The development of a solid rind or carapace at the surface of lava flows and domes results in a transition in deformation mechanism from dominantly viscous to elastic or plastic. This transition has a significant impact on the rate and style of emplacement, including on the construction of channelized flows, over-steepened margins, and flow advance due to lava breakouts. These processes are particularly important in subaqueous, subglacial, and extraterrestrial environments in which cooling is accelerated, requiring models specifically calibrated for these environments. We present a new numerical model, Viscous-Elastic Numerically Unified Solver for Solidifying flows (VENUSS), for cooling and solidifying free surface flows. The model couples a viscous fluid interior with an elastic shell whose thickness grows in response to cooling. As a demonstration of the impact of including a solidified crust in the flow model, we show that a dome-like shape fed from below with an elastic shell coupled to the basal topography results in more lateral expansion and less vertical uplift than a comparable highly-viscous rind, demonstrating the need for lateral transfer of stress in solid layers to accurately interpret and predict dome deformation.

Abstract Mineral reaction textures are fundamental archives of geological change. Amphibole reaction rims are among the most widely used to reconstruct pre-eruptive magmatic conditions, traditionally interpreted through changes in pressure, temperature and melt composition. However, these interpretations have largely overlooked the role of deformation, ubiquitous during magma ascent. Here we show that amphibole breakdown is not only thermodynamically sensitive, but also mechanically sensitive. Using electron backscatter diffraction (EBSD) analyses of experimental and natural samples, combined with numerical simulations of crystal rotation under magma flow, we demonstrate that pyroxene nucleates topotactically on amphibole, forming rims, but can later reorient in response to strain. In static experiments, gravitational settling alone produces measurable misorientations that can be tracked over time, while natural samples reveal signatures of externally imposed shear. The resulting rim textures encode evolving strain histories, with crystal misorientation distributions tracking both total strain and variations in rim crystallisation and/or deformation rates. With EBSD-derived crystal orientations now shown to capture both thermodynamic and mechanical histories, amphibole reaction rims emerge as four-dimensional petrological recorders, sensitive to pressure, temperature, composition and strain (P–T–X–ε), providing a powerful unified framework for reconstructing magma evolution and the mechanics of magma transport.

The Eifel region of Germany hosts hundreds of distributed volcanoes of Quaternary age in an intracontinental setting. This includes many maar volcanoes, for which the Eifel is the type locality. Laacher See volcano in the eastern part of the region stands out as a sizable (erupted volume of 6.3 km(3) dense rock equivalent or a volcanic explosivity index (VEI) of 6) and dormant but actively deforming and degassing system. Plutonic ejecta clasts in pyroclastic deposits of the Laacher See volcano provide evidence that it is underlain by one of the youngest silicate-carbonatite subvolcanic intrusive complexes worldwide. It has long been appreciated that the Laacher See region has potential to significantly enhance our knowledge on distributed volcanic fields and their specific hazards resulting from high CO2 fluxes from the mantle to the surface, causing active deformation, as well as diffuse and sometimes punctuated explosive degassing. This is largely due to the Eifel boasting an extensive record of past research, easy access, and excellent infrastructure that uniquely permits implementation of cutting-edge scientific methods. Recently, three workshops were held to sharpen scientific questions of global scope and relevance to study this type of distributed volcanism. Workshop participants discussed opportunities and challenges associated with drilling in the Laacher See region, identified promising sites, and explored the potential of novel drilling techniques. The clear conclusion of these workshops is that Laacher See would be an ideal test bed to evaluate the physical and chemical properties of a shallow (similar to 4-6 km depth at its top, thus making it accessible to drilling) silicate-carbonatite intrusive complex formed by volatile-rich melts and associated with active degassing. Only drilling can provide answers to key problems related to the geodynamics, geohazards, and resource potential of such magma systems. Questions include how and at what rates translithospheric transport of magma and fluids occurs in continental intraplate settings. It is also puzzling why shallow fluids above a residual magma system after an eruption that occurred only 13 000 years ago are seemingly cold, although the system still appears to be highly dynamic based on ongoing CO2 degassing, seismic activity, and exceptionally high uplift rates on spatial scales of hundreds of kilometres. Critically, drilling enables linking deep and shallow observables related to melt and fluid migration and provides access to samples of CO2-rich fluids and their host rocks at depth. Such samples are tangible evidence required to properly balance CO2 fluxes from degassing magma with CO2 sequestration in carbonatites or fluid-precipitated carbonates. Core samples from a maar structure proximally to the Laacher See volcano can establish an unprecedented geological record of precursor events prior to its cataclysmic eruption. Importantly, drilling also permits improved geophysical monitoring from instrumented wells that can reveal high-resolution details on maar diatreme architecture and deflation-related faulting resulting from the evacuation of the Laacher See magma reservoir. Lastly, silicate-carbonatite intrusions are globally recognised as major hosts for critical metal deposits, which, at Laacher See, could be topics of investigation in the making. Ultimately, this project can provide fundamental insights into processes of fluid-mediated element transport and sequestration not achievable in inactive carbonatites. Overall, these goals are best achieved in two phases that encompass drilling (1) four holes (300-2000 m) to enable detailed studies of the pre-eruptive evolution of the Laacher See volcano, its subvolcanic structures, and ongoing fluid or magma transport and (2) a subsequent deep hole (3000-4000 m) to penetrate and core a syenitic-carbonatitic intrusive carapace and its hydrothermal aureole.

