Barrier Islands in the United States

| |

Barrier islands are narrow stretches of land that run parallel to coastlines. Made up of deposited sand and vegetation, these islands can form protective barriers that reduce coastal erosion, purify water, and help protect wildlife and vegetation.

Barrier islands are separated from the mainland by a shallow body of water and can stretch for miles along the coast.  

Diagram showing  the cross-section of a barrier island progressing from ocean (on the right) to marsh and then lagoon (on the left).  Image: Betsy Boynton, Cherokee Nations Technologies, contracted to the USGS. Public domain.
Diagram showing the cross-section of a barrier island progressing from ocean (on the right) to marsh and then lagoon (on the left). Image: Betsy Boynton, Cherokee Nations Technologies, contracted to the USGS. Public domain.

Barrier islands help to protect the mainland by absorbing energy from incoming waves. By creating a protected area of water, barrier islands also allow wetlands to thrive which in turn creates a supportive environment for birds and other wildlife.

Barrier Islands Also Support Recreation and Fishing Industries

Barrier islands are also home to residents and support recreation and fishing. Wildwood is a New Jersey barrier island that is a popular beach destination along the Jersey Shore. With a year-round population of 5,325, this swells to a daytime population over 250,000 during the summer months.

Wildwood barrier island, New Jersey.  Satellite image from NASA, public domain.
Wildwood barrier island, New Jersey. Satellite image from NASA, public domain.

The United States Has the Most Barrier Islands

It is estimated that about 10% of coastlines in the world are protected by barrier islands. A survey of imagery in 2011 estimated at the time that there are 2,149 barriers islands in the world.

Barrier islands are found on all continents except for Antarctica. Seventy-four percent of barrier islands are located in the northern hemisphere.

Of those barrier islands, the United States has the most with a count of 450 barrier islands.

Fire Islands is an Atlantic Ocean barrier island off the southern shore of Long Island, New York. Photo: Jennifer Miselis, USGS. Public domain.
Fire Islands is an Atlantic Ocean barrier island off the southern shore of Long Island, New York. Photo: Jennifer Miselis, USGS. Public domain.

Where are Barrier Islands Found in the United States?

Most of the barrier islands in the United States are found along the East Coast and Gulf Coast. Every state in this area from Maine down to Florida and over to Texas has barrier islands.

There are no barrier islands along the Pacific coast of the United States due to its rocky shoreline and short continental shelf.

Alaska’s Arctic coast also has barrier islands. The 2011 study found that 272 barrier islands, representing 12.7% of the world’s inventory, are found along coastlines that face the Arctic Ocean.

Adult polar bear walking across a recently overwashed barrier island during a large Arctic storm in September 2016. The barrier island is offshore of Barter Island on Alaska’s north coast. Photo: Cordell Johnson, USGS Pacific Coastal and Marine Science Center. Public domain.
Adult polar bear walking across a recently overwashed barrier island during a large Arctic storm in September 2016. The barrier island is offshore of Barter Island on Alaska’s north coast. Photo: Cordell Johnson, USGS Pacific Coastal and Marine Science Center. Public domain.

Barrier Islands are Constantly Changing

Barrier islands are susceptible to storm damage due to their sand formation, which is less stable than that of the hard bedrock characteristic of larger islands and mainland. They also tend to have very low elevations, making it easy for water to wash over and immerse the island.

Erosion from wind and waves along with severe storms are constantly altering barrier islands. Storms can flatten dunes, erode beaches, and cause the destruction and flooding of structures on the barrier islands.

When an opening on a barrier island is created by a severe storm passing through, it is known as a breach. Fire Island suffered a breach in 2012 after Hurricane Sandy hit the barrier island, splitting the island in a small wilderness area. The split has continued to widen by the impact of several nor’easters (storms that form along the East Coast).

Before and after photos showing the breach on Fire Island after Hurricane Sandy.  Photo: USGS, public domain
Before and after photos showing the breach on Fire Island after Hurricane Sandy. Photo: USGS, public domain

Dauphin Island – a Barrier Island in Alabama

Dauphin Island in Alabama is the only barrier island that provides protection to much of the state’s coastal areas. Located in the Gulf of Mexico, Dauphin Island provides a protective barrier to Alabama’s coastal natural resources.

An egret walks in the shallow surf of an undeveloped beach on Dauphin Island, Alabama, with buildings viewed in the background from a different area on the island. Photo: Soupy Dalyander, USGS. Public domain.
An egret walks in the shallow surf of an undeveloped beach on Dauphin Island, Alabama, with buildings viewed in the background from a different area on the island. Photo: Soupy Dalyander, USGS. Public domain.

Dauphin Island is an important rest stop for migrating birds. The barrier island is the first land birds encounter when migrating north from South America.

Dauphin Island is also home to a town of the same name that has roughly 1,200 residents. The island supports recreational and commercial fishing industry as well as serving as one of the most important bird sanctuaries in the Southeast.

