URBAN GEOPHYSICAL STUDY OF KARST FEATURES IN SOUTHWEST SPRINGFIELD, MISSOURI

The Springfield Plateau in southwestern Missouri is composed of a series Paleozoic shelf carbonates interspersed with minor amounts of siliceous sediments. The entire Paleozoic sequence is located on the Ozark Dome which contains a series of northwest-trending joints formed mainly during the Ouachita orogeny. Of importance to this study, is the Mississippian Burlington-Keokuk Formation which consists of crinoid limestone with varying amounts of chert. The Burlington-Keokuk Formation is nearly horizontal and is susceptible to the formation of karst features including sinkholes and caves. Within the greater Springfield area, there are numerous sinkholes and additional sinkholes are formed each year. The majority of the newly formed sinkholes form without any topographic indication.

In order to investigate the existence of sinkholes and to trace subsurface passages in southwest Springfield, a series of geophysical investigations including gravity, direct-current resistivity and very low frequency electromagnetics (VLF-EM) were undertaken in a region between with known sinkholes and a large spring (Rader Spring). Previous dye-tracing studies indicated that there should be an underground passage between these two features. The geophysical surveys were conducted in two regions: 1) at the area of known sinkholes and 2) a region between the sinkholes and the spring. The data were collected in closely spaced profiles (5-10 meters) with readings every 2-5 meters. The data in the region between the sinkholes and the spring were collected so that 3D modeling could be attempted. Preliminary 2D modeling of the direct-current resistivity, gravity and VLF-EM data indicated that there was a roughly linear passage in this region. Gravity and direct-current resistivity data provided the best resolution in determining this feature. 3D modeling will be attempted in order to confirm and enhance these findings.