Did you know that archaeologists have tools that can see below the ground without digging? It’s true, and in fact we can map underground features, such as walls, in an area the size of a football field in as little as one day!
There are various techniques available for seeing below the surface, but ground-penetrating radar (GPR) is the only one that allows us to know a features’ exact depth. GPR data are collected with two antennas that are usually housed in one fiberglass case that is dragged along the ground surface. One antenna transmits energy into the ground and another antenna receives electromagnetic radar pulses.
Radar data are collected in equally spaced straight transect lines within a rectilinear grid. Each transect produces a two-dimensional reflection profile of the subsurface. Reflections are produced from differences in the electric or magnetic properties between buried objects/ features and the surrounding soil matrix. Once the entire region is scanned, the profiles can be vertically aligned and horizontally sliced to create plan view “slice” maps showing features at varying depths below the surface.
This spring I traveled to southern New Mexico with my colleague Jennie Sturm to conduct a GPR study for the US Forest Service. An intense surface concentration of ceramics of a datable style suggested that the area in question was a Mogollon pithouse village dating to roughly 700-900 AD. However, no excavations have ever been performed to understand if there actually are buried structures on the site. Unfortunately, the recent construction of a nearby road has caused severe erosion of the site, revealing even more artifacts in the cut banks of runoff channels. We used GPR to try and locate pithouses and fortunately had success in identifying one textbook example, and possibly two other partial pithouses. All within one day! Armed with this information the Forest Service can take the next steps to protect this important, yet disappearing site.
2D profile showing the walls and floor of a pithouse roughly 1 meter below the ground surface.
Plan view slice map at a depth of 1.05 meters showing a pithouse (warm colors) with a 4 meter diameter.
Jennie Sturm and Michele Koons collecting GPR data.