Energetic Eruptions Research Articles

High-energy insights from an escaping coronal mass ejection with Solar Orbiter/STIX observations

Solar eruptive events, including solar flares and coronal mass ejections (CMEs), are typically characterised by energetically significant X-ray emissions from flare-accelerated electrons and hot thermal plasmas. However, the intense brightness of solar flares often overshadows high-coronal X-ray emissions from the associated eruptions due to the limited dynamic range of current instrumentation. Occulted events, where the main flare is blocked by the solar limb, provide an opportunity to observe and analyse the X-ray emissions specifically associated with CMEs. This study investigates the X-ray and extreme ultraviolet (EUV) emissions associated with a large filament eruption and CME that occurred on February 15, 2022. This event was highly occulted from the three vantage points of Solar Orbiter (sim 45$^ circ $ behind the limb), Solar–TErrestrial RElations Observatory (STEREO-A), and Earth. We utilised X-ray observations from the Spectrometer/Telescope for Imaging X-rays (STIX) and EUV observations from the Full Sun Imager (FSI) of the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, supplemented by multi-viewpoint observations from STEREO-A/Extreme-UltraViolet Imager (EUVI). This enabled a comprehensive analysis of the X-ray emissions in relation to the filament structure observed in the EUV. We used STIX's imaging and spectroscopy capabilities to characterise the X-ray source associated with the eruption. Our analysis reveals that the X-ray emissions associated with the occulted eruption originate from an altitude exceeding 0.3 \(R_ above the main flare site. The X-ray time profile shows a sharp increase and exponential decay, and consists of both a hot thermal component at 17pm 2 MK and non-thermal emissions ($>11.4 keV) characterised by an electron spectral index of 3.9pm 0.2. Imaging analysis shows an extended X-ray source that coincides with the EUV emission as observed from EUI, and was imaged until the source grew to a size exceeding the STIX imaging limit (180 arcsec). Filament eruptions and associated CMEs have hot and non-thermal components, and the associated X-ray emissions are energetically significant. Our findings demonstrate that STIX combined with EUI provides a unique and powerful tool for examining the energetic properties of the CME component of solar energetic eruptions. Multi-viewpoint and multi-instrument observations are crucial for revealing such energetically significant sources in solar eruptions that might otherwise remain obscured.

An Energetic Eruption With Associated SO 1.707 Micron Emissions at Io's Kanehekili Fluctus and a Brightening Event at Loki Patera Observed by JWST

AbstractWe observed Io with the James Webb Space Telescope (JWST) while the satellite was in eclipse, and detected thermal emission from several volcanoes. The data were taken as part of our JWST‐ERS program #1373 on 15 November 2022. Kanehekili Fluctus was exceptionally bright, and Loki Patera had most likely entered a new brightening phase. Spectra were taken with NIRSpec/IFU at a resolving power R ≈ 2,700 between 1.65 and 5.3 µm. The spectra were matched by a combination of blackbody curves that showed that the highest temperature, ∼1,200 K, for Kanehekili Fluctus originated from an area ∼0.25 km2 in size, and for Loki Patera this high temperature was confined to an area of ∼0.06 km2. Lower temperatures, down to 300 K, cover areas of ∼2,000 km2 for Kanehekili Fluctus, and ∼5,000 km2 for Loki Patera. We further detected the a1Δ ⇒ X3Σ− 1.707 µm rovibronic forbidden SO emission band complex over the southern hemisphere, which peaked at the location of Kanehekili Fluctus. This is the first time this emission has been seen above an active volcano, and suggests that the origin of such emissions is ejection of SO molecules directly from the vent in an excited state, after having been equilibrated at temperatures of ∼1,500 K below the surface, as was previously hypothesized.

Tracking volcanic explosions using Shannon entropy at Volcán de Colima

The main objective of this work is to show that Shannon Entropy (SE) calculated on continuous seismic signals can be used in a volcanic eruption monitoring system. We analysed three years of volcanic activity of Volcán de Colima, México, recorded between January 2015 and May 2017. This period includes two large explosions, with pyroclastic and lava flows, and intense activity of less energetic explosion, culminating with a period of quiescence. In order to confirm the success of our results, we used images of the Visual Monitoring system of Colima Volcano Observatory. Another of the objectives of this work is to show how the decrease in SE values can be used to track minor explosive activity, helping Machine Learning algorithms to work more efficiently in the complex problem of distinguishing the explosion signals in the seismograms. We show that the two big eruptions selected were forecasted successfully (6 and 2 days respectively) using the decay of SE. We conclude that SE could be used as a complementary tool in seismic volcano monitoring, showing its successful behaviour prior to energetic eruptions, giving time enough to alert the population and prepare for the consequences of an imminent and well predicted moment of the eruption.

Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV candidate SDSS1133

ABSTRACT We present a comprehensive analysis of 20 yr worth of multicolour photometric light curves, multiepoch optical spectra, and X-ray data of an off-nuclear variable object SDSS1133 in Mrk 177 at z = 0.0079. The UV-optical light curves reveal that SDSS1133 experienced four outbursts in 2001, 2014, 2019, and 2021. The persistent UV-optical luminosity in the non-outbursting state is ∼1041 erg s−1 with small-scale flux variations, and peak luminosities during the outbursts reach ∼1042 erg s−1. The optical spectra exhibit enduring broad hydrogen Balmer P-Cygni profiles with the absorption minimum at ∼−2000 km s−1, indicating the presence of fast-moving ejecta. Chandra detected weak X-ray emission at a 0.3−10-keV luminosity of LX = 4 × 1038 erg s−1 after the 2019 outburst. These lines of evidence suggests that SDSS1133 is an extreme luminous blue variable (LBV) star experiencing multiple giant eruptions with interactions of the ejected shell with different shells and/or circumstellar medium (CSM), and disfavours the recoiling active galactic nuclei scenario suggested in the literature. We suggest that pulsational pair-instability may provide a viable explanation for the multiple energetic eruptions in SDSS1133. If the current activity of SDSS1133 is a precursor of a supernova explosion, we may be able to observe a few additional giant eruptions and then the terminal supernova explosion or collapse to a massive black hole in future observations.

Birthplaces of Extreme Ultraviolet Waves Driven by Impingement of Solar Jets upon Coronal Loops

Solar extreme ultraviolet (EUV) waves are large-scale propagating disturbances in the corona. It is generally believed that a vital key to the formation of EUV waves is the rapid expansion of the loops that overlie erupting cores in solar eruptions, such as coronal mass ejections (CMEs) and solar jets. However, the details of the interaction between the erupting cores and overlying loops are not clear because the overlying loops always instantly open after energetic eruptions. Here, we present three typical jet-driven EUV waves without CMEs to study the interaction between the jets and the overlying loops that remained closed during the events. All three jets emanated from magnetic flux cancellation sites in the source regions. Interestingly, after the interactions between the jets and overlying loops, three EUV waves respectively formed ahead of the top, the near end (close to the jet source), and the far (another) end of the overlying loops. According to the magnetic field distribution of the loops extrapolated through the potential field source surface method, it is confirmed that the birthplaces of three jet-driven EUV waves were around the parts of the overlying loops with the weakest magnetic field strengths. We suggest that the jet-driven EUV waves preferentially occur at the weakest part of the overlying loops, and the location can be subject to the magnetic field intensity around the ends of the loops.

Measurements of chromospheric Mg i emission lines of zero-age main-sequence stars

Abstract The chromosphere is the active atmosphere in which energetic eruption events, such as flares, occur. Chromospheric activity is driven by the magnetic field generated by stellar rotation and convection. The relationship between chromospheric activity and the Rossby number, the ratio of the rotational period to the convective turnover time, has been extensively examined for many types of stars, by using narrow chromospheric emission lines, such as the Ca ii lines and the Mg ii H and K lines. However, the stars with small Rossby numbers, i.e., stars with rapid rotations and/or long convective turnover times, show constant strengths of such lines against the Rossby number. In this study, we investigate the infrared Mg i emission lines at 8807 Å of 47 zero-age main-sequence (ZAMS) stars in IC 2391 and IC 2602 using the archive data of the Anglo-Australian Telescope at the University College London Echelle Spectrograph. After subtracting the photospheric absorption component, the Mg i line is detected as an emission line for 45 ZAMS stars, the equivalent widths of which are between 0.02 Å and 0.52 Å. A total of 42 ZAMS stars show the narrower Mg i emission lines instead of the Ca ii infrared triplet emission lines, suggesting that they are formed at different depths. The ZAMS stars with smaller Rossby numbers show stronger Mg i emission lines. The Mg i emission line is not saturated even in the saturated regime of the Ca ii emission lines, i.e., Rossby number <10−1.1. The Mg i emission line is considered to be a good indicator of chromospheric activity, particularly for active objects.

