Deep-sea fragmentation style of Havre revealed by dendrogrammatic analyses of particle morphometry

Abstract

In 2012, the eruption of deep-sea volcano Havre produced an abundance of fine ash at a depth of ~ 1000 m below sea level. In this study the 2D shapes of Havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments, which used remelted rhyolitic rock and pumice from the eruption site. A new statistical data analysis technique, denoted as Dendrogrammatic Analysis of Particle Morphology (DAPM) is introduced. It is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram. Further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features. The DAPM suggests that the majority of Havre ash was thermohydraulically produced by induced fuel coolant-interaction. A subset of ash particles features an elongated tube morphology. Their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching, and we infer that the natural particles were formed by synextrusive ash-venting.