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Tracing hydrogeochemical processes in the mineral waters of Furnas volcano

Letícia Ferreira (1), José Virgílio Cruz (1,2), Fátima Viveiros (1,2), Nuno Durães (3), César Andrade (1), Nuno Cabral (4), José Francisco Santos (3)

  • Affiliations:  (1) IVAR -- Instituto de Investigação em Vulcanologia e Avaliação de Riscos, Universidade dos Açores, Ponta Delgada, Portugal (2) FCT -- Faculdade de Ciências e Tecnologia, Universidade dos Açores, Ponta Delgada, Portugal (3) GeoBioTec -- Geobiociências, Geoengenharias e Geotecnologias, Departamento de Geociências, Universidade de Aveiro, 3810-193 Aveiro, Portugal (4) CIVISA -- Centro de Informação e Vigilância Sismovulcânica dos Açores, Universidade dos Açores, Ponta Delgada, Portugal 

  • Presentation type: Talk

  • Presentation time: Tuesday 09:45 - 10:00, Room S160

  • Programme No: 5.1.6

  • Theme 5 > Session 1

Abstract

Furnas volcano, one of the three active central volcanoes of São Miguel (Azores), hosts mineral waters with significant physicochemical variability. These waters are categorized as hyperthermal (89.4 - 95.4 °C), thermal (29.9 - 70.0 °C) and cold (14.2 -- 21.4 °C). Most are Na-HCO3 with neutral to slightly acidic pH, except one sample with a SO4-Na composition and low pH. Major element composition is primarily influenced by rock leaching and volcanic inputs. Volcanic inputs comprise two distinct environments: acid-sulfate boiling pools, formed by steam heating and H2S oxidation, and neutral-HCO3-Cl waters, where bicarbonate waters mix with deep neutral chloride fluids. Water-rock interactions contribute with lithium, iron, aluminum, rubidium, and strontium, while volcanic inputs provide boron, arsenic, antimony, and tungsten. Strontium isotopes reveal equilibrium with the host rock, with no seasonal changes or incongruent dissolution detected. Rare earth elements generally match local rock patterns, with light REEs enrichment over heavy REEs and negative europium anomalies. Positive Eu anomalies in the hyperthermal waters from the Village, may reflect rock weathering at temperatures exceeding 250 °C, due to the contributions of the deep fluids, while in the thermal and cold waters can result from reducing conditions.