Depositional coastal landforms


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Depositional coastal landforms

  1. 1. Depositional Coastal landforms Definitions Front
  2. 2. Depositional Coastal landforms Definitions Front
  3. 3. Spits  Spurn Head Definitions Front
  4. 4. Spits – Spurn Head & Orford Ness Spurn Head  Drift aligned  Aided by rapid input from glacial material  Little or no refraction from F.H.  Proximal retreat in balance with the Holderness coast  Humber channel “forced” south Orford Ness • Single spit • 15km long - vegetated • Diversion of R. Alde • Dynamic growth: • 64m p.a. 1962 to 1967 • 183m p.a. 1804 to 1812 • 2.9km 1812 to 1821 Definitions Front
  5. 5. Hooked/recurved/single spits Reworking Sheltered sedimentation zone Hurst Castle Multiple hooks Distal needs ↑ sediment as it reaches across deeper water Definitions Front
  6. 6. Double spits Poole Harbour Definitions Front
  7. 7. Double spits Christchurch Harbour Definitions Front
  8. 8. Double spits Poole Harbour Christchurch Harbour  1785 channel outflow  1880 spit extenison from through “Little Sea” south to north almost to  By 1875 entrance migrated Highcliffe Castle  Managed to maintain channel  1886 & 1935 spit breach by easterly storm  Migration due to off shore  Theory? bar inshore migrating  Northern spit is remnant of bar? PH = swash aligned, CH = drift aligned Definitions Front
  9. 9. Barrier beaches  Slapton sands Created during the Flandrian Transgression (10k-5k BP) Relic feature – positive eustatic change Ley fed by three streams, shallow lake – usually higher than sea level Bar beach easily breached – 2001 – normal conditions; 4m tidal range, 0.5m wave height (storm up to to 2m) Future impact of eustatic change? Slapton Ley
  10. 10. Slapton Ley
  11. 11. Slapton Ley Composition – flint pebbles – provenance 30/40km offshore @10k BP offshore barrier moved onshore by “roll over” process @5 k BP Intermediate step of forming barrier islands @3k BP emergent coastline created headland divisions of Start Bay Dynamic equilibrium – local sea level rise = 2-4mm p.a. evidence from current storm roll over = 0.5m p.a. inward migration LSD north and south in equilibrium over centuries if not smaller scales Short term storm: Roll over crest & remove forebeach Forebeach rebuilt over time. ↑ storms → reduced barrier
  12. 12. Definitions Swash aligned beaches ; Drift aligned beaches; Some beaches show oblique ·Smoothly curving concave alignments to the dominant wave beaches. fronts. · Beach face is orientated parallel Usually occurs where the beach to the fronts of the dominant gradient is steep and the wavelength waves. is short. · Beaches which face the waves This is because the crest breaks at are termed swash aligned. different times along the beach. Spits; Spits II; e.g. Spurn Head, Holderness, As spits build further in to deeper Barrier beaches Yorkshire. water, they require more sediment to Beach which stretches across from Dominant waves push material along build above the HWM. The waves one embayment to the other, and the coast in longshore drift. Coast have greater energy to attack the encloses a lagoon behind it turns inwards, and the material distal end, turning it inwards. , e.g. Slapton sands, Cornwall. continues to be deposited in line with Sometimes, the curves are due to the Feature is swash aligned, and has the coastal trend. Finer materials are changing of the predominant wind probably been driven landwards deposited in the sheltered side of the direction to another, causing from the offshore zone. spit. Marshes can build up, and this waves, and thus deposition to occur forces the river to the other side of the an a different angle. These recurves estuary. are sheltered by the spit and become prominent features, e.g. Hurst Castle Spit, The Solent. Front