In May we told you about what geophysics is. Apart from helping to keep me fit with sometimes ridiculous amounts of walking across fields, why else do we use geophysics as part of the archaeological investigations into a site?

Commercial archaeology is often about revealing and recording archaeological remains before new development takes place. Whilst sometimes the nature of the development can be altered or adjusted to allow preservation of the buried features, in many cases we are recording the archaeology before its destruction.

In order to reveal and record archaeological remains we first have to find them. No matter how much we might wish it, not every field has a buried Roman villa, or a medieval settlement just waiting for a keen archaeologist to come and dig it up. In many cases the most exciting hidden treasure within a field is a former field boundary and a few modern field drains.

This is where a geophysical survey can help provide the information necessary to evaluating the archaeological potential of an area and allowing the development of a suitable plan to gain as much information as possible before building work commences. The survey can allow specific pinpointing of trial trenches over the most interesting features. This is much like keyhole surgery, hopefully producing maximum results for minimum effort and cost.

So how effective can this keyhole approach to archaeological remains be? If we take as an example a site in northeast Lincolnshire near Grimsby, we can see how useful this approach can be. The entire site in question was approximately 19 hectares in size, of which 11 hectares was suitable for the geophysical survey. The remaining area was either too overgrown or flooded making it impossible to survey. Fortunately the 11 hectare area covered the entire area proposed for construction.

An assessment of the archaeological and historical background of the area had revealed possible prehistoric to Roman cropmarks to the northwest and west of the site, with medieval activity involving earthworks and find scatters located immediately to the southeast of the site. The geophysical survey revealed a lot lot more.

Results of the geophysical survey

Suddenly the archaeological potential of the site has increased markedly. Not only can we clearly see the modern system of land drains cutting across the site, but we can also see potential settlement and agricultural enclosures, as well as ridge and furrow cultivation practices. A large dipolar spike, the white circle with a black centre to the right of the centre of the site was also tentatively identified as a potential kiln.

So what happens next? Before geophysics was available, a number of trial trenches would likely have been placed within the field to attempt to reveal any archaeological remains. As you can see from the results however, there are large areas of the field where the geophysics has not revealed any archaeological features. Random trial trenches would be just as likely to miss the interesting areas as to hit them, and an incomplete picture of the archaeology would be more than likely obtained.

Now that a geophysical survey has been done, the trial trenches can be located to test the results. This is useful for two reasons, the first is that we can target archaeological features to gain a better understanding of what’s going on, and hopefully retrieve sufficient finds to allow us to comfortably and confidently date the features. The second reason is more for the benefit of the geophysicist. The results from the trial trenching can be used to validate the geophysical results. I was fortunate to be involved with the trial trenching and it was very satisfying to see how well the archaeological features within the trenches matched up with the geophysical results.

Trial trenches overlaying the geophysics

The yellow features within the trenches relate to archaeological features, whilst the black features represent furrows. Finds recovered from the features allowed us to date them from late Iron Age to the Roman period, with the furrows indicative of medieval farming practice. The large dipolar spike was revealed as hearth or kiln, although its precise date or function unfortunately remains unknown.

The results from the trial trenching correlated very well with the geophysical survey, and this allowed us to gain a much greater understanding into the archaeological potential within the site.

So why bother with geophysics? Hopefully I’ve managed to give you a window into just how useful it can be. I certainly think it’s worth all the walking I do, and although I don’t find something exciting every time I go out, I do feel I’m helping us to understand more about our buried past.