Eruptive Phase Research Articles

The pivotal role of Vulcanian activity in ending the explosive phase of rhyolitic eruptions: the case of the Big Obsidian Flow eruption (Newberry Volcano, USA)

The pivotal role of Vulcanian activity in ending the explosive phase of rhyolitic eruptions: the case of the Big Obsidian Flow eruption (Newberry Volcano, USA)

Exploring the Kinematic Structure of Mount Etna Volcano (Sicily, Italy) by Deformation Analysis and Gravity Gradient Tensors

Ground deformation monitoring of active volcanoes is used routinely to determine phases of vol‐ cano unrest and can provide insights in the evolving plumbing system of a volcano and the influence local tectonics structures have on the volcano tectonic evolution of the volcanic edifice. Volcanic deformation analysis can be performed using velocity and direction measurements of the ground surface using Global Navigation Satellite System (GNSS). In this study, we perform two‐dimen‐ sional deformation analyses of pre‐ and post‐eruptive phases with the scope of determining the strain before and after an eruptive phase at Mt. Etna Volcano (southern Italy) during 2004‐2006. In order to do so, we analyse the GNSS displacement data from Mt. Etna between 2004‐2005 and 2005‐2006 using the dedicated SSPX software. The extention, dilation and rotation maps of the study area were determined. The contraction and volumetric decrease concomitant the 2004‐2005 effusive eruptive period and extension and volumetric increase for the 2005‐2006 data series were observed. The deformation on the northeast part of Mt. Etna Volcano, which showed different characteristics with respect to its surroundings, was thought to be conditioned by the dynamic of the Pernicana fault system. Additionally, Complete Spherical Bouguer (CSB) gravity anomaly and the gravity gradient tensors were calculated giving insight on the subsurface structures of Mt. Etna Volcano and its surroundings.

Temporal shifts of the microbiome associated with antibiotic treatment of purpuric drug eruptions related to epidermal growth factor receptor inhibitors.

Epidermal growth factor receptor (EGFR) inhibitors are selective and effective treatments for cancers with relevant mutations. Purpuric drug eruptions are an uncommon but clinically significant dermatological side effect related to EGFR inhibitor use that are associated with positive bacterial cultures and responsive to antibiotic treatment. However, the longitudinal temporal shifts in the skin microbiome that occur before and after antibiotic treatment of purpuric drug eruptions remain largely unknown. To characterize temporal changes in the skin and mucosal microbiomes before and after antibiotic treatment of EGFR inhibitor-related purpuric drug eruptions. Twelve patients who experienced EGFR inhibitor-related purpuric drug eruptions were recruited from a dermato-oncology clinic in Taiwan from May 2017 to April 2018. Swabs were obtained from skin lesions and the nasal mucosa before and after antibiotic treatment of purpuric drug eruptions. After the amplification and sequencing of bacterial 16S rRNA genes, the diversity and compositions of microbiomes sampled at different time points were compared. The alpha diversity (represented by the Shannon index) of the skin microbiome increased significantly in the recovered phase of purpuric drug eruptions compared with that of the active phase. By contrast, the nasal microbiome showed no significant change in alpha diversity. The relative abundance of Staphylococcus significantly decreased in samples from skin of the recovered phase, which was confirmed by analysis of compositions of microbiomes (ANCOM) and the ALDEx2 analysis packages in R. The cutaneous microbiome of purpuric drug eruptions showed a significant increase in alpha diversity and a decrease in the relative abundance of Staphylococcus following antibiotic treatment. These findings may help guide antimicrobial therapy of this EGFR inhibitor-related condition.

Deep fluids migration and submarine emersion of the Kalang Anyar mud volcano (Java, Indonesia): A multidisciplinary study

