Low sulfur emissions from 2022 Hunga eruption due to seawater–magma interactions

The explosive January 2022 Hunga submarine eruption in Tonga injected unprecedented water volumes into the upper atmosphere, generating widespread climatic impacts. However, it ejected anomalously little sulfur compared with other eruptions of similar volume. We explain the missing sulfur with volatile budgets calculated from volcanic ash samples spanning the eruption. We show that magma was stored in a weakly stratified reservoir at 2.1 km to >5.6 km depth. Magma rose within <3 min and fragmented at 400–1,000 m below sea level. This preserves microscale chemical mingling including ~1 wt% contrasts in magmatic water concentrations. The 11-h eruption released a total of 319 Tg of magmatic water, which is <10% of that derived from magmatic seawater interaction. Comparing magmatic and residual glass sulfur concentrations shows a total release of 9.4 TgS, but >93% of this entered the ocean during submarine magma fragmentation. These results raise the concern that satellite SO₂ monitoring underestimates the magma output of submarine explosions and they are probably near invisible in ice-core records, despite their climate influence caused by water injection into the upper atmosphere.