Hogg C. auteur aut IRD Kiyan D. auteur aut IRD Rath V. auteur aut IRD Byrdina Svetlana auteur aut IRD Vandemeulebrouck J. auteur aut IRD Revil A. auteur aut IRD Viveiros F. auteur aut IRD Carmo R. auteur aut IRD Silva C. auteur aut IRD Ferreira T. auteur aut IRD text journalArticle eng text/pdf born digital access Accurate geophysical imaging of shallow subsurface features provides crucial constraints on understanding the dynamics of volcanic systems. At Furnas Volcano (Azores), intense circulation of volcanic fluids at depth leading to high CO2 outgassing and flank destabilization poses considerable threat to the local population. Presented is a novel 3-D electrical resistivity model developed from 39 magnetotelluric soundings that images the hydrothermal system of the Furnas Volcano to a depth of 1 km. The resistivity model images two 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(-1), which can be explained by clay mineral surface conduction with a mass fraction of at least 20 per cent smectite. The deeper conductor extends across the majority of the survey area. This deeper conductor is located at depths where smectite is generally replaced by chlorite and we interpret it as aqueous fluids near the boiling point and infer temperatures of at least 240 degrees C. 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. specialized Electrical properties Hydrothermal systems Magnetotellurics Numerical modeling ACORES ILES FURNAS VOLCAN 062 066 020 213 1 371-386 2018 0956-540X https://www.documentation.ird.fr/hor/fdi:010074350 10.1093/gji/ggx512 0956-540X [F B010074350] https://www.documentation.ird.fr/hor/fdi:010074350 https://www.documentation.ird.fr/intranet/publi/2018/11/010074350.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2018-12-06 2023-07-11 fdi:010074350 fre