Gas migration regimes and outgassing in particle-rich suspensions

Abstract

Understanding how gasses escape from particle-rich suspensions has important applications in nature and industry. Motivated by applications such as outgassing of crystal-rich magmas, we map gas migration patterns in experiments where we vary (1) particle fractions and liquid viscosity (10-500 Pa s), (2) container shape (horizontal parallel plates and upright cylinders), and (3) methods of bubble generation (single bubble injections, and multiple bubble generation with chemical reactions). We identify two successive changes in gas migration behavior that are determined by the normalized particle fraction (relative to random close packing), and are insensitive to liquid viscosity, bubble growth rate or container shape within the explored ranges. The first occurs at the random loose packing, when gas bubbles begin to deform; the second occurs near the random close packing, and is characterized by gas migration in a fracture-like manner. We suggest that changes in gas migration behavior are caused by dilation of the granular network, which locally resists bubble growth. The resulting bubble deformation increases the likelihood of bubble coalescence, and promotes the development of permeable pathways at low porosities. This behavior may explain the efficient loss of volatiles from viscous slurries such as crystal-rich magmas.

Causes of fragmented crystals in ignimbrites: a case study of the Cardones ignimbrite, Northern Chile

“…Although the upper boundary is comparable to that of crystal-poor pumice, the lower end suggests that high crystal contents may alter critical vesicularity thresholds for fragmentation. One possible explanation is the effect of high crystal contents on the development of permeability in these samples, as illustrated by analogue (Oppenheimer et al 2015) and high temperature (Lindoo et al 2017) experiments. This fragmentation mechanism does not, however, explain the pervasive crystal fragmentation observed in large ignimbrite eruptions.…”

A review of laboratory and numerical modelling in volcanology

“…Laboratory experiments of degassing crystal-rich magmas have shown using analogue materials that gas escape and the development of permeable pathways in particle-rich suspensions can be fracture-like or due to bubble formation, and that the migration pathways are controlled by particle fraction and the degree of particle packing (see Fig. 6e; Oppenheimer et al, 2015).…”

“…(e) Bubble injection experiments using a small-gap parallel-plate geometry to study the development of permeable pathways in a particle-rich suspension. Particle image velocimetry has been used to measure particle speed in three experiments with different crystal fraction (Oppenheimer et al, 2015). tained over much greater distances, controlled by the particle terminal velocity v:…”

A review of analogue and numerical modelling in volcanology

“…It therefore marks a significant 376 advancement in our understanding of magma behaviour through time and space, and will be 377 an important tool in future models to better constrain the impact of three-phase magma 378 rheology on volcanic eruptions. Gas escape and the development of permeable pathways in 379 particle-rich suspensions has applications to the study of degassing crystal-rich magmas, with 380 analogue experiments showing that migration patterns (either by bubble formation or 381 fracture-like) are controlled by particle fraction and the degree of particle-packing (see Figure 382 5e; Oppenheimer et al 2015). 383 Depending on the application and level of complexity, a variety of analogue materials have 384 been used to model magma (see Table 1 for a summary).…”

“…to study the development of permeable pathways in a particle-rich suspension. Particle image 1874 velocimetry has been used to measure particle speed in three experiments with different 1875 crystal fraction (Oppenheimer et al 2015). …”