Complex relationships between surface topography, ground motion, and cover sediments in covered karst, west-central Florida, USA

Sinkhole processes can be more complicated than vertical drainage or collapse of sediments into an underlying limestone void. To better understand the relationships between surface and underlying karst structures, geodetic and geophysical methods were applied to high-resolution mapping of active sinkhole features in covered karst, west-central Florida, USA. Cracks in a pool house at the Sandhill Scout Reservation prompted surface and subsurface investigations in a grassy open field with a distinct-60-m diameter topographic low west of the pool area. Beneath the smooth topographic low, ground-penetrating radar (GPR) with limited penetration (up to 6 m depth) shows incongruent smaller-scale (-5-20 m) variability in a horizon draping the limestone surface. Electrical Resistivity Tomography (ERT) profiles provide a broader overview of the underlying karst system (to depths-25-36 m) and show possible voids in the limestone bedrock beneath a local topographic high. Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) analysis of-2 yr of TerraSAR-X satellite data from two corner-reflectors installed in the topographic low reveals a 1 mm/yr subsidence rate on the flank of the topographic low but stability in its center. This suggests that subsidence has halted in the central topographic low and may be occurring on smaller scales elsewhere within the survey area. The data suggest that non-vertical fluxes of sediment significantly smooth surface topography relative to underlying heterogeneities and that activity migrates within complex systems. Our results also illustrate the benefits of corner reflector installations for resolving subsidence in vegetated environments. The 1-mm/yr rate of motion on the grassy field could not be resolved with InSAR before reflector installation. 0 2021 Elsevier B.V. All rights reserved.