Electrical conductivity and induced polarization investigations at Kilauea volcano, Hawai'i
Résumé
Two new datasets of core samples from Kilauea volcano have been used to conduct complex conductivity (induced
polarization) measurements from 10 mHz to 45 kHz at 3 or 4 salinities (NaCl, 10−2 to 10 S m−1 at 25
°C) depending on the core samples. The first dataset corresponds to 15 core samples collected in 2015 at the
ground surface in the caldera of Kilauea around theHalema'uma'u crater (dataset 1). The second data set (dataset
2) corresponds to 28 core samples from Keller's well (KW) in the south part of the caldera. A third dataset
(dataset 3) corresponds to 28 core samples from Well PTA-2 from the Humu'ula Groundwater Research Project
in Hawai'i. The electrical conductivity of these samples can be decomposed as the sum of a bulk conductivity and
a surface conductivity associated with electrical conduction in the electrical double layer coating the surface of
the grains. The variations of the in-phase conductivity with the porewater conductivity is used to infer the intrinsic
formation factor and the surface conductivity,which is a good indicator of alteration. The surface conductivity,
the normalized chargeability (determined fromthe dispersion of the in-phase conductivity curve as a function of
frequency), and the quadrature conductivity scalewith the cation exchange capacity. In addition, the normalized
chargeability and the quadrature conductivity of unaltered core samples show a signature associated with the
presence of (titano)magnetite. The quadrature conductivity (and therefore the normalized chargeability) depends
on temperature according to an Arrhenius's law with an activation energy close to 16 kJ Mol−1. We observe
that alteration yields a pronounced increase of surface conductivity, normalized chargeability, and
quadrature conductivity. These data are in turn used to help in the interpretation of a DC electrical conductivity
survey performed in the caldera of Kilauea. The conductivity response around Keller's KW-well is dominated by
the surface conductivity contribution associated with alteration and temperature.We propose a new method to
image equilibrium temperature from electrical conductivity tomography.