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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

KIYAN, D., HOGG, C., RATH, V., JUNGE, A., CARMO, R., SILVA, R., VIVEIROS, F. (2019) – Three-dimensional magnetotelluric imaging of Furnas and Fogo Volcanoes, São Miguel Island, Azores archipelago, Portugal (Poster). AGU Fall Meeting 2019, San Francisco, U.S.A., 9-13 December.


Accurate geophysical imaging of shallow subsurface features provides crucial constraints on understanding the dynamics of volcanic systems. The island of São Miguel, Azores (Portugal) is dominated by volcanic systems and can pose a threat to human populations in terms of elevated CO2 and radon degassing, and seismic swarm activity. At Furnas Volcano, intense circulation of volcanic fluids at depth leading to high CO2 outgassing and flank destabilisation poses considerable threat to the local population. The previous electrical resistivity model developed from 39 audio-magnetotelluric soundings that imaged the hydrothermal system of the Furnas Volcano to a depth of 1 km directly beneath the caldera, has now been expanded to include 35 additional broadband magnetotelluric soundings from a recent field campaign conducted in 2018, to image deeper and broader to gain new insights into the regional context of the Furnas volcanic system. The resistivity model constructed from high-frequency dataset delineated two enhanced conductive zones, one at 100 m and another at 500 m depth, separated by a resistive layer. The shallow conductor has conductivity less than 1 S/m, which can be explained by clay mineral surface conduction with a mass fraction of at least 20% smectite. The deeper conductor extends across the majority of the survey area and is located at depths where smectite is generally replaced by chlorite and being interpreted as aqueous fluids near the boiling point and infer temperatures of at least 240 oC. The less conductive layer found between these conductors is probably steam-dominated and coincides within the mixed-clay zone found in many volcanic hydrothermal systems. Preliminary inversions from the deep-probing data indicate continuation of a strong conductive zone towards the south, beneath the 1630 Dome which is the most recent phase of eruptive activity in the multi-caldera complex. During the 2018 field campaign, we have expanded our study to include 50 broadband soundings on the adjacent, volcano Fogo, which dominates the topography of the island. This region is subjected to seismic swarm activity and its relationship with the geo-electrical structure is being investigated.