DETERMINATION OF THE PRESENCE OF POSSIBLE DISSOLUTION CONDUITS USING ELECTRICAL RESISTIVITY, NORTH ANDROS ISLAND, BAHAMAS

The bedrock of North Andros Island, Bahamas, is composed entirely of limestone and contains numerous caves and dissolution channels. The top of the bedrock is often found at the surface, and is pock marked by dissolution cavities known as blue holes. The goals of this study were to determine any direction of resistivity anisotropy in the vicinity of Charlies Blue Hole, and to determine if a conduit connects the blue hole to the ocean. The anisotropy direction was explored using the Sting Swift system with a modified Wenner array designed for azimuthal data collection. The azimuthal survey results were analyzed using the R_anstrp program, which performs a Monte-Carlo inversion. This program yields the anisotropy direction as well as the anisotropy coefficient. To determine if there is a conduit extending from the blue hole in the direction of the ocean, a vertical profile was completed using the dipole-dipole method with the Sting Swift system. The resulting data from this survey were analyzed using RES2DINV, which produces an inverse model. The preliminary azimuthal survey results distinguish the anisotropy direction and coefficient for shallow, intermediate and deep levels. The results indicate a similar anisotropy direction for the intermediate and deep levels, while the shallow level is somewhat different. The dipole-dipole profile identifies a location having lower apparent resistivity than the surrounding bedrock, and is interpreted to be a conduit approximately 4 meters deep.