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Lagoon

earth science Maturity 11-13 Next article →

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform. This barrier might be a coral reef, a barrier island, or an isthmus. Lagoons are common coastal features found throughout the world. They play a major role in coastal ecosystems. Scientists often divide them into two main categories: coastal lagoons and atoll lagoons.

BalosLagoonCreta
BalosLagoonCreta

Coastal lagoons form along coasts with very gentle slopes. These lagoons appear when barrier islands or reefs develop offshore. This process often happens when sea levels rise relative to the land. This rise can be caused by the ocean rising or the land sinking. Because the coast slopes so gently, these lagoons remain quite shallow. They do not form along steep or rocky coasts.

Caspian Sea covered with plants near Bandar-e Anzali - Barry Kent
Caspian Sea covered with plants near Bandar-e Anzali - Barry Kent

Atoll lagoons form through a different biological and geological process. These lagoons develop as coral reefs grow upward toward the surface. While the reefs grow, the islands they surround begin to subside, or sink. Eventually, only the ring of coral reef remains above the sea level. This leaves a body of water in the center. Unlike coastal lagoons, atoll lagoons often contain deep portions.

Atafutrim
Atafutrim

Researchers sometimes debate the exact definition of a lagoon. Some authorities include fresh water bodies in the definition. Others say a lagoon must have some level of salinity, or saltiness. There is also a distinction between a lagoon and an estuary. Richard A. Davis Jr. suggests that lagoons have little fresh water inflow. He defines an estuary as a bay that receives regular fresh water. Timothy M. Kusky notes that lagoons are usually elongated parallel to the coast. In contrast, estuaries are often drowned river valleys perpendicular to the coast.

The term lagoon has a long history in the English language. It is derived from the Venetian word "laguna." This refers to the waters surrounding Venice, Italy. The word "laguna" was used in English by at least 1612. In 1697, William Dampier described a salt water lagoon in Mexico. Later, in 1769, Captain James Cook described an island with a lagoon in the middle.

Venice Lagoon December 9 2001
Venice Lagoon December 9 2001

Lagoons are incredibly widespread across the globe. They occur along nearly 15 percent of the world's shorelines. In the United States, they are found along more than 75 percent of the Eastern and Gulf Coasts. Coastal lagoons can be classified as leaky, restricted, or choked. Their water chemistry depends on several moving parts. For example, Lake St. Lucia in South Africa can become highly saline. This happens due to high evaporation and little ocean interchange. Conversely, the Wadden Sea has many wide inlets. These inlets create strong tidal currents that mix the water.

Kara-Bogaz Gol from space, September 1995
Kara-Bogaz Gol from space, September 1995

Many different factors influence the physical structure of a lagoon. Lagoons accumulate sediment from inflowing rivers and shoreline runoff. Tides also carry sediment through inlets into the lagoon. Large amounts of sediment may arrive during storm waves. These waves can wash material over barrier islands. Plants like mangroves and marsh plants help facilitate sediment accumulation. Additionally, benthic organisms can stabilize or destabilize these sediments. This makes lagoons dynamic and often short-lived in geological terms.

Hiddensee (2011-05-21)
Hiddensee (2011-05-21)
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🖼️ Images & Media (6)
File:BalosLagoonCreta.jpg
BalosLagoonCreta.jpg
File:Kara-Bogaz Gol from space, September 1995.jpg
Kara-Bogaz Gol from space, September 1995.jpg
File:Venice Lagoon December 9 2001.jpg
Venice Lagoon December 9 2001.jpg
File:Atafutrim.jpg
Atafutrim.jpg
File:Caspian Sea covered with plants near Bandar-e Anzali - Barry Kent.jpg
Caspian Sea covered with plants near...
File:Hiddensee (2011-05-21).JPG
Hiddensee (2011-05-21).JPG
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