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Active volcanoes often discharge hot (T ≫ 100 °C) magmatic gases whose original composition has been modified through partial interaction with an externally fed hydrothermal system. The study of methane (CH 4) in these volcanic discharges may provide useful information on the interplay between deep magmatic gases and shallow circulation of hydrothermal fluids. However, the origin of CH 4 in high-temperature volcanic gases and the factors exerting control on its abundance and stable isotope composition are still largely unknown. Here, we present the abundances and stable isotopic composition of CH 4 in hot (99–387 °C) volcanic gases from the La Fossa volcanic crater of Vulcano Island (Southern Italy). Our investigation revealed low (<1.5 μmol/mol) CH 4 concentrations and an extraordinarily large variability in CH 4 stable isotopic composition, with δ13C and δ2H values being positively correlated and varying from −35 to −9.2 ‰ and −670 to −102 ‰, respectively. Notably, CH 4 isotopes measured at Vulcano almost encompasses the global-scale variability observed in natural fluids, with δ2H values ≤ −500 ‰ being the first ever reported in nature. Gases showing extremely negative δ13C-CH 4 and δ2H-CH 4 values systematically display higher CH 4 abundances. We propose two possible scenarios in order to explain the observed huge variation in δ13C and δ2H: (1) mixing of 13C- and 2H-depleted CH 4 with 13C- and 2H-enriched CH 4 of thermogenic origin formed under hydrothermal conditions; (2) post-genetic removal and isotopic alteration of 13C- and 2H-depleted CH 4 occurring during the ascent of volcanic gases. Comparing our dataset with available isotopic data from naturally occurring and artificially produced CH 4 , a thermogenic origin for the isotopically light CH 4 seems unlikely. We postulate that the 13C- and 2H-depleted CH 4 may have formed via kinetically-controlled abiotic synthesis through CO (or CO 2) hydrogenation reactions in the hot ascending gas phase, possibly at temperatures intermediate between those typical of magmatic and hydrothermal conditions. Further investigations of methane in high-temperature volcanic gases are necessary to test this hypothesis. [ABSTRACT FROM AUTHOR]

The Sheveluch volcano is the most active volcano in Kamchatka. The paroxysmal explosive eruption of the volcano that destroyed the lava dome in the volcanic crater continued on April 10–13, 2023. According to various satellite data, the height of the separate eruptive clouds probably exceeded 15 km above sea level. A powerful cyclone, which dominated the entire Kamchatka Peninsula, pulled the eruptive cloud to the west, turned it to the south, stretched it to the north, and directed it to the east from the volcano. The dynamics of the development of ash and aerosol clouds of this eruption is reflected in the animations made from a series of Himawari-9 satellite images in the VolSatView IS from 08:00 UTC on April 10 to 07:00 UTC on April 14 (http://d33.infospace.ru/jr%5fd33/materials/2023v20n2/283-291/1683110898.webm) and of the Arctica-M1 satellite from 16:00 to 21:30 UTC on April 10 (http://d33.infospace.ru/jr%5fd33/materials/2023v20n2/283-291/1683821166.webm). It was noted that the eruptive column was not vertical: for example, at the initial moment of the eruption on April 10 at 13:20 UTC, it deviated to the north–northeast; on April 11, at 12:00 UTC to the northwest; and, on April 12, at 7:00 UTC to the southwest. During the paroxysmal eruption, sulfur dioxide continuously entered the atmosphere, the maximum amount of which was released on April 10–11, as a result of the explosive destruction of the lava dome of the Sheveluch volcano. Ash clouds along with aerosol clouds on April 10–13 were stretched into a strip more than 3500 km long from west to northeast. On April 21–22, the Sheveluch aerosol cloud was observed in the region of the Scandinavian Peninsula. The total area of the territory of Kamchatka and the Pacific Ocean where ash and aerosol plumes and clouds were observed during the April 10–13 eruption was about 3 280 000 km2. The paroxysmal eruption of Sheveluch volcano belongs to the sub-Plinian type because it is characterized by a large height of the eruptive cloud and a long event duration. For this eruption, the Volcanic Explosivity Index is estimated to be 3–4. A detailed description of the paroxysmal explosive eruption of the Sheveluch volcano and the spread of the eruptive cloud was performed based on data from various satellite systems (Himawari-9, NOAA-18/19, GOES-18, Terra, Aqua, JPSS-1, Suomi NPP, Arctica-M1, etc.) in the information system "Remote Monitoring of Kamchatka and Kuril Islands Volcanic Activity" (VolSatView, http://kamchatka.volcanoes.smislab.ru). [ABSTRACT FROM AUTHOR]

This work reports on data on a moderate effusive-explosive eruption of a summit crater of Alaid volcano (Atlasova Island, Northern Kuril Islands) observed from September 10 to December 1, 2022. Based on satellite and visual data, it was determined that the strombolian-vulcanian activity resulted in two lava flows, 2.6- and 1-km long, that outflowed onto the southern slope of the volcano and at least 16 emissions occurred to heights of 2.5 to 6 km a.s.l. The ash plumes spread out mainly in the southeast and east-southeast directions with their maximum length reaching 300–530 km. The eruption posed a danger to local airlines. The lava outflow provoked the formation of lahars that descended along the southern slope of the volcano and reached the island coast. The alluvial fan formed from mudflow masses partially deposited beyond the coastline, causing accretion of the island land. [ABSTRACT FROM AUTHOR]

