Viscous sintering of volcanic ash

Monday, 15 December 2014: 2:55 PM
Fabian B Wadsworth1, Bettina Scheu2, Jeremie Vasseur3, Hugh Tuffen4, Felix W. von Aulock5, Yan Lavallée6, Kai-Uwe Hess1 and Donald B Dingwell2, (1)Ludwig Maximilian University of Munich, Munich, Germany, (2)Ludwig Maximilian University of Munich, Earth & Environmental Sciences, Munich, Germany, (3)LMU Munich, Munich, Germany, (4)University of Lancaster, Lancaster, LA1, United Kingdom, (5)University of Liverpool, Liverpool, United Kingdom, (6)Univ of Liverpool, Liverpool, United Kingdom
Volcanic ash is often deposited in a hot state. Volcanic ash containing glass, deposited above the glass transition interval, has the potential to sinter viscously both to itself (particle-particle) and to exposed surfaces. Here, we constrain the kinetics of this process experimentally under isothermal and non-isothermal conditions using standard glasses and volcanic ash. In the absence of external load, this process is dominantly driven by surface relaxation. In such cases the sintering process is rate-limited by the melt viscosity, the size of the particles and the melt-vapour interfacial tension. We propose a polydisperse continuum model that describes the transition from a packing of particles to a dense pore-free melt and evaluate its efficacy in describing the kinetics of volcanic viscous sintering. We apply our model to viscous sintering scenarios for cooling crystal-poor rhyolitic ash using the 2008 eruption of Chaitén volcano as a case example. We predict that moderate cooling rates result in the common observation of incomplete sintering and the preservation of pore networks. Finally we discuss the effect of crystallisation, external loading and volatile degassing or regassing during viscous sintering and assert that such complexities must be considered in the volcanic scenario.