Magma Dynamics Research Articles

The efficacy of high frequency petrological investigation at open-conduit volcanoes: The case of May 11 2019 explosions at southwestern and northeastern craters of Stromboli

Petrological studies of active volcanoes typically focus on eruptive phenomena occurring over long timescales of the order of days to years, aiming at identifying major changes in the physico-chemical state of magma during ascent towards the surface. Exceptionally, we present results from an integrated petrological and statistical approach based on the compilation of ∼5300 major and trace element data for glass and crystals, in combination with volcanological data on eruptive events occurred over timescales of minutes at Stromboli volcano (Sicily). On May 11, 2019, we had the rare opportunity to collect individual fresh fallout ash products from eighteen mostly consecutive explosions, erupted in a 2-h time span and, at the same time, to acquire continuous high frequency (50 Hz) infrared thermal data of the same explosions. Through video analysis, we observe that explosions were more frequent and ash-dominated at the southwestern crater area (SCA, 8–10 events/h) than at the northeastern crater area (NCA, 3–5 events/h), where coarser material was ejected. The statistical analysis of glass and plagioclase compositions reveals differences in the products erupted from the two crater areas. SCA explosions tapped less differentiated magmas (Mg#∼42–46, ∼257–365 LaN, ∼0.7–0.9 Eu/Eu*) in equilibrium with more anorthitic plagioclase cores (An∼72–88), whereas NCA area explosions are more differentiated (Mg#∼40–44, ∼286–387 LaN, ∼0.6–0.8 Eu/Eu*) and in equilibrium with less anorthitic plagioclase cores (An∼68–82). Thermometric calculations based on major and trace element clinopyroxene-plagioclase-melt equilibrium modeling highlight that the SCA explosions were statistically fed by hotter magmas in comparison to NCA explosions. Plagioclase-based diffusion modeling also indicates longer timescales for the dynamic ascent of NCA magmas, leading to preferential groundmass crystallization at the conduit walls and transition from sideromelane to tachylite groundmass textures. The final emerging picture is that in May 2019, concurrent normal eruptions from different crater areas at Stromboli were heralds of compositionally and thermally diverse magmas rising at different rates within the uppermost branched part of the conduit region. High frequency petrological investigations aided by statistical treatment of data have the potential to constrain dynamic conduit processes related to transient, explosive eruptions in persistently active volcanoes, thereby offering new insights on the interplay between magma dynamics, ascent timescales, and eruptive behavior.

Focused Mid‐Crustal Magma Intrusion During Continental Break‐Up in Ethiopia

AbstractSignificant volumes of magma can be intruded into the crust during continental break‐up, influencing rift evolution by altering the thermo‐mechanical structure of the crust and its response to extensional stresses. Rift magmas additionally feed surface volcanic activity and can be globally significant sources of tectonic CO2 emissions. Understanding how magmatism may affect rift development requires knowledge on magma intrusion depths in the crust. Here, using data from olivine‐hosted melt inclusions, we investigate magma dynamics for basaltic intrusions in the Main Ethiopian Rift (MER). We find evidence for a spatially focused zone of magma intrusion at the MER upper‐lower crustal boundary (10–15 km depth), consistent with geophysical datasets. We propose that ascending melts in the MER are intruded over this depth range as discrete sills, likely creating a mechanically weak mid‐crustal layer. Our results have important implications for how magma addition can influence crustal rheology in a maturing continental rift.

Radon on Mt. Etna (Italy): a useful tracer of geodynamic processes and a potential health hazard to populations

Radon gas and its radioactive daughters have been extensively studied on Mt. Etna, both in local volcanic rocks and in all types of fluid emissions from the volcano (crater gases, fumaroles, mofettes, soil gases, groundwaters). The first measurements date back to 1976 and were carried out both in local volcanic rocks and in the crater plume. Since then, fifty-four scientific articles have been published. The largest majority of them (more than 50%) correlated radon emissions with volcanic activity and/or magma dynamics inside Mt. Etna. Many others were focused on possible correlations between time variations of in-soil radon and tectonic activity. The concentration of radionuclides in Etna volcanic rocks was measured on several occasions in order to set background values of radon parents and to study the dynamics of Etna magmas. Some articles analyzed the concentrations of radon in Etna groundwaters and their temporal changes in relation to volcanic activity. Only a few studies focused on methodological aspects of radon measurements in the laboratory. Finally, in recent years, geoscientists began to analyze the possible negative effects on human health from high concentrations of indoor radon in houses near active faults. The overall results show that, in most cases, it is possible to understand the endogenous mechanisms that cause changes in soil radon release from rocks and its migration to the surface. Several physical models were produced to explain how those changes were correlated with Etna’s volcanic activity, making them potential precursors, especially in the cases of eruptive paroxysms. More complex is the analysis of radon changes in relation to tectonic activity. Indeed, if measurements of radon in soil is now considered a robust methodology for identifying buried faults, radon time variations are not always clearly correlated with seismic activity. This difficulty is likely due to the complex interplay between tectonic stress, magma migration/eruption and gas release through faults. In any case, the potential high hazard for human health due to high concentrations of indoor radon in houses close to faults seems to be a well-established fact, which requires particular attention both from the scientific community and the public health authorities.

