WATER-LEVELS OF GLACIAL NARRAGANSETT DETERMINED USING GROUND-PENETRATING RADAR

The elevation of the delta plain-delta slope contact of nine Late Wisconsinan glacial deltas adjacent to present-day Narragansett Bay was determined using ground-penetrating radar (GPR) and a Real-time Kinematic GPS. These deltas were deposited into Glacial Lake Narragansett, which occupied much of the southern portion of the Narragansett Basin during deglaciation. The northern shoreline of Narragansett Bay is mixture of medium to high-density residential, commercial, and industrial development, and includes the capital city of Providence, Rhode Island. Anthropogenic development on the delta plain and the lack of outcrop necessitated the use of geophysics to determine the elevation of the delta plain-delta slope contact. The non-intrusive nature of GPR is ideal for working in these urban or developed areas. Results were combined with delta plain-delta slope contacts below sea level that were measured using a sub-bottom seismic reflection profiler. Linear regression through the delta plain-delta slope contacts reflect distinct water levels of Glacial Lake Narragansett. The measured trend further validate the ideas of delayed isostatic rebound, and the behavior of New England as a lithospheric block during rebound, as first suggested by Koteff and Larsen (1989).