Electrical conductivity and induced polarization investigations at Krafla volcano, Iceland

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Revil, A., Qi, Y., Ghorbani, A., Soueid Ahmed, A., Ricci, T., Labazuy, P.
• Other Authors: Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Department of Minning and Metallurgy, Yazd University, Department of Minning and Metallurgy, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Institut national des sciences de l'Univers (INSU - CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Hrafntinnuhryggur; Krafla; Obsidian Ridge; Iceland
• Online Access: https://hal.uca.fr/hal-01927668; https://doi.org/10.1016/j.jvolgeores.2018.11.008

International audience Electrical conductivity and polarization properties of 6 samples from Krafla volcano (Iceland) were measured inthe frequency range 1mHz–45 kHz and compared to the data obtained on various basaltic rock samples fromHawaii.The results indicate that for altered samples, the surface conductivity, normalized chargeability, and quadratureconductivity of the core samples scales linearly with the cation exchange capacity, taken as a proxy of thealteration facies. The surface conductivity of fresh samples is also controlled by the cation exchange capacity buttheir normalized chargeability is influenced by the presence of magnetite, especially for unaltered samples. Thetemperature dependence of quadrature conductivity and normalized chargeability can be modeled with an Arrheniusequation with an activation energy of 16–19 kJ mol−1. The experimental results agree with a model inwhich the polarization of the metallic and non-metallic grains are both considered in a unified framework.These results are used to interpret two 3D induced polarization surveys performed in the South and East partsof Krafla volcano using two 1.3 km-long cables with 32 electrodes each. The electrical conductivity is in therange 0.3 (clay cap) to 5 × 10−5Sm−1 (unaltered rock)while the normalized chargeability is typically comprisedbetween 10−2 (clay cap) and 10−5 S m−1 (unaltered rock). Induced polarization is used to image porosity andthe cation exchange capacity. A long 5.6 km electrical conductivity profile was also performed connecting thetwo 3Dsites and crossing a rhyolitic obsidian ridge called Hrafntinnuhryggur. Hrafntinnuhryggur is characterizedby very low conductivity values on the order of 10−4 Sm−1. The long conductivity profile shows the position ofthe inner and outer caldera rims and the feeder dike of Hrafntinnuhryggur. A self-potential survey performedalong this long profile shows no shallowactive geothermal features in this area, as expected fromthe lowpermeabilityof the clay cap.