Stromboli is an open-conduit active volcano located in the southern Tyrrhenian Sea and is the easternmost island of the Aeolian Archipelago. It is known as "the lighthouse of the Mediterranean" for its continuous and mild Strombolian-type explosive activity, occurring at the summit craters. Sometimes the volcano undergoes more intense explosions, called "major explosions" if they affect just the summit above 500 m a.s.l. or "paroxysms" if the whole island is threatened. Effusive eruptions are less frequent, normally occurring every 3–5 years, and may be accompanied or preceded by landslides, crater collapses and tsunamis. Given the small size of the island (maximum diameter of 5 km, NE–SW) and the consequent proximity of the inhabited areas to the active craters (maximum distance 2.5 km), it is of paramount importance to use all available information to forecast the volcano's eruptive activity. The availability of a detailed record of the volcano's eruptive activity spanning some centuries has prompted evaluations on its possible short-term evolution. The aim of this paper is to present some statistical insights on the eruptive activity at Stromboli using a catalogue dating back to 1879 and reviewed for the events during the last two decades. Our results confirm the recent trend of a significant increase in major explosions, small lava flows and summit crater collapses at the volcano, and might help monitoring research institutions and stakeholders to evaluate volcanic hazards from eruptive activity at this and possibly other open-vent active basaltic volcanoes. [ABSTRACT FROM AUTHOR]

Volcano crater lakes, while picturesque, can sometimes mask the occurrence of small eruptions or hydrothermal fluid release events. However, these seemingly hidden events hold a wealth of valuable information about the underlying volcanic conduit and may pose risks to those near the volcano's summit. This study presents a novel method for identifying these hard‐to‐detect fluid release events by examining seismic data from Ruapehu volcano in New Zealand. We undertake a multi‐timescale template‐matching analysis that uses a newly discovered seismic eruption precursor, to identify patterns related to the rapid consolidation of hydrothermal seals, pressurization processes, and the subsequent release of hydrothermal fluids. As a result, we identified a potential instance of sudden fluid‐release events that were previously unnoticed due to the presence of the crater lake. Our findings support a conceptual model of cyclic pressure variation within the conduit beneath an active crater lake. This model involves the formation and disruption of seals, followed by depressurization through hydrothermal fluid release events. Fluid discharge recession recorded as seismic amplitude decay, provides information about the properties of the reservoir, conduit, and the fluid being discharged. We also applied this technique to Kawah‐Ijen (Indonesia) and Copahue (Chile‐Argentina), identifying multiple potential events at these volcanoes. These findings enhance our understanding of the conditions leading to explosive eruptions, including those that could breach the crater lake. Plain Language Summary: We analyzed seismic data from Ruapehu volcano (New Zealand) to improve volcanic event catalogs by locating signatures of rapid hydrothermal seal formation and failure. Events are detected temporally within the seismic record using an empirical model of sealing/pressurization/eruption proposed for Whakaari volcano in New Zealand. The approach allows us to identify fluid release events that might have been obscured by Ruapehu's crater lake or have been too small to be noticed by standard monitoring techniques. Our analysis has revealed several fluid release episodes, including reported eruptions, where a peak in displacement seismic amplitude ratio is followed by a sharp increase in real‐time seismic amplitude measurement and an exponential decay in the hours and days following the events. We model this decay using a linear dependence on the degassing rate, and exponential relaxation from a discharging linear reservoir. These findings can help us conceptualize the conditions leading to explosive, potentially lake breaching eruptions. Key Points: Volcano crater lakes can obscure volcanic fluid release eventsThrough volcano seismic data in a template‐matching approach, we identified short‐term sealing, pressurization, and fluid‐release pulsesWe identified several fluid‐released events at Ruapehu (New Zealand), Copahue (Chile/Argentina), and Kawah Ijen (Indonesia) volcanoes [ABSTRACT FROM AUTHOR]

Volcanic glow, which is often observed at active craters during nighttime, contains information on high-temperature zones deep in the crater that are hidden from view. We analyzed 90 eruption videos capturing volcanic glow before the onset of Vulcanian eruptions at the Showa crater of Sakurajima volcano (Japan), and found that they show clear temporal changes. The red (R)-value and the green-to-red ratio (GR ratio) are used to track glow intensity and temperature change, respectively. We found two types of temporal change in glow intensity: a short-term change approximately 1 s before the onset of explosions, and a long-term change 3 to 330 s before an explosion. Short-term changes were observed for 28 of 90 eruptions, and coincided with an increase in the GR ratio and with a modest precursory infrasound pressure increase. Since an increasing GR ratio means a temperature increase, we consider that the change was associated with the opening of tensile cracks on the crater floor before an explosion. However, the other 62 eruptions did not show short-term changes, suggesting that the opening of cracks is sporadic. Long-term changes were observed for 73 of 90 eruptions, the GR ratio did not exhibit a significant increase. We suggest that long-term changes are caused by gradual gas leakage, which precedes initiation of Vulcanian eruptions. We hypothesize that the long-term gas leakage causes gradual decompression of the conduit, which induces supersaturation of volatile-rich magma beneath the lava plug causing explosive expansion, thereby triggering an eruption. [ABSTRACT FROM AUTHOR]

