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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

FREIRE, P., COSTA, A., COUTINHO, R., CRUZ, J.V. (2008) - Mineral Water Geochemistry in the Azores Archipelago (Portugal): characterisitics and hydrogeochemical mapping. IAVCEI 2008 General Assembly. Reykjavik, Iceland (Poster).


Numerous mineral water discharges are observed in the Azores archipelago (Portugal), mainly of CO2-rich cold waters and thermal waters, namely spread along São Miguel, Terceira, Graciosa, Pico, Faial, São Jorge and Flores islands. Springs discharge from perched-water bodies, or from the basal aquifer system, and present a large range of water types and mineralization magnitude.
In the course of a research project, on which the main objective was to study variations on the chemical composition of mineral waters from the Azores, in the setting of volcano surveillance, an extensive campaign of sample collection was made in all islands through a field survey. Waters are mainly from the sodium bicarbonate to sodium chloride types, despite the fact that the composition of a few samples is dominated by SO4. The pH range between 2.2 and 7.82, discharge temperature between 15ºC and 99.5ºC (median=35ºC), and conductivity varies between 139 and 43100 µS/cm (median=906 µS/cm).
The main hydrogeochemical processes are the CO2-dominated volatile absorption, water-rock interaction and mixture with hydrothermal fluids. Sulfate dominated composition is explained by the influence of steam heating, and the Cl-Na water type result from mixture with sea salts.
Data was divided in classes according to quartile values and spatial analysis was made through thematic mapping, which constitutes the geochemical atlas of the mineral waters from Azores archipelago.
Mapping was made using ESRI ArcGis 9.1 software and some examples are shown in the present work. Maps were made for discharge temperature, pH, conductivity, free CO2, major elements and water types. For the discharge temperature map the Schoeller classification criteria was also used.
Results are currently being used for the seismovolcanic surveillance at the archipelago, and a data bank -Base de Dados Hydrovulc- was created, containing information about 2042 analysis performed between 1817 and 2008.