sediment particles are deposited.
- Larger and heavier particles require more energy to transport them, so as flow velocity decreases the largest particles carried are deposited first.
- This occurs sequentially until the finest particles are deposited
Define longshore drift
The process by which sediment deposited on the shore is moved along the shoreline.
On what type of coastal landscape does fluvial processes have a large influence on?
- Low energy estuarine coasts.
Outline the relationship between fluvial processes and deposition
- At the mouth of rivers (where they enter the sea) there is a reduction in their velocity when flowing water enters a relatively static body of sea water.
- Tides and currents may be moving in opposite direction to river flow, providing major resistance to forward movement. Energy is reduced as a result and sediment load is deposited.
What is the role of fluvial deposition being ‘sequential’ on formation of estuarine environments
- Reduction in energy is progressive and deposition is sequential
- The largest particles are deposited first and the finest are carried out further to sea.
What is flocculation? (fluvial)
- Where the mixing of fresh water and salt water causes clumping of fine, light clay materials.
- This is because there are differences in electrical charges between them in saline conditions
- They become heavier as a result and sink to the seabed.
Define aeolian processes
Erosion, transport and deposition facilitated by the wind
What is deflation
An aeolian process where winds pick up sand particles and moves them in
Estuarine features such as mudflats and salt marshes are associated with large tidal ranges, true or false?
True
Large tidal ranges have powerful currents to transport large quantities of fine sediment
Why is attrition on land particularly effective in wind?
Particles tend to be carried for much greater distances than in water.
When does deposition occur in aeolian processes?
- When wind speed falls
How are cliffs formed?
- Cliffs are an erosional landform
- Cliffs are formed when destructive waves break on relatively steeply sloping coastlines, creating an undercutting effect.
- Undercutting occurs between high and low tide and creates a wave-cut notch.
- This process of continued undercutting weakens support for the rock strata above, and the strata eventually collapses, producing a steep profile and a cliff.
State a characteristic of a wave cut platform
- A cliff face retreats due to undercutting, which produces a gently sloping forefront of the cliff left over - a wave cut platform.
- This is eroded by abrasion and hydraulic action, and when exposed it is subject to weathering and sub-aerial processes.
What is a geo?
- A narrow, steep sided inlet.
How are geos formed?
- Due to the presence of joints and faults in rock.
- These are more rapidly eroded by wave action compared to resistant rock around them
What erosional process is especially important in the formation of geos and why?
- Hydraulic action
- It forces air and water into the joints which weakens the rock strata.
Name an example of a geo
Huntsman’s leap in Pembrokeshire.
This is 35m deep and eroded along a large joint in carboniferous limestone.
How is a blowhole formed?
- Formed from the continual erosion of a geo being enlarged (weaknesses in faults or joints).
- The roof of a geo collapses, creating a blowhole which is a vertical shaft that reaches the cliff top
What human activity can the formation of geos and blowholes be associated with?
Mining, such as in Trevone Cornwall associated with old tin mining shafts.
What is a blowhole?
- A vertical shaft that reaches the cliff top.
Outline how bays and headlands are formed
- Waves approach a discordant coastline which creates wave refraction
- From wave refraction, waves develop a configuration increasingly parallel to the coastline.
- The wave nears the shallow headland water and is slowed by friction.
- From friction, the wave crest in deeper water moves faster due to not being slowed like in the shallower water.
- This means the wave bends or refracts around the headland and orthogonals converge.
- Wave energy is focused on the headland so erosion is concentrated here.
- The orthogonals diverge in the bay and energy is dissipated leading to deposition
What is the relationship between longshore drift and wave refraction?
As waves break on the sides of a headland at an angle, there is longshore movement of eroded material into bays, adding to build up of beach sediment.
Outline how caves, arches, stacks and stumps are formed
1) Due to wave refraction, energy is concentrated on the sides of headlands. Any points of weaknesses in the headlands such as joints or faults are exploited by erosional processes.
2) A small cave can develop on the headland when wave attack is concentrated between high and low tide levels.
3) The cave enlarges to the point it breaks and extends through the headland, producing an arch.
4) Continued erosion widens the arch and weakens it’s support leading to collapse - leaving an isolated stack separated from the headland.
5) Finally, further erosion at the base of the stack can cause further collapse - leaving a small flat portion of the original stack as a stump.
What are beaches?
