Cases and solutions Environmental Geology 40 (3) January 2001 7 Q Springer-Verlag 359 A. Chabas (Y) Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR 7583, Universités Paris VII et Paris XII, CNRS, 61 avenue du Général de Gaulle, 94010 Créteil, France D. Jeannette Centre de Géochimie de la Surface, EOST, UMR 7517, CNRS-ULP, 1 rue Blessig, 67084 Strasbourg, France Weathering of marbles and granites in marine environment: petrophysical properties and special role of atmospheric salts A. Chabas 7 D. Jeannette Abstract The aim of this paper was to study the weathering mechanism of marbles and granites ex- posed to the marine environment at the Delos ar- chaeological site. Alterations, as granular disinte- gration, contour scaling and alveolus formations, can be observed either at the base of blocks and columns, or at the median-high zones of monu- ments. A white marble, which originated from Nax- os Island, had a weak porosity (0.2%). Its porous network was organized into two subnetworks of rectilinear and sinuous cracks, which limited capil- lary transfer to F10 cm. The granite, which origi- nated from Delos Island, had a relatively high por- osity (2.15%), and had a well-connected system of cracks and microporous zones of weathered miner- als. This homogeneous network allowed good capil- lary transfer for long distances (1–2 m). For the marble, as for the granite, evaporation occurred mainly at depth in the stone, and encouraged its deterioration. This damage depends on the dissolu- tion and crystallization of salts, which occur in cy- cles. First, by the capillary transfer of water and salt from the ground, when the stones are located near the sea. This processes can explain the deteri- oration of the marble and the granite bases, and the decay of granite on all its surfaces. Second, by fixation of water vapor by sea salt deposited on the stone by wind. This phenomenon can explain the degradations observed on the median-high parts of monuments in marble and granite, even though, for the granite, the first mechanism was more ac- tive. Keywords Delos Island 7 Granite 7 Marble 7 Seaspray deposit 7 Weathering Introduction Located in the Cyclades, at 150 km south-east of Athens, Delos is a small island (5 km from north to south; 1.3 km from west to east) and a famous archaeological site. Mar- bles and granites used for monuments show degradation by scale or slab detachment, and by the formation of pits and alveoli. These decay phenomena have been identified at Delos by Beloyannis and Dascalakis (1989), Sterflinger and Krumbein (1997), Chatzidakis and others (1997), and in other coastal environments, but on materials with higher porosity, by McGreevy (1985), Zezza and Macri (1995), Vendrell-Saz and others (1996) and Smith and others (1997). Without taking into account biological degradation and hydrological or thermal dilatation, most of the damage observed on Delos monument stones is a result of salt accumulation, which is controlled by the migration of so- lution through the porous network of the stone. These solutions originate from rainwater, condensation water or from groundwater penetration, which migrate under the influence of capillary tensions through the porous net- work of the stones until they reach areas where they can evaporate. While the solutions migrate, they leach out stones and masonry components (Snethlage 1984; Arnold and Zehnder 1989; Winkler 1994), and dissolve atmos- pheric deposits from the stones (Chabas 1997; Chabas and others 2000). With an equivalent exposure to weather and identical so- lution supply, weathering varies with the type of stone and, in particular, with the volume and the connectivity of its porous network. These properties determine the migration of the solution by capillarity and by evapora- tion, and thus the salt precipitation at the stones surfaces or inside the porous network. It is the position of the salt in relation to the stone surface that determines the forms of weathering (Mertz 1991; Jeannette and Hammecker 1992; Hammecker 1993; Jeannette 1997). At Delos, if some degradations observed are the result of capillary transfer of saline solutions from the ground and their evaporation inside the stone, others deteriorations can not be explained by this mechanism. An other mech- anisms is therefore proposed taking into account field observations, exposure conditions and petrophysical properties of the marbles and granites.