The Earth's crust contains networks of fractures that facilitates fluid flow at all depths, influencing processes such as seismicity and subsurface storage. Fracture transmissivity is governed by stress conditions at depth and strongly influenced by fracture scale and surface roughness - factors that remain only partly constrained. This study investigates the hydraulic properties of Westerly granite under hydrostatic stress cycled to 150 MPa, using intact samples and those with controlled fracture characteristics: (1) micro-fractures created by thermal treatment, (2) macro-fractures with fabricated roughness from smooth (Ra approximate to 1.5 mu m) to rough (Ra approximate to 10 mu m), and (3) tensile fractures produced by Brazilian splitting, representing natural tensile fractures (Ra approximate to 164 mu m). All samples exhibit transmissivity reduction with increasing effective pressure. Thermally generated micro-fracturing can increase permeability by two orders of magnitude over intact granite (matrix permeability similar to 10(-21) m(2)), depending on treatment temperature, whereas a single fabricated macro-fracture can increase transmissivity by up to six orders of magnitude. Although well-mated fractures close rapidly under load, they remain 2-3 orders of magnitude more transmissive than intact matrix. At 150 MPa, smooth fabricated macro-fractures achieve transmissivities comparable to rough analogue tensile fractures. Contrastingly, unmated rough fractures resist closure due to asperity propping, maintaining higher transmissivities. Upon unloading, transmissivity does not retrace the loading path, particularly in unmated rough fractures, indicating both elastic and permanent deformation that limits fracture reopening. These results demonstrate how fracture morphology controls transmissivity evolution under variable stress - key to understanding crustal fluid flow and related geological processes.

Induced seismicity related to fluid injection in the upper crust is a major concern in the context of geothermal energy production. For exploited high-temperature geothermal systems in tectonically and volcanically active areas, such as Krafla caldera in NE Iceland, understanding the processes that trigger seismicity and changes in the local stress field can be difficult to unravel. We observe a link between anthropogenic activity and changes in the local stress field, since the appearance of a strike-slip cluster coincides with changes in the seismic anisotropy around an injection well during an injection interruption period. By analyzing the shear-wave splitting phenomenon, 90[Formula: see text] flips of the fast S-wave polarization and a decrease in the time delays between the fast and the slow S-wave component is observed, starting within hours after an injection stop, coinciding with a sharp increase of strike-slip events in the vicinity of the well. When the injection restarts, the seismic quiescence and increase of time delays may suggest a resumption of the previous state. The changes in seismicity patterns and variations of the seismic anisotropy might be linked to changes in the pore pressure and a possible activation of a shear-fault due to anthropogenic activity.

