Skip to content

Seasonal variability in hydrogeochemistry of Fogo volcano mineral waters

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: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 10

  • Programme No: 5.1.16

  • Theme 5 > Session 1

Abstract

A total of 10 mineral waters samples from Fogo volcano were collected during February and August 2022, in order to ascertain seasonal variations in their chemical and isotopic signatures. The thermal waters temperatures ranged from 27.2 to 58.4°C in winter and 28.2 to 58.4°C in summer, generally with lower pH values in both seasons. Cold waters temperatures ranged between 13.0 and 21.2°C in winter and 13.5 and 21.3°C in summer. A negative correlation between pH and temperature reflects the volcanic input, while electrical conductivity and bicarbonate concentration show a positive correlation linked to rock weathering. These waters are predominantly Na-HCO3, with one sample classified as Na-HCO3-Cl, showing minimal variation in the major components. Rare earth elements patterns resemble local rocks, though the majority present europium anomalies, either positive or negative. Positive Eu anomalies seem to be associated to rainwater recharge, which depicts the same spike, that fades during summer due to higher rock-water interaction, while negative Eu anomalies are linked to incongruent dissolution of the rock, with preferential dissolution of minerals such as pyroxene and amphibole. Strontium isotopes show different behaviors across samples, some showing stability and other exhibiting seasonal shifts. Samples with fluctuating 87Sr/86Sr ratios also display variable REE patterns, reflecting incongruent dissolution of the rock.