Geophysical Investigations of United States Revolutionary War Era (1777–1778) Mass Burial Sites in Pennsylvania, USA

The United States Revolutionary War (1775–1783) resulted in numerous mass burials in the eastern United States, with deaths occurring not just directly related to the battles fought, but also from disease, starvation, and exposure. Current information relating to these mass burials is often gathered from myths and rumors, leaving the truth of the historical aspects of that time period ambiguous. Geophysical techniques are increasingly utilized in archaeologic and forensic studies to locate unmarked burials. GPR, magnetics, and electrical resistivity have been used to successfully identify burial locations around the world in a non-invasive manner. This paper aims to illustrate how different burials of the US Revolutionary War period can be detected and characterized with geophysics, providing important knowledge of a better historical understanding of that time period, as well as optimizing equipment instrumentation and processing procedures for such targeted investigations. Three case studies of Revolutionary War Era mass burial sites in Pennsylvania, USA are described here: the Paoli Battlefield Memorial, the Old Charlestown Cemetery, and Saint Peter's Church in the Great Valley. These sites are within 9 km of each other and have historic records that suggest mass burials during this period. Results show GPR to provide the most useful data overall, with supporting information gathered from the supplemental geophysical techniques of magnetometry and resistivity. 2D profiles tend to provide a more valuable image of the subsurface than 3D slices. Larger burials leave a greater footprint and have a higher chance of causing a geophysical disturbance that can be measured more than 200 years after the burial. Soil moisture content and vegetation type can impact quality of results. Study implications demonstrate the challenges and potential usefulness of geophysical techniques to successfully locate and characterize mass burials of this time period.