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LANDFORM DEVELOPMENT (Geomorphic Processes (Wave Processes (Erosion…

- - - - Breakdown of rock is largely bc of these processes
      - Produces smaller fragments of the same rock
      - Increasing exposed surface area = further weathering
      - Presence of sea in many coastal landscapes (e.g. Europe) = moderation of air temps = reduced extent of fluctuations = some processes are ineffective
      - Freeze-thaw
        
        Water enters cracks + joints + expands nearly 10% when it freezes
        
        The pressure of rock = splits + breaks into smaller peices
        
        Affects resistant rocks
      - Pressure release
        
        When overlying rocks are removed, the underlying rock expands + fractures parallel to the saurface
        
        = exposure of sub-surface rocks e.g. granite
        
        Dilation
        
        Parallel fractures - pseudo-bedding planes
      - Thermal expansion
        
        Frequent cycles to temperature fluctuations = outer layers crack + fall off
        
        Insolation
        
        Doubt over effectiveness unless water is present
      - Salt crystalisation
        
        Salt solutions seep into pore spaces of porous rocks
        
        Salts precipitate = crystals
        
        Crystal growth = stress = disintegration
        
        Sodium sulphate + Sodium carbonate are v effective - expand by 300% in areas where temp. fluctuates between 26-28 degrees
    - - = decay of rock
      - Chemical reactions between moisture and some minerals in the rock
      - Can reduce rock to its chemical components or alter its chemical mineral composition
      - Produce weak residues of different material that can then be easily moved by erosion + transportation
      - Rate increases with temperature
        
        10 degree increase int emperature = 2.5 times increase in rate of reaction
        
        Most effective in tropical areas
        
        Carbonation can be more effective in lower temperatures bc CO2 is more soluble in cold water
      - Oxidation
        
        Some minerals react with O2 in air/water
        
        Iron is v susceptible
        
        Becomes soluble in v acidic conditions + original structure is destroyed
        
        Attacks the Fe-rich cements that bind sand grains together in sandstone
      - Carbonation
        
        Rainwater combines with dissolved CO2 from atmosphere = weak carbonic acid
        
        Carbonic acid reacts with CaCo3 = calcium bicarboante - this is soluble
        
        Limestone
        
        Reversible process
        
        Precipitation of calcite in evaporation of C-rich water in caves = stalactites + stalagmites
      - Solution
        
        Some salts are soluble in water; some only soluble in very acidic water
        
        Mineral-specific processes e.g. carbonation, can be identified
      - Hydrolysis
        
        Chemical reaction between rock minerals + water
        
        Silicates combien with water = secondary minerals e.g. clays
        
        Feldspar in granite reacts with H in water = kaolin (china clay)
      - Hydration
        
        Water molecules added to rock minerals = new minerals of a larger volume
        
        Anhydrite takes up water to form gypsum
        
        = surface flaking - partly because some minerals also expand by 0.5% during chemical change bc they absorb water
      - Sea water is normally neutral-alkaline - unless affected by pollution
        
        Climate change + increasing CO2 = rainfall and therefore sea water is becoming more acidic
    - - Physical actions e.g. plant growth
      - Chemical processes e.g. chelation by organic acids
      - Tree roots
        
        Grow in cracks/joints = outward pressure
        
        Trees topple = roots exert leverage on rock + soil = brings them to surface + exposes them to further weathering
        
        Burrowing aniamls have a similar effect
        
        Significant on cliff tops + faces
      - Organic acids
        
        Produced in decomposition = acidification of soil water = reactions with some minerals - CHELATION
        
        Blue-green algae can produce a shiny film of Fe + magnese oxides on rocks
        
        At shore platforms, molluscs may secrete acids that produce small surface hollows in rock
  - - - Addition of material to sediment budget
    - - Cliffs of 40 degrees or more
      - Rocks detach from slope by physical weathering
      - Wave processes usually remove this material
      - Material can accumulate as a scree slope
    - - Linear - movement along a straight-line slip-plane e.g. fault/bedding plane between rock layers
      - Rotational - movement along a curved slip plane - also known as SLUMPS
      - Occur bc of undercutting by wave erosion at base of cliff
      - Slumps common in weak rocks e.g. clay
        
