Geophysical Prospecting in Archaeology

Geophysical Prospecting in Archaeology. . , Geophysics applies the methods of physics to remotely investigate and define objects or materials in the earth's subsurface without direct contact. Geophysical investigations do not disturb the soil and cultural features, as do traditional excavations. Excavations, when combined with geophysical surveys, reveal information about prehistoric architecture and people's use of space within a village. , What is a magnetic survey? , Magnetometry measures changes in the magnetic properties that occur in the soil. Burned houses, hearths, and iron artifacts are highly magnetic and readily sensed. The map on the far right reveals the basic structure of Double Ditch Village. This geophysical survey constitutes one of the largest magnetic data sets in the Americas and the world. The magnetic survey revealed many new aspects about the site, in particular two previously unknown fortification ditches (Ditches 3 and 4) with multiple bastions. , What is a resistivity survey? , Resistivity methods use probes to pass an electrical current through the earth. Resistance to the current, caused by buried objects or soil variations, is recorded. Though it produces less distinct results, the resistivity survey compliments the magnetic survey. Soil moisture greatly influences resistivity, with moister low areas – ditches, house depressions, and basins – exhibiting low resistivity (white) and drier high points, like mounds or middens, showing high resistivity (black). , Captions: , Magnetic data being collected , Resistance data being collected , Aerial view of Double Ditch Village , An electrical resistance map of the entire village , A magnetic survey map of the entire village. Large magnetic measurements, shown in black, reveal burned cultural features like houses (large black areas), hearths (small black points), and recent historic iron (black points paired with white).