North-east Java is part of a large sedimentary basin containing hydrocarbon provinces that feature diffuse hydrothermal systems, mud volcanoes, and degassing sites. Seismic profiles acquired to explore the basin reveal a broad distribution of palaeo- and modern piercement structures. The Watukosek fault system links the volcanic arc, to the south, with the Sidoarjo province, to the north. Several piercement structures, including the Kalang Anyar mud volcano, are hosted along this left-lateral strike-slip system that favors the migration of crustal fluids in this part of the basin. Here, we present a multidisciplinary geological, geophysical and geochemical study conducted at Kalang Anyar where dozens of seepage sites are active in the crater area and intermittently emit bursts oil, gas, mud, and water. The emitted gasses are methane-dominated with smaller amounts of heavier hydrocarbons and CO2. Unlike most mud volcanoes, at Kalang Anyar the mixed-thermogenic origin of the methane is coupled with geothermal anomalies, as indicated by helium and CO2 isotopic values (δ13CCO2 as high as −4‰) that suggest the input of mantle-derived gas. Our gas flux measurements reveal that Kalang Anyar emits about 1.62 and 5.75 t yr−1 of CO2 and CH4, respectively. The intense bubbling gives rise to a typical drumbeat seismic signal characterized by dominant frequencies around of 3–4 Hz (and up to 15 Hz). We interpret the drumbeat as fluids rising and resonating through shallow plumbing system of Kalang Anyar. Erupted clasts with different lithologies and shells are scattered across the mud volcano area, while the edges of the crater zone include cubic meter-sized carbonate-cemented blocks and ridges that contain siliciclastic sediments and abundant chemosymbiotic bivalves. Carbon isotope analyses of the carbonate cement (δ13C as low as −48.8‰) identify the latter as methanogenic chemoherms. Radiocarbon (14C) dating of bivalves cemented in the blocks indicates an age of 1890-1488 BP. These results indicate that the activity of Kalang Anyar MV dates from when the area was below sea level and that the microbially-mediated precipitation of carbonates was ongoing during subaqueous methane seepage at the crater site.To the best of our knowledge, Kalang Anyar is the first example of a mud volcano that progressed from subaqueous to subaerial conditions during marine regression, displaying evidence of former marine activity (i.e. methanogenic carbonates) and current subaerial degassing at numerous seepage sites. Potentially eruptive phases represent a clear geohazard for the numerous settlements constructed inside the mud volcano. In light of this, it may be prudent to apply stricter rules for development activities, such as housing construction permits that consider the possibility of potentially catastrophic events, and apply steps to mitigate these hazards.

Assembly and development of large active calderas hosting geothermal systems: Insights from Los Humeros volcanic complex (Mexico)

Caldera volcanoes are complex geological systems that show, during and after their formation, a wide variability in terms of eruptive styles, magmatic and geochemical evolution, and volcanic structures. Los Humeros Volcanic Complex (LHVC) is a key area where to study these factors. It is located in the easternmost sector of the Trans-Mexican Volcanic Belt and hosts an active geothermal system. LHVC exemplifies the complex nature of calderas, recording periods of alternated effusive and explosive eruptive phases, a heterogenous magmatic source, diverse basaltic to rhyolitic products, and the overlapping of caldera collapse events. This study provides an up-to-date interpretation of the caldera framework. Our work is based on a detailed analysis of literature and novel data aimed at the morpho-structural caldera configuration, and supported by geophysical modeling, and petrology of the volcanic products. The new results confirm a more complex evolution of LHVC involving geometric configurations related to multiple caldera collapse events producing both asymmetric trapdoor, and piecemeal styles. The present configuration of the caldera framework involved the initial formation (at 164 ka) of a large caldera (Los Humeros) of ca. 15–17 km diam (shorter than previously reported), which was overlapped asymmetrically by the younger (69 ka) and smaller (ca. 8.5–10 km diam) Los Potreros caldera over the west side, as a result of multiple sequential collapsing events. The final configuration of the caldera rims (scarps) was promoted by incremental growth. A post-caldera resurgence phase was induced by the injection of multiple shallow intrusions of silicic bodies, causing a more localized deformation of the caldera floor. The Holocene volcanism records the recurrent injection of compositionally distinct magma batches uprising from different depths of the LHVC transcrustal magmatic plumbing system. This latter indicates the transition from the caldera stage magmatic system dominated by a single, large, and shallow magmatic body to a more complex, polybaric post-caldera stage plumbing system, made up of a lower crust mafic reservoir feeding smaller magma batches vertically distributed in the whole crust. The integration of all the existing data constitutes the archive to better understand how large active calderas hosting exploitable geothermal systems assemble through time.