The present work aims to characterize the ephemeral mineral assemblage related to the fumarolic fields of the Tajogaite volcano, formed in 2021 in La Palma Island (Canary Islands, Spain). A set of 73 samples was obtained after two sampling campaigns in different fumarole sectors of the studied area. Mineralization related to these fumaroles formed efflorescent patches located at variable distance from the main volcanic craters. Distal patches are predominantly whitish, while in the vicinities they typically show yellowish to orange colours. Field observations also revealed that fumaroles usually occur in elevated topographic areas as well as over fractured and porous volcanic pyroclastic materials. The mineralogical and textural characterisation of the Tajogaite fumaroles unfolds a complex mineral assemblage, comprising cryptocrystalline phases related to low (< 200 °C) and medium temperature (200–400 °C) conditions. In Tajogaite, we propose a classification of three different fumarolic mineralization types: (1) fluorides and chlorides located in proximal fumarolic areas (~ 300–180 °C); (2) native sulphur associated with gypsum, mascagnite and salammoniac (~ 120–100 °C) and (3) sulphates and alkaline carbonates typically occurred in distal fumarolic areas (< 100 °C). Finally, we present a schematic model of the formation of Tajogaite fumarolic mineralization and their compositional evolution developed during the cooling of the volcanic system. [ABSTRACT FROM AUTHOR]

Spatial approaches, based on the deformation measurement of volcanic domes and crater rims, is key in evaluating the activity of a volcano, such as Merapi Volcano, where associated disaster risk regularly takes lives. Within this framework, this study aims to detect localized topographic change in the summit area that has occurred concomitantly with the dome growth and explosion reported. The methodology was focused on two sets of data, one LiDAR-based dataset from 2012 and one UAV dataset from 2014. The results show that during the period 2012–2014, the crater walls were 100–120 m above the crater floor at its maximum (from the north to the east–southeast sector), while the west and north sectors present a topographic range of 40–80 m. During the period 2012–2014, the evolution of the crater rim around the dome was generally stable (no large collapse). The opening of a new vent on the surface of the dome has displaced an equivalent volume of 2.04 × 104 m3, corresponding to a maximum −9 m (+/−0.9 m) vertically. The exploded material has partly fallen within the crater, increasing the accumulated loose material while leaving "hollows" where the vents are located, although the potential presence of debris inside these vents made it difficult to determine the exact size of these openings. Despite a measure of the error from the two DEMs, adding a previously published dataset shows further discrepancies, suggesting that there is also a technical need to develop point-cloud technologies for active volcanic craters. [ABSTRACT FROM AUTHOR]

Active Haleakala volcano on the island of Maui is the second largest volcano in the Hawaiian Island chain. Prominently incised in Haleakala's slopes are four large (great) valleys. Haleakala Crater, a prominent summit depression, formed by coalescence of two of the great valleys. The great valleys and summit crater have long been attributed solely to fluvial erosion, but two significant enigmas exist in the theory. First, the great valleys of upper Keanae/Koolau Gap, Haleakala Crater, and Kaupo Gap are located in areas of relatively low annual rainfall. Second, the axes of some valley segments are oblique for long distances across the volcanic slopes. This study tested the prevailing erosional theory by reconstructing the volcano's topography just prior to valley incision. The reconstruction produces a belt along the volcano's east rift zone with a morphology that is inconsistent with volcanic aggradation alone, but it is readily explained if it is assumed the surface was displaced along scarps formed by a giant landslide on Haleakala's northeastern flank. Although the landslide head location is well defined, topographic evidence is lacking for the toe and lateral margins. Consequently, the slope failure is interpreted as a sackung-style landslide with a zone of deep-seated distributed shear and broad surface warping downslope of the failure head. Maximum downslope displacement was likely in the range of 400-800 m. Capture of runoff at the headscarps formed atypically large streams that carved Haleakala's great valleys and explains their existence in low-rainfall areas and their slopeoblique orientations. Sackung-style landslides may be more prevalent on Hawaiian volcanoes than previously recognized. [ABSTRACT FROM AUTHOR]

