Reworking of limestone (CaCO3) by magma is an important source of carbon in volcanic arc emissions. However, while it is broadly understood that CO2 is liberated during magma-limestone interaction, the degassing behaviour of calcite in silicate melts is less well constrained. In this study, we carried out microspectroscopic analysis of volatiles within fluid inclusions and glass (former melt) in the products of short-term experiments simulating limestone assimilation in mafic arc melt (T = 1200 degrees C, P = 0.5 GPa, runtimes of 0 to 300 s). The experimental products consist of partly to wholly assimilated limestone xenoliths enveloped by CaO-rich silicate glass (reacting melt) that grades into mafic glass (host melt). Micro-to milli-metric sized fluid-filled bubbles permeate the experimental products. This study reveals that limestone assimilation induces extremely fast apparent diffusivity of CO2 (DCO2 greater than or similar to 10-7 m2/s) through both the reacting melt and the host melt. Volatile saturation is thus quickly reached, triggering nucleation of bubbles mainly containing CO2 +/- CO, CH4, N2, H2, and H2O. Crucially, we find that the host melt contains dissolved CO2 from limestone, despite showing no other compositional evidence for limestone assimilation. Mafic melts in volcanic regions underlain by limestone may therefore mobilise and transport more carbon than previously thought, with implications for eruptive behaviour, volcanic CO2 inventories, and long-term climate warming.

Volcanic eruptions are driven by the nucleation and growth of gas bubbles that form when volatile species dissolved in magma become supersaturated. Previous models for bubble growth have focussed on H2O; however, CO2 also plays a fundamental role in the nucleation and growth of gas bubbles. Here, we develop a numerical model to explore the nucleation and growth of bubbles containing both H2O and CO2 in magma of arbitrary composition. Nucleation is modelled as a Poisson process using classical nucleation theory with compositionappropriate solubility models for the mixed H2O-CO2 fluid. We find that CO2 dramatically increases the depth of bubble nucleation compared with H2O-only systems; for a case-study rhyolite (Krafla, Iceland) CO2 increases nucleation depth from 130 m (H2O-only) to 760 m if CO2 is included (a factor of 6 increase in nucleation pressure); for a case-study basalt (Fagradalsfjall, Iceland), nucleation occurs at 13 km depth if CO2 is included, but does not occur at all if H2O is the only volatile species. Post-nucleation growth of the bubbles is investigated by extending a 'shell model' to include CO2 as well as H2O. The species are coupled via a mixed equation-of-state for the gas phase, introducing a co-dependence on their solubility that allows H2O to exsolve at greater depth when CO2 is present. As a result, exsolution of a small volume of CO2 can trigger the exsolution of a much larger volume of H2O, driving rapid, disequilibrium bubble growth. Our findings show that accounting for mixed H2O-CO2 volatile compositions is essential for accurate modelling of magma ascent and eruption dynamics.

Fe-rich filamentary textures are almost ubiquitous in products from explosive eruptions at basaltic volcanoes and, in particular, they characterize the groundmass of ash and lapilli emitted during high-energy events. Here, we present a multidisciplinary study integrating petrological analyses with computational fluid dynamics simulations to propose a new mechanism responsible for their formation. Detailed textural and compositional features of Fe-rich filaments were examined in the products of explosive eruptions with different intensities from Stromboli and Etna (Italy) volcanoes. Results reveal that they represent compositional boundary layers developed at the plagioclase-melt interface in response to the interaction between magmas with different compositions and volatile contents. Numerical simulations indicate that boundary layers can detach from crystals and disperse into resident melts due to their higher density and can survive as metastable melts for some days under magmatic conditions. We suggest that Fe-rich filaments testify to the recharging of deep magma a few days before high-energy explosive events at basaltic open-vent volcanoes, even when primitive magmas are not erupted.

We present a study aimed at evaluating how experiment-driven communication, in particular in the field of volcanology, seismology and tsunami sciences, is effective in conveying quantitative concepts and increasing the understanding of natural phenomena. We conducted two dissemination initiatives dedicated to creating the general public's awareness and appreciation of geoscience, each targeting a different type of audience. The first initiative was a lesson delivered to high-school students with a humanistic background as part of the European Researchers' Night. The second was an interactive experiment/activity carried out in a booth hosted by the Italian Civil Protection Department, focused on best practices for risk mitigation. It was presented during an international event dedicated to fandom culture (Lucca Comics and Games), which was entirely unrelated to geoscience. The core of both initiatives - focused on volcanic conduit dynamics, earthquake localization and magnitude calculation, and volcanic landslide-induced tsunami - consisted of hands-on experiments, corroborated by the determination of parameter values, adding a quantitative dimension to the phenomenological experience. We also delivered questionnaires to all participants aimed at evaluating the effectiveness of the conveyed messages. One questionnaire was delivered to the 62 high-school students during the European Researchers' Night and two questionnaires (pre- and post-experiment) were delivered to 26 participants during Lucca Comics and Games. The results of the survey show that our experiments were well-received and, as a general conclusion, underline that geophysical hands-on experiences can successfully foster the engagement of people, even when providing quantitative evidence. However, it is also important to adapt the dissemination initiative to the target audience, by considering the amount of time available and the background of the attendee. For external instructors who present experiments to high school classes, we once again assessed the importance of the synergy between school teachers and external communicators before and after the events, in order to avoid contradictory messages delivered to students. We finally underline the importance of finding new ways to promote a modern and interactive way to communicate geoscience.

