The area within the Furnas Volcano (São Miguel, Azores) influenced by secondary geothermal manifestations is not particularly big. You can walk all of it in about 30 minutes. Despite this the diversity of geothermal activity is impressive. The entire area is situated few tens of meters from the caldera lake, and effluents from the hydrothermal area flow directly into the lake waters. The hydrothermally altered ground in the main area is about the size of a football field, and contain solfataras, boiling pools, numerous fumaroles, boiling mud pools and several degassing and hot spots in the entire zone.
Satellite view (Google Maps) of the Furnas caldera lake in São Miguel, Azores
There are also numerous diffuse degassing areas on the shores of the lake, and underwater degassing and hot fluids vents are evident venturing few feet into the water.
View of the geothermally influenced area of Furnas Volcano from the nearby parking lot. Credit DCO/Katie Pratt
For the sampling we selected an area representative of the diverse environments, yet safe enough for numerous people to work at the same time. Geothermally altered grounds, especially if still active, can be extremely unstable, and often be made of a thin crust covering large pools of near-boiling waters. For everyone safety we decided to limit our sampling to and area considered relatively stable.
A Birdseye view of the sampling location obtained by photomosaic. Credit Donato Giovannelli
As you can see in the picture above, the area we selected (delimited by the red line) contains different features, including soils not influenced by the geothermal activity (F). The large red square marked with *, represent the area were DCOECS15 participants Matteo Masotta, with the help of local expert and DCOECS15 participant Vittorio Zanon, performed the stratigraphy already appeared on this blog.
The sampled locations within this plot were: A the sediments of a hot pool; B the fluids and sediments of a bubbling fumarole; while D, C and E represented different point along the outflow channel connecting the fumarole and hot pool with the lake, located outside the field of view of the previous picture on the right side; F was a control site not directly influenced by the geothermal activity.
Diversity of the sampling environments. Credit Donato Giovannelli
For each site we performed a large number of measurements and collected numerous samples for further laboratory analyses. Among others, this included CO2 fluxes for the entire area, gas composition measurement and isotopes, mineralogical analyses, major and minor elements, geochemistry, quality and quantity of the organic matter and a suite of microbiological analyses. Sometime in the near future my colleagues will start to blog about the results that we are slowly compiling in a large database.