[S-GC37] Volatiles in the Earth - from Surface to Deep Mantle

[SGC37-12] Magma Degassing and Explosive Eruption of Hunga Volcano

★Invited Papers

*Soyeon Kim¹、Hyunwoo Lee¹、Dongwhan Kim^1,3、Wonhee Lee¹、Sung-Hyun Park²、Naoto Takahata³、Kenji Shimizu⁴、Takayuki Ushikubo⁴、Yuji Sano⁵、Tobias P. Fischer⁶ (1.School of Earth and Environmental Sciences, Seoul National University, Republic of Korea、2.Korea Polar Research Institute, Republic of Korea、3.Atmosphere and Ocean Research Institute, The University of Tokyo, Japan、4.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Japan、5.Marine Core Research Institute, Kochi University, Japan、6.Department of Earth and Planetary Sciences, University of New Mexico, USA)

キーワード：Volatiles, Degassing, Explosive eruption

At the Hunga Tonga-Hunga Ha’apai volcano (Hunga volcano), located in the Tonga-Kermadec Arc, an explosive eruption with a volcanic eruption index (VEI) of 5 occurred on January 15, 2022. During this eruption, the maximum altitude of the eruption column was 57 km, reaching the mesosphere and supplying a huge amount of water vapor and volcanic ash to the entire stratosphere. To probe mechanisms of the explosive eruption, this study investigated volatiles of volcanic rocks obtained from the Caldera interior and the southern seamount (Volcano A). Here, we report helium, oxygen, and hydrogen isotope compositions along with volatile contents in olivine, clinopyroxene and lava fragments.
The primary melt could be represented by olivine-hosted melt inclusions, which show basaltic andesite compositions with high water contents (H₂O =1.88 to 4.95 wt.%). According to the total alkali-silica (TAS) classification, most lava fragments are basaltic andesite, with some samples evolving into andesite and dacite. Helium and oxygen isotope compositions (³He/⁴He = 2.27 to 6.54 Ra; δ¹⁸O = 5.49 to 6.37‰) in mineral grains and glass fragments show the range between the upper mantle and crustal material. This indicates that the primary melt and volatiles originated from the hydrated mantle wedge and evolved by interacting with crustal materials within the thick crust beneath the Tonga-Kermadec Arc. In addition, hydrogen isotopes (δD = -97 to +25‰) and volatile contents (H₂O = 0.20 to 4.95 wt.%; CO₂ = 1 to 87 ppm; S = 0 to 857 ppm) from melt inclusions to erupted lavas reveal that the magma system underwent extensive degassing prior to the eruption. Based on the degassed water content and estimates of erupted magma volume (~6.3 km³ by Henley et al., 2024; ~9.5 km³ by Le Mével et al., 2023), the amount of water vapor released was estimated to be approximately 474 to 714 Tg, which is much higher than the Aura Microwave Limb Sounder (MLS) record (~146 Tg from Millan et al., 2022). Our findings suggest that a prolonged degassing process from December 2021 contributed to a much larger total water release than the amount observed during the eruption itself.