Insights into magma dynamics at Etna (Sicily) from SO2 and HCl fluxes during the 2008–2009 eruption

Abstract Magma convection, where low-viscosity, gas-rich magma ascends, degasses, and crystallizes before sinking down the same conduit in either annular or side-by-side flows, has been proposed for active basaltic volcanoes, where excess gas fluxes relative to erupted lava volume can be observed. Experimental studies show that convection is produced by buoyant ascending gas-rich magma and descending degassed magmas following density difference contrast, while geophysical studies point to the endogenous growth of active volcanoes through magma accumulation in plutons. However, many aspects of the convection process remain unclear, in particular, the depth to which magma ascends before overturning. Models have been proposed where overturn occurs near the surface and also at depths greater than 2 km from the top of the magma-filled conduit. The long-term monitoring of volcanic gas compositions may reveal new insights into the convection process, as each gas has a unique solubility-pressure profile. We report measurements of SO2 and HCl gas fluxes from Etna between October 2007 and May 2011, in which an ~90% collapse in halogen flux was observed together with an effusive eruption. This observation indicates that the halogen fluxes, during quiescent periods on Etna, require both magma supply to the shallowest levels and a period of residence. The lava effusion has the effect of reducing the shallow residence time, drastically reducing the halogen flux. These results provide a new interpretative framework for the degassing process and gas composition monitoring to explain subtle variations in magma supply and residence times in basaltic volcanism.

Coupling Flank Collapse and Magma Dynamics on Stratovolcanoes: The Mt. Etna Example from InSAR and GNSS Observations

Volcano ground deformation is a tricky puzzle in which different phenomena contribute to the surface displacements with different spatial–temporal patterns. We documented some high variable deformation patterns in response to the different volcanic and seismic activities occurring at Mt. Etna through the January 2015–March 2021 period by exploiting an extensive dataset of GNSS and InSAR observations. The most spectacular pattern is the superfast seaward motion of the eastern flank. We also observed that rare flank motion reversal indicates that the short-term contraction of the volcano occasionally overcomes the gravity-controlled sliding of the eastern flank. Conversely, fast dike intrusion led to the acceleration of the sliding flank, which could potentially evolve into sudden collapses, fault creep, and seismic release, increasing the hazard. A better comprehension of these interactions can be of relevance for addressing short-term scenarios, yielding a tentative forecasting of the quantity of magma accumulating within the plumbing system.

A data driven approach to mineral chemistry unveils magmatic processes associated with long-lasting, low-intensity volcanic activity

The most frequent volcanic eruptions are of low-intensity and small magnitude. They produce abundant ash-sized (< 2 mm) clasts, which are too small to establish quantitative links between magmatic processes and eruptive dynamics using classic approaches. This inhibits our ability to study the past behaviour of frequently erupting volcanoes, essential to predict their future activity and mitigate their impact. The Palizzi unit (10–13th century, Vulcano, Italy) includes a prototype sequence of ash deposits resulting from prolonged Vulcanian eruptions punctuated by those of two larger sub-Plinian events. We apply Hierarchical Clustering to chemical analyses of clinopyroxene collected along the stratigraphy to decipher magma dynamics during this eruptive period. We identify periods of magma input and we link deep magmatic processes to eruptive dynamics, also showing that our approach can be used to connect magma and eruptive dynamics in any volcanic sequence. This is essential to track the processes occurring during frequent eruptions and to identify the build-up to larger explosive events.

