US: Earth has 657 more barrier islands than previously thought, announced two geologists, Orrin Pilkey and Matthew Stutz. They conducted a global survey of barrier islands using satellite images, topographical maps and navigational charts. Their study has been published in the current issue of the Journal of Coastal Research.
Pilkey is the James B. Duke Professor Emeritus of Geology at Duke University’s Nicholas School of the Environment. Stutz is an assistant professor of geosciences at Meredith College.
Pilkey and Stutz’s discovery include islands off the coast of Columbia, Brazil, Siberia, Alaska and Canada’s Arctic. A previous survey in 2001 had pegged the number of barrier islands at 1,492. Pilkey pointed out the islands didn’t suddenly materialise over the last decade. Rather the islands hadn’t been noticed or were too remote to be included in the last count. The previous survey was conducted without the help of satellite images.
The 2,149 barrier islands are found along all continents except for the Antarctica. Seventy-four per cent of them are in the northern hemisphere. They measure a total of 20,783 kilometres in length and make up approximately 10 per cent of the Earth’s continental shorelines.
A barrier island often forms as a chain of long, low, narrow offshore deposits of sand and sediment. They run parallel to the coast line but are divided by lagoons, bays and estuaries. They are defined as an unconsolidated body of sand that is surrounded by water and usually has an inlet at either end that lets water in and out of a lagoon.
The islands have a unique role in the ecosystem, protecting low-lying mainland coasts against erosion and storm damage. They are often important wildlife habitats.
Many of the barrier islands in the survey are two to 4,000 years old. But many of the islands will soon be threatened by the rising sea levels that have come with climate change.