Deformation of magmas and hot rocks occurs at a range of strain rates in natural systems including rapid deformation as magma is sheared against the conduit wall upon ascent or during collapse of parts of the volcanic edifice. The initiation of cracks and fractures in magma is crucial to the development of permeable pathways through which volatiles may degas and alleviate overpressure in the system. Yet, experimental data on the deformation of hot magmas at high strain rates remains sparse, with the majority of tests conducted at strain rates on the order of 10-5 s-1. Using a drop tower equipped with a furnace, we subject high temperature (890 – 950 °C) rhyolitic obsidians to high strain rate impacts (100-102 s-1) at various impact energies. Our results indicate a strong effect of both temperature and strain rate on the peak stress recorded in the melts. Despite being far above their glass transition temperature (717 °C), the samples all deform in a brittle manner, owing to the ratio between relaxation to observation timescales which is expressed as the dimensionless Deborah number (De). At colder temperatures (890 – 930 °C), samples behave predominantly elastic-brittle whereas at higher temperature (950 °C) the increasing viscous component of deformation weakens the melt, causing lower peak stresses and more comprehensive fragmentation. Our findings provide insights into how changes in temperature, energy and strain rate affect the rupture behaviour of melts, thereby improving our understanding of dynamic magmatic processes such as magma-conduit interaction upon magma ascent.

The conditions under which magma accumulates and is stored are fundamental to unravelling the processes of crust formation, planetary differentiation, geothermal heat recharge and volcanic eruptions. Storage pressure, temperature and volatile saturation are typically inferred from erupted volcanic products. However, changes during kilometres of magma ascent induce disequilibrium crystallization and vesiculation, and inverting back to storage conditions comes with unresolvable uncertainties. Here we explore opportunities arising from magma drilling at Krafla volcano, Iceland, to reconstruct real, in situ magmatic conditions. The findings show that, over the approximately 5 min in which the magma is quenched, vapour bubbles consisting of H2O and CO2 exsolve, grow and resorb, but the changes can be accounted for by multiparametric inversion (for chemistry, vesicularity and vitrification), and that the magma was stored under volatile-saturated lithostatic conditions, unlike previous assertions of lower vapour pressures based on classic methods1. These new disequilibrium simulations reconcile the glass chemistry with conceptual models of magma storage and provide us with the unique pairing of precisely measured depth and volatile pressure on a single magma body and thus a robust method to improve our understanding of magma storage conditions and evolution.

Bubble growth in silicate melts drives significant volume expansion, which has a first order control on magma transport dynamics. When magmas are exposed to external environments, heat and volatile loss at free surfaces can reverse bubble growth, leading to shrinkage and complex feedbacks between diffusion, rheology, and flow. To resolve how magma flow controls, or is controlled by, bubble expansion, we couple a micro-mechanical model for volatile diffusion into individual bubbles, with a macro-scale thermal evolution and fluid flow of the surrounding magmatic suspension. This two-way coupling captures the co-evolution of bubble size, melt viscosity, and pressure gradients, allowing both growth and resorption to emerge naturally from local conditions. We identify distinct dynamical regimes governed by (i) bubble growth limited by (a) viscous resistance or (b) diffusion at the bubble scale, (ii) viscous transport of the suspension, (iii) outgassing through permeable porous networks and exposed magma-fluid interfaces, and (iv) thermal quenching. Across these regimes, thin, high-viscosity boundary layers arising from temperature and volatile concentration gradients play a central role in modulating flow and bubble evolution. The model is implemented in a flexible, modular numerical framework (Multiscale Vesiculation, Fluid flow, Failure, and Interaction Nonlinear model: MVFFIN) enabling extension to a wide range of systems and applications, including conduit flow and pyroclast evolution. By resolving the interplay between internal bubble dynamics and external boundary conditions, this approach provides a unified framework for understanding multiscale degassing and its impact on magmatic transport and fragmentation.