Ash deposits from short-lived vulcanian eruptions are ubiquitous at active volcanoes and are important for understanding the development of a volcanic edifice. In this study, we investigated the sedimentary system of ash deposits produced by long-term vulcanian activity from Showa crater of Sakurajima volcano, Japan, based on the grain size characteristics of ash from individual eruptions. We collected falling ash samples from 20 individual vulcanian eruptions between March 3 and 11, 2010. The grain size distributions of the ash samples were unimodal, bimodal, and trimodal, depending on the event. The median particle size of the main subpopulation decreases with distance from vent. The low standard deviation of the grain size of the main subpopulation implies deposition from transient volcanic plumes. For the finest subpopulation in the polymodal samples, the median grain size is very fine ash (<30 μm), indicating that this subpopulation was derived from ash aggregates. Overall, the sedimentary system of the long-term vulcanian activity at Sakurajima volcano is explained by accumulation of ash particles from repeated transient plumes and ash aggregation, and the latter controlled the behavior of the very fine ash. [ABSTRACT FROM AUTHOR]

Active volcanic craters are highly dynamic geological features that undergo morphological changes on a broad range of spatial and temporal scales. Such changes have implications for the stability of the edifice, the eruptive style and the associated hazards. However, monitoring the morphological evolution of active craters at high spatial resolution and over long periods of time can be challenging, especially at remote volcanoes. In this study, we demonstrate the potential of Structure-from-Motion Multi-View Stereo photogrammetry technique based on crowd-sourced data, applied to the case study of Oldoinyo Lengai (OL) volcano in northern Tanzania. Following the 2007–08 paroxysm, OL volcano resumed its characteristic effusive activity and started to fill in with lava the newly-formed 300 m wide and 130 m deep pit crater. Monitoring capability is limited at OL due to its location in a remote non-urbanized area, therefore, the eruptive and morphological evolution is poorly constrained (e.g., lava emission rates, number of vents, location of unstable areas), with hazard implications for tourists visiting the summit area. Here we use crowd-sourced images, including Unoccupied Aircraft System (UAS) images, ground-based videos and pictures collected between October 2014 and June 2022, to reconstruct high-resolution topographic time-series of OL's summit crater. With these data, we have generated 7 Digital Elevation Models (DEMs) of OL's pit crater spanning the past 8 years, and estimated the emitted volume of lava and the corresponding time averaged discharge rates (TADR). From this we characterize the geomorphological evolution of OL pit crater since the 2007–08 paroxysm and perform a preliminary hazard assessment of the crater area. InSAR COSMO-SkyMed and Sentinel-1 data covering the periods 2013–2014 and 2018–2019 were also used in this study to complement our observations. Our results indicate that the main location of lava emission within the crater floor has repeatedly shifted over the years and that the 2008 cone has experienced a subsidence over time. OL's TADR has increased over the years, reaching values one order of magnitude higher in the period 2021–2022 compared to 2014–2018. Assuming similar TADR in the coming years, the crater could be filled in by lava within the next decade, leading to new lava overflows on the flanks of the volcano. • Photogrammetric time-series provide a 3D reconstruction of Oldoinyo Lengai crater. • Volumetric changes measured at Oldoinyo Lengai. • Oldoinyo Lengai's natrocarbonatite emission rate has increased in the past 8 years. • Oldoinyo Lengai's pit crater could be completely filled within the next decade. [ABSTRACT FROM AUTHOR]

Sakurajima Muography Observatory captured the formation of a volcanic plug beneath the Showa crater with a spatial resolution of ∼60 m in accordance with the end of the eruption episode of Showa crater and the reactivation of Minamidake crater. The increase of average density was observed with above 3 σ standard deviation for both above the floor of Minamidake crater and beneath the floor of Showa crater, respectively, being interpreted as volcanic ejecta deposition and the formation of a volcanic plug laterally extended within a few hundreds of meters. Plain Language Summary: Muography is an imaging technique that provides information about the amount of material across kilometer‐thick geological structures by the measurement of the yield of cosmic rays, similarly to X‐raying of human body. We applied muography to capture two muon images of Minamidake and Showa craters of Sakurajima volcano before and after the shift of eruption activities occurred between the two craters at the end of 2017. The comparison of the images revealed the presence of increased material across the activated Minamidake and beneath the deactivated Showa crater. Muography detected the formation of a magma plug in the conduit of Showa crater that was not detected earlier by any other geophysical technique. These results demonstrate the applicability of cosmic muon imaging for monitoring of magma movements inside active volcanoes. Key Points: Two muographic images were taken across the erupting Sakurajima volcano with a spatial resolution of 60 mIncreased average densities were observed beneath the deactivated crater after the shift of eruption sequenceMuography data suggest that uprising magma formed a plug in the conduit of Showa crater [ABSTRACT FROM AUTHOR]

Lunar volcanism play an important role on studying the thermal and compositional evolution of the Moon. However, the studies on the relationships among composition, location and age of Lunar volcanos are still limit. The high-quality and multi-source remote sensing data offer the opportunity to obtain significant features of the Lunar volcanism and the evolution of the Moon. Specifically, the high-quality gravitational features of volcanic landforms of the Moon are observed by the Gravity Recovery and Interior Laboratory. Besides, the lunar reconnaissance orbiter camera provides detail morphologic features of Lunar volcanos based on high-resolution optical images. This paper aims to find the characteristic of lunar volcanos by observing the gravitational and morphologic features in the center of craters. The final results show that most of the craters with central peaks have gravity anomalies except the Mendeleev crater (5.7 °N and 140.9 °E) whose central area contains significant gravity anomalies but no central peaks. The area of gravity anomaly may indicate heat source under the ground. [ABSTRACT FROM AUTHOR]

