RECONSTRUCTING THE PREHISTORIC LANDSCAPE OF STONEHENGE (UK) THROUGH MULTI-RECEIVER EMI SURVEY

Abstract

To reconstruct the archaeological landscape of the Stonehenge World Heritage Site (UK), different high resolution geophysical surveys are being conducted to map the archaeological landscape. Mainly magnetometry and ground penetrating radar are used to collect a spatially-extensive survey dataset that should provide insight into the “surface and sub-surface archaeological features and structures”. While these surveys have offered new insights into the spread and nature of the prehistoric archaeology at Stonehenge, until now little effort has been put in creating a detailed map of the natural buried landscape. In addition, a number of areas are heavily contaminated by recent metallic rubble, related to music festivals in the 1970s-80s, and military activity in the early 20th century. These magnetic features introduce a wide scatter of small anomalies in, especially magnetic, geophysical data, limiting their interpretative potential. To bridge these gaps, we have begun surveying a 2.5 km2 area at Stonehenge with a multi-receiver electromagnetic induction (EMI) instrument. This four-receiver instrument allows recording the apparent electrical conductivity (ECa) and magnetic susceptibility (MSa) of four different soil volumes simultaneously, and down to a maximum depth of 3 m below the sensor. To date, 50 ha have been mapped with this instrument at a 1.2 m by 0.25 m sampling resolution. First results show the potential of the method, as the combined analyses of the multi-layered ECa and MSa data allows reducing the influence of metallic topsoil scatter, rendering a clearer visualization of the underlying archaeology. Furthermore, soil variations were detected that indicate a previously unknown palaeotopographical variation. The presentation of these first results, along with the processing of high-resolution, multi-receiver EMI data, forms the core of this paper.