Identification of Unmarked Graves (2008-01)

Near-surface geophysical techniques, including ground-penetrating radar, magnetometry, electrical resistivity, and electromagnetic conductivity, have become primary tools in the detection of unmarked human interments. The main advantages of these techniques are that, unlike archaeological excavation, they are relatively rapid and do not involve grave disturbance. Disadvantages are that most surveys do not offer foolproof detection of all or even most graves, and the absolute identification of these anomalies as interments is rarely positive and often requires additional invasive archeological fieldwork. Stripping, excavation, or other invasive tests, however, are not acceptable to many Native American tribes and other groups.

This project has explored techniques of down-hole magnetic susceptibility and soil magnetism as a means of improving the detection of unmarked graves. These relatively non-destructive techniques were tested at two historic Native American family cemeteries located in Kansas and Nebraska and at an Anglo-American cemetery in Kentucky that was being excavated in advance of development. Down-hole tests explored geophysical anomalies and grave shafts at each of these cemeteries, comparing these to tests of undisturbed ground in the search for distinctive magnetic characteristics of grave shafts that could be used in the evaluation of geophysical anomalies. At select locations, soil samples were collected when making the hole for the down-hole sensor and these samples were analyzed in the laboratory using a number of magnetic techniques in order to understand the origin of observed magnetic contrasts. Magnetic characteristics of the burials themselves, which might be useful for grave identification in certain contexts, were investigated only at the cemetery that was being excavated.

Results indicated distinctive magnetic characteristics of both shafts and interments related to the burial process and transformation of the interment over time. Grave shafts, per unit volume, tended to be less magnetic, apparently as a result of soils that are less-compact than surrounding undisturbed ground. Compaction information provided by penetrometer studies did not consistently identify grave shafts, although this failure is probably related to the insufficient depth sampled by the pentrometer. Soil magnetic studies showed a patterned magnetic enhancement of interments useful for burial identification during excavation when grave goods and skeletal remains are lacking. The magnetic signatures documented were not invariable, but by combining near-surface geophysical, down-hole magnetic susceptibility, and soil magnetic techniques, there is a potential for improved capabilities in the identification, evaluation, and thus the preservation of unmarked human burials.

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