SUBsurface pressure Modulation causing ERuptions of Strokkur GEyser, Iceland

• Applicant: Professorin Dr. Eva Eibl
• Subject Area: Geophysics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 571577001

Geysers are natural phenomena fascinating visitors and scientists alike. They are hot springs cyclically ejecting hydrothermal fluids up to several tens of meters into the air. The time between eruptions may span from minutes to days. Geysers are fueled by a heat source hosted in the nearby shallow subsurface causing specific pressure and temperature conditions in the hydrothermal reservoir. Fluids cyclically transition across the liquid-vapor boundary causing geysering. Only about 1000 sprouting springs and geysers exist worldwide and their subsurface structure including the underlying aquifer, recharge processes and conduit conditions are still poorly constrained with respect to the eruption frequency or dynamics. SUBMERGE aims to constrain the processes taking place in the plumbing system of Strokkur geyser, Iceland, and investigate its responses (or lack of) to external forcing (such as remote earthquakes, eruptions, or major meteoric changes). Strokkur lies in the Haukadalur geothermal field in southern Iceland that features several hot springs as well as the Great Geysir geyser. SUBMERGE will study Strokkur within the wider context of the geothermal field and its magmatic heat source. Based on seismological source locations (Eibl et al. 2021) Strokkur is suggested to be fed by a bubble reservoir located at 23.7 ± 4.4 m depth west of the conduit. Such a reservoir can explain single eruptions, but the multi-tuple eruptions featured by Strokkur require a more complex conceptual model that is not compatible with a single bubble reservoir. Furthermore, the link of the shallow plumbing system with the deeper aquifer is also not well constrained. SUBMERGE combines (i) Long- and short-term passive seismological methods (such as nodal ambient noise tomography and high-resolution temporal seismological data analysis with (ii) pressure and temperature measurements in the conduit. SUBMERGE progresses towards three well-defined objectives: (I) Image and locate structures within the wider geothermal area around Strokkur and the magmatic heat reservoir, (II) characterize the charging and discharging processes and bubble reservoir geometries at high spatial and temporal resolution, as well as (III) assessing the internal and external factors influencing the geysering behavior short-term or long–term (e.g. peculiarities such as eruption coda, multi-tuple eruptions). German and Swiss colleagues will work jointly towards these objectives across distinct and yet complementary work packages. SUBMERGE foresees joint field work to collect data that will be used to improve our understanding of high-enthalpy systems and more particularly of the subsurface structure of Strokkur. SUBMERGE will shed light on the interplay between heat and mass transport and geophysical signals, while contributing to the refinement of high-resolution images of hydrothermal and groundwater systems.

• DFG Programme: Research Grants
• International Connection: Iceland, Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Cooperation Partners: Egill Gudnason; Kristin Jonsdottir; Professor Dr. Matteo Lupi