User:Donald Albury/Barrier islands of Florida

Three regions:

Atlantic coast
The Atlantic coast of Florida has 550 km of barrier beaches, stretching from the border with Georgia at the mouth of the St. Marys River to Key Biscayne south of Miami Beach. There are 22 inlets through the barrier beaches in that stretch. Cape Canaveral sits close to the middle of that barrier system. The part of the coast from the St. Marys River to Cape Canaveral is the southern end of the Georgia Bight, an embayment, or shallow, open bay, which extends from Cape Canaveral to Cape Fear, North Carolina. Tidal range is relatively low at Cape Canaveral and Cape Fear, but increases towards the center of the bight at Saint Helena Sound in South Carolina. Accordingly, tidal flux, of minimal influence on barrier island dynamics at Cape Canaveral and Cape Fear compared to wave energy, plays an increasing role in shaping islands towards the center of the bight. South of Cape Canaveral tidal range is low and wave energy dominates the barrier beaches.

Some barrier beaches on the Atlantic coast are welded to the mainland. Tidal inlets, tidal flats, tidal marshes, and back-barrier bays are features commonly associated with barrier island and spits. North of Matanzas Inlet on the Atlantic Coast of Florida, the barrier system shows a mix of tidal and wave energy influences. Barrier islands are relatively short, with well-developed dunes. There are extensive tidal flats and marshes asociated with the barrier islands. South of the Matanzas Inlet, in the southern end of the Georgia Bight, and along the coast south of Cape Canaveral, the barrier system is dominated by wave energy. Barrier beaches in that section range from narrow and steep to wide and gently sloping. The islands are relatively long, and the inlets, before being artifically constrained, were unstable. The back-barrier bays tend to be narrow, with limited tidal flats and marshes. Combined with the distances between inlets, the back-barrier bays have much reduced salinity in areas away from the inlets.

The barrier system of the Atlantic coast of Florida is dominated by quartz sand of Holocene origin. The sand is transported south along the coast by longshore drift. The volume of the sand transported decreases as it is carried south. About 600,000 cubic meters of sand move past the mouth of the St. Johns River per year, while only some 10,000 cubic meters per year reach Key Biscayne. There is negligible transport of quartz sand south of Key Biscayne. On some parts of the coast, the longshore drift may reverse, forming littoral cells. Converging littoral cels build up barrier islands, and may be responsible for Cape Canaveral; diverging littoral cells tend to erode existing barrier beaches.

Sea Islands - state line to mouth of St. Johns River

 * Amelia Island
 * Big Talbot Island
 * Little Talbot Island
 * Fort George Island
 * Anastasia Island


 * Southeastern coast - Cape Canaveral to Cape Florida

West coast of peninsula
A beach barrier system extends for 300 km along the west coast of the Florida peninsula from Anclote Key to Kice Island at Cape Romano. As of 1997, the system included 29 barrier islands and 30 inlets. Some of the islands are long and narrow, dominated by wave energy. Others are "drumstick" shaped, produced by a mixture of wave and tidal energy. Some have been produced by upbuilding shoals, while other have resulted from elongation of spits. With the exception og Sanibel Island, the island lie in a fairly straight lone along the coast. The position of many of the islands is controlled by the underlying geology, aligning with buried structures of Pleistocene and Neogene age. Richard Davis states that this system "has the most diverse morphology of any barrier system in the world."

Both tidal and wave energy are low along the west coast of the Florida peninsula, and the morphology of the barrier islands can change significantly in response to small changes in the balance between tidal and wave energy, often due to the refraction of waves over shoals that develop outside an inlet. Hurricanes also have a significant impact on the islands, opening and closing inlets. Some inlets opened by hurricanes later close as the result of longshore sand transport, but others remain stable for many years. Four inlets opened, nine closed, and five others both opened and closed along this coast during the 20th century.

Several barrier islands emerged in the west coast system during the second half of the 20th century, including: the North and South Anclote Bars associated with Anclote Key, Three Rooker Island, Shell Key, and South Bunces Key. While South Bunces Key had disappeared by 2016, the other new barriers islands still existed in 2023. The new islands were quickly colonized by vegetation, with coppice mounds (sand built up around plants) forming soon after, followed by dunes more than one meter taller than the back beach.

The barrier island system of the west coast of Florida is a product of the recent Holocene era. The oldest barrier islands in the system are about 3,000 years old. Sediments under the current barrier islands are 4,200 to 4,500 years old. Unlike the east coast of Florida, there is no outside source of quartz sand for the west coast barrier islands. All of the sand in the barrier islands has been reworked from pre-Holocene deposits along the coast. The sand is thickest under the islands, and thins out both towards the open water of the Gulf, disappearing by the time the water is five or six meters deep, and towards the mainland, disappearing at the mainland coast. Along the line of the islands, the sand is usually less than eight meters thick, and is as little as three meters thick ion places.

The islands probably formed close to their current locations, although some migration towards the mainland may have occurred due to overwashing. Older islands in the system that developed 3,000 years ago have extensive beach ridges that protect them from overwash during storms. These islands, which include Siesta Key, Gasparilla Island, Cayo Costa, Sanibel Island, and Marco Island, formed in areas with abundant sand. Islands that have formed where sand is less abundant are younger, tend to be long and narrow, and are subject to overwash in storms.

Anclote Key to Cape Romano


 * Panhandle coast - Dog Island to Perdido Key
 * Apalachicola delta

Panhadle coast
The panhandle coast of Florida has a series of barrier islands, barrier spits, and mainland beaches extending from Dog Island, south of Carabelle, to Perdido Key, which extends into Alabama. The eastern part of the panhandle coast consists of the Apalachicola Delta, which has been produced by sediment carried by the Apalachicola River, with a basin draining much of Georgia and Alabama. The delta formed during the Quarternary, but sea level rise during the Holocene has corresponded to a reduction in sediment carried by the river. The sand of the delta has been reworked by littoral cells into the barrier islands of Dog Island, St. George Island (which originally included Cape St. George Island), St. Vincent Island, and the barrier spit of Cape San Blas and St. Joseph Peninsula. Sand from the Apalachicola Delta is carried westward by longshore currents, feeding mainland beaches, barrier spits, and the barrier islands of Santa Rosa Island and Perdido Key.