VIKING UNST PROJECT: FIELD SEASON 2008 - Nabo

iron within the soils (Gaffney & Gater 2003; 38; Tite & Mullins 1971; 209-210; Linford2004; 178). Both of these processes can occur in archaeological deposits. The patterns ofenhancement across the structure will therefore be useful in the interpretation of the site.In terms of the magnetic viscosity, this provides a measure of the ease of which magneticgrains become aligned with an external magnetic field. Materials with higher magneticviscosity values are dominated by larger magnetic grains, as these take longer/more energyto align with the magnetic field (Gaffney & Gater 2003; 46). It has been noted that therepeated heating and cooling of magnetic materials tends to reduce the size of the magneticgrains, corresponding to a decrease in the magnetic viscosity (Gaffney & Gater 2003; 46).An assessment of this parameter will therefore provide some indication as to the intensityof activity within the area, as well as the occurrence of industrial activities such as metalworking.In addition to the individual measurements of magnetic susceptibility and viscosity, thebenefits of combining the assessments have been demonstrated. By simply determining therelationship between these two parameters, Gaffney and Gater have shown that adistinction can be made between samples enhanced through industrial and domesticactivities, providing further information regarding the intensity of the activities carried outat Hamar and the Upper House, Underhoull (Gaffney & Gater 2003; Figure 157).The measurements of magnetic susceptibility and viscosity are carried out on 50g of driedand sieved samples. The assessment of magnetic susceptibility will be carried out using alow field A.C. susceptibility bridge (Evans & Heller 2003; 63), while the magneticviscosity will be assessed using a pulsed induction meter (P.I.M). In addition to thelaboratory measurements of magnetic susceptibility, in situ assessments were carried out inthe field using an Exploranium KT-9 Kappameter across a 5cm grid of the lower room ofHouse 1.The preliminary results from the use of the Exploranium meter have been very encouragingfor the measurements collected from the lower room of House 1 at Hamar during the 2007season. The background level of magnetic susceptibility was subtracted from the readingsbefore being plotted as a 2-dimensional contour map; higher values were represented as thedarker areas of the plot and therefore highlighted potential ‘hotspots’ of activity within thelower room. It was clear that there were two main areas of high magnetic susceptibilitymeasurements, corresponding to the area adjacent to the southern doorway, and a smallcircle within the upper area of the lower room, which appears to correspond to a small gullyfeature running down the centre towards the upper room (figure 4.1). It is not yet clear whatthese ‘hotspots’ relate as the other geoarchaeological techniques applied to the sampleshave not yet been completed.4.6.2 Phosphate analysisThe use of phosphate for geochemical prospection is a well documented technique (Bethell& Máté 1989). Phosphorus is abundant within soil systems, being present in both inorganicand organic forms, as well as in both soluble and insoluble forms. The use of this elementin prospection is based on the fact that different activities enhance the levels of phosphate61