EXPLORATION OF DIAMOND CAVERNS, KENTUCKY, USING ELECTRICAL RESISTIVITY GROUND IMAGING (ERGI)

Caves are readily detected using electrical resistivity methods because air is a poor conductor of electrical current and exhibits very high resistivity relative to surrounding limestone. ERGI was deployed at Diamond Caverns, a commercial cave in west-central Kentucky, using a 28-electrode AGI Super Sting R1 IP earth resistivity meter. The purpose was to explore the potential relation between known passage and an adjacent sinkhole to the northeast, which was enlarged to reveal a large sediment-filled passage. Four profiles, arranged in a zigzag pattern extending from known passage, revealed multiple cave passages trending adjacent, but not connected to the main Diamond Caverns passage. Using an electrode spacing of 6 m, the maximum depth of the profiles ranged from 30-40 m. Resistivity values for limestone locally ranged from 500-4000 ohm-m. Cave passages exhibited resistivities greater than 11,000 ohm-m. Passage shapes were tubular with widths as great as 14 m and maximum heights of 10 m, consistent with Diamond Cavern passage. The floor of the passages defined by ERGI occur between 187-203 m above sea level (9-19 m below the surface) and ceiling elevations range from 194-210 m (5-10 m below the surface). Tubular zones of similar dimension and elevation range and which align with proposed cave passages, but with resistivities between 6000-7000 ohm-m, likely represent sediment filled passages. Both types of passages lie within the range of elevations for the commercial passages of Diamond Caverns, and their scale and elevation suggest they formed contemporaneously. Regionally, the tubular and sediment-filled nature of the passages is consistent with Level B (Palmer, 1981). Projecting a gradient similar to that between present-day Hawkins River, directly beneath Diamond Caverns, and Green River, the regional discharge point for groundwater in the Mammoth Cave area, from the floor elevation of these passages to Green River supports the Level B designation (Granger and others, 2001).