​VIVEIROS, F., MORENO, L., CARREIRO-SILVA, M., COUTO, R., SILVA, C., RANGE, P., GERALDES, D., PARRA, H., FERREIRA, T., PACHECO, J.E. (2016) - Volcanic gas emissions offshore of São Miguel and Faial islands (Azores archipelago). Actas das 4as Jornadas de Engenharia Hidrográfica, Instituto Hidrográfico, 320-323.

​Several gas emissions are found offshore of some of the Azorean islands and represent secondary manifestations of the volcanic nature of the islands. Since 2012 several sampling surveys

were performed in the submarine emissions located offshore of Faial and Sao Miguel islands to characterize the main gas composition and identify eventual variations that can represent eventual unrest of the volcanic systems. Most of the gas emissions are cold and carbon dioxide is the main gas released in the dry phase (with more than 98 molar%). Hydrogen sulfide and hydrogen were detected only in the emissions located close to Ribeira Quente village (south coast of São Miguel Island) and the sulfuric component is present only when the gas flux is medium to high. These emissions are similar to the inland Furnas Volcano hydrothermal fumaroles. All the gas emissions have variable compositions of nitrogen, oxygen, argon and methane.