Volcanic activity excites low frequency acoustic waves, termed infrasound, in the atmosphere. Infrasound observations can be used to provide constraints on eruption properties, such as crater geometry and volume flux. At open-vent volcanoes, such as Erebus (Antarctica) and Villarrica (Chile), the infrasound signal is modulated by the crater properties. Eruptive activity at the bottom of the crater, such as unsteady degassing or explosions, can excite the air mass within the crater into resonance leading to infrasound generation with signals possessing clear spectral peaks, termed harmonics. Therefore, the effect of the crater on the infrasound signal, or crater acoustic response, must be accounted for when inverting harmonic infrasound observations for eruption properties at open-vent volcanoes. Here we develop a linearized model of quasi-one-dimensional (1D) wave propagation inside volcanic crater coupled with 3D axisymmetric radiation into the atmosphere from the crater, with waves generated by a volumetric flow rate source at the bottom of the crater. We perform simulations for a range of volcanic crater geometries, temperature profiles, gas compositions, and source descriptions to explore the influence of these properties on the infrasound signal. The observed infrasound signal depends on the flow rate source-time function, but interference of up- and down-going waves within the crater selectively amplifies the signal at the resonant frequencies of the crater. The crater resonance model presented here is verified by comparison with an established three-dimensional (3D) infrasound code and is shown to be appropriate for realistic crater geometries when the crater radius is less than approximately one quarter of the acoustic wavelength. The model presented here is more computationally efficient and can be used to invert infrasound observations for a range of properties, such as crater geometry or volumetric flow rate associated with eruptions. We demonstrate the utility of our efficient modeling framework by inverting harmonic infrasound observations for the crater geometry and position of the lava lake at Villarrica volcano. This technique may be used at other open-vent volcanoes to constrain dynamic crater geometry and provide insights about lava lake motions and infrasound producing eruption sources. • Harmonic infrasound from open-vent volcanoes is explained by resonance of crater. • We develop an efficient quasi-1D crater model that describes crater acoustic resonance. • Can invert harmonic infrasound signals for volcano properties, such as crater geometry [ABSTRACT FROM AUTHOR]

During July 2016, the first integrated heat flow, CO2, and 3He emission survey was conducted across 0.5 km2 of the summit cone and crater of Teide volcano, Tenerife, Canary Islands, Spain. The thermal energy released from Teide summit cone by diffuse degassing was 2.2 MW, and the heat flux calculated through Dawson's method was 8.1 MW, difference due to the comparison of purely convective areas as the crater with diffusive areas as the flanks of the volcano. Diffuse CO2 output was 211±20 t d-1, and 3He emission was estimated to be within a range between 0.35 and 0.89 mol y-1. The obtained values of diffuse degassing and heat fluxes are close to others obtained for similar volcanic areas. The calculation of 3He/heat ratio for the first time in this volcanic system supports the presence of an important mantle source for the degassing of Teide volcano. [ABSTRACT FROM AUTHOR]

Abstract Monogenetic volcanoes are widespread in the East African Rift. Their morphologies are diverse with positive (scoria and tuff cones) and negative reliefs (tuff rings and maars). The Manyara Rift (Tanzania) and Albertine Rift (Uganda) are characterised by a singular abundance of negative volcanic reliefs with about 300 and 350 maars and tuff rings, respectively, covering a surface of about ∼3000 km2 in each country. Such high density of explosive craters is not observed elsewhere in the East African Rift. We perform spatial distribution and alignment analyses using two different approaches (Two Point Analysis and Point Alignments) to study the link between the distribution of the monogenetic volcanic vents, the rift structures, and the stress field. Both methods give similar results although the Point Alignments perform better for large radius of investigations. Volcanic alignments in the Manyara rift suggest a dominant control of the old basement and rift structures on dyke emplacement and distribution of volcanic vents, under an oblique rifting. However, data further suggest that this influence is reducing, and the rift is entering a more mature phase with orthogonal rifting. On the other hand, volcanic alignments in the Albertine rift imply a dominant control of the stress field on dyke emplacement and on the distribution of volcanic vents under orthogonal rifting. This suggests that the Albertine rift is a mature rift since at least the past 50 000 yrs. We further tested the influence of rift structures and stress field on maar and tuff ring morphologies. Most of the craters are near-circular, or a least not strongly elongated, and show minor complexities in shape which we attribute to lateral migration of explosions. Few maars and tuff rings in Manyara show that lateral migration have followed pre-existing faults. In general, we advise not to fit an ellipse to individual maars and tuff rings to assess the orientation of the feeder intrusions. Highlights • The Manyara Rift (Tanzania) and Albertine Rift (Uganda) are characterised by a singular abundance of maars and tuff rings. • Volcanic alignments in Manyara suggest a dominant control of the old basement and rift structures on dyke emplacement and distribution of volcanic vents, under an oblique rifting. • The influence of the old basement in Manyara is reducing, and the rift is entering a more mature phase with orthogonal rifting. • Volcanic alignments in Albertine imply a dominant control of the stress field on dyke emplacement and on the distribution of volcanic vents under orthogonal rifting. [ABSTRACT FROM AUTHOR]

