Role of deposition in formation of landforms

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Role of deposition in formation of landforms
  1. Deposition
    1. Occurs when water not enough energy so drops particles
      1. In areas where swash brings material up beach but backwash not enough energy to bring down again
      2. Rowen spit
        1. Spit doesn't form from change in direction of coast
          1. Instead, LSD deflected by tidal flow and into deeper water
            1. Waves don't break -> no swash/backwash
              1. Material is deposited
            2. Spit increased in size by LSD, waves and wind move sediment along coast and big swash, small backwash mean sediment is deposited, increasing the length
              1. Curved end
                1. SW winds and wave refraction
                  1. destructive energy dissipates as waves refract into bay allowing constructive waves to build up curved end
                2. Biggest particles deposited out of 3 landforms as subjected to highest wave energy, so pebbles on spit as well as sand
                3. Sand dunes
                  1. Situated on Rowen spit and Barmouth beach
                    1. Develop where strong offshore winds and a low gradient near shore slope
                      1. Sand is deposited in this environment and starts to build up
                      2. Marram grass establishes and roots hold sand in place, allowing consolidation and growth
                        1. Forms a more effective wind break starting a positive feedback loop: sand is deposited so dunes get higher, which means more sand is trapped and dunes get higher and so on
                        2. Human processes can encourage deposition and so, growth of sand dunes
                          1. 1972 causeway built across Bar Bach channel
                            1. Caused a large amount of deposition behind the causeway, facilitating the development of sand dunes
                          2. Sand dunes are effective form of natural coastal management, during high spring tide they act as natural wall, protecting what is behind them
                          3. Salt marsh
                            1. Area behind Rowen spit sheltered, only open to tidal flow and some refracted waves
                              1. They carry very fine grained sediments from river estuary, clay & silt
                                1. Particles flocculate in salt water to form larger particles, which are mainly deposited around high tide, as the flow velocities are low
                              2. The rate of deposition is highest on mud flats, where flow velocities are lowest and the low energy means the material is more likely to be deposited
                                1. From high tide mark, deposition extends seawards, which expands the mud flats
                                2. Salt marsh builds up higher, frequency of tidal flooding falls
                                  1. Allowing vegetation to colonise. The plants (eg spartina) trap sediment, like marram grass, as energy from water is reduced - and so more sediment is deposited
                                    1. Most vegetation is found in the lowest energy environment. (Areas only flooded in a high spring tide)
                                      1. Plants which can withstand saline conditions, allow more deposition as they can withstand tide change
                                  2. Conclusion
                                    1. These landforms controlled by the energy the wind and waves have and so, governed by deposition
                                      1. Enhanced greenhouse effect (312 ppm 1960s to over 400ppm today)
                                        1. Results in rising global average temps which means eustatic sea level rise, due to melting of land based ice and thermal expansion of sea water
                                          1. Deposition will change with rising sea levels
                                            1. Dramatic sea level rise could mean spit submerged, destroyed sand dunes and inundated salt marsh
                                              1. Gentle sea level rise, effects less severe, salt marsh and sand dunes could grow and rise with sea level
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