The role of bubbles in generating fine ash during hydromagmatic eruptions

Abstract

Research Article| March 01, 2015 The role of bubbles in generating fine ash during hydromagmatic eruptions E.J. Liu; E.J. Liu * 1Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK *E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar K.V. Cashman; K.V. Cashman 1Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar A.C. Rust; A.C. Rust 1Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar S.R. Gislason S.R. Gislason 2Institute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (3): 239–242. https://doi.org/10.1130/G36336.1 Article history received: 07 Oct 2014 rev-recd: 19 Dec 2014 accepted: 07 Jan 2015 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E.J. Liu, K.V. Cashman, A.C. Rust, S.R. Gislason; The role of bubbles in generating fine ash during hydromagmatic eruptions. Geology 2015;; 43 (3): 239–242. doi: https://doi.org/10.1130/G36336.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The abundant fine ash produced in the 2011 subglacial eruption of Grímsvötn, Iceland, highlights the fragmentation efficiency of mafic hydromagmatic eruptions, which is considerably higher than for comparable "dry" eruptions. Ash from the 2011 eruption can be divided into three morphological components—vesicular particles, shards, and dense fragments—distinguished by the size and abundance of constituent vesicles. We use the vesicle characteristics to define a new shape factor, the concavity index, which provides an unbiased way to classify individual ash particles as either bubbly (vesicular particles and shards) or dense. The relative proportion of bubbly and dense particles varies systematically with grain size, with the proportion of bubbly grains decreasing as the particle size approaches the modal bubble diameter. Measured bubble volume distributions are similar to those of rapidly quenched pyroclasts from Hawaiian fountains and suggest a comparable degassing history during magma ascent. Yet concordance between the size distributions of ash and of bubbles in the Grímsvötn samples stands in contrast to the size distributions in Hawaiian fountains, where pyroclasts are orders of magnitude larger than individual bubbles. We propose that the Grímsvötn ash formed by brittle disintegration of vesicular pyroclasts and that fragmentation efficiency was amplified by residual thermal stresses in glass quenched by glacial water. The strong control of resulting particle sizes and morphologies by the size and spatial distribution of bubbles demonstrates that the bubble population cannot be ignored when modeling hydromagmatic fragmentation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.