• First detailed mapping of the hidden active crater of Lascar volcano by UAS. • Topographical changes of the active crater quantified by DEM of difference analysis. • Thermal orthomosaic helps to determine thermal anomalies and fumaroles. • Nested ring structures have been identified on the crater floor. • Ring structures imply a narrow conduit top less than 40 m in diameter. Details of ongoing changes in geomorphology and structure of nested volcanic craters are lacking due to the difficult and hazardous access. In this study, we present a novel unoccupied aircraft system (UAS) dataset collected at Lascar, northern Chile, one of the most active volcanoes in the Central Volcanic Zone of the Andes. Lascar features nested craters, the deepest crater of which has experienced repeated lava dome emplacement and numerous violent explosions in recent decades. We performed UAS surveys in 2017 and 2020 to collect the optical and thermal imaging data of the active crater. By applying the Structure-from-Motion (SfM) method, we obtained centimeter-scale optical and thermal orthomosaics as well as digital terrain models. We quantify the spatial and volumetric changes that occurred during the observation period. The results show material removal from the crater wall and a significant accumulation of volcanic material on the crater floor. The thermal orthomosaic helps identify thermal anomalies and the spatial distribution of fumaroles. The highest thermal anomaly was found on the crater floor and delimited by ring structures. Both the optical orthomosaics and DEMs from 2017 and 2020 showed a consistent ring structure, which remained stable following two explosive events. Possible localized subsidence was observed within the ring structure. Consequently, we hypothesize that the ring structure represents the surface expression of underlying concentric fracture systems and constrains a narrow conduit top. Our results provide important insights into an active crater's morphological, structural, and thermal features, with implications for understanding the formation mechanism and evolution of volcanic craters. [ABSTRACT FROM AUTHOR]

A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (>3000 m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation. Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive database of intact maar morphometry is also beneficial for the hunt for maar-diatremes on other planets. [ABSTRACT FROM AUTHOR]

Mafic to intermediate shield volcanoes with multi-cubic-kilometer eruptive volumes are common in the Cascades Volcanic Arc, but little is known about their eruptive histories as either singular or sustained episodes, or the total time required for their construction. Paleomagnetic data were collected from the lava flows of Ash Creek Butte (17 sites) and Crater Mountain (14 sites) in northern California; both volcanoes are large shields with total volumes of ∼11 km3 each. Tightly clustered paleomagnetic results at both volcanoes, when coupled with analysis of geomagnetic secular variation, suggest that each edifice was built in only a few centuries, possibly in as little time as 50–90 years, indicating sub-century to century scale eruptive durations for two sizeable regional shield volcanoes within the Cascades Arc. These rapidly built shield volcanoes are substantially larger than typically defined monogenetic volcanoes, yet both are wholly formed within a single 'episode' at the limits of temporal resolution. Paleomagnetic methods provide a high-resolution tool that can be applied to understanding the tempo of regional volcanism in arcs. • Two 11 km3 shield volcanoes in northern California were erupted in under a few centuries • Paleomagnetic sampling and secular variation analysis tightly defines volcanic episodes • Effusion rate calculations support a brief volcanic episode at Crater Mountain [ABSTRACT FROM AUTHOR]

On 5 July 2014, an eruptive fissure opened on the eastern flank of Etna volcano (Italy) at ~3.000 m a.s.l. Strombolian activity and lava effusion occurred simultaneously at two neighbouring vents. In the following weeks, eruptive activity led to the build-up of two cones, tens of meters high, here named Crater N and Crater S. To characterize the short-term (days) dynamics of this multi-vent system, we performed a multi-parametric investigation by means of a dense instrumental network. The experimental setup, deployed on July 15-16th at ca. 300 m from the eruption site, comprised two broadband seismometers and three microphones as well as high speed video and thermal cameras. Thermal analyses enabled us to characterize the style of eruptive activity at each vent. In particular, explosive activity at Crater N featured higher thermal amplitudes and a lower explosion frequency than at Crater S. Several episodes of switching between puffing and Strombolian activity were noted at Crater S through both visual observation and thermal data; oppositely, Crater N exhibited a quasi-periodic activity. The quantification of the eruptive style of each vent enabled us to infer the geometry of the eruptive system: a branched conduit, prone to rapid changes of gas flux accommodated at the most inclined conduit (i.e. Crater S). Accordingly, we were able to correctly interpret acoustic data and thereby extend the characterization of this two-vent system. [ABSTRACT FROM AUTHOR]