Depositional landforms representing the accumulation of material deposited between the lowest tides and the highest storm waves.
What materials do beaches consist of and what are their sources
- Sand and shingle (pebbles and cobbles).
- These are from 3 main sources: cliff erosion, offshore stores and rivers.
Shingle produces steeper beaches, true or false?
- True
- Bigger shingle means there is rapid percolation at the upper part of the beach.
- This means that little backwash occurs so material is left at the top of the beach?
Why do sand beaches often have gentle gradients?
- Sand has a small particle size which means that it is compact when wet.
- This allows little percolation during backwash.
- Little energy is lost to friction and little volume of water is lost to percolation so material is carried back down the beach rather than remaining at the top.
- This results in a gentle gradient and the development of ridges and runnels.
What is a storm beach?
A beach formed when storm waves hurl pebbles and cobbles to the back of the beach, forming a storm beach or storm ridge.
What is a berm?
A depositional beach landform of smaller ridges developing at the position of the mean high tide mark - resulting from depositon at the top of the swash.
What is a cusp?
A small semi-circular depression in the beach.
How are cusps formed?
- Cusps are temporary features formed by a collection of waves reaching the same point when swash and backwash have similar strength.
- The sides of the cusp will channel incoming swash into the centre of the depression and this produces a strong backwash that drags material down to enlarge the depression.
Beaches are dynamic, true or false?
True
- Their profile changes over time as wind strength and energy changes.
- They respond to this change by developing an equilibrium profile, a balance between erosion and depositon?
What do high-energy destructive waves do to beaches?
- High-energy destructive waves remove sediment offshore and create flatter beach profiles.
- This results in shallower water, more friction and a reduction in wave energy.
What do low-energy, constructive waves do to beaches?
- Low-energy constructive waves transfer sediment in the opposite direction to form steeper profiles.
- This produces deeper water, less friction and an increase in wave energy.
What is a spit?
A depositional landform that are *long, narrow beaches of sand or shingle that attach to the land at one end and extend across a bay, estuary or indentation.
How are spits formed?
- They are generally formed by longshore drift occurring in one dominant direction.
- This carries beach material to the end of the beach and then beyond into the open water.
- These are built up over time, becoming more substantial and permanent.
- The end becomes recurved as a result of wave refraction around the end of the spit (and possible secondary wind/wave direction).
What is an example of a spit?
Orford Ness in East Anglia.
What occurs in the sheltered area behind a spit?
- In the sheltered area behind the spit, deposition will occur as wave energy is reduced.
- Silt and mud deposited will build up and eventually become a salt marsh when colonized.
What is a salt marsh?
A salt marsh is a vegetated area of deposited silt and clays.
What is an onshore bar?
A depositional landform formed when a spit extends across an indentation until it joins onto land at the other end.
How is a lagoon formed?
- When a spit joins the other side of the coastal indentation, forming an onshore bar.
- Behind the onshore bar is a body of brackish water: a lagoon.
What is a tombolo?
Beaches that connect the mainland to an offshore island.
How are tombolo’s often formed?
- They are often formed from spits that have continued to grow seawards until they reach and join an island.
What is an offshore bar?
A ridge of material, semi-submerged seawards of the refer zone.
How is a salt marsh consolidated?
- In the sheltered area behind the spit, silt and mud build up.
- These are subjected twice daily to inundation and exposure from tides.
- Salt tolerant plants such as eel grass help trap sediment, increasing the height of the marsh.
- The stems and leaves trap sediment whereas roots stabilize it.
- The higher the marsh, the less inundation occurs and the conditions become less saline - allowing a greater diversity of species to survive such as reeds.
What are saltpans?
What are erosional features in a landscape?
- Headlands and bays
- Caves, arches, stacks and stumps
- Cliffs and wave cut platforms
- Geos and blowholes
What are depositional features in a landscape?
- Beaches
- Spits
- Onshore bars
- Tombolos
- Salt marshes
What does the development of salt marshes depend on?
The rate of accumulation of sediment, which can be reliant on erosional processes
What 2 things help the development of salt marshes?
- Rivers losing energy as they slow and enter the sea, depositing fine sediment
- Flocculation: tiny clay particles carryinh an electrical charge are attracted to each other in salt water, combining together to form flocs.
- Flocs are larger and heavier, therefore not being able to be carried - so they settle out of suspension at relatively high velocities.
What is a delta?
