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

Abstract

Abstract This study reports a unique pumice texture generated by the instantaneous bursting of melt inclusions in alkali feldspars during the 946 CE Plinian eruption at Baekdusan. The burst produced super-vesicular (80−90 vol.% voids), subspherical (i.e., non-sheared), and subcentimeter-sized “bubble pockets” indicating their formation at the moment of magma fragmentation. Their volume fraction (6–24 vol.%) suggests that the melt inclusions acted as an additional volcanic gas source and increased significantly the volume of the erupting magma at the moment of magma fragmentation. The “excess explosivity” induced by the bursting melt inclusions should be taken into account when modeling eruption dynamics and assessing volcanic hazards, therefore having broad volcanological implications. Two distinctive feldspar–glass assemblages of either sanidine-bearing trachyte or anorthoclase-bearing rhyolite in the bubble pockets also indicate that the chemical bimodality of the hemisphere-scale, 946 CE Baekdusan tephra resulted from cryptic mixing of two magmas.