Magmatic volatiles control the sub-plinian basaltic eruptions at Ambae volcano, Vanuatu

The 2017–2018 eruption of Ambae volcano provided a rare opportunity to investigate gas emissions during a sub-Plinian basaltic eruption. Here we document the gas emissions during this eruption using satellite observation, alongside gas measurements and geochemical analyses. Our results indicate that the volcano released 3.3 teragrams of sulfur dioxide, 7.7 of carbon dioxide, 134 of water vapour, 0.2 of hydrogen sulfide, and 0,001 of dihydrogen, ranking Ambae among the world’s top volcanic gas emitters. Despite these substantial emissions, the relatively modest volume of 0.47 cubic kilometer of magma that fueled the eruption indicates a volatile-rich magma source. This enrichment is likely linked to the geodynamic setting, where subduction of the faulted, carbonate-rich D’Entrecasteaux Ridge, coupled with an influx of fertile mantle, fostered the formation of volatile-rich magma. High concentrations of volatiles, can drive substantial gas exsolution, increasing magma buoyancy, resulting in greater magma supply and faster ascent rates. Rapid ascent prevents volatile separation from the melt, resulting in powerful gas surges that drive the transition from effusive to basaltic sub-Plinian eruption phases. The basaltic sub-Plinian eruptions of Ambae Volcano, Vanuatu, are driven by rapid magma ascent, due to high concentration of dissolved volatile. This conclusion is supported by satellite observations, alongside gas measurements and geochemical analyses.