A new experimental setup for combination of SIP measurements with X-ray µCT scanning: an application to the Gunnuhver geothermal system in Iceland

Many volcanoes contain hydrothermal systems, which significantly contribute to the occurrence of volcanic eruptions. Unlike eruptions that emit magma, these events forcefully expel existing rock, volcanic gases (CO2, H2S, etc..), and steam, presenting a considerable danger to human safety. Recent devastating events highlight the challenges in predicting sudden hydrothermal explosions, revealing the limitations of current predictive capabilities. The main challenge is the lack of clear warning signs, which complicates the prediction of such eruptions. These phenomena can be initiated by the addition of mass and energy from magma, or by the formation of mineral seals over vents without direct magma involvement. It is crucial to enhance our understanding and prediction of these hydrothermal events to reduce their potential impacts on humans and the environment.

In the ERUPT research project, we investigate the geoelectrical behavior of volcanic hydrothermal systems (VHS) on a laboratory scale. Our research combines electrical properties, specifically Spectral Induced Polarization (SIP) measurements, with X-ray pore-scale (4D µCT) imaging to decipher the complex electrical signatures of volcanic systems through rock samples from the area of study. Spectral Induced Polarization (SIP) is a geophysical technique that assesses the complex electrical impedance of materials across a broad frequency range, offering valuable insights into the electrical characteristics of porous media. This method has been effectively applied to study rock samples from Volcanic Hydrothermal Systems (VHS). SIP responses are influenced by factors such as surface area, pore size distribution, and fluid content, as well as the movement of fluids within the rocks. Conversely, X-ray micro-CT is a technique that generates detailed, three-dimensional representations of a sample's internal structure, allowing for the examination of internal morphology, porosity, and other structural details at the micrometer scale, as well as the analysis of fluid pathways and dynamics.

By integrating these two techniques, we aim to achieve a deeper understanding of the geoelectrical properties and internal composition of rock samples. This is accomplished by examining SIP responses across various frequencies and linking them with µCT images to understand how changes in geoelectrical properties correlate with fluid movement within the rock matrix and the effects of mineral alteration or precipitation. We have developed an innovative experimental setup that combines SIP and µCT techniques simultaneously. This novel prototype was meticulously designed with specific technical features to ensure optimal SIP signal acquisition under controlled temperature and pressure conditions, along with high-resolution 4D µCT analysis. The new experimental setup has been successfully tested for its pressure resistance under high confining liquid pressures, demonstrating effective sealing and leakage prevention. It has also enabled consistent Spectral Induced Polarization (SIP) measurements across various sample materials. This approach holds significant potential for advancing research in geophysics, hydrogeology, reservoir characterization, and other related field.