Multi-level magma storage and continuous mafic recharge controlling explosive activity in Raung volcano, Indonesia: Evidence from thermobarometric estimate

The study of magma plumbing system underneath a volcano is important to understand eruption triggers, estimate the probability of another eruption, and predict future eruptive behavior. Raung Volcano, located in East Java, Indonesia, is a very active volcano with a long-established basaltic to dacitic magma system. The most recent activity in 2022 was dominated by andesitic Strombolian explosions. However, several Plinian eruptions in the VEI-4 to VEI-5 scale had been documented in both andesite and dacite composition. Despite its variety of eruptive behaviors and potential hazards, Raung magma plumbing system is poorly understood. We investigate the depth and temperature of magma storage underneath Raung volcano by applying several thermobarometer models, including clinopyroxene-melt thermobarometry, orthopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, and olivine-melt thermometry. Our findings reveal that there are five levels of crystallization below Raung from the upper crust to the crust-mantle boundary, at depths of 1.5 – 11 km, 11 – 15 km, 15 – 22 km, 18 – 26 km, and 26 – 30 km. These depths correspond to the major lithological boundary of East Java's sediment thickness (10 – 15 km), crust thickness (10 – 25 km), and Moho depth (25 – 39 km). This suggests that Raung magma storage is controlled by crustal structure. Textural features such as mantled pyroxene, sieved plagioclase, and oscillatory zoned crystals indicate a significant rate of continuous hotter, mafic magma recharge, supplying heat and volatiles into shallower reservoir. These features imply that multi-level magma storage and highly dynamic magma plumbing system play major roles in triggering Raung explosive eruption. Better understanding of Raung complex magma system is important for forecasting the timing and explosivity of potential eruptions, as well as improving long-term hazard mitigation.