Archeological Investigations using High Sensitivity Magnetometers

Archeological Investigations:
Discovering Mankind’s Hidden Secrets

For the past 14 field seasons, Dr. Tatyana Smekalova, Physical Institute of the St. Petersburg State University, Russia, has contributed to numerous archeological projects in the search to discover the secrets of man’s past history. Her work has taken her and her colleagues to sites in Armenia, Denmark, Egypt, Estonia, Germany, Greece, Norway, Russia, Sweden (Skane), Syria, Turkey, Ukraine (Crimea), and Wales. It’s a world of adventure … and a world in which magnetics plays a key role.

Dr. Smekalova at work with a GSM-19
and sensor carried in inverted position
for proximity to near-surface sources.

As noted by Dr. Smekalova, “magnetometer surveys are one of the most effective and universal among geophysical methods for archaeological applications. Many objects can be readily distinguished at surface according to the characteristic anomalies associated with them. Magnetic prospecting (in favourable conditions) has also proven itself as the most effective, fast and non-destructive method for the investigation of archaeological sites. As well, the information obtained is very similar to that revealed during archaeological excavations.”

The reasons for the effectiveness of magnetics in archeology are related to several factors, including alteration of magnetic properties due to fire and magnetic susceptibility contrasts in soils. The image below shows some of the anomalies associated with various magnetic artifacts.

In ancient days, the use of fire for heating, cooking, production and industry changed the magnetic properties of clay, stones and earth – to the extent that they can be readily mapped using magnetometers. Earthen structures typically exhibit local magnetic anomalies in the range of 1-20 nT whereas “fired” structures can range between 10 to 1000 nT. Ferrous objects, including iron-smelting slag blocks, are rarer with anomalies that range between 20 to 2,000 nT.

Variations in magnetic susceptibility between topsoil, subsoil and rocks (topsoil is normally more magnetic than subsoil) are another important factor. These variations make it possible to detect ditches, pits and other silted-up features that were excavated and then silted or back-filled with topsoil. Back-filled areas produce positive anomalies. Conversely, less magnetic material introduced into topsoil, including many kinds of masonry (for example, limestone walls) produce negative anomalies on the order of 2 to 12 nT.

TOP

Dr. Smekalova uses a variety of systems, including:

The GEM Overhauser gradiometer GSM-19WG as a main instrument GEM_Overhauser_Brochure

Results are documented in a publication, called “Magnetic Prospecting in Archeology” that shows results from many types of sites, including:

Flint mines
Stone Age barrows
Cooking pits
Iron smelting sites with slag pits
Early Iron Age sites
Ancient fortifications
Medieval pottery kilns
Islamic fortresses and cemeteries

You can access Dr. Smekalova’s case histories by selecting from the list below. These resources provide a fascinating look into some of the artifacts left by our ancestors in many parts of the world, and are filled with many examples of geophysical data, ancient maps and artifacts.

In addition the high sensitivity Potassium Magnetometers are ideal for looking for the most subtle features. These systems can be carried or mounted on towed specially designed carts.