Discovery of basaltic and magnesian andesite magmas within the Hunga volcanic system, Tonga arc

The climactic explosive eruption of Hunga volcano in January 2022 destroyed a significant portion of the Hunga Tonga-Hunga Ha'apai islands, deepening the caldera floor by over 600 m and depositing 3.5 km³ of material onto its submarine flanks. In April-May 2022, just three months after the event, we conducted a rapid-response marine survey. Through hard-rock dredging across the submerged edifice, we recovered a comprehensive sample suite to investigate the geochemical evolution of the Hunga magma system. The dredged rocks span a compositional range from basalt to rhyolite, categorized into four groups: basalt-basaltic andesite (50.9-53.2 wt%), magnesian andesite (53.6-55.7 wt%), andesite-dacite (54.3-64.8 wt%), and rhyolite (70.8-73.2 wt%). A distinct 5 wt% gap exists between the dacites and rhyolites. While previously reported subaerial andesites largely overlap with the andesite-dacite group, our findings reveal a broader compositional diversity. These new data suggest the co-existence of both primary basaltic and primary andesitic magmas, offering new insights into the plumbing system of the 2022 eruption and similar arc volcanoes.