The impact of landslides and salt weathering on Roman structures at high latitudes—Conway Castle, Great Britain: a case study

Abstract

Conway Castle is an immense historical structure, dating back to 1289 AC. It was built on highly dipping thickbeds of indurated shale (argillite) and sandstone. It is surrounded by Conway Bay, railway lines, and tall dense forests indicating high relative humidity and rainfall in this coastal area. The castle suffers from weathering noted as honeycomb, black crust, exfoliation, and discoloration with white salt efflorescence at some parts; these are diagnostic features for salt weathering as confirmed by the laboratory investigations using scanning electron microscopy, X-ray diffraction (XRD), point XRD, and hydrochemical analysis. The salt is found to be from three sources, namely, water spray from Conway Bay that is part of the Irish Sea, chemical alteration of the mortar’s carbonate content into sulfate salts by acid rain, and wet deposition of air pollutants on the surface of the stone. The cracks noted in the southwestern tower of this castle are a result of landslides in this area that resulted from three factors: (a) high dip angle of the indurated sandstone and shale thickbeds (about 60–65° to the south) under this castle, (b) undercutting of these beds in the dip direction by the surface water of Conway Bay, and (c) seismic waves generated by the trains passing close to this castle. All these factors result in land sliding even at a low rate; however, the net result is cracks in the tower close to these factors.