AN URBAN KARST GEOPHYSICAL STUDY IN SPRINGFIELD, MISSOURI

Southwestern Missouri is located on the Springfield Plateau which mainly consists of Paleozoic carbonates and minor amounts of siliceous sediments. The dominant formation exposed in the area is the Mississippian Burlington-Keokuk Limestone which is nearly horizontal and susceptible to the formation of karst features such as sinkholes and caves. Near surface geophysical methods including electrical resistivity, electromagnetic, and gravity are useful in determining the location and nature of karst features, especially those that are not visible on the surface.

Numerous sinkholes form in the Springfield area every year with some causing devastating effects to infrastructure. A number of these features have formed in regions without any topographic indication. A field site was chosen in a region that is close to a trend of mapped sinkholes and where dye trace studies have indicated a large, long underground passage. This region may be susceptible to additional sinkhole formation. For example, one field site recently had a house demolished due to sinkhole formation. This study will attempt to geophysically map fracture(s) in the bedrock that could possibly link the sinkholes together. Preliminary electrical resistivity profiles have been collected and inverse modeling indicates pinnacles of highly resistive material with areas of low resistive material between them, indicating possible fractures in the bedrock. Very low frequency electromagnetic and gravity data are currently being collected and should be available soon along the electrical resistivity profiles. The profiles will be collected in such a way that three-dimensional modeling of the data will be performed and these models will be presented along with interpretations to determine the depth, size and extent of the subsurface passage.