The coastal zone

• primary coasts

  dominated by land-based processes such as deposition at the coast from rivers or new coastal land formed by lava flows
• secondary coasts

  dominated by marine erosion or deposition processes
• cliffed coast

  • the transition from land to sea is abrupt
  • at low tide the foreshore zone is exposed as a rocky platform (wave-cut platform)
  • the cliffs here are vertical, but cliffs angles can be much lower
  • eg. chalk cliffs at flamborough head in yorkshire
• sandy coastline

  • at high tides the sandy beach is inundated, but the vegetated dunes are not
  • dune vegetation plays a crucial role in stabilising the coast and preventing erosion
• estuarine coastline

  • extensive mud flats, cut by channels, are exposed at low tide but inundated at high tide
  • closer to the back shore the mud flats are vegetated, forming a salt marsh
  • the type of coastline gradually transitions from land to sea
• Globally, over 1 billion people live on coasts that are at risk of flooding and almost 1/2 of the world's population live within 200km of the coast
• The coast is a dynamic environment as:

  • they are a boundary where land and sea meet and where both marine and terrestrial processes operate and interact
  • they experience extreme events, including tropical cyclones, storms and tsunamis which can be rare but cause significant, rapid change
  • human development on coasts is very varied (ports and transport, industrial location, residential and tourism land uses) and constantly changing
• Littoral zone

  • the wider coastal zone including land areas and shallow parts of the sea just offshore
  • coast, backshore, foreshore, nearshore, offshore
• Backshore

  • above high tide level
  • only affected by waves during extreme (spring) tides and major storms
• Foreshore

  • between high and low tide marks
• Nearshore

  • shallow water areas close to land
  • often has lots of human activity like fishing and leisure
  • part of physical system of the coastline thorough transfers of sediment
• types of coast:

  • rocky - has cliffs varying in height and create a clear distinction between land and sea
  • coastal plains - land gradually slopes towards the sea with depositional landforms like sand dunes and mud flats and have a more blurred boundary between land and sea
• rocky coastline

  • around 1000km of UK coastline consists of cliffs with variable relief/height
  • Conachair (outer hebrides/ St Kilda) has a sea cliff of 427m, the highest in the UK and made of granite
• Emergent coast

  • coasts are rising relative to sea level eg because of tectonic uplift
• Submergent coasts

  • are being flooded by the sea either because of rising sea levels and/or subsiding land
• Tidal range

  • microtidal coasts: range of 0 - 2 m
  • mesotidal coasts: range of 2 - 4 m
  • macrotidal coasts: range > 4 m
• low wave energy

  • sheltered coasts with limited fetch and low wind speeds resulting in small waves
• High wave energy

  • exposed coasts facing prevailing winds and long wave fetch resulting in powerful waves
• cliff profile

  • the height and angle of a cliff face as well as its features, such as wave cut notches or changes in slope angle
• the two main cliff profiles:

  • where marine erosion by wave action dominates, cliffs tend to be steep, unvegetated and there is little rock debris at the base as it is quickly broken up and carried away
  • cliffs not actively eroded have shallower, curved profiles and lower relief but these cliffs have sub-aerial processes like surface run off erosion and mass movement that slowly move rock and sediment downslope but because of the little marine erosion it is not removed
• Sub-aerial processes

  • cliffs are not just caused by wave action, other processes are termed as sub-aerial (and are more important when the cliff is less resistant) like:
  • weathering - chemical, biological and mechanical breakdown of rocks into smaller fragments and new minerals in situ
  • mass movement - landslides, slumps and rock falls move material downslope because of gravity
  • surface run off - water, usually during heavy rain, flows down the cliff face and erode it
• Erosion resistance

  resistance refers to the hardness of rock and is influenced by:

  • how reactive minerals in the rock are when exposed to chemical weathering; calcite in limestone can be weathered by solution whereas quartz in sandstone is not subject to chemical weathering
  • if rocks are clastic (sedimentary is cemented sediment particles) or crystalline (igneous and metamorphic made of interlocking crystals) which is more resistant
  • the degree to which rocks have cracks, fractures and fissures which are weaknesses that can be exploited
• Sedimentary rocks

  • if the cement holding sediment together (usually minerals like iron oxide, calcite or quartz) is weak, the rock will be weak
  • Sedimentary rocks are the weakest as they are barely cemented so are called unconsolidated which includes gravels, boulder clay and sands
• Coastal recession rates (cm per year)

  • granite, igneous, 0.1 - 0.3
  • limestone, sedimentary, 1 - 2
  • chalk, sedimentary, 1 - 100
  • sandstone, sedimentary, 10 - 100
  • boulder clay, unconsolidated, 100 - 1000
• coastal plains form by:

  • a fall in sea level exposing the sea bed of what used to be a shallow continental shelf eg the Atlantic coastal plain, USA
  • deposition of sediment from the land that is brought to the coast by river systems and can cause coastal accretion where the coastline gradually moves seaward eg a river delta
• Dynamic equilibrium

  • the balanced state of a system when inputs and outputs are balanced over time
  • if one element of the system changes (because of an outside influence) the internal equilibrium of the system is upset and other components change
  • by the process of feedback, the system adjusts to the change and the equilibrium is regained