We used two different methods of geophysical survey on Peeling Back the Layers. These were magnetometry and resistivity, and we were delighted to have Trent and Peak Archaeology (part of York Archaeological Trust) on board to undertake them!
Magnetometry measures and maps magnetism in the soil. We don’t do this just for the sake of it, though. Minute variations in soil magnetism in relation to the general background magnetic field can indicate signs of past activity (archaeology) under the ground. This shows up as a higher or lower reading. Areas of burnt material are generally higher and show up darker/black. Walls are generally lower and show up lighter/white. Bacteria can also alter soil magnetism which usually happens in wet soil and can indicate old river channels etc.
We hoped that this would be useful in our investigations at Under Whitle, for there are a number of residences/houses mentioned in documents that there is little trace of on the ground. Find out how useful the magnetometry proved to be on our Discoveries… page!
Magnetometry, however, is hopeless if there is interference from magnetic materials. Whilst we were sure there was nothing to cause interference in the immediate landscape, e.g. metal fencing, there were a few rules that the person undertaking the survey had to follow, such as no watches, credit cards or metallic zips. As magnetometry is a relatively speedy process, where the practitioner has to walk at a consistently quick pace along each transect to keep up with the beeps, the survey proper was carried out in the main by staff of TPA, although participants were able to handle the equipment and learn how it all worked.
Resistivity is another technique we used. Similar to magnetometry, this method measures variations underground to detect hidden archaeology. Resistivity, as it names suggests, measures resistance in the soil to an electrical current passed through it. The resistance is measured and plotted.
Everything has some resistance to an electrical current but ditches that have a lot of moisture content have less whereas walls and stones have much more. So, like the magnetometry, this technique should’ve helped us locate any missing buildings as well as other past activity. Visit our Discoveries… page to see if this was the case!
The two techniques together provide not only different data sets but also some confirmation for what each one finds. So, as well as helping us locate hidden archaeology that we went on to excavate, this allowed us and participants in the project to compare and contrast the different techniques.
Click on the links to read about what pupils of St Thomas More’s Catholic School and Buxton Community School got up to, as well as members of the Peak District Young Archaeologists’ Club when they visited and took part in the survey.