This paper presents all direct precise leveling measurements of elevations between permanent benchmarks that stand along two lines in the Avacha Geodynamic Test Site from 1962 to 1995. These data are of special importance for future researchers. We show that the vertical strain increases as one approaches the volcanic edifice, while at the same time being oscillatory in character. The fluctuations of benchmark elevations at distances of 6-7 km from the volcano show amplitudes of -4.2 cm to +3.0 cm relative to a benchmark that is 17.4 km distant from the crater. It is hypothesized that the oscillatory character of vertical movements around the volcano is due to the varying influence of crustal stresses on the magma chamber beneath the volcano and these stresses are subject to variation in the subduction zone of the Pacific and Eurasian plates. Under these conditions the magma chamber 'operates' as a natural giant strainmeter. The leveling observations revealed subsidence on the shore of Avacha Bay in the seaport area, probably by as much as over 13 cm at the time of the large earthquake that occurred in November 1971 and whose epicenter was in the Avacha Bay at a distance of approximately 70 km from the city. [ABSTRACT FROM AUTHOR]

There are many buried craters on Mars invisible in imaging or topographic data; however, the residual gravity anomaly separated from the Mars Bouguer gravity anomaly by minimum curvature separation method can reveal these buried craters. In our research, gravity separation results exposed 39 residual gravity anomaly highs (RGAHs), which may represent deeply buried impact craters with 300–500 ​km diameter. The RGAHs are widely distributed across the surface of Mars, but are especially concentrated in volcanic areas like Tharsis and Elysium, which indicates that there might be more craters buried in these regions. Older craters in volcanic regions were likely buried by subsequent volcanism coming from surrounding volcanoes, so the retention age of craters in all areas where RGAHs are located will be older than reported in the existing research based on topographic data alone. This study will help improve the chronological model of Mars. • The impact craters of Mars with diameter of 300–500 km appear central positive residual gravity anomalies. • The gravity separation results exposed 39 anomaly highs, that is inferred to be buried impact craters. • The most RGAHs are concentrated in volcanic areas just like Tharsis and Elysium. [ABSTRACT FROM AUTHOR]

Shallow, implosive non-double-couple (NDC) earthquakes have been detected beneath Unzen Volcano, Japan, by a routinely operated seismometer network. Here, we analyze the waveforms from 14 temporary seismic stations around Mt. Fugen (Fugendake) and Heisei-Shinzan Lava Dome, which formed during the 1990–1995 eruptions, to further investigate this shallow seismicity. We also estimate the subsurface electrical resistivity structure using broadband magnetotelluric observations and investigate its relationship to the shallow seismicity. We find that (1) implosive NDC earthquakes occur at the craters that were active during the 1990–1991 eruptions, which are currently buried by the approximately 200-m-thick Heisei-Shinzan Lava Dome; (2) the detected NDC earthquakes generally possess downward P-wave arrivals, although upward P-wave arrivals are observed at a few seismic stations; (3) the tensile axes of the NDC earthquakes show various slip directions; (4) repeated NDC earthquakes are in some cases detected within 20 s of the initial event; and (5) a high-resistivity zone exists beneath the NDC earthquakes. We conclude that the implosive NDC earthquakes were generated by the collapse of small, randomly oriented, vapor-filled voids at the two buried craters, with active volcanic conduits still present beneath these craters. The shallow DC earthquakes consist of two clusters that are located 2–3 km below the NDC earthquakes. The focal mechanisms of the shallower cluster (approximately 2 km depth) indicate various fault mechanism, whereas those of the deeper cluster (approximately 3 km depth) indicate strike-slip faulting. The top of the shallower cluster corresponds to the base of the conductive zone, which suggests that the DC earthquakes in the shallower cluster are generated in a zone of high pore pressure that is capped by a hydrothermally altered clay layer. • Implosive non-double-couple (NDC) earthquakes occur at buried volcanic craters. • A high-resistivity zone exists beneath the NDC earthquakes. • NDC earthquakes are generated by void collapse above active volcanic conduits. • DC earthquakes occur 2–3 km beneath the NDC earthquakes. • High-pore-pressure zone capped by a clay layer generates shallower DC earthquakes. [ABSTRACT FROM AUTHOR]

Basaltic volcanoes produce a range of eruptive styles, from Strombolian to low-intensity fire fountaining to, much more rarely, highly explosive Plinian eruptions. Although the hazards posed by highly explosive eruptions are considerable, controlling mechanisms remain unclear, and thus improving our understanding of such mechanisms is an important research objective. To elucidate these mechanisms, we investigate the magma ascent dynamics of basaltic systems using a 1D numerical conduit model. We find that variations in magmatic pressure at depth play a key role in controlling modelled eruption characteristics. Our most significant result is that a decrease in pressure at depth, consistent with the emptying of a magma chamber, results in enhanced volatile exsolution and in deepening fragmentation depth. The corresponding decrease in conduit pressure ultimately produces a collapse of the conduit walls. This type of collapse may be a key mechanism responsible for the cessation of individual explosive eruptions, a notion previously explored for silicic eruptions, but never before for basaltic systems. Using previously published field and sample analysis to constrain model parameters, we simulate scenarios consistent with sub-Plinian eruptions, similar to those at Sunset Crater volcano in ~1085 CE in terms of mass eruption rates and duration. By combining these analyses with a chamber-emptying model, we constrain the size of the magma chamber at Sunset Crater to be on the order of tens of km3. During the 1085 CE Sunset Crater eruption, there were three main sub-Plinian events that erupted between 0.12 and 0.33 km3 of tephra (non-DRE), indicating that ~1% of the total chamber volume was erupted during each sub-Plinian pulse. • We reproduce a sub-Plinian eruption consistent with that occurred at Sunset Crater. • A decrease in pressure at depth results in a deepening fragmentation depth. • The decrease in conduit pressure ultimately produces the collapse of conduit walls. • We constrain the size of the magma storage zone at Sunset Crater to be ~10 km3. • We infer that during Sunset Crater eruption ~1% of the chamber volume was erupted. [ABSTRACT FROM AUTHOR]