Periodic Oscillations in LASCO Coronal Mass Ejection Speeds: Space Seismology

Abstract Coronal mass ejections (CMEs) are energetic eruptions of organized magnetic structures from the Sun. Therefore, the reconnection of the magnetic field during ejection can excite periodic speed oscillations of CMEs. A previous study showed that speed oscillations are frequently associated with CME propagation. The Solar and Heliospheric Observatory mission’s white-light coronagraphs have observed about 30,000 CMEs from 1996 January to the end of 2019 December. This period of time covers two solar cycles (23 and 24). In the present study, the basic attributes of speed oscillations during this period of time were analyzed. We showed that the oscillation parameters (period and amplitude) significantly depend not only on the phase of a given solar cycle but also on the intensity of individual cycles as well. This reveals that the basic attributes of speed oscillation are closely related to the physical conditions prevailing inside the CMEs as well as in the interplanetary medium in which they propagate. Using this approximation, we estimated that, on average, the CME internal magnetic field varies from 18 up to 25 mG between minimum and maximum solar activity. The obtained results show that a detailed analysis of speed oscillations can be a very efficient tool for studying not only the physical properties of the ejections themselves but also the condition of the interplanetary medium in which they expand. This creates completely new perspectives for studying the physical parameters of CMEs shortly after their eruption in the Sun’s environment (space seismology).

Solar activity and space weather

After providing an overview of solar activity as measured by the sunspot number (SSN) and space weather events during solar cycles (SCs) 21-24, we focus on the weak solar activity in SC 24. The weak solar activity reduces the number of energetic eruptions from the Sun and hence the number of space weather events. The speeds of coronal mass ejections (CMEs), interplanetary (IP) shocks, and the background solar wind all declined in SC 24. One of the main heliospheric consequences of weak solar activity is the reduced total (magnetic + gas) pressure, magnetic field strength, and Alfvén speed. There are three groups of phenomena that decline to different degrees in SC 24 relative to the corresponding ones in SC 23: (i) those that decline more than SSN does, (ii) those that decline like SSN, and (iii) those that decline less than SSN does. The decrease in the number of severe space weather events such as high-energy solar energetic particle (SEP) events and intense geomagnetic storms is deeper than the decline in SSN. The reduction in the number of severe space weather events can be explained by the backreaction of the weak heliosphere on CMEs. CMEs expand anomalously and hence their magnetic content is diluted resulting in weaker geomagnetic storms. The reduction in the number of intense geomagnetic storms caused by corotating interaction regions is also drastic. The diminished heliospheric magnetic field in SC 24 reduces the efficiency of particle acceleration, resulting in fewer high-energy SEP events. The numbers of IP type II radio bursts, IP socks, and high-intensity energetic storm particle events closely follow the number of fast and wide CMEs (and approximately SSN) because all these phenomena are closely related to CME-driven shocks. The number of halo CMEs in SC 24 declines less than SSN does, mainly due to the weak heliospheric state. Phenomena such as IP CMEs and magnetic clouds related to frontside halos also do not decline significantly. The mild space weather is likely to continue in SC 25, whose strength has been predicted to be not too different from that of SC 24.

Modeling the multi-level plumbing system of the Changbaishan caldera from geochemical, mineralogical, Sr-Nd isotopic and integrated geophysical data

Changbaishan, an intraplate volcano, is characterized by an approximately 6 km wide summit caldera and last erupted in 1903. Changbaishan experienced a period of unrest between 2002 and 2006. The activity developed in three main stages, including shield volcano (basalts), cone-construction (trachyandesites to trachytes with minor basalts), and caldera-forming stages (trachytes to comendites). This last stage is associated with one of the more energetic eruptions of the last millennium on Earth, the 946 CE, VEI 7 Millennium Eruption (ME), which emitted over 100 km3 of pyroclastics. Compared to other active calderas, the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained. Here, we merge new whole-rock, glass, mineral, isotopic, and geobarometry data with geophysical data and present a model of the plumbing system. The results show that the volcano is characterized by at least three main magma reservoirs at different depths: a basaltic reservoir at the Moho/lower crust depth, an intermediate reservoir at 10–15 km depth, and a shallower reservoir at 0.5–3 km depth. The shallower reservoir was involved in the ME eruption, which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored. The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material, while the less evolved melts assimilate lower crust material. Syn-eruptive magma mingling occurred during the ME eruption phase. The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage. The depth of the magma storage zones is controlled by the layering of the crust. The plumbing system of Changbaishan is vertically extensive, with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth. Unlike other volcanoes, evidence of a basaltic recharge is lacking. The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system. A new arrival of magma may destabilize a part of or the entire system, thus triggering eruptions of different sizes and styles. The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.

