A new and more comprehensive survey conducted by researchers from Duke University and Meredith College have increased the number of known barrier islands by 657, from 1,492 identified in a 2001 survey to 2,149, identified in the most recent study with the aid of publically available satellite imagery.
Barrier Islands 101
According to Wikipedia, barrier islands “are relatively narrow strips of sand that parallel the mainland coast,” (as seen in the images below).
They are formed as chains of long, low, narrow offshore deposits of sand that have been moved around by the tide, running parallel to a coast but separated from it by water, often bays, estuaries of lagoons.
Barrier islands build up, erode, move, and reform over time, in response to waves, tides, currents and whatever else is moving the water around.
The new study finds barrier islands located off the coast of every continent except Antarctica, with the United States home to the most barrier islands, with 405, including those along the Alaskan Arctic shoreline.
“This provides proof that barrier islands exist in every climate and in every tide-wave combination,” says Orrin H. Pilkey, James B. Duke Professor Emeritus of Geology at Duke’s Nicholas School of the Environment. “We found that everywhere there is a flat piece of land next to the coast, a reasonable supply of sand, enough waves to move sand or sediment about, and a recent sea-level rise that caused a crooked shoreline, barrier islands exist.”
Changing How We Look
One of the reasons for the increase in barrier islands is not that they have just miraculously appeared, nor solely because researchers now have access to publically available satellite images like those available in Google Maps, but rather in how they classified just where a barrier island could form.
Previously, scientists believed that barrier islands couldn’t form off coasts which suffered seasonal tides of more than four metres.
Unsurprisingly to anyone who has a sense of the ironic, the longest chain of barrier islands is found along a stretch of the equatorial coast of Brazil, where spring tides can reach up to seven metres. The barrier island chain contains 54 islands, and extends 571 kilometres along the fringe of a mangrove forest south of the mouth of the Amazon River.
Source: Duke University