The 1257 CE cataclysmic eruption of Samalas volcano (Indonesia) revealed by indigenous written sources: Forgotten kingdoms, emergency response, and societal recovery

Historical and archaeological findings have revealed that many human civilizations have been strongly affected by natural hazards, such as volcanic eruptions. An issue that still lacks attention is the response of ancient populations following eruptions as well as their resilience strategies. Three written sources from Lombok, Indonesia, provide descriptions of the ancient landscape of Lombok and the population's response to the Samalas volcano eruption in 1257 CE. The sources depict the conditions of Lombok and the surrounding areas during the pre-, onset-, and post-eruption phases of a catastrophic volcanic eruption with a volcanic explosivity index 7. Various responses of the inhabitants to the eruption are described in the sources, such as fleeing to the hills, avoiding hazards, and escaping to neighboring villages or islands. Several geographic features and toponyms are mentioned, allowing us to reconstruct the evacuation process during the crisis period. The sources also describe recovery strategies in the post-eruption period, including governance strategies, the rebuilding of cities and villages, and agriculture. The historical record suggests that Lombok may have taken up to a century to recover from the eruption and that new kingdoms and principalities became established by the fourteenth century. Disaster management related to the eruption is described in the texts from Lombok, but not in older written sources from Indonesia.

Timing of Tectonic and Magmatic Events in the Philippine Sea Plate Since 50 Ma From High‐Resolution Magnetostratigraphy of IODP Site U1438

The Philippine Sea Plate in the West Pacific is a unique natural laboratory to study subduction dynamics and the evolution of upper plate magmatism following subduction initiation. To investigate these processes, International Ocean Discovery Program Expedition 351 recovered at Site U1438, located in a rear-arc position, a complete sedimentary sequence from recent age to the early Eocene and the top of the underlying volcanic basement. The recovered cores offered the opportunity to study for the first time and in unprecedented detail the styles, products, and timing of the volcanic events that marked the emplacement, growth, and demise of the Kyushu-Palau volcanic arc following the inception of the Izu-Bonin-Mariana subduction. Here, we report a magnetostratigraphy for Site U1438 based on ∼60,000 remanence directions isolated from 1,063 archive half core sections and 429 discrete specimens. We identified 142 magnetic reversals and correlated 115 of them with the geomagnetic polarity timescale. When combined with additional biostratigraphic and geochronological constraints, our magnetostratigraphy allowed construction of a high-resolution age model for Site U1438 and the determination of changes in sedimentation rates. We show that following subduction initiation at 52–50 Ma and the emplacement of basalts in the rear-arc at 48.7 Ma, a diffuse volcanism in the rear-arc (48.4–45.6 Ma) preceded the true emplacement of the Kyushu-Palau arc at 40.2 Ma, which then grew through four compositionally distinct eruptive phases until 28.8 Ma. Subsequent rollback of the Pacific slab triggered rifting of the arc (28.8–24.3 Ma) and ultimately back-arc spreading in the Shikoku and Parece Vela basins.

Episodic volcanic eruption and arid climate during the Triassic-Jurassic transition in the Qiangtang Basin, eastern Tethys: A possible linkage with the end-Triassic biotic crises

During the Triassic-Jurassic (Tr-J) transition, a negative basin inversion, massive volcanic eruption and biological crises occurred in the Qiangtang Basin (eastern Tethys), while the volcanic eruption phases and the paleoenvironment characteristics during this transition were paid little attention. Here we present petrology, whole-rock geochemistry and zircon U-Pb isotopes data from the continuous Triassic-Jurassic sedimentary strata in the northern Qiangtang Basin, in order to reveal the volcanic eruption episodes, paleoenvironment characteristics during this transition, and to discuss the possible linkage with the biological extinction event. Our results show that the Late Triassic volcanic event displays episodic eruption process and contains about four phases. Zircon U-Pb ages of four tuff samples from the Quemo Co south section are, from bottom to top, 220.4 ± 1.1 Ma, 210.9 ± 0.9 Ma, 208.3 ± 0.8 Ma, and 202.9 ± 1.1 Ma, respectively. Statistical analysis of the zircon ages of the Late Triassic suggests that the age of the Late Triassic magmatic event ranges from 227 Ma to 201 Ma and shows about five age peaks. The Tr-J boundary is suggested to be located between the E’erlongba and Quemo Co formations in the eastern Qiangtang Basin. Geochemical indicators such as CIAcorr, C-value, Sr/Cu, and Rb/K ratios indicate that a moderate to high chemical weathering condition, semi-arid to semi-humid climate and normal marine water condition before the Tr-J transition, and suddenly changed to be low chemical weathering, arid to extreme arid climate, and freshwater water environment during the Tr-J transition, and then rebounded to be moderate to high chemical weathering and semi-humid to humid climate after the Tr-J transition. These evidences suggest that the basin inversion, significant paleoenvironment shift and regional regression occurred nearly coincidentally during the Tr-J transition. The extreme arid climate (probably cool) and ocean acidification may play an important role in the end-Triassic mass extinction in the eastern Tethys.

