depositional landforms

  • Created by: beaw18
  • Created on: 18-04-19 15:43

beaches

  • beach material consists of of sand, pebbles and cobbles coming from 3 main sources: cliff erosion, offshore (from seabed, typically during rising sea levels) and rivers (suspended and bedload through river mouths - about 90% of sediment)
  • sand creates beaches at a gentle gradient
    • small particle size, compact when wet.
    • material carried back down to beach as it is light.
  • shingle (pebble) beaches have a steeper gradientstorm beaches occur when storm waves throw pebbles and cobbles to the back of the beach, creating the steepest gradient.
    • swash is stronger than backwash; leaving heavy shingle at the top of the beach, and dragging smaller sediment back to sea.
  • ridge - hump of sand created by wave action that runs parrallel to beach. berms are smaller ridges that develop at the tide line
  • beach profiles change over time as wind strength (and therefore wave energy) change.high energy, destructive waves create flatter beach profiles, whilst low energy, constructive waves form steeper profiles
    • develop equilibrium - balance between erosion and deposition.
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spits

  • long, narrow beaches of sand/shingle attached to land at one end and extend across body of water
  • formed by longshore drift occuring in one dominant direction - carries beach material past beach and into open water
  • end of spit often becomes curved due to wave refraction, or sometimes an opposing wave/wind direction
  • behind spit deposition occurs as wave energy is reduced, may lead to the formation of salt marshes - salt tolerant vegetation
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onshore bars

  • develop if a spit continues to grow across an indentation (meaning inward part of coastline such as bay or cove) and joins to land at other end
  • creates inland area of low energy water
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tombolos

  • beaches that connect the mainland to an offshore island 
  • often formed from spits which grow seawards until they reach and join an island
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salt marshes

  • form on the inland side of spits, and estuaries
  • due to  low-energy nature of environment, sediment is deposited and builds up
  • salt tolerant plant species grow too, such as eelgrass and spartina - help trap sediment and increase marsh height
  • flooded twice a day due to tide rise and fall, however the higher the marsh, less if it is submerged by sea water, meaning less saline conditions
  • closer to the spit, conditions for life in the marsh is poor and so diversity is low
  • further inland, the conditions less harsh and so diversity is greater
  • shallow gradient which slopes seawards
  • development of the marsh is dependent on how quickly sediment is deposited
  • rivers loose energy as they enter the sea, causing higher rates of deposition
  • flocculation - sediment particles group together to form flocs which are then heavy then deposited
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deltas

  • large areas of sediment found at the mouth of many rivers - sediment is deposited by rivers and tidal currents - form when rivers and tidal currents deposit sediment at faster rates then tides and waves can remove it. formed when:
    • rivers enter sea carrying large sediment loads
    • continental shelf margins (seabed which is much shallower than the rest of the ocean) is pre-existing, provides raised platform for sediment accumulation
    • tidal ranges low
  • structures of delta:
    • upper delta plain - furthest inland, composed of river deposits, out of reach to tides
    • lower delta plain - in the inter-tidal zone (in the sea), regularly submerged and made from both marine and river deposits
    • submerged delta plain - lies below water (submerged) and made from marine deposits
  • 3 most common types of delta:
    • cuspate - pointed shape, caused by gentle currents from opposite directions moving sediment
    • arcuate - wider, rounded shape. grows seawards due to plent of sediment, wave action keeps edges rounded
    • bird's foot - branching pattern formed by distributaries, river sediment supply exceeds waves and currents
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