Geophysics and Archaeology

Geophysics and Archaeology. Fort Clark State Historic Site. Geophysics is the application of the methods of physics to the study of object or materials beneath the surface of the earth. Archeo-geophysics applies geophysical principles to the study of near-surface archaeological deposits. The goal is to discover, map, and understand archaeological sites and the features and deposits within them. , How does geophysics work? , Archeo-geophysical surveys measure physical properties of the soil, based on numerous measurements take at regular intervals throughout a region of study. A buried object, like a wall, house floor, or hearth, will tend to yield changes in the geophysical measurements recorded at the surface owing to its different physical properties. This creates a contrast against the natural level of background measurements. These contrasts are referred to as "anomalies" until their sources can be identified, a task that often requires archaeological excavations. , Magnetometry quantifies changes in soil magnetism. Fires around hearths or burned houses tend to be highly magnetic, as are many kinds of rocks. Iron artifacts also yield very strong magnetic measurements that are readily apparent in magnetic data sets. , Electric Resistivity methods use probes to inject a current into the soil. Resistance to that current resulting from buried objects and soil changes is recorded. These methods are very sensitive to the occurrence of subsurface rocks or stones as might occur within buried floors or walls, More subtle soil changes may also be detected. , Resistivity Findings , At a shallow depth of 50 cm (near right) many linear and rectilinear alignments are visible, but perhaps one-third of these are former trench excavations from archaeological digs in the 1970s. The remainder signify buried rooms and walls. At a depth of 1.5 m (far right) several deep trenches are visible that once held the stout members of the trading post's outer palisade. A series of such trenches to the southwest indicates expansion of the trading post from a square to a rectangular form through time.