Quantifying Microstructural Evolution in Moving Magma

Many of the grand challenges in volcanic and magmatic research are focused on understanding the dynamics of highly heterogeneous systems and the critical conditions that enable magmas to move or eruptions to initiate. From the formation and development of magma reservoirs, through propagation and arrest of magma, to the conditions in the conduit, gas escape, eruption dynamics, and beyond into the environmental impacts of that eruption, we are trying to define how processes occur, their rates and timings, and their causes and consequences. However, we are usually unable to observe the processes directly. Here we give a short synopsis of the new capabilities and highlight the potential insights that in situ observation can provide. We present the XRheo and Pele furnace experimental apparatus and analytical toolkit for the in situ X-ray tomography-based quantification of magmatic microstructural evolution during rheological testing. We present the first 3D data showing the evolving textural heterogeneity within a shearing magma, highlighting the dynamic changes to microstructure that occur from the initiation of shear, and the variability of the microstructural response to that shear as deformation progresses. The particular shear experiments highlighted here focus on the effect of shear on bubble coalescence with a view to shedding light on both magma transport and fragmentation processes. The XRheo system is intended to help us understand the microstructural controls on the complex and non-Newtonian evolution of magma rheology, and is therefore used to elucidate the many mobilization, transport, and eruption phenomena controlled by the rheological evolution of a multi-phase magmatic flows. The detailed, in situ characterization of sample textures presented here therefore represents the opening of a new field for the accurate parameterization of dynamic microstructural control on rheological behavior

Evolution of methane density during melting in nanopores

International audiencePhase properties of gases adsorbed in small nanopores are mainly determined by the pore size and shape as well as the structural heterogeneity of the adsorbate. Here we analyze the evolution of the melting mechanism that occurs in pores <3 nm in size. Melting in slit-shaped graphene pores is compared with melting in SURMOF channel pores with square cross-sections. We show how the melting transformation is related to the adsorption mechanism. We use a graphical representation of the evolution of molecular density as a function of temperature in the nanopores

Bubble Formation in Magma

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions. ▪ We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate. ▪ Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism. ▪ Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation. ▪ Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways

From magma ascent to ash generation: Investigating volcanic conduit processes by integrating experiments, numerical modeling, and observations

Processes occurring in volcanic conduits, the pathways through which magma travels from its storage region to the surface, have a fundamental control on the nature of eruptions and associated phenomena. It has been well established that magma flows, crystallizes, degasses, and fragments in conduits, that fluids migrate in and out of conduits, and that seismic and acoustic waves are generated and travel within conduits. A better understanding of volcanic conduits and related processes is of paramount importance for improving eruption forecasting, volcanic hazard assessment and risk mitigation. However, despite escalating advances in the characterization of individual conduit processes, our understanding of their mutual interactions and the consequent control on volcanic activity is still limited. With the purpose of addressing this topic, a multidisciplinary workshop led by a group of international scientists was hosted from 25 to 27 October 2014 by the Pisa branch of the Istituto Nazionale di Geofisica e Vulcanologia under the sponsorship of the MeMoVolc Research Networking Programme of the European Science Foundation. The workshop brought together the experimental, theoretical, and observational communities devoted to volcanological research. After 3 days of oral and poster presentations, breakout sessions, and plenary discussions, the participants identified three main outstanding issues common to experimental, analytical, numerical, and observational volcanology: un steadiness (or transience), disequilibrium, and uncertainty. A key outcome of the workshop was to identify the specific knowledge areas in which exchange of information among the sub-disciplines would lead to efficient progress in addressing these three main outstanding issues. It was clear that multidisciplinary collaboration of this sort is essential for progressing the state of the art in understanding of conduit magma dynamics and eruption behavior. This holistic approach has the ultimate aim to deliver fundamental improvements in understanding the underlying processes generating and controlling volcanic activity