The short-term, syn-eruptive interaction of magma with crustal carbonates can largely affect the eruptive style and drive even low-viscosity magmas toward large explosive eruptions. Only a few studies focus on the short-term interaction and the physical processes behind the experimental observations are still poorly understood. In this work, we study for the first time the short-term magma-carbonate interaction process through a modelling approach that provides an interpretative key of the experimental and field observations. We developed thermodynamic and dynamic models for the carbonate dissolution and the mixing and mingling between the contaminated magmapockets and the host magma. We find that mixing and mingling can play a central role in modulating the efficiency of volatile exsolution. The increasing viscosity of the host melt slows down the mingling, hence the mixing process, limiting volatile exsolution. Less efficient mixing and mingling imply that the fingerprints of the short-term magma-carbonate interaction can be preserved in the volcanic deposits. Finally, we highlight a key question that needs to be answered to constrain the mechanism and timescale of the carbonate dissolution process.

The Krafla caldera, located in the Northern Volcanic Zone of Iceland has become the most studied volcano in the country since its last eruption, the Krafla Fires, happened between 1975 and 1984. From that moment, an extensive monitoring system has been developed in the caldera, focused on both geothermal exploration and production, as well as scientific research. In 2009, the IDDP-1 exploratory well aiming to 4 km depth in search of supercritical hydrothermal fluids got stuck at 2.1 km, retrieving quenched glass cuttings. It was then understood that an unexpected and undetected rhyolitic magma body had been drilled. This body stood without apparent signs of crystallization at the rooftop, opposing the most common belief that magmatic bodies at shallow depths should present a mushy region adjacent to the body’s walls. We aim to simulate the dynamics of the magma encountered in Krafla. We perform 2D numerical simulations of the magma thermo-fluid dynamics, assuming thermodynamic equilibrium in a sill-like, disk-shaped body 1200 metres wide and 260 metres deep. We include a 100 metres thick aureola with fixed boundary temperature of 350 ºC and initial linear temperature gradient up to 900 ºC in the magmatic body. In order to simulate the magma dynamics we use the software GALES (Garg and Papale, Frontiers in Earth Sciences 2022), which solves the 4D dynamics of multi-component fluids in geometrically complex domains. Melt-solid-gas thermodynamic are computed with rhyoliteMELTS (Gualda et al., J. Petrol. 2012) using the alphaMELTS-2 front end (Smith & Asimow, GCubed 2005). The properties density, heat capacities, single-phase and multiphase non-Newtonian viscosity, thermal conductivity, and compressibility, are locally computed as a function of pressure, temperature, phase distribution, and phase composition. The results allow a first evaluation of the conditions under which a crystal mush can form and be stable close to the roof and margins of a shallow magmatic intrusion.

Abstract. Numerical simulations of volcanic processes play a fundamental role in understanding the dynamics of magma storage, ascent and eruption. The recent extraordinary progress in computer performance and improvements in numerical modeling techniques allow simulating multiphase systems in mechanical and thermodynamical disequilibrium. Nonetheless, the growing complexity of these simulations requires the development of flexible computational tools that can easily switch between sub-models and solution techniques. In this work we present MagmaFOAM, a library based on the open source computational fluid dynamics software OpenFOAM, that incorporates models for solving the dynamics of multiphase, multicomponent magmatic systems. Retaining the modular structure of OpenFOAM, MagmaFOAM allows run-time selection of the solution technique depending on the physics of the specific process, and sets a solid framework for in-house and community model development, testing and comparison. MagmaFOAM models thermo-mechanical non-equilibrium phase coupling and phase change, and implements state-of-the-art multiple volatile saturation models and constitutive equations with composition-dependent and space-time local computation of thermodynamic and transport properties. Code testing is performed using different multiphase modeling approches for processes relevant to magmatic systems: Rayleigh-Taylor instability, for buyoancy-driven magmatic processes; multiphase shock tube simulations, propedeutical to conduit dynamics studies; bubble growth and breakage in basaltic melts. Benchmark simulations illustrate the capabilities and potential of MagmaFOAM to account for the variety of non-linear physical and thermodynamical processes characterizing the dynamics of volcanic systems.