- Large areas of sediment found at the mouths of many rivers.
What are deltaic sediments deposited by?
- Rivers and tidal currents
When do deltas form?
When rivers and tidal currents deposit material at a faster rate than waves and tides can remove it.
Where do deltas typically form?
- Where rivers entering the sea are carrying large sediment loads
- Where there is a broad continental shelf margin at the river mouth, providing a platform for sediment accumulation
- Low energy environments
- When tidal ranges are low
What are the 3 distinctive components of a deltas structure?
- The upper delta plain
The part of the delta furthest inland, beyond the reach of tides. Composed of entirely fluvial sediments - The lower delta plain
In the inter-tidal zone, regularly submerged and composed of BOTH marine and fluvial deposits. - The submerged delta plain
The part lying below the mean low water mark, composed of mainly marine sediments. Represents the seaward growth of the delta.
What helps to develop a delta?
- The fact that deltas are criss-crossed by distributaries.
- When overloaded with sediment, deposition in the channel forms bars that causes the channel to split.
- This produces two channels with reduced energy levels, so more deposition and further dividing occurs.
What are the 3 types of delta?
- Cuspate delta
- Arcuate delta
- Bird foot delta
Define ‘eustatic change’
- The global change in volume of sea water resulting from a rise or fall of the sea itself
- For example, caused by retreat of ice following a glacial period
- These changes are influenced by variations in mean global temperatures, affecting both amount of water in the ocean store and it’s density.
Define ‘isostatic change’
- A local change in sea level resulting from the land rising or falling relative to the sea
- For example: isostatic rebound or tectonic movements.
What natural physical factors can change global temperature and volume of water in oceans?
- Variation in the Earth’s orbit around the sun, typically every 400000 years.
- Variations in energy produced by the sun, with a solar maximum of every 11 years or so.
- Changes to the composition of the atmosphere due to volcanic eruptions, reducing incident solar radiation (TECTONIC LINK)
How can climate change influence sea level fall?
- A decrease in global temperature leads to more precipitation being in the form of snow.
- This snow will turn to ice and water is stored on land when solidified rather than returning to the ocean store as liquid.
- As a result, there is a reduction in the volume of water in the ocean store and sea level fall.
- Also, as temperature drops, water molecules contract, leading to an increased density and reduced volume
What are climate changes that happened in a previous time period leading to resultant sea level fall?
- 130000 years ago, during the Tyrrhenian inter-glacial period, global mean temperatures were about 3 degrees higher than today and sea level was around 20m above current position.
- Temperatures fell during the onset of the Riss glacial period, reaching a minimum of around 7 degrees lower than today around 108000 years ago.
- As a result of this temperature decrease, less water was returned to the ocean store and sea levels dropped by over 100m - 83m lower than the present day.
What landforms does sea level fall produce?
Emergent landforms
List 3 emergent landforms that develop from sea level fall
- Raised beaches
- Marine terraces
- Abandoned cliffs
Where can emergent landforms be found?
- Well inland, some distance from the modern coastline.
- This is because these landforms were shaped by wave processes during times of high sea level, and are exposed when sea level falls.
What are raised beaches?
- Areas of former shore platforms that are left at higher level than present sea level.
- These are usually positioned in front of ‘abandoned cliffs’ with wave cut notches, caves and even arches and stacks.
What are marine terraces, and how are they different to raised beaches?
- Marine terraces are much larger scale landscape features than raised beaches, as raised beaches are small scale and localized at the base of relic cliffs.
- Marine terraces do not necessarily have cliffs above them, unlike raised beaches
- As marine terraces are formed over a longer time scale compared to raised beaches, explaining why they are substantially larger.
- Despite this, their formation is the same as raised beaches - marine erosion during a previous period of high sea level.
What is an example of a raised beach and how was it formed?
- A distinct raised beach at the Southern tip of the Isle of Portland near Weymouth, Dorset.
- It has a height of around 15m above present day sea level.
- It was formed around 125000 years ago during the Tyrrhenian INTER-glacial period when sea levels were higher.
- Portland limestone here was eroded by hydraulic wave action that exploited the bedding plane weakness.
What is meant by ‘modification of landforms’ in terms of emergent landforms?
The notion that, although the landforms are no longer affected by wave processes, they continue to be affected by weathering and mass movement.
How has emergent landforms been modified?
