USING MICROGRAVITY TO DELINEATE THE WATERSHED OFRATTLESNAKE SPRINGS, CARLSBAD CAVERNS NATIONAL PARK

摘要

We performed a series of geophysical investigations at the Rattlesnake Springs portion of theCarlsbad Caverns National Park, New Mexico in an effort to characterize the watershed of the springs.As part of this effort we conducted a precision microgravity survey of the area surrounding the springsusing a grid with 200 to 300 m spacing with station positions and elevations determined usingdifferential GPS. The survey was designed to map the depth to gypsum bedrock in the study area andpinpoint the locations of faults/fractures that could control groundwater movement toward the springs.A free-air anomaly map generated from our initial survey results clearly reflects known bedrock highsand lows. The map contours suggest an underlying fracture system that is mimicked by surficialdrainage patterns and features we believe are the remnants of dissolution structures within the gypsumbedrock. These results suggest groundwater flow from the west-northwest into the springs (inagreement with other geophysical surveys we conducted near the springs). The gravity data suggest aneast-north east trending fault/fracture located just east of the springs serves as a barrier to groundwaterflow causing upflow at the springs.