Rhyolitic melt production in the midst of a continental arc flare-up—The heterogeneous Caspana ignimbrite of the Altiplano-Puna volcanic complex of the Central Andes

Abstract The ~5 km3, 4.54–4.09 Ma Caspana ignimbrite of the Altiplano-Puna volcanic complex (APVC) of the Central Andes records the eruption of an andesite and two distinct rhyolitic magmas. It provides a unique opportunity to investigate the production of silicic magmas in a continental arc flare-up, where small volumes of magma rarely survive homogenization into the regional magmatic system that is dominated by supereruptions of monotonous dacitic ignimbrites. The fall deposit and thin flow unit that record the first stage of the eruption (Phase 1) tapped a crystal-poor peraluminous rhyolite. The petrological and geochemical characteristics of Phase 1 are best explained by partial melting of or reheating and melt extraction from a granodioritic intrusion. Phase 2 of the eruption records the emplacement of a more extensive flow unit with a crystal-poor, fayalite-bearing rhyolite and a porphyritic to glomeroporphyritic andesite containing abundant plagioclase-orthopyroxene-Fe-Ti oxide (norite) glomerocrysts. The isotopic composition of Phase 2 is significantly more “crustal” than Phase 1, indicating a separate petrogenetic path. The mineral assemblage of the noritic glomerocrysts and the observed trend between andesite and Phase 2 rhyolite are reproduced by rhyolite-MELTS–based models. Pressure-temperature-water (P-T-H2O) estimates indicate that the main (Phase 2) reservoir resided between 400 and 200 MPa, with the andesite recording the deeper pressures and a temperature range of 920–1060 °C. Rhyolite phase equilibria predict an estimated temperature of ~775 °C and ~5 wt% H2O. Pressures derived from phase equilibria indicate that the rhyolite was extracted directly from the noritic cumulate at ~340 MPa and stored at slightly shallower pressures (200–300 MPa) prior to eruption. The rhyolite-MELTS models reveal that latent-heat buffering during the extraction and storage process results in a shallow liquidus during the extensive crystallization that produced a noritic cumulate in equilibrium with a rhyodacitic residual liquid. Spikes in latent heat facilitated the segregation of the residual liquid, creating the pre-eruptive compositional gap of ~16 wt% SiO2 between the andesite and the Phase 2 rhyolite. Unlike typical Altiplano-Puna volcanic complex (APVC) magmas, low fO2 conditions in the andesite promoted co-crystallization of orthopyroxene and ilmenite in lieu of clinopyroxene and magnetite. This resulted in relatively high Fe concentrations in the rhyodacite and Phase 2 rhyolite. Combined with the co-crystallization of plagioclase, this low oxidation state forced high Fe2+/Mg and Fe/Ca in the Phase 2 rhyolite, which promoted fayalite stability. The dominance of low Fe3+/FeTot and Fe-Ti oxide equilibria indicates low fO2 (ΔFMQ 0 − ΔFMQ − 1) conditions in the rhyolite were inherited from the andesite. We propose that the serendipitous location on the periphery of the regional thermal anomaly of the Altiplano-Puna magma body (APMB) permitted the small-volume magma reservoir that fed the Caspana ignimbrite eruption to retain its heterogeneous character. This resulted in the record of rhyolitic liquids with disparate origins that evaded assimilation into the large dacite supereruption-feeding APMB. As such, the Caspana ignimbrite provides a unique window into the multi scale processes that build longlived continental silicic magma systems.