Magma recharge and mush rejuvenation drive paroxysmal activity at Stromboli volcano

Open-conduit basaltic volcanoes can be characterised by sudden large explosive events (paroxysms) that interrupt normal effusive and mild explosive activity. In June-August 2019, one major explosion and two paroxysms occurred at Stromboli volcano (Italy) within only 64 days. Here, via a multifaceted approach using clinopyroxene, we show arrival of mafic recharges up to a few days before the onset of these events and their effects on the eruption pattern at Stromboli, as a prime example of a persistently active, open-conduit basaltic volcano. Our data indicate a rejuvenated Stromboli plumbing system where the extant crystal mush is efficiently permeated by recharge magmas with minimum remobilisation promoting a direct linkage between the deeper and the shallow reservoirs that sustains the currently observed larger variability of eruptive behaviour. Our approach provides vital insights into magma dynamics and their effects on monitoring signals demonstrating the power of petrological studies in interpreting patterns of surficial activity.

Widespread phosphorous excess in olivine, rapid crystal growth, and implications for magma dynamics

Trace element zoning is often used to unravel the crystallization history of phenocrysts in magmatic systems, but interpretation requires quantifying the relative importance of equilibrium versus disequilibrium. Published partition coefficients for phosphorous (P) in olivine vary by more than a factor of ten. After considering kinetic effects, a new equilibrium partition coefficient was extrapolated from a re-examination of natural and experimental systems, indicating that P partition coefficients in olivine are significantly over-estimated. These new partitioning constraints allow us to establish a theoretical P Equilibrium Fractionation Array (PEFA) for mid-ocean ridge basalts (MORBs), revealing that most olivines from MORBs have excess P (2–15 times PEFA) and are thus in disequilibrium. Using an independent case study of natural dendritic olivines, we show that such P enrichments can be explained by diffusion-limited incorporation of P during rapid crystal growth. If growth rate can be related to cooling, the rapid growth rates of olivines have implications for magma system dynamics, such as the size of magma bodies or where crystallization occurs within the body.

Infrasonic gliding reflects a rising magma column at Mount Etna (Italy)

Infrasound is increasing applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity.

Quaternary off-rift volcanism along a section of the East African Rift System (EARS), from the south Ethiopia to the south Kenya

The magmatic-tectonic evolution of the EARS has been accompanied, since the initial stages of crustal deformation, by the formation of volcanic structures that formed outside of the main rift depression and are described with the general term of flank or off-rift volcanism. In this contribution, six Quaternary off-rift volcanic fields, from southern Ethiopia to southern Kenya are studied in terms of their map view shape, vent distribution and volcanic structures and constructions. They are, from the North one: Mega, Hurry Hills, Marsabit, Nyambeni Hills, Mount Kenya and Chyulu Hills. These six Quaternary off-rift volcanic fields formed far (> 80 km) from the rift’s main border faults and all have an elongated shape having their axis at a high angle to the nearly N-S southern Ethiopian and the nearly N-S trending Kenya rifts and to the transversal, roughly NW-SE-trending, pre- existing Mesozoic Anza Graben. The shape, the spatial distribution of vents as well as the volcanic structures of the fields indicate that each volcanic field records the interaction between the magma dynamics, the crustal structural architecture and the local stress field. The volcanic fields are located at the border of a very cold and stiff lithosphere as inferred by geophysical data. In summary, the location and the evolution of the analysed off-rift volcanic fields are controlled by the inner structures of the EARS whereas their vent spatial distribution and shape are controlled by the local shallow structure of the crust and local stress field.

Inferences on the magmatic plumbing system at Stromboli volcano (Italy) from trace element geochemistry of matrix glasses and minerals in different types of explosive eruptions

Stromboli (Italy) is a basaltic volcano characterized by persistent, mild strombolian activity, occasionally interrupted by lava effusion and more violent explosive events, named major explosions and paroxysms depending on their intensity and magnitude. The normal activity is fed by a shallow and degassed highly porphyritic (HP) shoshonitic basalt carrying about 50 vol.% crystals settled in a shoshonitic glassy matrix (K2O > 3.8 wt.%). The more energetic explosions erupt a deep, volatile-rich, low-porphyritic (LP) magma with < 10 vol.% crystals in a shoshonitic basaltic glassy matrix (K2O < 2.4 wt.%). Products with intermediate glass composition are also found in the more violent explosive events. In this study, we present a new data set of major and trace element contents in matrix glasses and minerals performed in products from different types of explosive activity that occurred at Stromboli between 1998 and 2020. This large data set is used to put constraints on the evolution and architecture of the intermediate plumbing system, where the transformation from LP to HP occurs. Results indicate that, compared to paroxysms, the glassy matrices of the LP pumices from major explosions are richer in incompatible trace elements (and K2O wt.%) due to < 15 wt.% fractionation of clinopyroxene and olivine. This points to a chemical zoning of the deep reservoir and suggests that major explosions are fed by magmas residing in its upper part. Among the major explosions, the homogeneous intermediate glasses in the products from the 19 July 2020 event originate from the interplay of mixing and crystal fractionation processes. The crystallization of euhedral microphenocrysts of An-rich plagioclase suggests that batches of magma can pond and crystallize for few days (< 11) at the base of the intermediate zone of the plumbing system, at pressure coinciding with the entering of plagioclase into the system (< 100 MPa). As a relevant point for understanding the pre- and syn-eruptive magma dynamics, data indicate a positive correlation between the magnitude of the explosions and the depth of the supply magma.

