The Case of the Vanishing Islands
National Geographic, Eye in the Sky, April 28, 2000
Marsh grass and fiddler crab holes fill some of the front yards. Other yards have become mud flats, and hip boots may be required to navigate Main Street during twice-monthly high tides. Nevertheless, some 450 hardy souls stubbornly cling to a way of life on Maryland's Smith Island. Residents of this remote speck of land in the Chesapeake Bay, first inhabited by English colonists in the 17th century, still speak a brogue that they trace back to Elizabethan times. But the island seems about to join others that already have sunk beneath the waves - a microcosm, say scientists, of the effects of rising sea levels around the world. "The people of Smith Island are out of time," said Florida International University's Stephen P. Leatherman, who has extensively studied coastal erosion. "I wish it were otherwise, but I don't see any answer for them. Many will hold out for as long as they can, but the next time a really big hurricane comes through, I think that'll be it. Their heritage is slipping away under the sea." Debate continues over the cause of rising sea levels, especially concerning the effects of fossil fuel-burning, which theoretically promotes global warming by increasing the amount of greenhouse gasses in the atmosphere.
But whatever the reason, the unmistakable fact is that the sea is gobbling up dry land at an alarming rate in many parts of the world. Entire nations, including the low-lying Maldives in the Indian Ocean and Vanuatu in the southwest Pacific, face extinction. If current trends continue, the major coastal cities of the world also could be at risk. "What's going on in the Chesapeake Bay is going on worldwide," said Duncan M. Fitzgerald, a Boston University geologist. "I don't think people understand that an increase in the rate of rise of sea level is going to have a devastating, cataclysmic effect." Nowhere is the phenomenon more striking than in the Chesapeake Bay - a 193-mile (311-kilometer) inlet of the Atlantic Ocean that lies along the shores of Maryland and Virginia.
"Our best estimate at present is that perhaps an area the size of Washington, D.C. is being lost in the Chesapeake Bay every century now," said Michael S. Kearney of the University of Maryland. "The water is probably rising somewhere between 30 and 40 centimeters per century, a little more than a foot and a half. Considering that I looked at long-term trends for the last thousand years, it's a six-fold increase. That's a big deal." Kearney's studies of historical records, along with such indicators as pollens found in sediment samples, show that islands in the bay were slowly eroding from the colonial period until around 1850, when the rate of land loss took a sudden and dramatic upturn. The 1850s period is generally recognized as the beginning of the industrial revolution, with its massive use of coal and oil to power manufacturing plants. "A lot of islands that had been lived on for several centuries were abandoned in the period between 1920 and 1940," said Kearney. "All of a sudden these communities disappeared, a lot of them lost altogether, the famous example being Sharps Island."
Around the beginning of the 19th century, Sharps Island was a roughly600-acre (240-hectare) farming and fishing community at the mouth of Maryland's Choptank River. At one time it boasted schools, a post office and a popular resort hotel, where vacationers from Baltimore and other locations would arrive by boat to while away the lazy summer days. But between 1850 and 1900, the island lost 80 percent of its land mass, and by 1960 it had been reduced to a shoal. Today it is entirely underwater, marked only by a partly submerged lighthouse. "A lot of history has been lost," said Kearney. "Some of these islands were plantations. We tried to find an old graveyard that was marked on survey maps of James Island as late as the 1930s. Apparently it's gone in the drink." Other islands that either have been deserted or have disappeared altogether are Poplar, Barren, Hambleton, Royston, Cows, Punch, Herring, Powell, Swan, and Turtle Egg. Scientists attribute these losses to a combination of factors, including global warming-possibly accelerated by human activity. Another well-documented cause is the withdrawal of groundwater for agricultural and other uses, resulting in the land essentially falling in on itself. Additional sinking could be caused by the sheer volume of sediments being dumped into the bay by runoff from farmland and housing developments throughout the watershed. This load may be weighing down the earth's mantle, allowing more water to come in.
One potentially good result from all this loss of dry land is the creation of salt marshes, which not only provide vital habitat for wildlife but also help filter out some of the fertilizers and other toxins from the runoff. The north end of Smith Island, once farmland, is now a marshy refuge. However, scientists fear that the rate of sea-level rise now is so great that the newly formed marshes themselves will be quickly overwhelmed. Kearney said his data indicate that within 10 to 20 years, if present trends continue, "we could lose about 70 percent of all coastal marshes in the Chesapeake Bay."
Eye in the Sky is a weekly series that brings you the story behind the headlines using satellite imagery, remote sensing, aerial photography, and maps. This feature is developed by National Geographic News with the sponsorship of the National Imagery and Mapping Agency (NIMA) and Earth-Info.