Bubble growth is one of the key processes that govern the degassing of magmatic systems and drive volcanic eruptions. Typically, the gas exsolution process begins with the nucleation of bubbles in an oversaturated melt and continues with bubble growth. Bubbles grow by mass diffusion, when the silicate melt is oversaturated in volatiles, and by mechanical expansion as a response to pressure decrease. The viscosity of the surrounding melt and the surface tension oppose a resistance to bubble growth and control the mechanical disequilibrium between the bubbles and the melt itself. The combination of the Rayleigh-Plesset equation with a diffusion equation represents a common approach to describe diffusive bubble growth. A number of models have been developed for describing bubble growth dynamics in magmas, most of them accounting for a single volatile specie. Nevertheless, the multicomponent nature of magmatic volatiles has long been recognised to play a major role in controlling magmatic exsolution process. Here we present a model describing bubble growth in magmas in the presence of multiple volatile species through a fully non-ideal multicomponent saturation model. Numerical simulations show the role of the different species (e.g., water and carbon dioxide) in the dynamics of diffusive bubble growth for different melt compositions. The new model is implemented in the MagmaFOAM library, a dedicated computational tool to solve multiphase flows characterizing magmatic systems that extends the open-source library OpenFOAM. Within the MagmaFOAM framework it is possible to combine the bubble growth model with fluid solvers in order to fully capture the multi-scale nature of liquid and gas phases in magmatic systems.

Explosive eruptions are the surface manifestation of dynamics that involve transfer of magma from the underground regions of magma accumulation. Evidence of the involvement of compositionally different magmas from different reservoirs is continuously increasing to countless cases. Yet, models of eruption dynamics consider only the uppermost portion of the plumbing system, neglecting connections to deeper regions of magma storage. Here we show that the extent and efficiency of the interconnections between different magma storage regions largely control the size of the eruptions, their evolution, the causes of their termination, and ultimately their impact on the surrounding environment. Our numerical simulations first reproduce the magnitude-intensity relationship observed for explosive eruptions on Earth and explain the observed variable evolutions of eruption mass flow rates. Because deep magmatic interconnections are largely inaccessible to present-day imaging capabilities, our results motivate the need to better image and characterize extant magma bodies.

The significant efforts of the last years in new monitoring techniques and networks have led to large datasets and improved our capabilities to measure volcano conditions. Thus nowadays the challenge is to retrieve information from this huge amount of data to significantly improve our capability to automatically recognize signs of potentially hazardous unrest. Unrest detection from unlabeled data is a particularly challenging task, since the lack of annotations on the temporal localization of these phenomena makes it impossible to train a machine learning model in a supervised way. The proposed approach, therefore, aims at learning unsupervised low-dimensional representations of the input signal during normal volcanic activity by training a variational autoencoder (VAE) to compress, reconstruct and synthesize input signals. Thanks to the internal structure of the proposed VAE architecture, with 1-dimensional convolutional layers with residual blocks and attention mechanism, the representation learned by the model can be employed to detect deviations from normal volcanic activity. In our experiments, we test and evaluate two techniques for unrest detection: a generative approach, with a bank of synthetic signals used to assess the degree of correspondence between normal activity and an input signal; and a discriminative approach, employing unsupervised clustering in the VAE representation space to identify prototypes of normal activity for comparison with an input signal.

Magmas discharged during individual volcanic eruptions commonly display compositional variations interpreted as new arrivals at shallow depth of more primitive, hotter, volatile-rich magma batches mixing with resident, colder, partially degassed magma. Heterogeneities in eruption products are often interpreted as evidence of short times of order tens of hours from new magma arrival to eruption, raising concerns for emergency planning. We show here, through numerical simulations, that magma convection and mixing in a shallow magma chamber can result in long-lived, dynamically stable configurations with coexistence of magmas from nearly pure to variably mixed end-member compositions. Short mixing time scales may therefore relate to sin-eruptive processes, as heterogeneities found in the eruptive products are not necessarily the fingerprint of new magma arrival shortly preceding or triggering the eruption.

The dynamics of magma ascent along volcanic conduits toward the Earth's surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive versus explosive eruptive behavior. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of magma flow in volcanic conduits. We develop a quasi 2-D model of magma ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase magma. Non-Newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting that the non-Newtonian effect of bubble-bearing magmas may result in misinterpretation of the deposit and, consequently, eruptive behavior.

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: unsteadiness (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.