Hot hydrous pyroclasts vesiculate, diffusively outgas, and sinter during deposition which leads to continuous evolution of their porous-permeable networks. Welded ignimbrites, tuffisites, and sintered in-conduit pyroclasts, all exhibit variable degrees of sintering as well as a broad grain size distribution. How this polydispersity in grain sizes influences evolution has not yet been understood. Where polydisperse models for sintering exist, they are limited to relatively small ash particles (1-50 mu m) and do not account for vesiculation that occurs in relatively larger pyroclasts. Here, we perform high-temperature sintering experiments using relatively coarse ash-to-lapilli (0.5-2.5 mm) clasts. First, we find that polydisperse systems exhibit more efficient initial packing relative to monodisperse systems. Second, polydisperse samples with fine grains between larger grains may undergo differential size-dependent sintering and vesiculation. Third, for larger grains, particle-particle contact areas are enhanced by vesiculation-driven clast expansion onto neighbouring grains, with some contact flattening. Because both sintering and diffusive outgassing are grain-size dependent, any population at a given time will contain grains that differ in internal vesicularity, H2O content, and size; each evolving on different timescales. We compare our results to sintering models which account for H2O loss and we augment these by empirically capturing the effect of a time-dependent particle radius due to vesiculation. To distinguish between the three dominant processes-sintering, vesiculation, and diffusive outgassing-we introduce a regime diagram. Models for sintering that accommodate the complexity of processes occurring in volcanic environments will be particularly impactful for our conceptual understanding of the conditions under which sintering in conduits or tuffisites may influence eruptive behaviour as a whole.

Abstract Explosive volcanic eruptions occur when coherent bubbly magma breaks apart in a process called “fragmentation.” Accurate conceptual and numerical models of fragmentation are a pre‐requisite for prediction of eruption explosivity. However, existing models, which neglect bubble‐scale magma physics, agree poorly with new experimental evidence that we present. Here, we derive and validate a mathematical model for magma fragmentation, based on viscoelastic failure of the liquid around rapidly growing bubbles in magma. The model, which explicitly captures processes at the bubble scale, shows excellent agreement with experiments, accurately predicting the conditions under which magma does and does not fragment. We apply the new numerical model to predict the critical rate of magma decompression during ascent required for explosive eruption across different magma types. The predicted rates are consistent with chemical and textural proxies for the decompression rate, providing further validation of the model under natural eruption conditions.