Molecular remnant of Nova 1670 (CK Vulpeculae)

CK Vul is the remnant of an energetic eruption known as Nova 1670 that is thought to be caused by a stellar merger. The remnant is composed of (1) a large hourglass nebula of recombining gas (of 71′′ in size), very similar to some classical planetary and pre-planetary nebulae (PPNe), and (2) a much smaller and cooler inner remnant that is prominent in millimeter-wave emission from molecules. We investigate the three-dimensional spatio-kinematic structure of both components. Our analysis of the hourglass structure yields a revised distance to the object of >2.6 kpc, at least 3.7 times greater than previously assumed. At this distance, the stellar remnant has a bolometric luminosity >12 L⊙ and is surrounded by molecular material with a total mass >0.8 M⊙ (the latter value has a large systematic uncertainty). We also analyzed the architecture of the inner molecular nebula using ALMA observations of rotational emission lines obtained at subarcsecond resolution. We find that the distribution of neutral and ionized gas in the lobes can be reproduced by several nested and incomplete shells or jets with different velocity fields and varying orientations. The analysis indicates that the molecular remnant was created in several ejection episodes, possibly involving an interacting binary system. We calculated the linear momentum (≈1040 g cm s−1) and kinetic energy (≈1047 erg) of the CK Vul outflows and find values that are within the limits typical for classical PPNe. Given the similarities of the CK Vul outflows to PPNe, we suggest there may be CK Vul analogs among wrongly classified PPNe with low intrinsic luminosities, especially among PPNe with post-red-giant-branch central stars.

Flares in open clusters with K2

Context. Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. However, before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. Aims. This work sets out to quantify the flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Methods. Drawing from the complete K2 archive, we searched 3435 ∼80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. Results. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M 67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with exponent α ≈ 1.84−2.39. Conclusions. We confirm that flaring rates decline with age, and decline faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We find evidence that a rapid decline in flaring activity occurred in M1–M2 dwarfs around the ages of the Hyades and Praesepe, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may point to the limitations of using rotation as an age indicator without additional constraints from stellar activity.

Statistical analysis of characteristics of classified type II radio bursts and their associated solar energetic particle events

In this paper, we investigate 273 type II radio burst events detected by Wind, STEREO spacecraft from January 2010 to March 2018 during the 24th solar cycle. We classify all events as five groups or sub-types according to their starting and ending frequencies, and then analyze the observed characteristics of each group of type II radio bursts and the correlation between the occurrence of solar energetic particle (SEP) events and the associated coronal mass ejection (CME) or type II radio bursts. What we find is as follows. 1) In each group of type II radio burst events, the CME speed (<i>v</i>), width (WD), mass (<i>m</i>), and kinetic energy (<i>E</i><sub>k</sub>) associated with SEP events are generally greater than those with no SEP events, indicating that the generation of SEP events requires a fast and wide energetic CME eruption. 2) Compared with type II radio bursts starting from the DH band, type II radio bursts starting from the metric band have a higher proportion of large SEP events. Multi-band type II radio bursts are more likely to produce SEP events than single-band events, where M-DH-KM type II bursts have the highest proportion of SEP events (73%), and the DH IIs only have the lowest one (19%). 3) In each kind of type II radio bursts, the type IIs with SEP events usually have higher starting frequencies (lower shock forming heights), lower ending frequencies (higher ending heights) and longer durations than those with no SEP events; coronal shock waves that are easy to produce SEP events (especially large SEP events) generally begin to form at a lower height (such as < 3<i>R</i><sub>s</sub>, <i>R</i><sub>s</sub>: solar radius), and are sustained to a much larger height (such as > 30<i>R</i><sub>s</sub>). 4) There exists a strong negative correlation between the duration and the ending frequency of type II radio burst (<i>cc</i> = –0.93). The proportion of SEP events increases with the increase of the duration of type II radio burst, and decreases with the increase of the ending frequency, which largely depends on the CME speed and other properties. The results of this paper further show that the generation of SEP events is greatly related to the sub-types and characteristics of type II radio bursts. The higher the starting frequencies and the lower the ending frequencies of type II radio bursts, such as M-DH-KM type II bursts, of which the CME drives to forming shock waves at a very low height and propagates to a very large height, the longer the duration of the shock, the longer the time it takes to accelerate the particles, and the greater the probability of SEP events (especially large SEP events) is.

