[S-VC30] International Volcanology

[SVC30-07] Volcanic fluid–rock interactions in the laboratory

*Jamie Ian Farquharson¹, Kyoko S Kataoka¹, Takumi Imura² (1.Niigata University, 2.Yamagata University)

Keywords:Fluid-rock interactions, Hydrothermal alteration, Permeability, Volcano, Permeameter, Acid

Fluid-rock interactions are ubiquitous in volcanic systems. For example, Adatara volcano in Fukushima Prefecture (Japan) is home to multiple complex hydrothermal processes, broadly divided across four alteration zones. Operative reactive processes include pyrite alteration, the formation of clays, silica redistribution, and precipitation of sulfates and other minerals. Intriguingly, evidence for low-temperature hydrothermal alteration is found in direct contact with zones of extreme high-temperature alteration, highlighting that the reaction conditions (pressure-temperature-composition: PTX) are highly spatially and temporally variable. Through a series of batch reaction experiments and hydrothermal flow-through experiments at elevated temperatures and pressures, we aim to “reverse engineer” some of the diverse alteration textures observed in the field. In turn, this will allow us to map out the PTX parameter space dominating the different alteration zones, and give insight into volcanic hazards at Adatara—a volcano characterised by cycles of phreatic and magmatic explosive activity, but not by extensive collapse events akin to the neighbouring Bandai volcano. The novel flow-through apparatus comprises a pressure vessel encased in a custom-fabricated heating mantle. A combination of fluid pumps allows the delivery of hydrothermal fluids (e.g. sulfuric acid) through nominally pristine volcanic materials. Sensors allow us to track permeability changes over time, providing insight into pressure generation or dissipation mechanisms in the volcanic setting as a function of geochemical processes. In concert with extensive geochemical characterisation, field surveying, and reactive modelling, these experiments form part of a larger effort to understand the nature of the hydrothermal system at Adatara, and fluid–rock interactions more generally.