Magnetic gradiometry

December 29, 2012

At Titris Hoyuk, we undertook extensive magnetic field gradiometry mapping in the early 1990s to map as much of the Early Bronze Age city as possible. Over the course of three seasons, well over half of the 32 hectare site was mapped using this technique. The geophysical maps showed the location of streets, building foundations, and kilns. Of particular importance are the streets, which had a strongly positive magnetic signature, and which form the skeleton of the ancient city. The magnetic properties of the streets was due to their construction; the streets comprise a thick 80-90cm layer of packed potsherds, which are highly magnetic due to their iron content and the process of firing involved in ceramic manufacture. A second key finding of the geophysical surveys was the location and plan of houses and large buildings in the Lower and Outer Towns. The stone wall foundations are made of limestone. The iron-poor limestone contrasts nicely with the surrounding iron-rich soils, making the Early Bronze Age architecture of Titris Hoyuk an ideal target for magnetic field gradiometry.

Outer Town gradiometry map.

A magnetic field gradiometer is a machine which measures minute fluctuations in the Earth's magnetic field. These fluctuations, or anomalies, are caused by changes in underlying geological features and, in part, by immediately subsurface archaeological features such as walls, pits and kilns. Archaeologists take measurements of the strength and direction of the Earth's magnetic field along an established grid. By mapping the changes in the magnetic field over a given area, it is possible to produce maps showing buried features without excavation.

Lower Town gradiometry map.