A site-wide and comprehensive assessment of salt-induced tuff deterioration in the Archaeological Park of Herculaneum

Abstract

The Archaeological Park of Herculaneum, buried by the 79 CE eruption of Mount Vesuvius, faces a significant conservation challenge, the degradation of the volcanic tuff walls. Building upon previous studies, this work presents the first large-scale assessment of this degradation phenomenon, employing a comprehensive analytical approach that extends across the entire archaeological park. In detail, this study combines in-situ and laboratory analyses to investigate the origin and composition of the soluble salts that take part in this degradation process. Thermographic imaging identified moisture accumulation at the base of walls, confirming the capillary rise of humidity from the soil. Raman and FT-IR spectroscopy revealed that sodium sulfate, in both anhydrous (thenardite) and hydrated (mirabilite) forms, is the predominant salt, with additional contributions from calcium sulfate and minor nitrates. Ion chromatography of soil samples confirmed significant spatial and seasonal variations, with sulfates more concentrated in northern areas and increasing overall in winter. The results demonstrate that a combined approach using ion chromatography, thermographic imaging, and handheld Raman spectroscopy provides an efficient diagnostic tool for assessing salt-related deterioration. This protocol could be extended to other archaeological sites to guide conservation strategies and mitigate the impact of salt-induced decay on built heritage.