Pre-eruptive excess volatiles and their relationship to effusive and explosive eruption styles in semi-plugged volcanoes

Understanding the role of various factors influencing eruption style is challenging, but it can aid in adapting different hazard mitigations and crisis responses for explosive or effusive events. Here, we focus on the role of magma storage conditions in controlling eruption styles at basaltic andesite volcanoes, and how they can be related to monitoring data. We study the cycle of explosive (1990, sub-Plinian) → effusive (2007, dome) → explosive (2014, sub-Plinian) eruptions from Kelud (Kelut) volcano, Indonesia. We conducted petrological analyses of the eruption products and phase equilibria experiments using pumice and explored a range of temperatures, pressures, oxygen fugacity, and volatile contents. We show that we can reproduce the main mineral assemblage (plagioclase ± pyroxenes ± magnetite ± amphibole ± olivine) and phenocryst content (30–50 wt%) of the magmas from the three eruptions at T = 975 ± 39°C, p = 175 ± 25 MPa, fO2 = nickel–nickel oxide buffer, and about 4–6 wt% water in the melt (ca. 3 to 5 wt% and ca. 4 to 7 wt% for the 1990 and 2014 eruptions, respectively). However, geothermobarometric results also indicate that some crystals of amphibole were sourced from higher pressures. We infer from a synthesis of our data and historical observations that the high phenocryst content of the 2007 dome (∼70 wt%) likely resulted from slow magma ascent toward the surface alongside progressive degassing and re-equilibration at a lower volatile content (∼1 wt% water in the melt). Mass balance calculations on the sulfur budget of the 1990, 2007, and 2014 magmas show that the explosive events contained an excess fluid phase at pre-eruptive conditions, and we propose that this led to their higher explosivity compared to the 2007 dome. The accumulation of excess fluids during decadal-long repose depends on how plugged the volcanic system is, or its ability to passively release magmatic fluids, prior to eruption. Such condition could be inferred from monitoring records, including changes in gravity of the plumbing system over time, and thus contribute to better anticipate eruptive style.

Satellite Detection of a Massive Phytoplankton Bloom Following the 2022 Submarine Eruption of the Hunga Tonga‐Hunga Haʻapai Volcano

AbstractThe largest submarine volcanic eruption of this century led to a dramatic phytoplankton bloom north of the island of Tongatapu, in the Kingdom of Tonga. In the absence of shipboard observations, we reconstructed the dynamics of this event by using a suite of satellite observations. Two independent bio‐optical approaches confirmed that the phytoplankton bloom was a robust observation and not an optical artifact due to volcanogenic material. Furthermore, the timing, size, and position of the phytoplankton bloom suggest that plankton growth was primarily stimulated by nutrients released from volcanic ash rather than by nutrients upwelled through submarine volcanic activity. The appearance of a large region with high chlorophyll a concentrations <48 hr after the largest eruptive phase indicates a fast ecosystem response to nutrient fertilization. However, net phytoplankton growth probably initiated before the main eruption, when weaker volcanism had already fertilized the ocean.

Hydro-Volcanism in the Longgang Volcanic Field, Northeast China: Insights from Topography, Stratigraphy, Granulometry and Microtexture of Xidadianzi Maar Volcano

Hydro-volcanism in the Longgang volcanic field (LVF) of Northeast China has produced a dozen maars with features of complex sequences. To better understand the formation mechanism of maar volcanos in the LVF, this study focuses on the Xidadianzi (XDDZ) maar volcano, located in the Jinchuan valley of the LVF. Based on detailed stratigraphy analysis, 14C geochronology, grain-size distribution, and scanning electron microscopy (SEM) analysis, the eruptive sequence of the XDDZ volcano, including the South Crater and the North Crater, was constructed. The whole sequence was formed after four eruptive phases, including a wet phreatomagmatic eruption, an explosive magmatic eruption, a dry and hot phreatomagmatic eruption, and a small explosive magmatic eruption. 14C geochronology indicates that the formation age of XDDZ is 15,900 ± 70 years, BP. Topographic and stratigraphic characteristics show that the landforms of two craters were damaged and buried because of the destruction of lava flows and agricultural modification. The NE- trending fissure in the hard rock area is thought to participate in the formation of the XDDZ maar volcano.

