In-situ monitoring of 3He/4He in summit gases of Kilauea Volcano (Hawaii) prior to the 2020 eruption

Abstract

We present He isotope (3He/4He) data from a fumarole and near-ground gases measured in-situ at the Sulfur Banks solfatara field at the summit of Kilauea Volcano, Hawaii. We used a field-deployable mass-spectrometer-based system: the Helium Isotope Monitor (HIM) previously described in McMurtry et al. (2019a, b). The in-situ instrument was deployed using solar power for the first time and results were ground-truthed against data determined using conventional gas analytical and noble gas mass spectrometry techniques. The HIM instrumentation, associated Vent Gas Purification System (VGPS), and related sampling equipment and strategy are described. Cloudy and rainy weather conditions hampered the deployment, which was reorganized to reduce power loads and resulted in less sampling than planned. Nevertheless, we obtained daily sampling of the volcanic vent gas. Results from the Old Well fumarole indicate a ~ 2 RA increase in 3He/4He on the day of the December 20th, 2020 eruption of nearby Halema‘uma‘u Crater, reaching 17.0 RA using the in-situ instrument and 16.0 ± 0.67 RA using conventional techniques. This finding suggests that a new 3He-enriched magma source is driving the current, ongoing eruption phase of Kilauea and, if so, confirms that the deep summit caldera fault system that hosts the Sulfur Banks field is connected to the Halema‘uma‘u Crater magmatic system. Overall, these findings illustrate how time-series helium isotope data, which are well established by ongoing discrete monitoring at low temporal resolution, can help forecast forthcoming eruptive events that may not be foreseen by other volcanic monitoring methods.