Insights into the recurrent energetic eruptions that drive Awu, among the deadliest volcanoes on Earth

Abstract. The little-known Awu volcano (Sangihe Islands, Indonesia) is among the deadliest, with a cumulative death toll of 11 048. In less than 4 centuries, 18 eruptions were recorded, including two VEI 4 and three VEI 3 eruptions with worldwide impacts. The regional geodynamic setting is controlled by a divergent-double-subduction collision and an arc–arc collision. In that context, the slab stalls in the mantle, undergoes an increase in temperature, and becomes prone to melting, a process that sustained the magmatic supply. Awu also has the particularity of hosting alternatively and simultaneously a lava dome and a crater lake throughout its activity. The lava dome passively erupted through the crater lake and induced strong water evaporation from the crater. A conduit plug associated with this dome emplacement subsequently channeled the gas emission to the crater wall. However, with the lava dome cooling, the high annual rainfall eventually reconstituted the crater lake and created a hazardous situation on Awu. Indeed with a new magma injection, rapid pressure buildup may pulverize the conduit plug and the lava dome, allowing lake water injection and subsequent explosive water–magma interaction. The past vigorous eruptions are likely induced by these phenomena, possible scenarios for future events.

Late Pleistocene–Holocene climatic and volcanic events in the bathyal area of the Eastern Tyrrhenian Sea and the stratigraphic signature of the 39 ka Campanian Ignimbrite eruption

Abstract A multidisciplinary study, based on integration of eco-biostratigraphy and tephrostratigraphy, was applied to the sedimentary record of core CET2, recovered in a bathyal area of the Eastern Tyrrhenian Sea, along the Campania Continental Margin. An event stratigraphy of the Late Pleistocene–Holocene succession was obtained, also through the integration of the results coming from the study of the nearby CET1 core. A very detailed integrated stratigraphic framework was reconstructed for the last 40-ka time span, basing on the planktonic foraminifera eco-biozones and correlations of tephra layers. In the time interval older than 40 ka, the relationship between climatic events and tephra layers were highlighted. Some reworked intervals were identified at different stratigraphic levels; the thickest among these was identified just below the Campanian Ignimbrite tephra and interpreted as a debris flow. This deposit is here considered as the stratigraphic signature of the volcano-tectonic event of the Campanian Ignimbrite eruption. Other mass-transport deposits were identified below tephra layers related to very energetic eruptions, thus suggesting a possible link between the huge volcanic explosive eruptions of the Campania Volcanic Zone, coeval fault activity and the occurrence of mass-transport events in the study area.

First ALMA Millimeter-wavelength Maps of Jupiter, with a Multiwavelength Study of Convection

Abstract We obtained the first maps of Jupiter at 1–3 mm wavelength with the Atacama Large Millimeter/Submillimeter Array (ALMA) on 2017 January 3–5, just days after an energetic eruption at 16.°5S jovigraphic latitude had been reported by the amateur community, and about two to three months after the detection of similarly energetic eruptions in the northern hemisphere, at 22.°2–23.°0N. Our observations, probing below the ammonia cloud deck, show that the erupting plumes in the South Equatorial Belt bring up ammonia gas from the deep atmosphere. While models of plume eruptions that are triggered at the water condensation level explain data taken at uv–visible and mid-infrared wavelengths, our ALMA observations provide a crucial, hitherto missing, link in the moist convection theory by showing that ammonia gas from the deep atmosphere is indeed brought up in these plumes. Contemporaneous Hubble Space Telescope data show that the plumes reach altitudes as high as the tropopause. We suggest that the plumes at 22.°2–23.°0N also rise up well above the ammonia cloud deck and that descending air may dry the neighboring belts even more than in quiescent times, which would explain our observations in the north.

Magnetic cage and rope as the key for solar eruptions.

