Archeology, Magnetic Methods

Abstract

Magnetic methods have become important tools for the scientific investigation of archaeological sites, with magnetic prospection surveys and archaeomagnetic dating being the most prominent ones. The principles behind these techniques were initially applied to larger and older features, for example prospecting for ore deposits (see Magnetic anomalies for geology and resources) or paleomagnetic dating (see Paleomagnetism). When these techniques were adapted for archaeological targets it was soon established that very different methodologies were required. Archaeological features are relatively small and buried at shallow depth, and the required dating accuracy is in the order of tens of years. More importantly, the relationship between archaeological features and magnetism is often difficult to predict and the planning of investigations can hence be complicated. Related is the problem of interpretation. Geophysical results on their own are only of limited use to resolve an archaeological problem. It is the archaeological interpretation of the results, using all possible background information (site conditions, archaeological background knowledge, results from other investigations etc.), which provides useful new insights. If the relationship between magnetic properties and their archaeological formation is unknown, such interpretation may become speculative. All magnetic investigations depend on the contrast in a magnetic property between the feature of interest and its surrounding environment, for example the enclosing soil matrix. The most important magnetic properties for archaeological studies are magnetisation and magnetic susceptibility.