Investigation of Dominant Controls on Electrical Properties of Granitic Regolith

The Earth's critical zone is the thin layer that extends from the top of the bedrock to the canopy of trees. Despite its relatively thin thickness, the critical zone plays a vital role in our society by providing life-sustaining resources such as water and food. Knowing the internal structure of the underground part of the critical zone is an important step that will help us understand and predict its role in global water, energy, carbon, and nutrient cycles. Geophysical imaging is used to "see" the unseen critical zone underneath the surface. However, the acquired geophysical images need to be translated into physical properties such as density, moisture content, and chemical composition that are understandable and usable to other scientists. This project will advance current understanding of the physical properties of geological materials in the critical zones by using a combination of laboratory and geophysical field investigations. The outcome of this project will help scientists better depict the subsurface of this thin but invaluable critical zone layer of the Earth. The researchers will investigate the dominant controls on the electrical properties of granitic regolith from a combination of field sampling, laboratory experiments, and theoretical modeling. Granitic regolith samples will be collected from the field, and their electrical properties, under controlled hydraulic states, will be measured using a newly developed soil column and a pressure plate extractor equipped with novel hydro-geophysical probes. Experimental data will be used to quantify the relative influences of hydraulic state, chemical weathering-induced textural change, and chemical weathering-induced mineralogy alternation on the electrical properties of the samples in both fully developed regolith and the weathering front. A new electrical model integrating chemical weathering will be developed to describe the entire regolith. This process-based understanding and modeling will enhance our ability to see into the complex underground environment and monitor various important subsurface processes. This project is jointly funded by the Hydrologic Sciences, the Established Program to Stimulate Competitive Research (EPSCoR), and Geobiology and Low Temperature geochemistry programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.