        These rocks become heavier when wet = addition to downslope force
        
        Sand above clay = water penetrates thru sand but not the clay = increase in pore pressure in sands
  - - - Abrasion/corrasion
        
        Waves containing rock particles scour the coastline; rock rubs against each other
      - Attrition
        
        When rock particles, transported by wave action, collide and progressively become worn away; they become smoother + more rounded + smaller - eventually becomes sand
      - Hydrraulic action
        
        Waves break against a cliff face, and air + water trapped in the cracks becomes compressed - as waves recede, pressure is released - air + water suddenly expands = crack is widened
      - Pounding
        
        When mass of a breaking wave exerts pressure on the rock so it weakens
      - Solution/corrosion
        
        Dissolving minerals e.g. magnesium carbonate minerals, in coastal rock - only is significant when the water is polluted/acidic, and even then only rocks with significant amounts of soluble minerals will be affected
    - - Solution
        
        Minerals that have been dissolved into the water - minerals will remain in solution until water is evaporated and they precipitate out of the solution
      - Suspension
        
        Small particles of sediment carried by currents - larger particles can be carried during storm events
      - Saltation
        
        Is a series of irregular movements of material which is too heavy to be carried continuously in suspension
        
        Turbulent flow enables sand-sized particles to be picked up and carried for a short distance - ENTRAINMENT
        
        Other partciles may be dislodged by the impacts = water gets beneath then = entrainment
      - Traction
        
        Largest particles in the load may be pushed along the floor by the force of the flow; movement is rarely continuous; large boulders can undertake a partial rotation before continuing to rest again
      - When deposited, sediment can be moved along the shoreline by LSD
        
        LSD occurs when waves approach the coastline at an angle due to the direction of the dominant wind
        
        When the waves have broken, the swash carries particles diagonally up the beach
        
        Backwash moves particles perpendicularly back down the beach under the influence of gravity
        
        Repeated movement = movement of material along a beach
        
        Also causes attrition of beach sediment, so particles become smaller + more rounded
    - - Material deposition is where there is a loss of energy caused by a decrease in elocity adn/or volume of water
      - Occurs:
        
        Where rate of sediment accumulation exceeds rate of removal
        
        When waves slow down immediately after breaking
        
        At the top of the swash, the water stops moving for a brief movement
        
        During backwash, when water percolates into the beach material
      - Settling velocity - velocity at which particles are deposited
        
        Larger + heavier particles require more energy for transport
        
        As flow velocity decreases, the largest particles are deposited first
  - - - Fluvial erosion in uppe catchment is the main source of river's sediment load
      - Rivers use similar erosional processes to waves
      - Most chnnel erosion occurs during high-flow, high-energy events
      - Sediment alos derived from weathering + mass movement events
    - - Traction, suspension, saltation + solution
    - - Large reduction in velocity as river enters sea bc flowing water moving thru the channel enters the relatively static body of the sea
      - Tides + currents can move in oppo direction to river flow = major resistance
      - As the reduction in energy is progressive, deposition is sequential - largest particles are deposited first
      - Meeting of fresh + salt water = flocculation of clay particles
        
        These fine, light materials clummp together bc of electrical charges between them in saline conditions - they become heavier + sink
  - - - Wind can pick up and move sand particles by deflation
      - Creep + saltation movements
      - Not carried in suspension bc grains of this size are relatively heavy compared to silt + clay particles
        
