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CO2 and CH4 fluxes from Congro and Santiago volcanic lakes (São Miguel, Azores)

César Andrade 2 , J. Virgílio Cruz 1, 2 , Letícia Ferreira 1 , Franco Tassi 3, 4 , Fátima Viveiros 1, 2 , António Cordeiro 2 , Diogo Braga 2

  • Affiliations: 1Faculdade de Ciências e Tecnologia, Universidade dos Açores, Ponta Delgada, Portugal; 2IVAR -- Instituto de Investigação em Vulcanologia e Avaliação de Riscos, Universidade dos Açores, Ponta Delgada, Portugal. 3Department of Earth Sciences, University of Florence, Florence, Italy 4Institute of Geosciences and Earth Resources, National Research Council of Italy 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 89

  • Programme No: 6.8.15

  • Theme 6 > Session 8

Abstract

Congro Lake is located in the SW quadrant of the Congro Fissural Volcanic System, the easternmost of the two active fissural systems of São Miguel Island (São Miguel, Azores). Lagoa de Santiago is located on the SE sector of the Sete Cidades central volcano caldera. Both lakes are associated to maar craters, the former corresponding to a crater of broadly circular shape and a diameter of approximately 500 m, and the latter occupying a crater measuring 1.1 km by 0.8 km across. The surface area and maximum depth are equal to 0.04 km2 and 22 m, for Congro, and 0.25 km2 and 33 m, for Santiago, being the estimated water residence times respectively about 7.3 and 24.5 years. To measure the CO2 and CH4 diffusive fluxes two surveys were conducted in both lakes using accumulation chambers. For CO2, 65 and 100 measurements were made in Congro, respectively for surveys 1 and 2, and 173 and 140 measurements were carried out in Santiago.  For CH4, several transepts were made, each with 6 static floating chambers, totalizing 3 and 6 transepts for Congro and 2 and 6 for Santiago, respectively for the 1st and 2nd surveys. Using the sGs method, CO2 flux at Congro range between 0.11 to 0.18 t/d (2.75 t.km-2.d-1 - 4.74 t.km-2.d-1) and at Santiago between 0.22 to 1.88 t/d (0.95 t.km-2.d-1 -- 7.43 t.km-2.d-1). Instead, extrapolating the measured CH4 flux, values are much smaller, being equal to 15.1×10-6 kg.m-2.d-1 and 7.4×10-6 kg.m-2.d-1, respectively for Congro and Santiago lakes.