These conditions foster the growth of extensive long and narrow offshore deposits, many of which are exposed above the water as sandspits or barrier islands.
These deposits are constantly being reshaped, sometimes extremely slowly and sometimes quite rapidly, by the forces of water and wind.
It is common along flooded coastal plains for drowned river valleys to empty into lagoons that have been created behind the sandspites and barrier islands tather than emptying directly into the ocean.
These lagoons support vigorous biological activity inasmuch as they are shallow, which causes them to heat up quickty, and they are fed by a constant inflow of nutrient-rich sediments.
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Some changes to the deposits can take place gradually over decades, while other changes can be quite radical changes in a period of only a few hours as the result of major strom activity.
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