Dunstaffnage Castle survey

Date April 2007 - June 2007

Event ID 556305

Category Project

Type Project

Permalink http://canmore.org.uk/event/556305

NM 8826 3449 In April and June 2007 a team of researchers drawn from the School of Environmental Science at the University of Ulster with support from the Queen's University of Belfast conducted an integrated landscape survey and assessment of the environs of Dunstaffnage Castle. The primary purpose of the survey was to undertake extensive terrestrial and marine topographic and geophysical survey of the landscape area of the castle with a view to reconstructing the formation processes of the headland and recording buried cultural remains. This project was carried out with both financial and logistical support of Historic Scotland which is gratefully acknowledged.

The Castle is located on an upthrown block of conglomerate whose NW vertical face lies along a NE trending fault line that can be traced along the edge of the conglomerate block, down to the shore along a topographic low (preferentially eroded along the fault plane) and onto Eilean Mor to the NE. Not only does the upthrown block of the fault lend an elevated position to the Castle, but the vertical face created by the fault plane also adds to the natural defences of the structure.

Geophysical survey was conducted both in the marine environment and on land. The geophysical survey of Dunstaffnage Bay and surrounding waters comprised an EdgeTech Model 272-TD dual-frequency digital side-scan sonar acquisition system and a high-resolution digital echo-sounder. Bathymetric data was contoured to produce 2- and 3-dimensional landscape models of the bay area and act as basemaps for further data presentation and interpretation. These data were combined with onshore topographic surveys to produce seamless digital terrain models depicting the coastal landscape. The side-scan sonar survey resulted in the production of seafloor maps outlining both sediment types and the potential presence and location of sites of archaeological potential. Unfortunately no cultural anomalies were detected on the seabed in the immediate vicinity of the castle. Data was ground-truthed by a combination of sediment

sampling exercises and diver-truthing.

Three primary forms of terrestrial geophysical survey were undertaken, Ground Penetrating Radar (GPR), Resistivity survey and Magnetometry. The magnetometry data is still being processed and its usefulness is under question due to the nature of the underlying geology. The GPR consisted of a series of transects running both north-south and east-west across the various survey areas. Resistivity survey was undertaken in three primary survey grids, with an attempt to cover as much of the available ground as possible. Both data sets were integrated and georeferenced with the topographic data obtained using a combination of total station survey coupled with GPS positioning.

The GPR survey carried out in the environs of Dunstaffanage castle indicated a ditch of varying size located close to the base of the bedrock. This feature was present at the SW, S, SE, NE and NW sides of the castle and is likely to be continuous around the structure. There is considerable variation in its appearance, being from 2-10m wide and 0.5-1.7m deep, and in one instance shows a hint that it may have been amended or re-cut. A number of visible surface features on the NE and SE sides of the castle were tested. These appeared as three subtle sub-rectangular features, sometimes evidenced only by vegetation change. These features were prominent in the resistivity survey. Two SE features were more promising and showed a strong consolidated reflection perhaps indicative of flooring or introduced material for a vegetable plot. To the SW a number of probable 'naust' features proved to be shallow.

The interior of the church showed no signs of burials, although there was shallow disturbance.

Finally, a number of topographic features were also identified including 1 Pond and associated channel features located directly N of chapel.

2 Two stone-built circular features with the appearance of hut/round house.

3 Series of level rectangular features located E and NE of castle. Quantities of post-medieval artefactual material contained in soil upcast in vicinity of these features.

4 Large level rectangular earthwork feature with second smaller feature directly to the S of castle.

5 Two, and possibly a third, earthwork features which have the appearance of boat nausts.

Funder: University of Ulster and Historic Scotland

Colin Breen, Wes Forsythe and Dan Rhodes, 2007.