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Sintering of vesiculating and diffusively outgassing pyroclasts in the presence of crystals

^^ Julia Schunke1^^ , Janine Birnbaum1, Jackie E. Kendrick1, Anthony Lamur1, Fabian B. Wadsworth1, Jonathan Castro2, Yan Lavallée1

  • Affiliations: 1Ludwig-Maximilians-Universität München, Germany 2Johannes Gutenberg-Universität Mainz, Germany 

  • Presentation type: Talk

  • Presentation time: Tuesday 14:30 - 14:45, Room S150

  • Programme No: 3.2.6

  • Theme 3 > Session 2

Abstract

Shifts in the eruptive style are strongly influenced by the evolution of permeable outgassing pathways, such as fractures and interconnected pores. These pathways allow gases to escape the system mitigating pressure buildup, magma buoyancy, and its eruptibility. Our observations at the Mono-Inyo Craters, USA, reveal that conduits are commonly infilled by polydisperse (different sizes) pyroclasts with varying vesicularity and degrees of sintering, a surface-tension driven process that progressively decreases permeability and shuts pathways. Unlike sintering of anhydrous fragmental systems, saturated pyroclasts undergoing sintering may vesiculate and diffusively outgas simultaneously, causing hysteretic volume and rheological changes that can inhibit sintering. Additionally, the starting polydispersivity of the granular pack influences the permeability evolution as systems with lower polydispersivity are more closely packed, favouring droplet-droplet interactions. In natural systems, the presence of crystals will both limit droplet-droplet contacts, but also viscous processes. We posit that the addition of crystals to the pack will thus inhibit sintering kinetics, propping open permeable pathways for a longer time. Here we perform experiments using a polydisperse pack of obsidian fragments mixed with different crystal fractions for varying sintering times. We measure the connected porosity and permeability of the sintered pack at a range of confining pressures. Our results show that as the crystal fraction increases, the sintering efficiency decreases, allowing for the permeable pathways to stay open. We conclude that these results have important implications for the degassing dynamics during volcanic eruptions as fragment-filled fractures are ubiquitous to all silicic volcanic settings.