        Limited effect on abrasion and erosion of rock outcrops+ cliffs
      - Attrition to land is effective by (dry) particles tend to be carried for much greater distances than water, and these particles are not protected from collision bu the film of water around them
    - - With exception of solution, air can transport materials via same mechanisms as water
      - When particles have been entrained, they can be carried at velocities as low as 20km/hr
    - - Material carried by wind will be deposited when wind speed falls - usually bc of surface friction
      - In coastal areas, this occurs inland, where friction from vegetation + surface irregularities is much greater than on open sea
- - - - Destructive waves break repeatedly on relatively steeply sloping coastlines = wave-cut notches between the high + low tide levels = undercutting
      - Continued undercutting weakens the support for the rck strata above = collapse = steep profile + a cliff
      - Regular removal of debris at foot of cliff by wave action = relatively steep profile + cliffs retreat inland parallel to the coast
      - Cliff profiles vary depending on their geology
        
        Horizontally bedded + landward dipping rock strata = steep profile
        
        Seaward inclined rock strata = profile follows the angle of the dipping strata
        
        Cliff becomes higher as undercutting, collpase + retreat continues
      - Shore platform
        
        This is cut into the solid rock at the base of cliff
        
        Gently sloping, but deeply dissected by abrasion bc of rock debris dragged across its surface
        
        Boulder-sized rock debris = too large to be removed by waves and will accumulate on platform
        
        Platform will become so wide that it produces shallow water + small waves
        
        Friction form platform slows approaching waves enough for them to break on the platform rather than base of cliff = undercutting slows + ceases
        
        Shore platforms reach a maximum width of 500m before this happens
        
        Mostly formed by erosion, but weathering is also important
        
        Solution, freeze-thaw + salt crystalisation - can occur depending on rock type + climatic conditions
        
        Algae can accelerate weathering at low tide when platform is exposed
        
        Algae releases CO2 which combines with sea water = more acidic = higher rates of chemical weathering
        
        Features
        
        Water levels are constant for longest at high + low tides = erosion greatest at these points
        
        High tide = ramp
        
        Low tide = small cliff
        
        Develop best when tidal range is less than 4 m
        
        Higher = erosion spread over a wider area of the platform; water is at its high + low tide positions for a shorter time = shore platform is more unifrm and steeply sloping
    - - Normally form adjacent to each other
      - Presence of bands of rocks of differing erosion resistance
      - Discordant coastlines
        
        If rock outcrops are perpendicular to coastline, the weaker rocks are eroded more rapidly = bays, whilst resistant rocks = headlands
        
        Width of bays is determined by width of band of weaker rock
        
        Bay depth depends on differential rates of erosion between the more resistant + weaker rocks
      - Concordant coastlines
        
        Rocks parallel to coast
        
        If most resistant rock is on the seaward side, it protects weaker rocks inland
        
        Straight + even coastline
        
        Small bays and coves can be eroded at points of weaknesses e.g. fault lines
      - Isle of Purbeck, Doreset
        
        Has both types of coastline
        
        When waves approach an irregularly-shaped coastline, they refract + enter parallel to the coastline - occurs where there are headlands + bays
        
        As each wave nears the coast, it is slowed by friction in the shallower water off the headland
        
        At the same time, the part of the crest in deeper water moves faster bc it is not being slowed by friction
        
        = the waves refracts around the headland and the orthongles converge
        
        So wave energy is focused on the headland and erosion in concentrated there
        
        In the bays, orthogonals diverge and energy is dissipated
        
        As waves break on the sides of the headland at an angle, there is LSD movement of eroded material into the bays = increased sed. build-up
    - - Geos
        
        Narrow, steep-sided inlets
        
        Initially form as tunnel-like caves that become enlarged by continual erosion = roof collapse = geo
      - Resistant coastlines
        
        Can be eroded where there are weaknesses e.g. joints + faults
        
        The weaknesses are eroded quicker than the resistant rock around them
        
        Hydraulic is important in forcing air + water into the joints + weakening the rock structure
      - Blowhole
        
        When part of the roof of a tunnel-like cave collapses along a master joint = vertical shaft that reaches the cliff top = blowhole
        
        Large waves can force spray out of it as plumes of white, aerated water
        
        Associated with mining shafts or the collapse of a cave roof
    - - Represent a sequence of erosional landforms that often develop around headlands
      - Bc of wave refraction, energy is concentrated on the sides of headlands
      - Points fo weaknesses are exploited by erosion processes