Solar flares are spectacular coronal events that release large amounts of energy. They are classified as either eruptive or confined, depending on whether they are associated with a coronal mass ejection. Two types of model have been developed to identify the mechanism that triggers confined flares, although it has hitherto not been possible to decide between them because the magnetic field at the origin of the flares could not be determined with the required accuracy. In the first type of model, the triggering is related to the topological complexity of the flaring structure, which implies the presence of magnetically singular surfaces. This picture is observationally supported by the fact that radiative emission occurs near these features in many flaring regions. The second type of model attributes a key role to the formation of a twisted flux rope, which becomes unstable. Its plausibility is supported by simulations, by interpretations of some observations and by laboratory experiments. Here we report modelling of a confined event that uses the measured photospheric magnetic field as input. We first use a static model to compute the slowly evolving magnetic state of the corona before the eruption, and then use a dynamical model to determine the evolution during the eruption itself. We find that a magnetic flux rope must be present throughout the entire event to match the field measurements. This rope evolves slowly before saturating and suddenly erupting. Its energy is insufficient to break through the overlying field, whose lines form a confining cage, but its twist is large enough to trigger a kink instability, leading to the confined flare, as previously suggested. Topology is not the main cause of the flare, but it traces out the locations of the X-ray emission. We show that a weaker magnetic cage would have produced a more energetic eruption with a coronal mass ejection, associated with a predicted energy upper bound for a given region.

Ultrafast syn-eruptive degassing and ascent trigger high-energy basic eruptions

Lithium gradients in plagioclase are capable of recording extremely short-lived processes associated with gas loss from magmas prior to extrusion at the surface. We present SIMS profiles of the 7Li/30Si ion ratio in plagioclase crystals from products of the paroxysmal sequence that occurred in the period 2011–2013 at Mt. Etna (Italy) in an attempt to constrain the final ascent and degassing processes leading to these powerful eruptions involving basic magma. The observed Li concentrations reflect cycles of Li addition to the melt through gas flushing, and a syn-eruptive stage of magma degassing driven by decompression that finally produce significant Li depletion from the melt. Modeling the decreases in Li concentration in plagioclase by diffusion allowed determination of magma ascent timescales that are on the order of minutes or less. Knowledge of the storage depth beneath the volcano has led to the quantification of a mean magma ascent velocity of ~43 m/s for paroxysmal eruptions at Etna. The importance of these results relies on the application of methods, recently used exclusively for closed-system volcanoes producing violent eruptions, to open-conduit systems that have generally quiet eruptive periods of activity sometimes interrupted by sudden re-awakening and the production of anomalously energetic eruptions.

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star.

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

Using infrasound waves to monitor tropospheric weather and crater morphology changes at Volcán Tungurahua, Ecuador

We use infrasound waves generated during eruptions of Volcán Tungurahua (Ecuador) to study both, changing atmospheric conditions and volcanic source characteristics. Analyzed infrasound data were recorded for a 32-month period by a five-station network located within 6.5km from the vent. We use cross-network correlation to quantify the recurrent eruptive behavior of Tungurahua and results are corroborated by reports from the Ecuadorian monitoring agency. Cross-network lag times vary over short time periods (minutes to days) when vent location is stable and attribute these variations to changes in atmospheric structure. Assuming a fixed source location, we invert for average air temperatures and winds in Tungurahua's vicinity (<6.5km) and find evidence for diurnal and semidiurnal tropospheric tides. We also use cross-network correlation lag times to compute infrasound source positions with resolutions of ~11.6m, taking into account coarse NOAA atmospheric models for local winds and temperatures. Variable infrasound-derived source locations suggest source migration during the 32months of analyzed data. Such source position variability is expected following energetic eruptions that destructively altered the crater/vent morphology as confirmed by imagery obtained during regular overflights.

The 2015 Wolf volcano (Galápagos) eruption studied using Sentinel‐1 and ALOS‐2 data

AbstractAn energetic eruption started on 25 May 2015 from a circumferential fissure at the summit of Wolf volcano on Isabela Island, western Galápagos. Further eruptive activity within the Wolf caldera followed in mid‐June 2015. As no geodetic observations of earlier eruptions at Wolf exist, this eruption provides an opportunity to study the volcano's magmatic plumbing system for the first time. Here we use interferometric synthetic aperture radar (InSAR) data from both the Sentinel‐1A and ALOS‐2 satellites to map and analyze the surface deformation at four time periods during the activity. These data allow us to identify the two eruption phases and reveal strong coeruptive subsidence within the Wolf caldera that is superimposed on a larger volcano‐wide subsidence signal. Modeling of the surface displacements shows that two shallow magma reservoirs located under Wolf at ~1 km and ~5 km below sea level explain the subsidence and that these reservoirs appear to be hydraulically connected. We also suggest that the transition from the circumferential to the intracaldera eruption may have involved ring fault activity.