Seismicity during the recent activity (2009–2020) of Turrialba volcano, Costa Rica

Turrialba is a stratovolcano located at the easternmost part of the Costa Rican volcanic front. After remaining quiescent for more than a century, in 1996 it started to show signs of unrest, until a first phreatomagmatic explosion occurred on January, 2010. Since then, the activity evolved from phreatic to magmatic, in a series of distinct eruptive phases. In this paper, we investigate the seismic records that span the whole eruptive process (2010-present), in order to identify precursory signals and characterize the volcanic evolution. A long-term analysis was carried out based on the continuous records, as well as seismic catalogs (volcano-tectonic seismicity, harmonic tremor, etc.). In addition, the gradual character of the evolution of this eruption allowed for the analysis of independent precursory stages. Thus, we inspected in detail the most important of those periods, particularly, prior to the first 2010 phreatomagmatic eruption, and prior to the 2016 transition to an open vent system. Temporary tremor amplitude decreases were found to precede most of the eruptive phases. In total, 9 pre-eruptive tremor abatement periods were identified spanning several days (5–44), which often concurred with a decrease in the SO2 flux. The analysis of the volcano-tectonic seismicity highlights the migration of magma from a deep (6–10 km) reservoir beneath the neighboring Irazú volcano towards Turrialba volcano, especially between the years 2015 and 2016. This activity peaked on December 2016 when a Mw 5.5 earthquake took place between both volcanoes. Harmonic tremor episodes thrived in the later phase when the system finally opened (2017–2018). In the short-term, compounded tonal seismic signals were identified as precursor events, such as long-period events followed by harmonic tremor or by a multichromatic coda similar to tornillo-type events. The co-occurrence of tremor amplitude decreases and tonal seismic signals is interpreted to be caused by a sealing of the hydrothermal system, which blocked the circulation of fluids and permitted the resonances in the inner cavities. This process leaded to pressure accumulation and the consequent eruptions. Thus, trough a series of cycles of sealing and rupture the system of conduits gradually opened. The seismic characterization of this eruption constitutes insightful knowledge useful for monitoring and risk assessment purposes.

Reporte de un aparato network modificado

Una modificación al sistema Network se reporta en este artículo con el sólo propósito de aportar a la comunidad odontológica que maneja la ortopedia funcional, una opción más para el tratamiento de sus pacientes. El aparato tiene en la parte maxilar las características de cualquier SN, en la mandíbula se le coloca un «arco de conducción continuo» con el objetivo de mantener el estímulo de crecimiento presente en ambos maxilares, además de mantener los objetivos ya logrados. El aparato puede ser usado con excelentes resultados, sobre todo en la fase de erupción de los premolares y hasta el término del tratamiento.

Multi-parametric study of an eruptive phase comprising unrest, major explosions, crater failure, pyroclastic density currents and lava flows: Stromboli volcano, 1 December 2020–30 June 2021

Open conduit volcanoes like Stromboli can display elusive changes in activity before major eruptive events. Starting on December 2020, Stromboli volcano displayed an increasing eruptive activity, that on 19 May 2021 led to a crater-rim collapse, with pyroclastic density currents (PDCs) that spread along the barren NW flank, entered the sea and ran across it for more than 1 km. This episode was followed by lava flow output from the crater rim lasting a few hours, followed by another phase of lava flow in June 2021. These episodes are potentially very dangerous on island volcanoes since a landslide of hot material that turns into a pyroclastic density current and spreads on the sea surface can threaten mariners and coastal communities, as happened at Stromboli on 3 July and 28 August 2019. In addition, on entering the sea, if their volume is large enough, landslides may trigger tsunamis, as occurred at Stromboli on 30 December 2002. In this paper, we present an integration of multidisciplinary monitoring data, including thermal and visible camera images, ground deformation data gathered from GNSS, tilt, strainmeter and GBInSAR, seismicity, SO2 plume and CO2 ground fluxes and thermal data from the ground and satellite imagery, together with petrological analyses of the erupted products compared with samples from previous similar events. We aim at characterizing the preparatory phase of the volcano that began on December 2020 and led to the May–June 2021 eruptive activity, distinguishing this small intrusion of magma from the much greater 2019 eruptive phase, which was fed by gas-rich magma responsible for the paroxysmal explosive and effusive phases of July–August 2019. These complex eruption scenarios have important implications for hazard assessment and the lessons learned at Stromboli volcano may prove useful for other open conduit active basaltic volcanoes.

