The submarine volcano Hunga Tonga-Hunga Ha'apai (Hunga volcano) in the South Pacific Tonga Arc caused an unprecedented giant eruption in January 2022. It was previously known that this volcano has features similar to Nishinoshima located in Japan's Ogasawara Islands and so was an important survey target for verifying the geological model (Nishinoshima model) proposed in surveys of Nishinoshima. The fundamental concept of the model is that "andesite, the raw material of continents, is directly produced from oceanic island arcs with thin crusts" holds the key to the birth of continents.
Senior Researcher Yoshihiko Tamura and colleagues at the Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), in an international joint research team with GNS Science (New Zealand) and the National Institute of Advanced Industrial Science and Technology (AIST), conducted a survey at Hunga volcano using a vessel from GNS Science. The research team analyzed the magma system (magma generation mechanism) of Hunga volcano in detail petrologically.
When sampling was conducted on the submarine flank of Hunga volcano after the eruption, they succeeded for the first time in collecting rock samples of the volcano body itself (basaltic lava and magnesian andesite lava) from the seafloor. Through detailed analysis of these rock samples, they made two major scientific discoveries. The results were published in Scientific Reports.
From a volcanological perspective, calculations restoring the collected rocks to primary magmas revealed that two "primary magmas (basaltic and andesitic)" existed independently at different depths (pressures) of the mantle. Then, they pointed out the possibility that rapid mixing of these two magmas existing at different depths in the shallow subsurface was the direct factor triggering the unprecedented explosive eruption at Hunga volcano in 2022. Explosiveness due to similar magma mixing was also confirmed in recent Nishinoshima (2020 eruption), serving as extremely important knowledge in submarine volcano eruption prediction and disaster prevention monitoring.
On the other hand, geologically, new implications were obtained regarding "continent formation." Conventionally, the process where "rocks made from primary basaltic magma remelt to become andesite" was generally considered standard. In contrast to this, the new Earth evolution theory that "under thin crusts, andesitic magma is generated directly from the mantle and accumulates to grow into continents" is the Nishinoshima model. In these findings, because primary andesitic magma was discovered even at Hunga volcano in the South Pacific far away from Nishinoshima, it is considered that exactly the same process as Nishinoshima occurred. There is a possibility that the Nishinoshima model is not a phenomenon unique to Nishinoshima but can be called a universal "mechanism of continent formation" on a global scale.
Journal Information
Publication: Scientific Reports
Title: Discovery of basaltic and magnesian andesite magmas within the Hunga volcanic system, Tonga arc
DOI: 10.1038/s41598-026-59118-1
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.