COLUMBIA UNIVERSITY RECORD February 25, 1994 Vol. 19 No. 18 LAMONT TO STUDY HOW BIG STORMS ALTER NE COASTS Every Nor'easter that pummels the East Coast snatches a bit of the shoreline and takes it out to sea. Where does all that sand go? Is it forever lost or does it makes its way back to beaches? Do major storms disrupt fishing grounds, fill in boating channels and bury underwater cables? A newly launched study, led by a scientist at Columbia's Lamont- Doherty Earth Observatory, will explore the effects of Nor'easters on coastal systems and establish a "natural laboratory" in Block Island Sound. This July, a team of four scientists will map the ocean floor in the Sound. By comparing their findings with a sonar survey of the same area done for the Navy in 1991, they will see how the ocean floor was resculpted in intervening years by Nor'easters, including the major Nor'easter of December 1992 and the so-called "storm of the century" in March of 1993. The research will lead to greater understanding of coastal dynamics in Block Island Sound and in other East Coast continental shelf areas, such as Long Island's South Shore, Cape Cod and Cape Hatteras--all of which have seen extensive destruction caused by Nor'easters in recent years, said Neal Driscoll, a geophysicist at Lamont-Doherty and the study's principal investigator. DEADLIER THAN HURRICANES "Nor'easters potentially cause more destruction over wider coastal areas than hurricanes, and they occur much more frequently," Driscoll said. "They are called Nor'easters because their winds come from the northeast. These winds often reach 25 to 30 miles per hour and last several days, driving monstrous waves directly toward the East Coast. These waves batter and inundate coastlines, causing extensive beach erosion." For the study, funded by the Office of Naval Research, the scientists will survey a 10-by-10-nautical-mile area ranging from the waters off Stonington, Conn., and Montauk Point, L.I., in the west to Weekapaug, R.I., and Block Island in the east. They will use two types of sonar to map detailed features of the seafloor and underlying structures. They will tow an underwater camera in the 90- to 120-foot-deep waters to photograph seafloor features, and they will take samples of the sand and sediments on the bottom of Block Island Sound. The two-week survey will be done aboard the "R/V Cape Henlopen," a 120-foot coastal zone research vessel operated by the University of Delaware. The research team will include David Twichell of the U.S. Geological Survey in Woods Hole, Mass.; John Ladd of Lamont- Doherty, and Barbara Hecker of Hecker Environmental Consulting in Woods Hole. The survey is expected to reveal a rich tapestry of features called sand waves and sand ribbons, both crafted by currents and tides in much the same way that winds sculpt undulating sand dunes in deserts. It will also reveal thin trenches cut by fishing trawlers dragging their nets along the sandy bottom, as well as more permanent features such as submerged valleys that might channel the flow of sand. BEACH EROSION "In our initial survey, we want to see if some of these features were obliterated or redistributed by the effects of Nor'easters," Driscoll said. "If the bottom has changed dramatically since 1991, that has implications for beach erosion, fishing grounds and estuaries. We want to see if we can identify, year to year, whether the sand eroded from beaches by Nor'easters simply vacations at the bottom for a time, only to be used eventually to rebuild a beach next door in fair weather. Or is it lost to the system by being transported northeast toward Martha's Vineyard, or right off the continental shelf and out to sea? Or does it temporarily fill in submarine canyons, clogging the quickest pathways out to sea? "We want to see to what extent sand moved and stirred up by Nor'easters might damage cables, pipelines, fishing traps, offshore wells and boating channels," he said. Because submarines from the U.S. base in Groton, Conn., traverse the seaway, the Navy is interested in how storms might rearrange bottom sediments and change sonar patterns reflected off them, he said. "Once we establish a baseline picture of the Block Island Sound seafloor, we want to be able to rapidly deploy instruments immediately after major storms to see their effects," Driscoll said. "We hope to establish a natural laboratory in the Sound to monitor how long it takes for shallow-water environments to recover from large storms." Nor'easters typically occur from October to April, when large temperature contrasts form between cold air masses over continents and warm air masses over relatively warmer ocean waters. Tropical air masses from Bermuda to Cape Hatteras clash with the winter path of the Jet Stream, which brings a blast of polar air down and across the United States. The temperature gradient between the two air masses is resolved via a violent energy-releasing storm that tracks up the Eastern Seaboard. STORM LINGERS The final ingredient for a Nor'easter is the simultaneous development of a strong, stable high-pressure system that is common in winter months over eastern Canada, which prevents the developing storm system from moving swiftly northward and out to sea. Instead, the storm lingers on the coast, with its counterclockwise winds funneling moist air and heavy snow or rain from the northeast directly toward the East Coast. The gale-force winds drive towering waves over wide areas that batter the coast over several days and tidal cycles. Adding to wave heights is a phenomenon known as storm surge--the combined effect of wind-driven water piling up along the East Coast and the storm's low air pressure. Ocean waters rise as air pressures above them diminish. The combination of all these factors during Nor'easters commonly produces waves of 5 to 30 feet. ONCE A LAKE Driscoll said that Block Island Sound is a geologically interesting area. About 15,000 to 19,000 years ago, Long Island Sound was a lake called Lake Connecticut. It was formed as great glaciers surged from Canada, bulldozing boulders and sediments ahead of them. These sediments formed a dam behind which glaciers periodically melted to fill the lake. Long Island, Fishers Island and Plum Island are vestiges of these ramparts formed by periodically surging glaciers. At the time, much of Earth's water was landlocked in these massive ice sheets, so sea levels were much lower. The continental shelf off Long Island, now submerged, was dry land. Occasionally,low or weak spots in these glacial dams were eroded and breached, and lake water poured through narrow gaps with great force, cutting deep river beds in what is now the continental shelf. Some of those riverbeds are now submerged valleys, like The Race, a well- known pathway of fast-running currents in the Sound. ROCK LAYERS As an added scientific bonus, the research should also provide clues about ancient storm deposits on the seafloor, which will help scientists predict whether global warming might increase or decrease storm frequencies and intensities in the future. Driscoll said he has found rock layers that appear to have been sculpted by major storms in the Cretaceous Period 145 million to 65 million years ago, when dinosaurs roamed the planet. However, many scientists believe that the Cretaceous did not experience storms like those of today because its carbon dioxide- rich atmosphere produced uniformly warm conditions throughout the planet. The continuing buildup of greenhouse gases in Earth's atmosphere today is leading toward conditions resembling those in the Cretaceous.