An Introduction to Coasts

By Alex Jackson

Last updated on

A coast is a narrow strip of land where the sea meets the land. Coasts are divided into zones depending on what the conditions are like on different sections of a coast.

A diagram of the coastal zones
The zones of a coast.

  • Backshore - This is the area between the high water mark and the landward limit of marine activity.
  • Foreshore - This is the area lying between the high water mark and the low water mark and is often seen as the most important area for marine activity.
  • Inshore - The area between the low water mark and the point where the waves cease to have any influence on the land around them.
  • Offshore - The area beyond the point where waves cease to impact the seabed and in which activity is limited to the deposition of sediments.

Factors Effecting Coasts


  • Rock type of the coast. If the coast is made from soft rock, it will be eroded far more quickly than if it is made of hard rock.
  • Deltas form where rivers meet the sea, which will alter the shape of coasts.
  • Composition of rock layers on coasts will affect their shapes.
  • Tectonics in the area will effect coasts. Earthquakes can move rock and trigger tsunamis, which can destroy entire coastlines.
  • Mangroves and coral reefs can alter the shape of coasts as they slow down incoming waves, decreasing the rate at which a coast is eroded.


  • Ports, docks and transport can be constructed and/or used on coasts, thus altering the shape of coasts. Boats can destroy coral reefs and hence increase the erosion of the coastline.
  • Coasts can be used for recreation and tourism. The increased foot traffic and demand for certain attractions on coastlines can alter their shape substantially.
  • Humans can settle on coastlines. Often, settlements on coastlines will thrive due to their proximity to the sea for trade and tourism.
  • Global warming is altering the shape of coastlines due to the rising sea levels resulting from it.


  • Certain types of weather can effect coasts. High winds and heavy rain will erode coasts.
  • The Moon (and the Sun and Jupiter to some extent) effects the tides substantially, which can alter the shape of coasts.
  • Temperatures alter the shape of coasts.


  • Biotic creatures such as Coral alter the shapes of coasts for the aforementioned reasons relating to the rate of erosion.
  • Waves, tides & salt spray all play their part in altering the shape of coasts.

Coastal System

Coasts are considered an example of an open system as they have inputs and outputs.


  • Energy is inputted in the form of waves, wind currents and tides. These will vary spatially and temporally (space and time, no not that space and time).
  • Sediment from other eroded coastlines, rivers and sub-aerial processes will be deposited along coasts.
  • Human activity will provide inputs for coastal systems.


  • Erosion, transportation and deposition all take place on coasts along with longshore drift, biological activity and wind transport (known as aeolian).


  • Landforms, sediment and the shape and position of the coastline are all examples of outputs.