K-State Geology Seminar Series Presents

'Using Geophysics to capture 'Earth burps' and other processes during flow through karst conduits'

by Dr. Andrew Luhmann, Assistant Professor of Geology at Wheaton College, IL

Thursday, 23 March 2023 | 4:00-5:00 PM

Virtually via Zoom

Title:  Using Geophysics to capture 'Earth burps' and other processes during flow through karst conduits

Abstract: One of the great challenges in karst aquifers is that most of the flow and transport through these systems occurs via conduits, but much about them is unknown. In this talk, I will discuss how we are trying to better understand seismic and tilt responses as a way to provide constraints about unknown conduits and their characteristics. During a pilot study in a karst aquifer in Minnesota, we monitored seismic responses during water injection experiments and following a 5 cm rainfall event, which caused discharge at Bear Spring to increase from 100 L/s to more than 300 L/s. This generated large amplitude seismic signals with ground motion up to ~0.5 mm/s. The signals were generated from multiple locations, and the timing suggests that they were unique events. Based on observations and accompanying 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 the poroelastic response from water pressurization in the conduits may provide information on conduit location and size, but heterogeneity in the aquifer complicates interpretations of field data. Still, 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 to delineate karst conduits and monitor for subsurface flow.

Bio: Andrew received his BS in Geology in 2006 from Wheaton College, IL, and his PhD in Geology in 2011 from the University of Minnesota, studying karst hydrogeology. After that, he spent four years as a postdoc at the University of Minnesota, where his research focused on experimental reactive transport in geologic carbon sequestration and serpentinization environments. He then spent three years as Assistant Professor of Hydrology at New Mexico Tech before returning to Wheaton College as Assistant Professor of Geology in 2018. His research involves karst hydrogeology, flow and transport, aqueous geochemistry, and fluid-rock interaction, and currently-funded research explores geophysical responses during recharge events in karst aquifers and mechanical impacts that arise from chemical reactions during geologic carbon sequestration.

Modality: Virtually via Zoom