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Coastal Landforms (Depositional Landforms (Salt Marshes (Low marsh…

- - - - Sources
        
        Cliff erosion - 5%
        
        Offshore - 5%
        
        Rivers - 90%
      - Sand
        
        Gentle gradient - less than 5 degrees
        
        Small particle size = compact when wet = little percolation during backwash
        
        Little energy lost to friction and little vol. lost to percolation
        
        =mat. carried back down beach - not accumulated at top
        
        = gentle gradient + runnels
      - Shingle
        
        Pebbles, and small-medium cobbles
        
        Steeper beaches
        
        Swash is stronger than backwash = new movement of shingle onshore
        
        Upper part of beach = shingle = rapid percolation
        
        Larger pore spaces = little backwash = mat. accumulates at top of beach
    - - Ridges that develop at the mean HWM
      - Result from deposition at top of swash
    - - Small, semi-circular depressions
      - Temporary features
      - Formed by collection of waves reaching same point + when swash and backwash have similar strength
      - Sides of cusp channel incoming swash into centre of depression - enlarges it
      - Self-organisation model - combines both pos. + neg. feedback
    - - Respond to changes in wind strength and wave energy
      - Balance erosion + deposition
      - Destructive waves remove sed. offshore = flatter profiles
        
        = shallower water, more friction + reduced wave energy
      - Constructive waves = steeper profiles
        
        = deeper water, less friction + increase in wave energy
    - - Straight
      - Lack LSD - waves approach perpendicularly to coast and are fully refracted
      - Closed systems
    - - Dominated by wind approaching obliquely = LSD
  - - - Carries beach mat. to end of beach + beyond into open water
    - - As spits continue to grow, several recurved ends can develop
    - - Bc of actions of river current
    - - Area behind spit is sheltered = deposition as wave energy is reduced
      - Silt + mud deposited accumulates
      - Salt-tolerant veg. colonises it
  - - - Brackish water
    - - 100m wide
      - Anomaly
        
        No dominant wind for LSD
        
        No obvious pattern of sed. size distribution
        
        Conclusion
        
        Partly formed by onshore movement of sed. during post-glacial sea level rise 6000 years ago
  - - - 30km shingle beach, Weymouth + Ise of Portland
      - Anomaly
        
        Formed by onshore movement of sediment
        
        Reached present position 6000 years ago
        
        E end
        
        Portland
        
        13m high ridge
        
        Flinty pebbles
        
        W end
        
        Burton Bradstock
        
        7m high ridge
        
        Smaller, pea-sized shingle
        
        Conclusion
        
        If it had been formed by LSD, E sed. would be smaller
        
        Onshore migration of sed. = uniform distribution of sed. sizes
        
        Strong longshore currents from SW have moved seds. of all sizes eastwards
        
        Weaker longshore currents from E have only been able to return smaller pieces westwards
  - - - Seaward side
      - High salinity
      - Turbid water
      - Long periods of submergence
      - Few plant species survive = low BD
    - - Deposition rates are still high - despite it being inundated less often
      - Low energy, slack water can be present for 2-3 hours
      - Greater veg. density helps trap + stabalise sed.
      - Extensive networks of creeks drain marsh at low tide + allows water to enter marsh at high tide
      - Shallow depressions found between the cracks
        
        Trap water when tide falls = saltpans
        
        Devoid of veg.
    - - Depends on rate of accumulation of sed. - 10cm avg.
      - Rivers
        
        Lose energy as they enter the sea = deposition of fine sed.
        
        Flocculation
        
        Tiny clay particles have an electric charge that attracts to each other in saline water = flocs
        
        Flocs are larger + heavier = unable to be carried in the river flow + settle out of suspension
  - - - Rivers entering sea are carrying large sed. loads
      - There is a broad continental shelf at river mouth = platform for comms.
      - There are low-energy environs. in the coastal area
      - Tidal ranges are low
    - - Upper delta plain
        
        Furthest inland
        
        Beyond reach of tides
        
        Composed entirely of river deposits
      - Lower delta plain
        
        ITZ
        
        Regularly submerged
        
        Both river + marine deposits
      - Submerged delta plain
        
        Below mean LWM
        
        Mostly marine seds.
        
