U.S. Geological Survey Open-File Report 2011–1005
Surficial Geology of the Sea Floor in Central Rhode Island Sound Southeast of Point Judith, Rhode Island
The bathymetry in the study area consists of several isolated bathymetric highs with depths as shallow as 30 m, separated by a system of connected channel-like bathymetric lows with depths up to 40 m (fig. 11). Several sea-floor features can be identified in the bathymetric imagery, including scour depressions, sand waves, trawl marks, and dredge spoils (fig. 12). The scour depressions, which are found in a variety of shapes from broad to elongate, occur on top and on the flanks of bathymetric highs. The depressions have steep sides, relatively flat floors, and are 10s to 100s of meters wide and about 0.5 m deep (fig. 13). Elongate depressions are more common on the flanks of the bathymetric highs. Further descriptions of scour depressions and the surrounding sea floor are discussed in the Bottom Photography section of this report. Sand waves located in the southwestern corner of the study area have wavelengths from several meters to more than 40 m and east-west oriented crests (fig. 14). The bathymetric high in the northwest has a hummocky appearance, which is probably a product of coalesced scour depressions and exposed underlying Pleistocene deposits. Trawl marks are present on the flanks of the bathymetric high and appear as thin depressed lines, often parallel to each other (fig. 15). This high is part of the submerged moraine, dating to 18,000 years ago (Uchupi and others, 2001), trending southeast from Point Judith, R.I. (fig. 2). A bathymetric low in the western edge of the study area has been used as a disposal site for the Providence River and Harbor, site 69b (Science Applications International Corporation, 2004), and contains distinct mounds of dredged material (fig. 16).