USING GEOPHYSICAL METHODS TO STUDY KARST IN URBAN 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 are useful in determining the location and nature of karst features, especially those that are not visible on the surface.

Electrical resistivity, gravity, and very low frequency electromagnetics have been collected along a trend of mapped sinkholes where previous dye traces have indicated a large, long underground passage. Inverse modeling of the electrical resistivity profiles indicates pinnacles of highly resistive material with areas of low resistive material between them, indicating possible fractures in the bedrock. Some of the resistivity lows could be buried sinkholes. Depth of karst features varies from 5-12 meters and deeper. Two-dimensional gravity modeling shows a similar trend in subsurface topography. Both methods show a similar roughly linear trend that correlates with known sinkholes. Very low frequency electromagnetics does not correlate as well due to its susceptibility to noise, but one-third of the profiles do correlate with the electrical resistivity profiles.