ANDRADE, C., CRUZ, J.V., VIVEIROS, F., COUTINHO, R. (2020) - CO₂ emissions from Fogo intracaldera volcanic lakes (São Miguel Island, Açores): a tool for volcanic monitoring. Journal of Volcanology and Geothermal Research, 400, 106915, doi: 10.1016/j.jvolgeores.2020.106915.

​A geochemical study was carried out at Fogo Lake during June 2016, in one of the deepest lakes on São Miguel Island, as well as on small associated pond, in order to identify possible anomalous degassing areas. Fogo Lake is located inside the summit caldera of Fogo Volcano, one of the three active central volcanoes that dominate São Miguel geology.

The hydrogeochemical profile carried out along the water column of the Fogo Lake suggests that the lake was thermally stratified, corresponding to poorly mineralized and cold Na-Cl type waters. The same composition is found in the small pond, but with a slight Ca-enrichment.

To measure the CO₂ flux at the lake surface, the modified accumulation chamber method was used, and a total of 1696 measurements were accomplished, covering an area of approximately 1.56 km². Measured CO₂ flux values are relatively low, ranging from 0 to 28.4 g m⁻² d⁻¹ (mean = 2.6 g m⁻² d⁻¹) and from 2.1 to 15.0 g m⁻² d⁻¹ (mean = 6.3 g m⁻² d⁻¹), respectively at Fogo Lake and at the small pond. The very low values measured in the central area of Fogo Lake are associated with the monomictic character of the lake, as the CO₂ is not able to ascend into the surface when the water column is stratified during the warmer period.