ABINGDON ARCHAEOLOGICAL GEOPHYSICS

These are my notes of the conference. They probably contain several misunderstandings of the talks and other errors. Apologies to those concerned -please contact us so matters can be remedied.

Recent Work in Archaeological Geophysics Geological Society Burlington House London 19 December 2006 

Environmental and Industrial Geophysics Group and International Society for Archaeological Prospection

The first talk was by Thomasz Herbich from the Polish Academy of Sciences on Magnetic Surveying of the Archaeological Sites in the Nile Delta Egypt 

At Tel el Farkha the presence of pottery within the tombs enabled them to be located. Graves without pots were less detectable. In order to get decent results they had to remove modern rubbish from the surface of the ground before they surveyed it. 

In Tell el Daba they carried out a survey using a Geoscan FM36 fluxgate magnetometer and another group used a Sintex Smartmag array system which has an array of caesium magnetometers. The smartmag array covers a lot of ground quickly and was good for locating the edge of the site where it ran down to a former shoreline but to me it appeared that the fluxgate data was as good if not better than the caesium data. 

In Tell el Farain their survey of a temple complex revealed a previously unknown temple and managed to identify the sections in which the 10 metre thick mud brick wall around the complex was built. Graves were also located because they were in ceramic coffins.

Pietro Consentino from Palermo University, Sicily gave a talk on Work in the Corridor of the great  Hunting Scene, villa del Casale (Piazza Armerina). This was about the various geophysical methods which they used to ascertain why the mosaic in the main corridor there had slumped by over a metre. Ground penetrating radar and resistivity pseudo- sections were used although the impossibility of putting probes into the mosaic of the corridor limited the usefulness of this method. They also used seismic retraction and thermal imaging cameras. The conclusion was that the villa had been built over a former stream channel and this had dried out causing the subsequent subsistence

Richard Jones from Glasgow University gave a talk on Work on the Antonine Frontier. In this air photographs, magnetometery and resistivity were used to try and locate vicus which could be alongside forts if they were like those of Hadrians wall. The main problem here was that the wall is in a belt of high population with the roads railways and other interferences these cause to surveys. Whilst some remains of field systems were located there were no signs of vicuses. Perhaps the occupation period of 142-158 AD was too small for them to develop. 

Louise Tizzard of Wessex Archaeology then talked on Seabed Prehstory and this was looking at the gravels and deposits under the southern part of the North Sea. This was funded by the Aggregates Levy. They mainly used side scanning sonar with cores taken to assess the results. Amongst other things these appear to have located the level of the Cromer forest bed where it goes under the sea. This is of some interest as it, when on land, it contains remains dating to some 700,000 years ago.(Current Archaeology vol 207 Jan/Feb 07 has had articles giving a wider view of this).

Paul Baggaley of Wessex Archaeology talked on Wrecks on the Seabed. Originally side scanning sonar was used but increasingly multi beam bathymetery is used although this only covers strips of sea bed approx 1metre wide it gives a digital map of the remains. A magnetometer is also often towed behind the boat with their sonar fish. The need to keep the magnetometer low is a problem. They were able to identify a site which was supposed to be a timber ship as being an American bomber, located a submarine some distance from where it was supposed to be and gave various other examples.

Alastair Ruffell of Queens University Belfast gave a talk on Underwater Ground Penetrating Radar. This needs fresh water and can be useful up to 20 metres depth. For depths of 2-3m a 100MHz signal is preferred with deeper having 50 MHz. They had located recent jet ski wreckage and sheep remains using this method.

Dave Stewart of Bournemouth University then gave a talk on Hod Hill Reappraised (it had a longer title).Various parts of the hill top had been ploughed between 1857 and the 1940's with only one segment being unploughed. The previous archaeology had found remains of buildings in the unploughed areas but little elsewhere. The purpose of this search was to investigate how much remained in due other areas. The survey grew and grew until it had surveyed the entire hill top. The result of this was that there is a good amount of occupation over the entire hill top although there are some blank areas. There are areas where there appears to be a trackway system which appears to have 4 post structures at the junctions of the tracks and blank areas to the part of the hill top which were the most ploughed. Work on these heavily ploughed areas was carried out using ground penetrating radar and resistivity. This then revealed that even these areas had surviving remains, albeit heavily damaged.

