UNDERSTANDING THE SPRINGFIELD AREA KARST SYSTEM USING CAVER OBSERVATIONS TO SUPPLEMENT TRADITIONAL METHODS

Springfield Missouri is built on land known for springs, sinkholes, and caves. Local cavers offer insight into region's karst, including a published concept based on 40 years of local cave exploration. Merging caver ideas with academic (dye-tracing, geophysical, thermal, and geochemical studies of both groundwater and sediments) has improved understanding of the region's karst.

Local geology generally consists of granitic basement under ~2000 feet of mostly carbonate units. In Springfield, the Mississippian Burlington limestone is most common at the surface. Beneath the Burlington lie the Elsey, Reeds Spring, and Pierson formations, each limestone with varying amounts of silica, often as chert nodules. These form the Springfield Aquifer hydrologic unit, with the Northview Formation, a shale, as a ‘leaky aquitard’ separation from the Ozark Aquifer below (>1000 feet of Ordovician limestones and dolostones). Typical karst landscape issues, such as sinkholes and losing/dry streams, has led to sustained interest in understanding how the karst affects development.

From 1970s to early 2000s (then Southwest Missouri State University) students mapped the karst features, providing a base on which recent dye tracing, geophysical, and geochemical studies could be built. Results from 10 Thesis projects and 10 undergrad projects, combined with caver insights published in Missouri Speleology (2018), suggests that much of the local karst landscape follows two common steps. The first step is where surface streams incise valleys and allow mass wasting to occur along the hillsides (be it landslides or simply creep). This mass wasting, facilitated by natural weathering at the soil- rock interface, leads to enlarged joints or fractures that are nearly vertical and often parallel to the stream valleys. Once these joints are opened, allowing water influx, groundwater seeps downward until it reaches the water table or finds a less-permeable horizon in the limestone, which becomes the second step. In this step, the waters typically begin more lateral (and less vertical) flow, which begins to open a sub-horizontal drainage to the edge of the hillside. This presentation will explain these processes and relate them to recent studies of geochemical signatures in the southwestern Missouri region.