STUDYING URBAN KARST FEATURES USING NEAR-SURFACE GEOPHYSICS IN SPRINGFIELD, MISSOURI: A COMPARISON OF APPLIED METHODS

Springfield, Missouri is located on the Springfield Plateau, consisting of Paleozoic carbonate and siliceous rocks with a thin soil cover. The uppermost exposed unit is the Mississippian Burlington Limestone, a nearly horizontal carbonate layer which is susceptible to karst formation. Karst features such as caves and sinkholes present hazards for engineering and groundwater contamination. An understanding of the location, size and geometry of these features is needed to adequately manage and prepare for karst related hazards. Shallow geophysical methods can be useful for studying these karst features, although some methods are better suited than others.

Surveys using multiple geophysical methods were implemented to study known karst features in the southern Springfield area. Two field sites were chosen for comparing geophysical methods: a previously mapped cave passage and a newly forming sinkhole. Direct current electrical resistivity (ER), induced polarization (IP), very-low frequency electromagnetics (VLF-EM), and ground penetrating radar (GPR) were used to profile each karst feature. This study compares the geophysical responses of the cave and sinkhole to each method, while also determining the pros and cons and noise sources of each method for shallow urban karst studies.

ER proved to be the most useful method overall for profiling both the sinkhole and cave as discrete subsurface resistivity anomalies. VLF-EM was useful for quickly surveying large areas, but was highly prone to noise interference, requiring many points to detect anomalies. IP was tested for possibly differentiating between clay, silt, or water-filled voids, but surveys produce noisy data while being time consuming to perform. GPR was the least effective method due to signal attenuation in the clay-rich soils of the area.

There are many different shallow-surface geophysical techniques, but not all are equally effective for all regions. This comparison benefits future karst geophysical surveys around Springfield, Missouri, by shedding light onto which methods are the most useful, and why. It is largely due to infrastructure noises sources, soil type, and karst the uniqueness of karst geology, that this comparison is made into which methods are the most useful.