The discovery of a rhyolitic magma body at a depth of 2.1 km during drilling of the first well in the Iceland Deep Drilling Project (IDDP-1) at Krafla volcano, NE Iceland, presented an unprecedented opportunity to explore shallow magma properties and the root of geothermal systems. Yet, to safely access this near-magma energy, we require an in-depth understanding of magmas’ response to drilling activity and power plant operations, which we target here using the natural samples retrieved in-situ from the magma body during IDDP-1. The glassy fragments display a spectrum of colors (light brown to black), different vesicularities and crystals of plagioclase, pyroxene, Ti-magnetite, and apatite; some crystals exhibit zonation and embayment. In this study we experimentally explore the stability of the rhyolitic magma to different P-T-X conditions to assess magma response to perturbations prompted by drilling. We tested pressures of 16, 35, and 45 MPa (between hydrostatic pressure and the pressure as estimated by dissolved H2O-CO2 concentration), temperatures ranging from 880 to 920°C, and durations spanning from 6 to 48 hours. All experiments were carried out under water-saturated conditions, with oxygen fugacity fixed by Ni and Co filler-rods to NNO+1 (more oxidized) or QFM (more reducing), respectively. We used the original glass chips (without remelting them) to see how the texture would evolve when subjected to different P, T, X. The main difference observed is when comparing experimental products at NNO+1 or QFM conditions which influenced glass color: darker hues appeared under NNO+1 condition and lighter hues prevailed under QFM condition. Whilst at NNO+1 the phases present in the original mineralogical assemblage were generally relatively stable (with one exception; see below). At 45 MPa, we observe no dissolution of the original phases but overgrowth of pyroxene in all charges. By reducing temperature from 900 ºC to 880 ºC or by increasing the oxygen fugacity (to NNO+1) we observed an increase in microlite content of the same original phases (except for apatite which did not crystallize). At the lower pressure of 35 MPa, the microlite content was higher than at 45 MPa; yet, the original mineralogical assemblage remained, whereby no dissolution took place and pyroxene overgrowth occurred. Again, by decreasing temperature from 920 ºC to 880 ºC or by increasing the oxygen fugacity the microlite content increased. Importantly, quartz crystallized at 880 °C, 35 MPa and under NNO+1 conditions; indicating that these conditions were likely not met during drilling. At 16 MPA, the experiments failed as the Au capsules ruptured due to pressure from excess fluids. Our initial findings suggest that the magma may reside in the crust at a minimum temperature of 900 °C, if at 45 MPa, or 920 °C, if at 35 MPa. This work establishes a “reference frame” for understanding shifts in magmatic parameters that may be triggered by drilling into active systems.

Shallow-crustal magma transport occurs mainly via dykes and inclined sheets, which may or may not reach the surface to erupt. Originating from various magma sources, dyke propagation is primarily controlled by magma overpressure, magma rheology, local stress fields and the mechanical properties of the host rock, shaping the complex spatio-temporal evolution of transcrustal plumbing systems. Here, we use finite element method numerical models to investigate how shallow-crust heterogeneities influence dyke pathways at Santorini volcano (Greece). In our models, subvertical dykes predominantly ascend from the roofs of sill-like magma chambers, whereas inclined sheets emerge from lateral chamber ends and occasionally reach the surface beyond the caldera. Our results show that layered systems with contrasting mechanical properties and vertically stacked magma storage promote stress rotations that favour dyke and sheet arrest. The initial site of dyke injection strongly controls whether magma propagates vertically or along an inclined trajectory, emphasizing the role of chamber depth, crustal heterogeneity, and regional stress in magma pathways and recharge locations. This study enhances our understanding of potential shallow and deep magma pathways providing new insights into future unrest episodes at Santorini volcano.

How can we not afford to scientifically probe magma? Fifteen years of accidental drilling encounters with magma have shown that it can be done safely with recovery of magmatic and partial melt samples quenched in situ. More could be gained if preceded by thorough scientific preparation and followed by long-term monitoring. Through the panoply of instruments now available, we can measure temperature, pressure, strain, heat and mass transport and changes over time. In 2009, the Iceland Deep Drilling Program well #1 reached rhyolitic magma at 2100 m depth under Krafla Caldera. The project was exemplary in sharing provocative results, but only hints at what is possible. Equilibrium temperatures were estimated by traditional petrologic techniques to be 850 – 1100 C. Pressure estimates range from 40 – 90 MPa with both extremes seemingly problematic, because for the first time we know the depth of a magma body to 4 significant figures. The lowest value is below lithostatic and the highest could be inherited from deeper levels. Now it appears that the lower pressure is what magma “feels”. But without drilling, would traditional estimates be good enough? Magma is somewhere between 1500 – 4000 m depth and with temperature corresponding to some type of magma? Actually, we would not even know that shallow magma is there but now in hindsight we see it geophysically. Ground-truth testing is how methodologies are improved. Our situation is like speculating about the nature of the Moon without sampling it. The cost of probing Earth’s magma is high and the probability of success uncertain, but far less so on either count than for extraterrestrial exploration. On Earth we are more restrained by self-imposed limits than by our technical capabilities. Besides understanding the differentiation of our planet, we have two compelling reasons for bold exploration: 1) We need the baseload, magma resource with its far higher temperature, energy density, and more extensive thermal fracturing than conventional geothermal; 2) We need to raise the level of reliability of eruption forecasts by testing our magma-dynamic models directly, thereby saving countless lives. As with other endeavors that are expensive for a single country to undertake but that benefit all humankind, a way forward is through an international infrastructure, where teams of scientists can conduct experiments with magma and superhot fluids. This is analogous to particle accelerators and the complement to outer space travel: inner space. The Krafla Magma Testbed is a much-needed step and an opportunity for all planetary, magma, volcano, and hydrothermal scientists to test their methods and ideas. KMT will drill a doublet of wells to magma for long-term monitoring and experimentation, respectively. The project, now organized as a legal entity within the Iceland Geothermal Research Cluster (GEORG), in partnership with the National Power Company of Iceland (Landsvirkjun), Iceland Energy GeoSurvey (ISOR), and a multinational team of scientists and engineers, under the aegis of the International Continental Scientific Drilling Program (ICDP), is ready. Magma could have been intentionally explored before. It is time to ask, “Why not now?”

