Investigation of suspected gulls in the Jurassic limestone strata of the Cotswold Hills, Gloucestershire, England using electrical resistivity tomography

• Dry linear hollows in the English Cotswolds investigated as possible gulls
• Underlying structures found to be vertical 80 metre-deep rubble-filled zones
• Electrical resistivity tomography confirmed as ideal to investigate cambering

An electrical resistivity tomography survey has clearly indicated the presence of substantial vertical zones of contrasting material beneath a set of conspicuous linear surface hollows that cut across a spur forming part of the Cotswold Hills escarpment in Gloucestershire. These zones are compared with nearby quarry exposures and are inferred to be gulls – graben-like structures at least 80 m deep filled with collapsed blocks of bedrock with intervening air-filled spaces, lying within areas of relatively undisrupted gently dipping strata, and which under some circumstances would present a significant geohazard. Our results confirm the great potential of this non-invasive and rapid survey technique for investigating such phenomena, and provide an exemplar for comparison with surveys elsewhere, to assist identification of similar features.