An aerial view of Dauphin Island, Alabama, shows a thin strip of road partially covered by sand, with undeveloped beach in the foreground and developed beach in the background.  Photo: Karen Morgan, USGS. Public domain.
An aerial view of Dauphin Island, Alabama, shows a thin strip of road partially covered by sand, with undeveloped beach in the foreground and developed beach in the background. Photo: Karen Morgan, USGS. Public domain.

Barrier Islands in Texas

The Texas coastline boasts of at least ten barrier islands of different lengths.  The better-known islands are more accessible to the mainland and include Galveston, Mustang, and Padre islands.  

Galveston Island

The most significant natural habitats of Galveston Islands are its bays and wetlands, beaches and dunes, and coastal prairies. This island is also considered to be a subtropical grassland region.  There are prairie areas where tallgrass grows and is home to small mammals and reptiles. (The University of Texas at Austin – Geologic Wonders of Texas)

Mustang Island

According to Texas Parks and Wildlife, Mustang Island as well as its neighboring barrier islands was formed within the last five thousand years as the oceans level increased.  Mustang Island as well as the other barrier islands acts as a bumper between the Gulf and the mainland.  Its 

They serve as buffers between the open gulf and the mainland. On the gulf side, rows of sand dunes often rise thirty feet or more. The inner coast side of the dunes creates a shield from wind and salt spray, producing a sheltered environment for vegetation and wildlife.  This is important since the coastal grasses native to this environment maintain dune integrity.  The grasses provide protection to the dunes, meadows, and other natural characteristics of the islands.

Padre Island

According to the Texas Bureau of Economic Geology, Padre Island was formed during the Holocene era, when the glaciers melted and the sea level reached a point close to what it is today.  During that time valleys were flooded forming existing bays and estuaries all along the Texas coastline.

Several systems are implicated in the formation of Padre Island and neighboring barrier islands: the wind and ocean.  Sand and depositions transported during storms continue to form Padre Island’s geology.  The Texas Bureau of Economic Geology also has recorded Padre Island’s maximum sediment thickness to be approximately 35 to 40 feet, depending on dune formations.

In addition to sand dunes formation, different sectors of Padre Island have undergone a stability phase, and possibly are now in the process of erosion.  As noted in the Texas Bureau of Economic Geology, a great section of the northern part of the island is in the stability phase, the rest of the island may already be in the erosion phase.  The Texas Bureau of Economic Geology also predicts that due to the decrease in sediment buildup, the rise of sea level, and tropical storms the island will retreat landward.

A Kemp's ridley sea turtle makes its way back to the ocean on Padres Island.  Photo: NPS, public domain
A Kemp’s ridley sea turtle makes its way back to the ocean on Padres Island. Photo: NPS, public domain

World’s Longest Stretch of Undeveloped Barrier Island

The United States is also home to the world’s longest stretch of undeveloped barrier island with a length of 13 mi (182 km). The largest barrier island in Texas, Padre Island is located off the coast of South Texas and is part of the Padre Island National Seashore, a national park

Padre Island has developments on either end of the barrier island with the town of South Padre Island on its southern end and the city of Corpus Christi at the northern end.

The barrier island separates the Gulf of Mexico from 70 miles of coastline of the South Texas coastline. In between lies Laguna Madre, one of the few hypersaline lagoons in the world.

Padre Island serves as a sanctuary for over 380 bird species and is a nesting ground for Kemp’s ridley sea turtle, the rarest species of sea turtle and the world’s most endangered species of sea turtles. Kemp’s ridley sea turtle are also the smallest marine turtles in the world.

World’s Longest Chain of Barrier Islands

The 2011 study also found that the world’s longest chain of barrier islands is a 54-island chain that “extends 571 kilometers along the fringe of a mangrove forest south of the mouth of the Amazon River”.

References

Alabama barrier island restoration assessment at Dauphin island. (n.d.). USGS.gov | Science for a changing world. https://www.usgs.gov/centers/wetland-and-aquatic-research-center-warc/science/alabama-barrier-island-restoration

Schreppel, H. (n.d.). Barrier islands. USGS. https://wim.usgs.gov/geonarrative/cch-bi/

Stutz, M. L., & Pilkey, O. H. (2011). Open-ocean barrier islands: global influence of climatic, oceanographic, and depositional settings. Journal of Coastal Research27(2), 207-222. https://doi.org/10.2112/09-1190.1

Texas Bureau of Economic Geology: Padre Island National Seashore: A guide to the geology, natural environments, a history of a Texas barrier island.  https://www.nps.gov/parkhistory/online_books/pais/1980-17/index.htm

Related

Share:


Enter your email to receive the Geography Realm newsletter:
Previous

Flooding Can Help Protect Wetlands From Climate Change

Exploring Rainbows and Moonbows

Next