        Represents seaward growth of delta
    - - Criss-crossed by a branching network of distribuaries
      - Bars form from deposition in channel
        
        2 channels with reduced energy levels = further deposition + dividing
      - Levees line the banks
        
        Are breached in floods = deposition in low-lying areas between levees - crevasse splays
    - - Cuspate
        
        Sed accumulates = pointed extension
        
        Extension is shaped by reg., gentle currents from all dirs.
      - Arcuate
        
        Wave action smooths + trims leading edge to prevent it from growing seawards
      - Bird's Foot
        
        Distributaries build out from coast
- - - - Vary depending on geology
      - Horizontally bedded + landward dipping strata = vertical profile
      - Horizontally bedded strata
        
        Undercutting = rock fall
        
        Cliffs retreat inland, parallel to coast
      - Seaward dipping strata
        
        Undercutting removes basal support
        
        Weathering = rock layers slide into sea along bedding planes
      - Landward dipping strata
        
        Rocks loosened by weathering + wave actiona re difficult to dislodge
        
        Profile is gradually lowered by weathering + mass movement
    - - Are not smooth bc of abrasion as rock debris is dragged across its surface by wave action
      - Boulder-sized debris will accumulate on platform
      - Platform will become so wide that it produces shallow water + small waves
      - Friction from platform = waves break on platform rather than cliff bases = reduced undercutting
      - Mostly formed from erosion, but weathering processes are also imp.
        
        Solution
        
        Freeze-thaw
        
        Salt crystalisation
        
        Algae
        
        CO2 released during resp. combines with sea water = accelerated chemical weathering
      - Slope seawards (angle of 0-3 degrees)
      - Erosion is greatest at high + low tide as water levels are constant for longest time period
        
        = ramp at high tide level
        
        = small cliff at low tide level
      - Tidal range over 4m
        
        = erosion spread over a wider areas of the platform
        
        Water is at its high + low tide positions for a shorter time
        
        = platform is more uniform + steeply sloping
  - - - Rock outcrops lie perpendicular to coastline
      - Weaker rocks eroded quicker = bays
        
        Width is determined by width of weaker band of rock
        
        Depth depends on differential rates of erosion between more resistant + weaker rocks
    - - Rocks lie parallel to coastline
      - Straight + even coastline
      - Small bays/coves can be eroded at points of weaknesses e.g. fault lines
    - - Has both discordant + concordant coastlines
      - E-facing coast - discordant
      - S-facing coast is concordant
      - Wave refraction
        
        Occurs when waves approach an irregularly shaped coastline
        
        Discordant coastlines
        
        Waves slowed by friction in the shallower water off the headland
        
        The part of the wave crest in the deeper water approaching the bay moves faster as it is not being slowed by friction
        
        = wave bends/refracts around headland + orthogonals converge
        
        = wave energy (+ erosion) focused on headland
        
        Orthogonals converge in bays + energy is dissipated = deposition
        
        Waves break on side of headland at an angle = LSD of eroded mat. into bays = increased build-up of beach sed.
  - - - Tunnel-like caves running at right angles to cliff line
        
        Enlarged by erosion = roof collapse = geo
        
        Geo = narrow, steep-sided inlet
        
        Part of the roof collapse along a master joint = vertical shaft that reach cliff top = blowhole
        
        Blowhole - waves spray out of this is storm events
  - - - Points of weakness are exploited = small caves
      - Caves develop in ITZ where wave attack is concentrated
      - Cave extends thru to other side of the headland = arch
      - Continued erosion widens arch + weakens its support = collapse = stack
      - Erosion at base of stack = collapse = stump - might only be visible at low tide