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

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.