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Topography, shaded relief, and backscatter intensity of the Hudson Shelf Valley, offshore of New York

The 150-km-long Hudson Shelf Valley, the largest physiographic feature on the midAtlantic continental shelf, bisects the New York Bight region. The Valley is the submerged seaward extension of the ancestral Hudson River drainage system that, unlike other valleys on the Atlantic shelf, has not been filled with sediment. A survey of the topography and backscatter intensity of the valley has been carried out using a Simrad Subsea EM 1000 multibeam sea floor mapping system. The valley head is located in a broad shallow basin and extends offshore 5-40 m below the shelf surface to a seaward terminus at a shelf-edge delta. The valley can be divided into upper, middle, lower and outer sections based on the topography, surficial sediments, and drainage pattern. The middle valley is characterized by 5 local topographic lows along the valley axis that have relief of 3-11 m below the valley floor. The northwestern portion of the study area has been affected by disposal of dredged and other materials since the late 1800's. Part of this area has been designated as the Historic Area Remediation Site (HARS). The sea floor of the HARS is being remediated by placing at least a one-meter cap of clean dredged material on top of the existing surface sediments that exhibit varying degrees of degradation. A large field of sand waves is located in the lower valley in 70-80 m water depth that cover an area approximately 30 km long and 4 km wide. This sand wave field is hypothesized to be part of a flood deposit that formed as a result of the break-out of glacial lakes in upstate New York approximately 13,500 years BP. In the eastern-most part of the survey area in water depths greater than about 110 m, the sea floor is marked by long narrow northeast-southwest-trending grooves that are interpreted to be iceberg scour marks.