Krafla volcano, located in Iceland's North Volcanic Zone, has been extensively studied using static gravity surveys since 1975. This study integrates measurements acquired between 2022 and 2023 with legacy data to produce a new gravity map of the area. We produce gravity gradient maps to delineate shallow subsurface density features and invert them to develop a 3D density model that images key subsurface structures. The combined survey coverage, extending from Fremrinámar to the Þeistareykir Volcanic Systems, reveals a range of features with contrasting densities which reflect the tectonic and volcanic processes that have shaped the area. Denser materials are associated with mafic intrusions along the principal faults related to caldera‐subsidence and ancillary faults within the caldera. In the Iceland Deep Drilling Project 1 (IDDP‐1) area, located inside the caldera, we identify a positive density anomaly at depths corresponding to magma encountered during drilling at 2.1 km depth. Negative gravity anomalies, indicative of relatively low‐density materials, are distributed within and outside the Krafla caldera. Within the caldera, these anomalies are interpreted as felsic intrusions and highly fractured geothermal zones. Beyond the caldera, a prominent negative density anomaly corresponds to the graben structure associated with the Húsavík‐Flatey Fault. Although strong near‐surface gravity anomalies and the spatial distribution of our gravity measurements limit the identification of deeper structures (>5 km), this study offers valuable insights into the distribution of the magmatic system features, as well as large tectonic characteristics in the area. These insights improve our understanding of magmatic and tectonic processes, volcanic hazards, and the future development of geothermal production in the area.

Long-term deformation is observed at many volcanoes worldwide, providing valuable insights into sub-volcanic processes. Deformation also informs on volcano flank instability, which presents a major hazard in the event of a complete or partial collapse of the edifice, which may further trigger a tsunami if the volcano is located near the sea. We explore InSAR datasets to investigate surface deformation of 20 potentially hazardous coastal volcanoes in Southeast Asia. We find that over 90% of them exhibit signs of persistent or episodic surface deformation. Most volcanoes experience line-of-sight (LOS) increase with displacement rates spanning a broad range and reaching up to 29 cm/yr at Ruang. These are either steady, or experience distinct acceleration periods, lasting for several months to years following increased volcanic activity measured as the volcanic radiative power (VRP) and reported periods of unrest or eruptions. We attribute the majority of observed deformation to gravity-driven processes and cooling of young surface deposits. Analysis of displacement components shows subsidence for all cases of LOS increase, coupled with varying horizontal displacements showing either (i) convergence, representing inwards displacements of the flanks due to volume loss by gravitational compaction and cooling contraction, (ii) divergence, representing outwards spreading due to instability of the volcano flanks via surficial downslope flank creep or fault sliding or (iii) near-unilateral horizontal displacements across most of the edifice, representing sliding via a deep detachment fault. We suggest that the horizontal component of InSAR deformation on volcanic edifices may be used to quickly assess the dominant deformation patterns. Applying this concept, we identify potential flank instability at four volcanoes (Anak Krakatau, Lewotobi, Sirung and Ulawun), which may pose future collapse hazards. This work offers new insights into the types and rates of volcano flank deformation, demonstrates a direct link between increased volcanic activity levels and deformation rates, and provides an improved comparative basis to other volcanic regions worldwide.

