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A cross-section of the cemetery measured via ERT

Soil science explores what lies 6 feet under (and beyond)

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Cemeteries can serve as archives of history. But if a headstone or marker is lost, so is that connection to the past.
 
This is the puzzle caretakers of the cemetery at First United Methodist Church in Franklin, North Carolina, were eager to solve. Headstones at the cemetery, which dates to the Revolutionary War, typically only covered portions of rows. Church members were curious: Were there more graves that had been lost to time?
 
A church friend and retired forest soils researcher with the U.S. Forest Service, Jennifer Knoepp, suggested they reach out to University of Georgia professor Daniel Markewitz for answers.
 
“Jennifer knew of my research looking at what lies beneath forests using geophysical techniques, for example, to map taproots,” said Markewitz, a professor of forest soils in the UGA Warnell School of Forestry and Natural Resources. “I was intrigued by another avenue to study soil, so we agreed to do a day of geophysical work at the cemetery.”
 
Markewitz used two geophysical techniques, electromagnetic induction and electrical resistivity tomography, to explore the site. Neither require any soil to be disturbed.
 
Electromagnetic induction, or EMI, is similar to a large metal detector. It passes an electrical current through the ground and measures the amount that returns. If soil is more conductive, it returns a stronger signal—typically this is due to moisture or fertilizers in the ground, or in this case, buried metals. This tool is useful for creating horizontal maps through an area, but its depth is limited.
 
To get an idea of what lies further beneath, Markewitz used electrical resistivity tomography, or ERT. This technique uses short metal probes and long electrical cables to inject current and measure its return. The result is a two-dimensional cross section that can measure up to 100 feet deep. “This technique is very good at detecting caverns or voids, since air carries very little electrical current,” added Markewitz. “In a cemetery, these caverns likely represent old burial sites.”
 
By combining these techniques, Markewitz was able to create a map of possible unmarked burial locations. The testing showed locations of about 50 unmarked graves at varying depths across the cemetery, many in unmarked locations. Some of the possible graves sit more than 10 feet below the surface.
 
He suspects some graves might have been unmarked from the start, while others were marked with wood or other materials that eroded away over time. “Also, some graves were located on top of another person, so one headstone might have replaced another,” he said.
 
Using this type of soil technology to determine unmarked graves is unconventional, but it could be a tool for archivists and historians to investigate burial grounds. Since his visit last year, the church has secured some funding for additional research, and Markewitz is now seeking a student with an interest in geophysics and grave hunting to assist with the work. By using these advanced methods, he says, we can continue to pay our respects.
 
“Respect for the dead and descendant communities is of paramount importance,” he said. “As natural resource professionals, many of us have likely come across marked burial sites in unlikely places. Understanding what lies beneath is one way to honor those who walked these spaces in previous generations.”
 
 
For details on getting involved, email Daniel Markewitz.

Slide/Banner Caption:
A cross-section of the cemetery measured via ERT.

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