Transition of eruptive style: pumice raft to dome-forming eruption at the Havre submarine volcano

Transitions in eruptive style are common at volcanoes. Understanding how and why remain some of the biggest challenges in hazard assessment. The 2012 eruption of the submarine Havre volcano in the Kermadec arc produced a raft of floating pumice followed by a pair of domes from the same vent. We use measurements on erupted magmas and constraints on the eruption rate, combined with a model for magma ascent, to identify the dominant controls on the transition in eruption style. During the pumice-raft forming stage, magma ascent was fast enough that little gas was lost. Magma reached the seafloor with great enough vesicularity to be buoyant and produce clasts that could float. As the eruption waned, the eruption rate decreased and the conduit narrowed. Sufficient gas was then lost to the surrounding country rocks during ascent that the erupted magma was no longer buoyant relative to seawater.