Amphibole phenocrysts are common in intermediate to felsic magmas where they record information on magma evolution through breakdown rim textures marking shifts in pressure, temperature, volatile concentrations, oxygen fugacity and melt chemistry during ascent. Our ability to track these variables throughout the volcanic plumbing system (e.g., via phase equilibria experiments, geothermobarometry, disequilibrium textures, melt inclusions) has provided the means for interpretating eruption trigger mechanisms, yet a lack of calibrated data on their influence on amphibole stability (and thus reaction rim formation) makes unambiguously distinguishing the mechanism problematic. One such elusive example is the role of CO2 flushing, deemed a likely phenomenon in magmatic systems, precluding an accurate interpretation of natural rim formation, previously assigned to decompression or heating. We performed high-temperature (830–880ºC), high-pressure (120 MPa) experiments to investigate the effects of XCO2 (0.3–0.7) on amphibole reaction rim development in H2O-saturated silicic magmas in shallow volcanic systems, providing new insights for interpreting amphibole rim textures. Our experiments quantify the significant impacts of CO2 on rapidly triggering amphibole breakdown over shorter timescales compared to heating or decompression. 2D textural analysis of the breakdown rim microlites reveal that crystal size, aspect ratio, number density and preferential alignment, together with mineralogy, can be related to a distinct breakdown mechanism. Furthermore, we apply high-resolution electron backscatter diffraction (EBSD) analysis to >100 experimental and natural amphibole reaction rims (Soufrière Hills Volcano, Unzen Volcano, Bezymianny and El Misti). Quantitative mapping reveals systematic variations in crystallographic orientations of the rim microlites relative to the host amphibole, enabling the development of an EBSD criteria that differentiates decompression-, heating-, and CO2-induced amphibole breakdown. The distinct textures produced provides new markers and a new framework for the interpretation of natural rim formation processes. Application of this new quantitative approach over a range of magmatic systems worldwide will improve interpretations of intensive parameters, ascent paths, eruption triggers, and amphibole stability from crystal record archives.

Volcaniclastic deposits compact during accumulation and burial, causing prolonged ground deformation, and potentially affecting edifice stability. Here we present the results of laboratory compaction experiments in which volcaniclastic material (in a confining cup) was progressively loaded with 0.1 MPa/min up to 20 MPa. We tested two lithologies consisting of natural basanitic scoria and crushed hyaloclastite, each sieved to a set of two grain sizes in the ash (0.5-2 mm) and lapilli (2-4 mm) range. During experiments, axial deformation and acoustic emissions were monitored, enabling us to quantify the progressive volume reduction and material properties. Two types of experiments were performed: dynamic loading tests and static creep test. The dynamic tests show that most of the deformation takes place within the first few MPa, decreasing non-linearly with load. Ultimately, samples compacted by up to 50 vol.% at 20 MPa (here equivalent to ~1,400 m depth). We use this compaction data to build a model of compaction and material properties as function of burial depth. In repeat experiments, static tests were undertaken at select target loads (2, 5, 10 and 20 MPa) to measure time-dependent creep deformation at these loads over 6 hours. We find that compaction continues under static load as creep occurs in stages, displaying (1) initially rapid decline in compaction strain rates, which (2) then diminish more slowly over time and (3) eventually reach stable creep strain rates in most of our tests. Moreover, both total creep strains and stable creep rates are dependent on the applied load. Stable strain rates were highest between 5 and 10 MPa for all samples. The data shows that the lithology also influences the deformation behavior as we found the hyaloclastites compacted more efficiently during initial loading compared to the scoria, but in-turn creep strain rates were nearly an order of magnitude lower due to the more efficient compaction during loading. Our results highlight the relevance of gravitational material compaction for investigations of ground deformation and volcano flank instability (e.g., measured with InSAR) and introduce new material constraints to improve the interpretation and analysis of such signals. Deposit-specific compaction data may be integrated with ground deformation monitoring to interpret flank instabilities and assess collapse hazards, particularly in eruptions where deposition of new materials rapidly shifts overburden stresses.