Trace element partitioning in zoned clinopyroxene as a proxy for undercooling: Experimental constraints from trachybasaltic magmas

Sector-zoned clinopyroxene records kinetic effects imposed by variable degrees of magma undercooling, ΔT, and can be utilised to track the dynamics of magmatic systems. The partitioning of trace elements into sectors grown in different crystallographic orientations can be used as a proxy for ΔT. However, an experimental assessment of the relationship between trace element zoning and ΔT has been lacking to date. Here we present trace element data from a series of undercooling crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy), at conditions of crustal storage (400 MPa, NNO + 2), and ΔT ranging from 23 to 173 °C. Changes in ΔT were modulated by varying both resting and liquidus temperatures, the latter via the melt-H2O content of the experiments. The resting temperature was retained for 24 h to ensure the attainment of near-equilibrium conditions.High-resolution elemental mapping reveals the distribution of trace elements in individual clinopyroxene zones. Increasing ΔT drives a shift from polyhedral morphologies with Al-rich prism and Al-poor hourglass sectors (ΔT = 23–25 °C), to skeletal (ΔT = 75–123 °C) and dendritic (ΔT = 132–173 °C) crystals with Al-rich skeletons and Al-poor overgrowths. Aluminium-rich zones have higher concentrations of rare earth elements (REE) and high field strength elements (HFSE) than Al-poor zones across all investigated ΔT conditions, and overall, Al, REE and HFSE contents increase with ΔT. This indicates that tetrahedral aluminium (TAl) and associated charge-balancing mechanisms govern the incorporation of REE and HFSE within clinopyroxene. Lattice strain parameters for REE in the M2 site indicate the incorporation of light relative to heavy REE in clinopyroxene is controlled by competing effects between the strain-free partition coefficient, D0, and the optimum cation radius, r0. Critically, the middle and heavy REE switch from incompatible to compatible with increasing ΔT. Used to model fractional crystallisation, our data demonstrate that fractionation of clinopyroxene at low ΔT controls pre-eruptive melt evolution. Importantly, this indicates crystallisation of clinopyroxene in the deep portions of Mt. Etna’s plumbing system is not rapid and is unlikely to result in the early formation of dendrites.We develop a parameterisation of ΔT based on REE partitioning between experimental clinopyroxene and coexisting melt, which can be applied to sector-zoned augite crystallising from mafic alkaline magmas, to reconstruct dynamic processes and thermal pathways during magma transport and storage. Applied to sector-zoned clinopyroxene microphenocrysts and groundmass microcrysts from the 1974 eccentric eruption at Mt. Etna, our parameterisation tracks an increase in ΔT with magma ascent and eruption, following recharge of Cr-rich mafic magma at depth. Sector-zoned clinopyroxene can track ΔT variations leading to volcanism at Mt. Etna and could be applied to quantify magma dynamics in other active volcanoes.

Pitted-Ground Volcanoes on Mercury

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

Basaltic cognate enclaves from Dokdo Island as a window for intraplate mafic alkaline OIB magma dynamics in a back-arc basin

Basaltic cognate enclaves from Dokdo Island as a window for intraplate mafic alkaline OIB magma dynamics in a back-arc basin

Shallow magma dynamics at open-vent volcanoes tracked by coupled thermal and SO2 observations

