littoral zone - 2B.1

• Littoral zone


  The area of shoreline where land is subject to wave action
• Zones of the littoral zone


  • Backshore
  • Foreshore
  • Nearshore
  • Offshore
• Offshore zone


  • The area of deeper water beyond the point at which waves begin to break
  • Friction between the waves and the sea bed may cause some distortion of the wave shape
• Nearshore zone


  • The area of shallow water beyond the low tide mark, within which friction between the seabed and waves distorts the wave sufficiently to cause it to break (breaker zone)
  • There may be a breakpoint bar between the offshore and nearshore zones
• Foreshore


  • The area between the high tide and the low tide mark
• Backshore


  • The area above the high tide mark, affected by wave action only during major storm events
• Types of coastal landscapes in the littoral zone

  • Rocky, cliffed coastline
  • Sandy coastline
  • Estuarine coastline
• Rocky, cliffed coastline


  • Areas of high relief varying from a few metres to hundreds of metres in height
  • Usually form in areas with resistant geology, in a high energy environment, where erosion is greater than deposition and big, stormy waves (destructive waves)
• Sandy coastline


  • Areas of low relief with sand dunes and beaches, that are much flatter
  • They usually form in areas with less resistant geology, a low energy environment, where deposition > erosion, and constructive waves
• Estuarine coastline


  • Areas of low relief with salt marshes and mudflats (estuaries)
  • They form in river mouths, where deposition > erosion, in a low energy environment, usually in areas of less resistant rock
• Dynamic zone


  • A zone of movement and change, with constantly changing inputs, through flows, and outputs of energy and material (short term)
  • Also long-term changes, e.g. sea level variation due to climate change
  • And short term changes, e.g. high and low tide variation over the lunar month; wave energy variation due to weather conditions
• Criteria for classifying coasts

  • Long term criteria (geology, sea level change)
  • Short term criteria (energy inputs, sediment inputs)
• Geology


  Characteristics of land, including lithology (rock type) and structure (arrangement of rock units)
• Concordant and discordant coasts


  Classified based on geology
• Emergent and submergent coasts


  Classified based on sea level change, caused by tectonic processes or climate change
• High energy and low energy coasts


  Classified based on energy inputs from waves, tides, currents, rivers, atmospheric processes, gravity and tectonics
• Advancing and retreating coasts


  Classified based on long-term processes (emergent/submergent) and short term (outbuilding/eroding)
• Rocky coasts


  • Result from resistant geology, often in a high-energy environment
  • Cliffs vary in height from high-relief to low-relief
• Coastal plain landscapes

  • Relatively flat, low relief areas adjacent to the sea
  • Often contain freshwater wetlands and marshes due to poor drainage
  • Littoral zone composed of sand dunes, beaches, mud flats and salt marshes
  • Form in low-energy environments where deposition > erosion, through coastal accretion from offshore and terrestrial sources
• Weathering is the breakdown of rock in situ, and may be a mechanical, biological or chemical process
• Erosion is the breakdown of rock and its immediate transport by the eroding agent
• Coasts are attacked by marine processes (e.g. wave erosion) and by terrestrial processes (e.g. weathering, mass movement, wind erosion, river erosion)
• Mass movement is the downslope movement of material due to the force of gravity
• Coastal plain formation


  • Usually by coastal accretion, where continuous net deposition causes the coastline to extend seawards
  • Also by sea level change, when the falling sea level exposes a flat continental shelf
• Where erosion = deposition, dynamic equilibrium exists as there's a continuous flow of energy and material through the coasts, but the size of stores (beach, salt marsh, mudflat) remains unchanged