The topic for the ESCONI June 2023 General Meeting was "Using geophysics to capture Earth burps and other processes during flow through karst conduits". Our speaker was Andrew Luhmann Assistant Professor of Geology in the Department of Earth and Environmental Science, Wheaton College, in Wheaton, IL.
Karst aquifers are important water resources that are susceptible to contamination from land surface activities. Traditional monitoring strategies rely on spring and well sampling to learn about these flow systems, but we are using geophysics to understand the karst aquifer architecture, including the conduits where much of the flow occurs through these systems as well as the relevant processes that happen within them. During a pilot study in a karst aquifer in Minnesota, we monitored seismic responses during water injection experiments and following a large rainfall event, which caused a discharge increase at Bear Spring and ground motion that originated from multiple source locations. Based on observations and calculations, we suggest that the largest signals resulted from the release of overpressurized air pockets in karst conduits as water levels were rising, where energy was released as the pressurized air encountered pathways to escape from the conduits. Furthermore, we monitored seismic and tilt responses over a three-year period at the Santa Fe River Sink-Rise flow system in Florida, where water flows through conduits 20 m in diameter that are 30 m below the surface. Our modeling efforts have shown that water pressure changes in the conduits cause land surface displacement and tilt, and that this may provide information on conduit location and size. Geophysical tools enable monitoring of fundamental flow processes and dynamics beyond what is possible with traditional monitoring strategies, and our ongoing research is trying to use this information to better characterize the subsurface, identify karst conduits, and monitor for subsurface flow.