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Cryoturbation
Periglacial conditions degraded the cliff from frost weathering processes, leading to rock fall from the cliff face. This is seen at the Isle of Portland displaying frost-shattered limestone debris
Cryoturbation is the frost churning of layers of regolith in peri-glacial environments. Cryoturbation is evident in contortions in fragmented limestone.
This is the result of freezing and thawingof permafrost in the subsoil in the final glacial phase. -
Post-glacial processes
Warmer and wetter conditions had led to the development of vegetation cover on many exposures, contributing to biological weathering. Biological weathering is also involved with the colonisation on raised beaches of marine organisms, such as whelks or limpets. -
Future changes
As the climate warms, future degradation is likely from chemical weathering, especially in carbonation of limestone cliffs and platforms.
If temperatures rise sufficiently, the associated sea level rise could lead to emergent landforms being found closer to or at the coastline once more. Then again they would be subjected to wave processes
How can climate change influence sea level rise?
- Increase in global temperature leads to higher rates of ice melting which had been stored on the land in ice sheets, ice caps and valley glaciers.
- This increases the volume of water in the oceans and consequent sea level rise.
- Water molecules expand as temperature rises, leading to a further increased volume.
What is the quantitative relationship between sea level rise and fall with temperature?
- A 1° rise in mean global temperature results in sea level rise of approximately 2m
- Oppositely, a 1° fall in mean global temperature results in sea level fall of approximately 2m
What are climate changes that happened in a previous time period leading to resultant sea level fall?
- At the end of the Wurm glacial period, temperatures were about 9° lower than today and sea level was 90m lower than the present.
- Since then, temperatures and sea levels have risen to their present level.
- This significant rise in sea level is called the Flandrian Transgression.
What landforms does sea level rise produce?
Submergent landforms
List 3 emergent landforms that develop from sea level rise
- Rias
- Fjords
- Shingle beaches
What is a ria?
- A submerged river valley
- The lower course and floodplains may be completely drowned, but higher land forming tops of the valley sides and upper-middle course remain exposed.
What is a real place example of a ria?
Fowey!
Differentiate between the characteristics of a ria and a fjord
- A ria is a submerged river valley whilst a fjord is a submerged glacial valley.
- A ria, in cross section has relatively shallow water becoming increasingly deep towards the center. A fjord has a U shaped cross section.
- Fjords tend to have straighter planforms compared to rias as glaciers truncated any interlocking spurs present
What are characteristics of a fjord?
- A fjord have steep, almost cliff like valley sides.
- It has a U-shaped cross section reflecting the original shape of the glacial valley
- It consists of a glacial rock basin with a shallower end known as a threshold
- This results from lower rates of erosion at the seaward end of the valley as ice has thinned in warmer conditions.
- They tend to have straighter planforms as the glacier would have truncated any interlocking spurs present.
How can shingle beaches be considered submergent landforms?
- Sea level falls as volume of land-based ice grows, and large areas of ‘new’ land emerges where sediment accumulates.
- As sea levels rose at the end of the last glacial period, wave action pushed these sediments onshore.
- This may form tombolos and bars
- The tombolo at Chesil Beach is formed this way from the Flandrian Transgression.
How was a ‘submergent’ shingle beach/tombolo formed at Chesil Beach?
- Sediment carried into the English Channel by meltwater accumulated in locations such as Lyme Bay.
- As sea levels rose, the sediment was carried north-east by the impact of southwesterly prevailing winds and resultant waves.
- It became attached to the Isle of Portland at one end and the mainland near Abbotsbury at the other.
- It is thought this happened as there is no recurvation indicating longshore drift.
How have submergent landforms been modified?
-
Rias and Fjords
Rias and fjords may have been modified by wave processes acting on their sides at present day sea-level. The valley sides, especially in fjords, may also be affected by sub-aerial processes. This may eventually lead to a reduction in the steepness of the fjord valley sides.
Sea level is predicted to rise 0.6m in the next 100 years, so water depth in rias and fjords will increase. Marine erosion is then likely to increase due to stormier conditions and larger waves. -
Shingle beaches
Shingle beaches are composed of unconsolidated material, meaning it is especially vulnerable to modification.
The tombolo at Chesil Beach has been affected significantly by current longshore drift processes. With further sea level rise, shingle may be moved even further to the northeast and a breach of the tombolo is likely in future storm events.
Sediment addition will become more common in future with higher sea levels and more storm events.