Volkmar Schultze of the Institute for High Technology, Weimar, Germany then talked on A Squid based system for Fast and sensitive Geomagnetic Archaeology. This uses a niobium sensor with liquid helium around it to keep it cool. Mounting several these on a trailer enabled 3 hectares to be surveyed in an hour. Whilst it is very sensitive it does not have the depth penetration of caesium sensors.(this is because, like fluxgate equipment, it is not a total field machine).

Wolfgang Neubauer talked on From Prospection to Reconstruction. This involved getting magnetometery and other data from Middle Neolithic circular ditched enclosures and making digital models of these. This then enabled the palisade slots to have posts digitally inserted in them together with the gaps where they were located by excavation. This then enabled the reconstructed site to be compared with the astronomical position of the stars at the date of the monument with the result at the openings tended to coincide with sunrise and sunset and star alignments at important times of the calendar. This virtual site has now been visited by over 350,000 people.

Armin Schmidt of Bradford University then gave a talk on Slack Roman fort-this was a fort which now has a motorway running along one side of it and a golf club put on it. They were trying to see if they had a vicus. Electromagnetic interference meant that resistivity was difficult and could only be carried out if the remote probes were as close to the mobile ones as was consistent with getting decent readings. Magnetometery was of more use and found the fort ditches and some internal features but there was a lot of noise probably caused by the construction of the golf club The dumping of clay over the site during the motorway works impeded the success of ground penetrating radar.

Jack Walpole of the University of Central London gave a talk on Geophysical Investigation of 17th century Copper Workings at Levers Water Mine Cumbria. Here they were trying to see whether a drainage tunnel which was built in the 17th century still existed. The entrance to the tunnel was reputed to have been covered by debris from later copper workings. They used ground penetrating radar and a caesium magnetometer to see if they could locate anything. Both methods appeared to show an anomaly under the mining waste but in questioning from the audience it appeared that no-one really knew why a shaft should cause a magnetic anomaly.

Jimmy Adcock of GSB Prospection Ltd then talked on Buckingham, Holyrood house and Windsor-investigations at three Royal palaces. This was a description of the geophysics which accompanied a Time Team programme last summer. Of the three palaces Buckingham Palace and Holyrood house produced little of interest for geophysics partly because they were disturbed by modern services. At Holyrood house however there were some remains of the previous monastic buildings. The best results were in Windsor where ground penetrating radar revealed a crescent which turned out to be the edge of the building which was constructed to have the round table which is where re enactments of Arthurian legends took place.

The final talk was by James Lyall of the Landscape Research Centre who gave a talk on It’s been a long walk-1000 hectares of Magnetic Surveying in the Vale of Pickering. This was an English Heritage funded project which over the last six years has enabled him to carry out this enormous survey. He has found a series of Iron Age ladder settlements on the 27 metre contour in the Icklingham area. Not only have prehistoric and Anglo Saxon sites been found but large numbers of them with dozens of sunken featured buildings showing the tendency of people to throw their rubbish into the holes of these buildings means that the show up magnetically. There would appear to be major Anglian settlements every three kilometres with smaller ones in between them. Anglian burials also appeared to prefer to be in pre- Roman burial areas such as near Bronze Age barrows. Not only has he found great quantities of sites he has also found new types of monument. These are small, say three metre diameter, circles which he interprets as being pallisade slots for a fence which then had earth piled inside it and a cremation urn on top of the pile of earth. He has also identified a class of semi- circular feature similar to the above. This is part of a project which includes air photographs and lidar and multi spectral images and excavation. It would appear that approximately one-third of the features visible on multi spectral images were not visible to magnetometery whilst there were many which were visible to magnetometery but not to the other imaging systems. He classifies all also his findings and tries to allocate them to a feature type and period. This is done by printing off the geophysical plot and tracing round the features on permatrace which is then digitised. This enables plans of the landscape at different periods to be produced.

General.

Burlington House is a good venue for this and although one suspects that most people find that getting into central London early in the morning is quite difficult it is hard to think of anywhere which does not have more drawbacks – particularly for those from abroad. The refreshments were good and there were enough staff to ensure that the queues were not too long. The price at £20 was about right and the documentation provided was good. If I had one suggestion it would be that the organisers could research the local pubs and similar establishments so that people know where to go for lunch to save them wandering around the West End