Islands that suddenly appear may sound like something out of a pirate myth. But a new survey has found hundreds of islands needing modern X marks on today's maps.
The islands weren't a result of Blackbeard's curse; they had always been there. But like the best buried treasure spot, their locations weren't common knowledge.
"The study developed as newer and higher resolution sources of free satellite images were made accessible to the public," geoscientist Mathew Stutz of Meredith University told Discovery News.
Stutz was one of the authors of a study published in the Journal of Coastal Research. The study added 657 islands to the world's list of barrier islands by the researchers from Duke University and Meredith College. The grand total is now 2,149.
"Needless to say, the people who lived in these areas knew they were on islands, but the geographic/geologic classification into barrier islands was not in their realm. All in all, this was very exciting, to 'discover' new islands," geologist and co-author Orrin H. Pilkey of Duke University told Discovery News.
Barrier islands form on the coasts of landmasses and provide important protection against erosion and storm damage. They are also important habitats for wildlife. A majority of the islands, 75 percent, exist in the northern hemisphere.
Barrier islands are often long, low, narrow deposits of sand and sediment (such as the thin arc of beaches boarding the northern rim of Wrangle Island in the image at right). They also tend to erode away or build up over time due to waves, tides and ocean currents. That can make them hard to find and pin down on a map.
An earlier survey missed these 657 "new" islands. "The 2001 study relied on topographic maps and the first generation of NASA's Geocover Landsat Program," Stutz said. "The initial Geocover was compiled from 1990-era Landsat 4/5 images, with 30-meter resolution. Small or narrow islands were still difficult to detect, a few were obscured by clouds."
"Even today, a few regions of the world (primarily Russia) are not included in this dataset," Stutz said.
"When the actual work was done for the first study, Google Earth was not available, at least not in its current form," Pilkey said. "We started out looking at maps and charts, which was quite an education."
Even public historical charts such as the New York Geographical Society's collection and the British Admiralty's survey of the continental shelf off the Pacific coast of Colombia missed many islands Pilkey and Stutz found using modern eyes in the sky.
"By 2004 NASA completed a Landsat 7 dataset (with 15-meter resolution) using 2000-era images and did include all the world's coasts. Prior to this program, hundreds if not thousands of satellite images would have to have been purchased individually at prohibitive cost for such a large scale survey," Stutz said.
Google Earth also uses Landsat imagery at a 15-meter resolution, said Stutz. But Google is in the process of replacing the images with higher quality 2.5 meter resolution images. At that resolution you can start to see objects like trees and cars.
"Basically nothing beats Google Earth for getting the whole story. Google Earth has opened up a whole new world for those who study physiography of the globe," Pilkey said.
The Inupiat village of Shishmaref in northern Alaska is located on an island chain facing the Bering Strait. Without sea ice buffering the barrier island it sits on, the village is under threat and in the process of relocation.
Pilkey and Stutz used Google Earth to verify some of the barrier island mapping study, but most of the new barrier island map they developed by printing out Earthsat Geocover Landsat images, then making meticulous measurements of spatial features.
"Some of the islands we did not "discover" until we visited them. That is, we weren't really sure they were barrier islands," said Pilkey.
Some of the newly identified islands are rule breakers. They exist in places were scientists didn't think barrier islands could form.
For example, the world's longest chain of barrier islands is one of these renegade landmasses. The 54 island chain stretches along 571 kilometers of Brazil's coast. The region experiences spring tides of seven meters (23 feet). Previously, scientists didn't think barrier islands could survive in areas with tides of more than four meters (about 13 feet).
The islands hadn't appeared on previous maps because they tend to blend into the coastal mangrove forest they help protect.
"This provides proof that barrier islands exist in every climate and in every tide-wave combination," said Pilkey, in a press release by that school.
"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," said Pilkey.
Ironically some of the newly discovered islands may be in danger of disappearing. Rising sea levels could wash away some of the islands.
"Are there clues there to predict which of today's islands might be in danger of disappearing in the near future?" Stutz asks in the Duke press release. Unfortunately their prized sands may be their downfall.
Development of hotels, businesses and other structures on barrier islands are a threat to their very stability. Once seawalls and jetties are in place, the island can't respond to changes in the ocean around it. "It essentially becomes a sitting duck," said Pilkey.
"Barrier islands, especially in the temperate zone, are under tremendous development pressure, a rush to the oceanfront that ironically is timed to a period of rising sea levels and shoreline retreat," Pilkey said.