[A-HW24] Isotope Hydrology 2024

[AHW24-03] Unlocking the secrets of the hydrogeology of Mt. Fuji with temporally and spatially highly resolved tracer observations

*Stephanie Musy¹, Friederike Currle¹, Ma. Teresa Nakajima Escobar², Yama Tomonaga^1,3, Yuji Sano², Oliver S. Schilling^1,4 (1.Hydrogeology, Department of Environmental Sciences, University of Basel, Switzerland , 2.Center for Advanced Marine Core Research, Kochi University, Japan, 3.Entracers GmbH, Duebendorf, Switzerland, 4.Department Water Resources and Drinking Water, Eawag–Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland)

Keywords:Groundwater, Mt. Fuji , Isotope, Tracers, Numerical Modelling

Mt. Fuji, Japan's most iconic volcano, also happens to be one of its most mysterious volcanic aquifer systems. In recent years, the long-standing conceptual model of laminar-flowing, un-mixed, and solely topographically driven groundwater was challenged by the discovery of significant deep, helium- and vanadium-rich inflow from the basement to numerous cold-water springs and pumping wells located in its southwestern foot (Schilling et al. 2023). This deep fraction is also characterized by an overproportionate amount of extremophile Archaea, which are optimally adapted to temperatures exceeding those of the surfacing waters and that was revealed by eDNA sequencing (Segawa et al. 2015).

These intriguing conclusions naturally lead one to question the spatial and temporal occurrence and variability of this upwelling. In this ongoing research, the dynamic response of the system to hydraulic and seismic forcings in the Fujikawa-kako Fault Zone is now observed continuously owing to a novel online monitoring station that combines dissolved noble and reactive gas concentration measurements with online microbial analyses. Additionally, water and gas samples are regularly collected in springs and wells scattered throughout Mt. Fuji’s watershed and analyzed for multiple tracers: He, Ar, Ne, Kr, Xe, V, major Ions, d¹⁸O, d²H, d¹⁵N. The preliminary results indicate that mixing processes are much more spatially distributed than previously assumed and that all types of water might be encountered throughout the watershed. To make the most out of these observations and project future groundwater quality and quantity under climate change, we are building both an updated 3-D geological and a fully integrated 3-D numerical surface-subsurface hydrological model. In this presentation, the latest results and modeling progress will be presented.