Open-vent volcanic activity is typically sustained by ascent and degassing of shallow magma, in which the rate of magma supply to the upper feeding system largely exceeds the rate of magma eruption. Such unbalance between supplied (input) and erupted (output) magma rates is thought to result from steady, degassing-driven, convective magma overturning in a shallow conduit/feeding dyke. Here, we characterize shallow magma circulation at Stromboli volcano by combining independent observations of heat (Volcanic Radiative Power; via satellite images) and gas (SO2, via UV camera) output in a temporal interval (from August 1, 2018 to April 30, 2020) encompassing the summer 2019 effusive eruption and two paroxysmal explosions (on July 3 and August 28, 2019). We show that, during the phase of ordinary strombolian explosive activity that preceded the 2019 effusive eruption, the average magma input rate (0.1-0.2 m3/s) exceeds the magma eruption rate (0.001-0.01 m3/s) by ∼2 orders of magnitude. Conversely, magma input and output rates converge to an average of ∼0.4 m3/s during the summer 2019 summit effusion, implying an overall suppression of magma recycling back into the feeding system, and hence of excess degassing. We find that, during the effusive eruption, the peak in SO2 emissions lags behind the thermal emission peak by ∼27 days, suggesting that magma output, feeding the lava flow field, initially dominates over magma input in the conduit. We propose that this conduit mass unloading, produced by this initial phase of the effusive eruption, leads to an overall decompression (of up to 30 Pa/s) of the shallow plumbing system, ultimately causing ascent of less-dense, volatile-rich magma batch(es) from depth, enhanced explosive activity, and elevated SO2 fluxes culminating into a paroxysmal explosion on August 28. Our results demonstrate that combined analysis of thermal and SO2 flux time-series paves the way to improved understanding of shallow magmatic system dynamics at open-vent volcanoes, and of the transition from explosive to effusive activity regimes.

Dendritic crystallization in hydrous basaltic magmas controls magma mobility within the Earth’s crust

The majority of basaltic magmas stall in the Earth’s crust as a result of the rheological evolution caused by crystallization during transport. However, the relationships between crystallinity, rheology and eruptibility remain uncertain because it is difficult to observe dynamic magma crystallization in real time. Here, we present in-situ 4D data for crystal growth kinetics and the textural evolution of pyroxene during crystallization of trachybasaltic magmas in high-temperature experiments under water-saturated conditions at crustal pressures. We observe dendritic growth of pyroxene on initially euhedral cores, and a surprisingly rapid increase in crystal fraction and aspect ratio at undercooling ≥30 °C. Rapid dendritic crystallization favours a rheological transition from Newtonian to non-Newtonian behaviour within minutes. We use a numerical model to quantify the impact of rapid dendritic crystallization on basaltic dike propagation, and demonstrate its dramatic effect on magma mobility and eruptibility. Our results provide insights into the processes that control whether intrusions lead to eruption or not.

The monotonous intermediate magma system of the Permian Wurzen caldera, Germany: Magma dynamics and petrogenetic constraints for a supereruption

The Lower Permian Wurzen caldera formed during a VEI 8 supereruption that tapped monotonous intermediate magmas in a continental rift. The well-preserved crystal-rich intracaldera ignimbrite (<58 vol%) and its related plutonic facies allow for compositional and textural studies on juvenile fragments and mineral phases, providing a unique opportunity to unravel the caldera's pre-eruptive evolution.The climactic Wurzen ignimbrite contains different fiamme of fine-grained mafic, fine-grained rhyolitic (71.8 to 76.6 wt% SiO2), porphyritic (trachy-) dacitic (64.5 to 67.6 wt% SiO2), and coarse porphyritic rhyodacitic composition (64.7 to 74.3 wt% SiO2), which point to a permanent interplay between rejuvenation, differentiation, and cooling in the Wurzen magma body. The similarity of their trace element concentrations suggests derivation from a shallow magma chamber (Nb and Ta at 22 and 1.6 ppm, respectively). The picture becomes more differentiated when considering mineral composition and thermobarometric estimations. Resorption textures in anorthitic plagioclase (An >45 mol%) are presumably formed by excess heat from underplating magmas. Coarse sieve textures in plagioclase indicate a rapid ascent of magma into the shallow magma body. In contrast, oscillatory zonation and rapakivi texture in quartz, albitic plagioclase, and sanidine indicate convection during crystal growth. The spatially discrete crystallization of augite and pigeonite indicates tapping of anhydrous Ca-saturated and -undersaturated magma. The presence of pigeonite indicates eruption from a superheated anhydrous (trachy-) dacitic magma batch at temperatures of 1010 °C, whereas the occurrence of annite implies simultaneous tapping of hydrous shallow magma chambers at low temperatures (~750 °C). By applied barometers on clinopyroxene and biotite, it suggests a deep-seated magma chamber at depths of 25 to 15 km and a shallow magma chamber at ca. 11 km, respectively.Mineral assemblage of the intracaldera Wurzen ignimbrite (quartz, sanidine, plagioclase, calcic and calcic-sodic clinopyroxene, pigeonite, annite) is more typical for crystal-poor, hot rhyolites like in the Snake River Plain (Idaho, USA) or Messum igneous complex (Namibia), than that of monotonous intermediates at active continental margins.