Dynamic strain anomalies detection at Stromboli before 2019 vulcanian explosions using machine learning

Identifying and characterizing the dynamics of explosive activity is impelling to build tools for hazard assessment at open-conduit volcanoes: machine learning techniques are now a feasible choice. During the summer of 2019, Stromboli experienced two paroxysmal eruptions that occurred in two different volcanic phases, which gave us the possibility to conceive and test an early-warning algorithm on a real use case: the paroxysm on July, 3 was clearly preceded by smaller and less perceptible changes in the volcano dynamics, while the second paroxysm, on August 28 concluded the eruptive phase. Among the changes observed in the weeks preceding the July paroxysm one of the most significant is represented by the shape variation of the ordinary minor explosions, filtered in the very long period (VLP 2–50 s) band, recorded by the Sacks-Evertson strainmeter installed near the village of Stromboli. Starting from these observations, the usage of two independent methods (an unsupervised machine learning strategy and a cross-correlation algorithm) to classify strain transients falling in the ultra long period (ULP 50–200 s) frequency band, allowed us to validate the robustness of the approach. This classification leads us to establish a link between VLP and ULP shape variation forms and volcanic activity, especially related to the unforeseen 3 July 2019 paroxysm. Previous warning times used to precede paroxysms at Stromboli are of a few minutes only. For paroxysmal events occurring outside any long-lasting eruption, the initial success of our approach, although applied only to the few available examples, could permit us to anticipate this time to several days by detecting medium-term strain anomalies: this could be crucial for risk mitigation by prohibiting access to the summit. Our innovative analysis of dynamic strain may be used to provide an early-warning system also on other open conduit active volcanoes.

CNES-ESA satellite contribution to the operational monitoring of volcanic activity: The 2021 Icelandic eruption of Mt. Fagradalsfjall

Within the framework of the CIEST2 (Cellule d'Intervention d'Expertise Scientifique et Technique new generation) and thanks to the support of CNES, the French space agency, the first phase of the Fagradalsfjall eruption was exceptionally well covered by high resolution optical satellite data, through daily acquisitions of Pléiades images in stereo mode. In this study, we show how Pléiades data provided real-time information useful for the operational monitoring of the ongoing eruption. An estimation of the volume of lava emitted as well as the corresponding effusion rate could be derived and delivered to the civil protection less than 6 h after the data acquisition. This information is complementary to and consistent with estimates obtained through the HOTVOLC service using SEVIRI (Spinning Enhanced Visible and Infrared Imager) sensor on-board Meteosat Second Generation (MGS) geostationary satellites, operated by the European Space Agency (ESA), characterized by a lower spatial resolution and a higher temporal one. In addition to the information provided on the lava emission, Pléiades data also helped characterize the intensity of the eruption by providing insight into the elevation and the velocity of the volcanic plume. The survey of this effusive eruption, well anticipated by a series of precursors, is a proof of concept of the efficiency of optical/thermal satellite data for volcanic crisis real-time monitoring.

New insights into carbon isotope systematics at Poás volcano, Costa Rica

In April 2017, an intense phreatomagmatic eruptive phase took place at Poás volcano in Costa Rica. This was the most significant eruptive activity at the volcano since the 1950's. Unlike previous eruptions, gas ratios were closely monitored during this event with the use of both ground-based MultiGAS and uncrewed aerial system (UAS) real-time monitoring, providing valuable insight into the nature of the eruption. This well-studied eruption presents a unique opportunity to examine hydrothermal and magmatic processes occurring at Poás during periods of unrest versus quiescent periods. Here, we present stable carbon isotopic results of volcanic CO2 at Poás spanning the pre-eruptive as well as eruptive and post-eruptive phases in 2017 through 2019. Samples were collected by a combination of direct sampling (analyzed by Isotope Ratio Mass Spectrometry [IRMS] or Cavity Ring Down Spectroscopy [CRDS]), as well as UAS and ground-based plume sampling (analyzed by CRDS). Direct samples range from −6.17 to −3.73 ‰ during 2017 to 2019. Using the Keeling approach, we calculate δ13C magmatic source values of −3.97 ± 1.94 ‰ and − 3.64 ± 0.48 ‰ using UAS sampling and ground-based sampling, respectively, for April 2019. We propose that these values for δ13C are being governed by a combination of magmatic and hydrothermal fluctuations related to sealing and unsealing of the upper magma carapace. This process results in comparatively heavy values when the system is being buffered by fluid-gas interaction as the hydrothermal system seals and expands, while lightest values are predominant during unsealed phases where degassed magma supplies the volatiles along with phreatic or phreatomagmatic activity. The significance of this work is two-fold: it demonstrates the use of a rapid volcanic gas sampling strategy applicable for monitoring at other volcanoes prone to phreatomagmatic and/or phreatic eruptions, and it provides a new conceptual model to interpret the phreatic/phreatomagmatic eruptive activity at Poás over the last 20 years.

