Physical weathering of slate gravestones in a Mediterranean climate

Abstract

The physical weathering of vertically emplaced slate gravestones in two metropolitan cemeteries in Adelaide, South Australia, is documented and evaluated with respect to the prevailing Mediterranean climate. The gravestones bear inscriptions dating back to the 1860s, thus providing a time frame of about 150 years. It is proposed that a prime factor in the weathering regime is seasonal hydration during mild wet winters, followed by desiccation during the hot dry summers. This causes repeated expansion and contraction of the exposed constituent minerals, weakening the cohesive forces within the rock. Thermal expansion has promoted cleavage spalling of dislocated sheets of about 3 mm thickness from both the inscribed faces and the backs of the gravestones. Growth of moss and lichen along the weakened cleavages has further promoted opening of cracks parallel to the slate cleavage. Salt crystallisation has substantially damaged the lower parts of all the observed slate stones.