Dissolution‐corrosion measurements with limestone and gypsum tablets in active sulphuric acid caves of southern Italy

Abstract

Dissolution‐corrosion (DC) represents an important factor for speleogenesis, and can be measured monitoring weight variation over time of carbonate and gypsum tablets exposed in underground environments. The oxidation of H2S produces H2SO4, which in carbonate host rock induces the surface of carbonate tablets to be rapidly corroded by sulphuric acid, whereby CaCO3 is replaced by CaSO4∙2H2O, producing a significant weight gain. We describe preliminary results of DC monitoring in four still‐active SAS systems, including Ninfe Cave and Terme Sibarite (Calabria), Fetida Cave (Apulia), and Acqua Fitusa Spring Cave (Sicily). The tablets have been set inside the caves, in three different conditions of exposure (i.e. underwater, air, interface zone) in the winter 2015‐2016 to monitor DC in five years. The results show how the condition of exposure is an important control for the behaviour of weight variation. Tablets set underwater displayed significant weight loss during the first period of exposure, whereas those located at the interface zone exhibited a tendency of weight variation significantly dependent on time, and tablets in air showed weight gain.