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Evolution of Landforms (Submergent Coastlines (Background (Eustatic rises…

- - - - Affects amount of water in ocean store + its density
    - - Variations on Earth's orbit - every 4000 years
      - Variations in amount of energy produced by sun
      - Changes in composition of atmosphere
        
        Major volcanic eruptions decrease incident solar radiation
      - Variations in tilt of Earth's axis - every 41,000 years
  - - - Decrease in global temps. = more precip. (snow)
        
        Snow becomes ice = water stored on land rather than ocean
        
        = global decrease in sea level
        
        = decrease in water vol. in ocean store
      - As temps. decrease, water molecules contract = increasing density + reduced vol.
      - 1 degree fall in eman global temps = sea level fall of 2 m
    - - Increased global temps. = higher rates of melting ice
        
        = global increase in water vol.
        
        = global rise in s.l.
        
        = increased water vol. as molecules expand when temp. rises
      - 1 degree rise in mean global temps. = 2m sea level rise
      - S.l. has been rising since the Wurm period 25,000 years ago - known as the Flandrian Transgression
  - - - Non-vegetated, soft sea habitats
      - Found between mean HWM+ LWM
      - Located in low energy environments e.g. estuaries
    - - Forms from the spreading out of waves' energy across a wide area = depression in sand
      - Common on shallow, sandy beaches
    - - Proportion of stream affected by ebb tides
      - Discharges to sea
      - This part of the stream has variable salinity
    - - Formed abruptly at increased storm velocities
      - 60cm - several metres long
    - - Formed from deposition of sed.
    - - Formed in shallow waters off the coast
      - Causes waves to break early
- - - - Longer river = more energy = more erosion
  - - - Raised beaches are areas of former shore platforms
      - Behind beach along emerging coastline there are many abandoned cliffs with:
        
        Wave cut notches
        
        Caves + arches
        
        Stack + stumps
    - - Raised beach 15m above present-day sea level
        
        Formed 125,000 years ago, during Tyrrhenian inter-glacial period when sea levels were higher
      - Portland limestone was eroded by hydraulic action via exploitation of bedding planes
      - Erosion rates were 1cm/year
      - Other raised beaches date back to 210,000 years ago
      - Modification of Landforms
        
        After emergence, landforms were no longer affected by wave processes, but still affected by weathering + mass movement
        
        Periglacial processes
        
        1m layer of frost shattered debris on top of abandoned cliff
        
        Cliff face was gradually degraded by frost weathering = rock fall
        
        Cryoturbation - evident in contortions of fragmented limestone
        
        Freeze-thaw of permafrost in subsoil in the final glacial phase
        
        Post-glacial period
        
        Warmer + wetter conds. = veg. cover
        
        Increased warming = increased degradation
        
        Increased chemical wethering
        
        Esp. carbonation of limestone
        
        Chem. reactions work faster in warmer conds.
        
        Increased biological weathering
        
        Colonisation of surface of raised beach by marine orgs.
- - - - As s.l. rose, glacial deposits dumped offshore as a bar where driven on land by rising sea = a barrier island
      - Formed as s.l. rose since the last glaciation during the Flandrian transgression
  - - - Concept
        
        There is fluvial deposition in Roas
        
        Long profile - is the gradient of a river fro the source to mouth
        
        Rivers attempt to form a graded profile: a balance between erosion + deposition
      - Reality
        
        The profile adjusts to discharge, load and base level changes
      - Sea Level Rise
        
        Rise in s.l. = positive change in base level
        
        = loss of energy + deposition in channel (aggradation) to raise the river to the new base level
  - - - Bc of prev. glacier;s reduced erosion rate
  - - - Wave processes act on sides
      - Sub-aerial processes act on valley sides
      - = decreased steepness of valley sides of fjords
      - S.l. rise = increased water depth
      - Stormier conds. + larger waves = increased marine erosion
    - - Composed of unconsolidated mat. = vulnerable to modification
      - Chesil Beach tombolo affected by present-day LSD
        
        Shingle might move further NE (17cm/year current rate)
        
        Breach is likely in storme vents
        
        Recent storms e.g. 2009 - waves over-topped the beach
- - - - Global rise/fall in s.l.
      - Absolute change in vol. of water stored in oceans
      - Development of mid-ocean ridges
      - Glaciation -s.l. falls
      - Climatic warming (interglacials) - s.l. rises
    - - Localised rise/fall in relative sea level
      - Vol. of water in ocean doesn't change
      - Isostatic subsidence - s.l. seems to rise
      - Isostaic rebound - s.l. seems to fall
      - Loading + unloading of mass during glaciation + deglaciation
      - Tectonic movements e.g. faulting
    - - Temp. decreases, galciers + ice sheets advance + s.l. falls eustatically (water is stored in ice)
      - Ice sheets thicken + weight causes land to lower isostatically
      - Ice melts, s.l. rises eustatically
      - Continued melting causes pressure release + the land rises isostatically