Temporal Changes of Magmas That Caused Lava-Dome Eruptions of Haruna Volcano in the Past 45,000 Years

We have studied four lava dome eruptions which occurred in 45–10 ka in Haruna volcano. Enclave parts (SiO2 50.9–55.1 wt%) and host parts (SiO2 59.5–64.5 wt%) in lava samples are all products of magma mixing. Characteristics of felsic endmember magmas are the same among four eruptions, while those of mafic endmember magmas vary slightly in terms of bulk composition. The felsic magma had SiO2 ≥ 63 wt% and a temperature of 760°C–860°C, and contained ≥60 vol% of orthopyroxene, amphibole, plagioclase, quartz, and Fe-Ti oxides. The mafic magma had SiO2 48–51 wt% and contained 0–10 vol% of olivine. The enclave magmas resulted from higher contribution of mafic magma and thus had higher temperature than the host magmas, which led to formation of enclave upon their interaction. Similarities of endmember magmas between the four eruptions and the Futatsudake-Ikaho eruption (late 6th–beginning of 7th century) suggest structure of magma plumbing system and eruption triggering process have been basically unchanged in past 45,000 years. The felsic magmas were commonly mush-like and had high viscosity. Therefore, generation of low-viscosity magma through magma mixing, and vent-opening by the low-viscosity magma are mandatory for eruption to initiate. Unlike the Futatsudake-Ikaho eruption, the older four eruptions did not proceed to eruptive phase where felsic magma erupts without mixing and explosively. The absence of quartz only in felsic magma of Futatsudake-Ikaho eruption is consistent with its less-evolved bulk composition and slightly higher temperature than those of older four eruptions.

Curie Temperatures and Emplacement Conditions of Pyroclastic Deposits From Popocatépetl Volcano, Mexico

AbstractMost pyroclastic deposits of Popocatépetl volcano were emplaced at high temperatures and have similar mafic to more evolved compositions, suggesting a long‐lived, interconnected magma environment. We performed a magnetic and microscopic study on different eruptive sequences <14 ky in age and found that temperature and field dependence of magnetic susceptibility are suited to separate eruption phases. We observed homogeneous titanomagnetite with Curie temperatures (TC) of 50–200°C and 200–400°C, together with different amounts of oxy‐exsolved titanomagnetite with TC ∼ 570°C. Some block‐and‐ash flow deposits show remarkably irreversible TC in heating and cooling branches with a positive ΔTC (TC heating–TC cooling) of up to 130°C in the center. The central part of this sequence is characterized by decreasing magnetic susceptibility and low field dependence of magnetic susceptibility (<10%), which is atypical for ulvöspinel‐rich titanomagnetite. The nonreversibility of heating and cooling runs measured with rates of around 10 K/min is probably related to vacancy‐enhanced nanoscale chemical clustering, which seems to occur preferentially during rapid quenching, possibly combined with subtle maghemitization. In contrast, pumice layers have the highest field dependence (∼20%) and contain Ti‐rich and intermediate titanomagnetite with TC < 100 and ∼300°C, which are in line with mafic and more evolved magma composition. In intermediate phases, irreversibility of TC is more common but with a relatively low ΔTC of ±20°C. We suggest that magneto‐mineralogy in pyroclastic density currents is complex but offers a complementary tool to the paleomagnetic directional analysis for emplacement temperature and contribute information on the volcanic material history and their emplacement conditions.