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Referência Bibliográfica

PACHECO, J.M., GASPAR, J.L., QUEIROZ, G., WALLENSTEIN, N., FERREIRA, T. (2023) - Furnas Volcano - the home of the greatest volcanic lake of the Azores. IAVCEI Commission on Volcanic Lakes 11th Workshop, São Miguel, Azores, 28 agosto - 5 setembro. IAVCEI Commission on Volcanic Lakes 11th Workshop, São Miguel, Azores, 28 agosto - 5 setembro.


Furnas Volcano is one of the three active central volcanoes of S. Miguel Island, in Azores. Located in the East part of the island, it does not have a significant topographic expression. Its maximum height is about 800 m asl and its E and W flanks are unclear because it coalesces to the E with the Povoação Volcano and to the W with the Congro Fissural Volcanic System. 

The top of the edifice, however, is dominated by a large depression corresponding to a caldera complex. A large caldera with about 7 x 4,5 km has an outline still partially clear and nested in it is a younger caldera with about 5,5 x 3,5 km. Inside this caldera there is a volcanic lake and are several pumice cones and domes. Main fault systems found on Furnas Volcano are the regional tectonic system WNW-ESE and the N-S and NESW systems that played a significant role on the development of the caldera complex and the subsequent intrcaldera volcanism. 

The eruptive record of Furnas Volcano dates back to more than 93.000 years. Most of the exposed deposits are trachytic (s.l.) and about 90% are pyroclastic deposits, indicating the clear predominance of trachytic explosive volcanism throughout its history. Furnas had several large explosive trachytic eruptions associated with the emplacement of welded ignimbrites. The most significant of those deposits is about 30.000 years, is probably the largest eruption of the volcano and is associated to the opening of the older caldera. 

Since the last 5.000 years Furnas Volcano had 10 moderately explosive trachytic eruptions of subPlinian character. A common characteristic of most of their deposits is the alternation of ash and lapilli layers, interpreted as alternating hydromagmatic and magmatic fragmentation, suggesting the presence of a welldeveloped hydrologic system. The last 2 eruptions were historical and the reports on youngest, in 1630, reveal the existence of lakes inside Furnas caldera and that at the end of the eruption only one lake remained. Currently, the volcano shows several hydrothermal springs, fumaroles, and a substantial diffuse degassing. Although not erupting, even now the volcano poses significant hazards, either from the released volcanic gases or from the unconsolidated materials prone to landslides in the volcanoe steep slopes.