INVESTIGATION OF THE MORPHOLOGY OF A LARGE SANDSTONE DEPRESSION ON THE CUMBERLAND PLATEAU OF TENNESSEE USING GEOMORPHIC MAPPING AND GPR

A large circular depression located in Van Buren County, TN atop the Cumberland Plateau was previously investigated using geomorphological and geophysical methods including P-wave seismic refraction, surface wave seismic, and electrical resistivity tomography. Data collected from this previous work supported a collapse hypothesis for its formation as proposed 80+ years ago. A new investigation employed detailed field mapping and ground penetrating radar (GPR) to further assess the morphology of the depression with the goal of understanding how this features’ shape evolved from initial collapse to present day form. Eight survey lines, emanating from a central point in the depression and radiating out every 45 degrees starting at azimuth 0 were measured with a 1.5 m Jacob Staff. Details of surface characteristics were recorded along and in between the lines including presence of organic matter, sandstone cobbles, and scattered and stacked boulders, boulder size, location of bedrock cliffs, and other features. A DJI M300 Drone with a Zenmuse L1 Lidar payload drone was flown over the field site to collect detailed elevation data. A Geophysical Survey Systems low frequency GPR cart system was lowered down the western slope near the 270 degree survey line with data collected along 3 additional transects across the relatively flat bottom of the depression. The sides of the depression varied in slope and morphology. Observed surface characteristics includes organic matter, sandstone cobbles and scattered boulders of various sizes and orientation. Sandstone bedrock exposures are common around the top rim of the depression. Some large bedrock boulders showed signs of slumping and an orientation dipping towards the center. GPR data indicates a possible defined central collapse feature within the lower portion of the depression, which appears to correlate with the previous geophysical surveys.