Investigating sinkholes related to a deep-seated interstratal karst in the Disney Wilderness Preserve (Florida) using an array of near-surface geophysical methods.

Abstract:

In recent years, Florida has seen a significant increase in sinkhole frequency and the associated damage. This trend can be attributed to both, human-induced hazard enhancement (e.g. aquifer overexploitation), and the increasing exposure related to population and development growth. Sinkhole genesis in Florida is often explained considering a simple geological model: cavernous limestone bedrock overlain by an unconsolidated cover affected by suffusion and collapse processes (mantled karst). However, in extensive tracts of Florida, sinkholes occur where the karst bedrock is overlain by significant non-soluble formations (interstratal karst). This deep-seated karst is found in a series of sinkholes investigated in the Disney Wilderness Preserve (DWP) in Central Florida. Here, the limestone of the Floridan Aquifer is overlain by the argillaceous Intermediate Confining Unit (Hawthorn Group, ca. 30 m) and the Surficial Aquifer System, dominated by sandy facies in the DWP (ca. 30 m thick), resulting in depths of more than 50 m to the top of the limestone. In this work, an array of near-surface geophysical methods is used to image the subsidence structures underlying several sinkholes typically 100 m across with subdued geomorphic expression. Methods included ground penetrating radar (GPR), electrical resistivity imaging (ERI), terrain conductivity, and shallow seismic and were constrained with a previous borehole core. The results presented here contribute to the improvement of previous sinkhole classifications incorporating the sagging mechanism (passive ductile bending) as a relevant subsidence process, with markedly different kinematics and damaging potential compared to collapse and suffusion. This work also shows the potential of near-surface geophysics for characterizing deep paleokarst relief that may not result in obvious surface expressions.