Excess explosivity driven by melt inclusions during the 946 CE Plinian eruption of Baekdusan

Abstract

Melt inclusions readily rupture and form gas bubbles during explosive volcanic eruptions, but their role as a volcanic gas source remains enigmatic. Here, we examined a pumice texture generated by the instantaneous bursting of melt inclusions during the 946 CE Plinian eruption at Baekdusan. The burst produced non-sheared, super-vesicular (>80 vol.% voids) bubble pockets, occupying volume fractions of 6–24% within the Millennium gray pumice. The bubble pocket texture suggests that the melt inclusions acted as an additional volcanic gas source that increased the volume of the erupting magma at the moment of magma fragmentation. Two distinctive feldspar–glass assemblages of either sanidine-bearing trachyte or anorthoclase-bearing rhyolite in the bubble pockets indicate that the chemical bimodality of the hemisphere-scale, 946 CE Baekdusan tephra resulted from cryptic mixing of two magmas. The excess explosivity induced by the bursting melt inclusions should be considered when modeling eruption dynamics and assessing volcanic hazards, therefore having broad volcanological implications.