Evolving magma temperature and volatile contents over the 2008-2018 summit eruption of Kīlauea Volcano.

Magma rheology and volatile contents exert primary and highly nonlinear controls on volcanic activity. Subtle changes in these magma properties can modulate eruption style and hazards, making in situ inference of their temporal evolution vital for volcano monitoring. Here, we study thousands of impulsive magma oscillations within the shallow conduit and lava lake of Kīlauea Volcano, Hawai‘i, USA, over the 2008–2018 summit eruptive sequence, encoded by “very-long-period” seismic events and ground deformation. Inversion of these data with a petrologically informed model of magma dynamics reveals significant variation in temperature and highly disequilibrium volatile contents over days to years, within a transport network that evolved over the eruption. Our results suggest a framework for inferring subsurface magma dynamics associated with prolonged eruptions in near real time that synthesizes petrologic and geophysical volcano monitoring approaches.

Impact of igneous intrusion and associated ground deformation on the stratigraphic record

Abstract The geomorphology and sediment systems of volcanic areas can be influenced by uplift (forced folding) related to subsurface migration and accumulation of magma. Seismic geomorphological analysis presents a unique tool to study how surface morphology and subsurface magma dynamics relate, given seismic reflection data can image buried landscapes and underlying intrusions in 3D at resolutions of only a few metres–decametres. However, differential compaction of the sedimentary sequence above incompressible igneous intrusions during burial modifies palaeosurface morphology. Here we use 3D seismic reflection data from offshore NW Australia to explore how the stratigraphic record of igneous intrusion and associated ground deformation can be unravelled. We focus on a forced fold that likely formed in the Early Cretaceous to accommodate intrusion of magma, but which was later amplified by burial-related differential compaction of the host sedimentary sequence. We show how: (1) marine channels and clinoforms may be deflected by syn-depositional intrusion-induced forced folds; and (2) differential compaction can locally change clinoforms depth post-deposition, potentially leading to erroneous interpretation of shoreline trajectories. Our results demonstrate seismic geomorphological analysis can help us better understand how magma emplacement translates into ground deformation, and how this shapes the landform of volcanic regions.

Insights Into Magma Storage Beneath a Frequently Erupting Arc Volcano (Villarrica, Chile) From Unsupervised Machine Learning Analysis of Mineral Compositions

AbstractA key method to investigate magma dynamics is the analysis of the crystal cargoes carried by erupted magmas. These cargoes may comprise crystals that crystallize in different parts of the magmatic system (throughout the crust) and/or at different times. While an individual eruption likely provides a partial view of the subvolcanic plumbing system, compiling data from multiple eruptions can build a picture of a whole magmatic system. In this study, we use machine learning techniques to analyze a large (&gt;2,000) compilation of mineral compositions from a highly active arc volcano: Villarrica, Chile. Villarrica's postglacial eruptive activity (14 ka–present) displays large variation in eruptive style (mafic ignimbrites to Hawaiian style effusive eruptions), yet its eruptive products have a near constant basalt‐basaltic andesite bulk‐rock composition. What therefore, is driving explosive eruptions at Villarrica and can differences in storage dynamics be related to eruptive style? Here, we use a hierarchical cluster analysis to detect previously unseen structure in the composition of olivine, plagioclase and clinopyroxene crystals erupted at Villarrica, revealing the presence of compositionally distinct clusters within each crystal population. Using rhyolite‐MELTS thermodynamic modeling, we related these clusters to intensive magmatic variables: temperature, pressure, water content, and oxygen fugacity. Our results provide evidence for the existence of multiple discrete (spatial and temporal) magma reservoirs beneath Villarrica where melts differentiate and mix with incoming more primitive magma. The compositional diversity within an erupted crystal cargo strongly correlates with eruptive intensity, and we postulate that mixing between primitive and differentiated magma drives explosive activity at Villarrica.