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USGS Coastal and Marine Geology Program


Potential for Shoreline Changes Due to Sea-Level Rise Along the U.S. Mid-Atlantic Region

D-Geological Characteristics of the Mid-Atlantic Coast

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The mid-Atlantic portion of the U.S. is classified as a trailing edge coast (Inman and Nordstrom, 1971) which is comprised of a low gradient coastal plain that has accumulated over millions of years in response to the erosion and denudation of the Appalachian mountain chain (Walker and Coleman, 1987). The resulting sedimentation has constructed a broad coastal plain and continental shelf that extends up to 300 km seaward of the present coast (Colquhoun and others, 1991). The current morphology of this coastal plain and continental shelf is the product of erosion by rivers that drain the region, the marine regressions and transgressions, and the construction of barrier islands and other coastal landforms on the intervening mainland. Repeated glaciations over the last 3 million years have resulted in sea-level fluctuations of up to 120-140 m (Lambeck and others, 2002; Miller and others, 2005). The major river systems (e.g., Hudson River, Delaware River, Susquehanna River, and Roanoke River) incised large valleys across the continental shelf during periods of low sea level that were subsequently flooded and partly filled with sediments during the Holocene transgression as sea level rose to present levels. At the northern limit of the focus area, Long Island formed from glacial outwash plains and two terminal moraines formed by the Laurentide Ice Sheet, which began to retreat at the end of the last glacial maximum approximately 21,000 years ago. The low gradient of the mid-Atlantic landscape in combination with slow rates of sea-level rise over the last few thousand years and the availability of sufficient sand have enabled the formation of the barrier spits and barrier islands along much of the coast.

Presently, the river systems along the mid-Atlantic coast mostly discharge into estuaries and bays and deliver minor amounts of coarse sediment to the open coast (Meade, 1972). As a result, the region is generally considered to be sediment starved (Wright, 1995). The sediments that form mainland beaches and barrier beaches are derived from the erosion of older, pre-existing coastal landforms and the seabed of the continental shelf. Since the largest waves and associated currents that transport sediments and mold landforms occur during storms, the Atlantic margin of the U.S. is often referred to as a storm-dominated coast (Davis and Hayes, 1984).

The majority of the open ocean coast along the mid-Atlantic Bight is comprised of sandy shores that include beach and barrier-island environments. While barriers comprise about 15 percent of the world coastline (Glaeser, 1978), they are the dominant shoreline type along the U.S. Atlantic coast. Along the portion of the mid-Atlantic Bight coast that we consider here, barriers line approximately 90 percent of the study area. Consequently, scientific investigations exploring coastal geology of this portion of North America have largely focused on understanding barrier island systems (Fisher, 1962; Pierce and Colquhoun, 1970; Kraft, 1971; Swift, 1975; Leatherman, 1979; Moslow and Heron, 1979; 1994; Oertel, 1985; Belknap and Kraft, 1985; Hine and Snyder, 1985; Davis, 1994; Oertel and Kraft, 1994; Pilkey and others, 1998).

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U.S. Department of the Interior | U.S. Geological Survey | Coastal and Marine Geology

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