Coastal and Oceanic Landform (30. Lagoon )

                                                                                                                                         Back to Coastal and Oceanic Landform

  • lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs

  • Commonly divided;

                                       1.Coastal lagoons
                                       2.Atoll lagoons

  • They have also been identified as occurring on mixed-sand and gravel coastlines.
  • There is an overlap between bodies of water classified as coastal lagoons.
  • Bodies of water classified as estuaries.
  • Lagoons are common coastal features around the world.
  • water with some degree of salinity. The distinction between "lagoon" and "estuary".

Atoll lagoons

  • Formed as coral reefs.
  • Grow upwards while the islands the reefs surround subside.
  • Eventually the reefs remain above sea level.
  • Unlike the lagoons form shore-ward of fringing reefs.
  • Atoll lagoons often contain some deep (>20m) portions.

Coastal lagoons
Coastal lagoon  Hiddensee near Stralsund, Germany.
Coastal lagoon  Hiddensee near Stralsund, Germany.

  • Gently sloping coasts where barrier islands /reefs  develop off-shore.
  • The sea-level is rising relative to the land along the shore.
  • Coastal lagoons are shallow.
  • They are sensitive to changes in sea level.
  •  A relative drop in sea level may leave a lagoon largely dry.
  • Coastal lagoons are young and dynamic.
  • Coastal lagoons are common nearly 15%  of the world's shorelines. 
  • Usually connected to the open ocean by inlets between barrier islands.
  • The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon.
  •  Little or no inflow of fresh water.

  • High evaporation rates;

                         Lake St. Lucia, in South Africa
  • Lagoons with no connection to the open ocean and significant inflow of fresh water

                          Lake Worth Lagoon in Florida
Garabogaz-Göl lagoon in Turkmenistan
Garabogaz-Göl lagoon in Turkmenistan

River-mouth lagoons on mixed sand and gravel (MSG) beaches 
  • River-coast interface typically braided.
  • River interacts with a coastal environment.
  • MSG coastlines are common on the east coast of the South Island, New Zealand.
  • Long  referred to as 'hapua' by the Māori.

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