The motion of a projectile is a classic topic and is used to illustrate physical and mathematical concepts and techniques. Despite the ubiquity of this problem in pedagogic contexts, there exist few available laboratory datasets and step-by-step exercises for how to use them for teaching at a wide range of levels—from high school through to college/university. Such datasets are particularly important for virtual learning environments where primary data collection may not be possible. Here, we present such a dataset for use with physics and science classes at a range of levels. We provide (1) derivations of the equations of motion, (2) experimental data for projectile motion at a wide range of launch angles and velocities to test predictions from the equations of motion, and (3) analysis steps for comparing theory with experiment. We discuss alternative and extension activities for both mathematical and experimental approaches, as well as a wide range of real-world applications of this problem. Taken together, we propose that this is a learning package that can be adapted for many teaching scenarios.

Silicate melts have highly temperature-dependent viscosity and at low temperatures, crystalize and/ or vitrify. The development of a solid rind or carapace results in a transition in deformation mechanism from dominantly viscous to elastic or plastic. This transition has a significant impact on the rate and style of emplacement of lava flows and domes, including on the construction of channelized flows, over-steepened margins, and advance due to lava flow breakouts. These processes are especially important in subaqueous, subglacial, and extraterrestrial environments in which cooling is accelerated, resulting in a current lack of models specifically calibrated for these environments. We develop a numerical model, Viscous-Elastic Numerically Unified Solver for Solidifying flows (VENUSS), for cooling and solidifying free surface flows. The model couples a viscous fluid interior with an elastic shell whose thickness grows in response to cooling. We use a numerically unified approach that solves for the velocity field in the viscous and elastic fields together. Interface tracking is provided using the level set method combined with an extended finite element (XFEM) approach to avoid costly remeshing. Simulations are performed in two-dimensional planar or axisymmetric conditions which allows for modeling natural geometries such as lava flows and lava domes. This approach presents an improvement upon existing models of lava flow and dome evolution that either neglect or greatly simplify the mechanical effects of a crust. As a validation/test of our model, we simulate the advance of meter-scale experimental lava flows from the Syracuse Lava Project. We find the flow propagation is highly sensitive to the boundary conditions applied at the flow base. Under no-slip conditions, the simulated flow arrests more quickly than the experiments. No-stress conditions at the flow base produce plug-like flow that propagates too quickly. Adding an imposed ruptured condition (no solidification and viscosity appropriate to the flow interior) in a thin layer at the flow base produces a lobate morphology that qualitatively resembles observations of natural and experimental flows. In our models, flows are slowed and stopped by the development of a coherent crust at the flow front, whereas natural flows would continue to propagate via rupture of the skin or crust, highlighting the importance of including these mechanisms in models. However, crust development and rupture are usually omitted from lava flow models, in which propagation and arrest are usually controlled by an increase in viscosity through the entire flow thickness. Our new model allows for investigation into the development and arrest of lava flows that depends on geometry, the competition between flow advance and cooling, and the mechanical properties of a solidified skin or crust. Such insight can be embedded into flow field scale models and allow for physics-based, complex flow fields impacted by breakouts, ooze-outs, channelization, and other critical crust-dominated processes.