30 Days of Tennessee Archaeology, Day 12
Eileen G. Ernenwein and Jay D. Franklin
East Tennessee State University
In last year’s blog post, we reported on the results of geophysical survey and excavation at the Cane Notch site, a mid to late sixteenth century Cherokee Town on the Nolichucky River in Upper East Tennessee. This work is also featured in the documentary film, Secrets of the Nolichucky River. A host of other pre-contact and contact-era sites are known along this stretch of the Middle Nolichucky, a region we believe represents an early Cherokee culture area where interactions with Spanish Explorers almost certainly took place. We continue to explore this idea with a focus on the Runion site (40WG20), some 10 miles downriver from Cane Notch.
In January 2017, we surveyed six hectares of the site with magnetic gradiometry (MG) using a SENSYS MXPDA push-cart system with five fluxgate sensors. The results (Figure 1) reveal a small village consisting of square houses almost identical (in the data) to those at Cane Notch. Twenty-one probable structures are highlighted in Figure 1b, while dozens of amorphous anomalies not highlighted could also be structures or associated features. One structure in the south is likely a townhouse given that it is roughly four times the size of the others (twice the length and width). We will refer to this structure as a townhouse hereafter. In addition, there is evidence of fortifications surrounding the houses on the north, west, and south, with the river along the east forming a natural defense. It is also possible that these curvilinear anomalies are related to river channel geomorphology, however, and are entirely natural.
Magnetic gradiometry (MG) is a well-known method for rapidly surveying large areas as a means of reconnaissance. The houses, possible fortifications, and other features are visible because they were burned, are filled with accumulated topsoil, or they contain rich cultural deposits (often with burned material such as charcoal). As with our results at Cane Notch, however, we know that there is much to gain by applying more than one geophysical method. Ground penetrating radar (GPR) and electromagnetic induction (EMI) often reveal more about known features aid discovery other features and their function, depth, composition, and level of preservation. GPR uses the elapsed time and amplitude of radio wave reflections to detect the depth and nature of archaeological and other subsurface layers and features. EMI, a less commonly used geophysical method, transmits much lower frequency electromagnetic waves to measure electrical conductivity (EC) and magnetic susceptibility (MS) at multiple depths.
We tested the effectiveness of GPR and EMI at Runion by collecting data in a 30 x 30 m grid over the townhouse and surrounding area (highlighted in green in Figure 1). Figure 2a shows a close-up of the townhouse as previously revealed by MG, illustrating the clear outer limits of the structure, a central hearth, and evidence that deep plowing has cut into it as revealed by the light colored lines trending north to south. MS data show portions of the townhouse quite clearly (Figure 2b-c), while EC data can only be interpreted within the context of the known structure (Figure 2d-e). GPR depth slices (Figure 3) show that this structure is situated approximately 28-56 cmbs and that there is a concentration of material that produces strong reflections in the northeast corner. Most interesting is that the GPR also shows a structure situated about 6m due north of the townhouse (circled in the fourth slice), a feature not clearly shown in any other dataset.
All data collected in the 30 x 30 m area were combined in GIS to see how they complement one another. Figure 4 maps anomalous areas of positive MG, the inverse of the average EC (labeled ER to indicate these are high electrical resistivity areas), average MS, and the mean of all strong GPR reflections. This representation makes it clear that the combination of data from all three instruments provides a detailed view of the townhouse and a better depiction of the nearby smaller structure. The fill inside the northeast portion of this structure is more electrically resistive (and therefore causes strong GPR reflections), while it is more magnetic (likely a higher concentration of burned materials) in the southwestern portion. Given these results, it is clear that we have much to gain by expanding EMI and GPR survey over as much of the site as possible this fall and winter. Excavations in our 2018 field school will target features revealed by geophysical survey with the aim of understanding what types of fill are associated with each anomaly type.
Acknowledgements. We thank Wolfgang Suess, Gorden Konieczek, and Michaela Schulze at SENSYS Sensorik & Systemtechnologie GmbH (http://www.sensysmagnetometer.com) for loan of the MXPDA magnetometer system and technical support. Thanks to the Runion family for allowing the research to take place on their property. Thanks to Nate Shreve and Claiborne Sea for help with site logistics and geophysical survey.