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imaging system onboard NASA's (National Aeronautics and Space Administration's) Terra satellite is capable of measuring multispectral reflectance of the earth's surface targets in visible and infrared (VNIR) to shortwave infrared (SWIR) (until 2006) as well as multispectral thermal infrared (TIR) regions. ASTER VNIR stereo imaging technique can provide high-resolution digital elevation models (DEMs) data. The DEMs data, three-dimensional (3D) perspective, and ratio images produced from the ASTER multispectral data are employed to analyze the geomorphologic and lithologic features of Wudalianchi volcanoes in the northeastern China. Our results indicate that the 14 major conical volcanic craters of Wudalianchi volcanoes are arranged as three sub-parallel zones, extending in a NE (Northeast) direction, which is similar to the direction of regional fault system based on the ASTER DEMs data. Among the 14 volcanic craters in Wudalianchi, the Laoheishan, and Huoshaoshan lavas flows, after the historic eruptions, pouring down from the crater, partially blocked the Baihe River, which forms the Five Large Connected Pools, known as the Wudalianchi Lake. Lithologic mapping shows that ASTER multispectral ratio imagery, particularly, the Lava Flow Index (LFI) (LFI = B10/B12) imagery, can clearly distinguish different lava flow units, and at least four stages of volcanic eruptions are revealed in the Wudalianchi Quaternary volcano cluster. Thus, ASTER multispectral TIR data can be used to determine relative dating of Quaternary volcanoes in the semi-arid region. Moreover, ASTER 3D perspective image can present an excellent view for tracking the flow directions of different lavas of Wudalianchi Holocene volcanoes. [ABSTRACT FROM AUTHOR]

Lava emplacement at monogenetic volcanoes has been seldom documented when compared to persistently active volcanoes such as Mt. Etna or Kilauea. To expand the scientific understanding of lava emplacement, and to help assess the hazards posed by monogenetic systems and of lava flows in general, we present an investigation of the lava field at Marcath volcano (~ 35 ka; Lunar Crater volcanic field, central Nevada, USA). Key data include lava surface characteristics as well as size and abundance data of rafted pyroclastic material derived from the source cone. Upon exiting the source crater, lava initially ponded in an upland saddle between Marcath and an older cone before breaking out to feed three lava lobes that spread out onto a flat valley floor below. Quantitative estimates based upon morphological parameters suggest time-averaged discharge rates of 40–100 m3 s−1, emplacement duration of 5–20 days, and bulk lava viscosities on the order of 106 to 107 Pa s in the main lobes. Sizes and distributions of 1021 mapped pyroclastic rafts suggest that the early stages of the eruption produced much of the total raft volume. The source of most of the raft material was likely the now-missing western portion of an early Marcath cone. After the initial breaching of the cone, the raft production rate likely kept pace with cone building over the eruption's duration such that once the cone was breached on one side, it did not heal. Rafts were not always passive passengers on the lava: they had an important impact on lava morphology in specific locations, as they caused bifurcation of entire flow lobes and produced other flow features. The common occurrence of rafts in monogenetic lava fields suggests that incorporation of raft-lava interactions may be important in lava propagation models. [ABSTRACT FROM AUTHOR]

Cuicocha (4.7 km2) is a volcanic lake located in the province of Imbabura, about 110 km north of Quito, and is one of the two active volcanic lakes of Ecuador. Cuicocha volcano is part of Ecuador's Western Andean volcanic cordillera together with some 16 other active volcanoes as result of interaction of the Nazca oceanic plate with the Caribbean and South American continental plates. Cuicocha represents the fourth most dangerous active volcano in Ecuador with its volcanic activity is represented by the upheating of its waters and a fumarolic activity expressed by gas bubbles and some dead vegetation due to the emission of CO2 through the soils. Monitoring Cuicocha volcanic crater lake has been a priority task due to the presence of a considerable amount of population living within a 20 km radius of Cuicocha caldera rim. We report herein the results of a CO2 efflux survey carried out at this crater lake during October 2018, with the aim of evaluating temporal variations of CO2 efflux and their relationships with volcanic activity since 2006. In the 2018 survey, a total of 113 CO2 efflux measurements were performed on the lake surface by means of a floating accumulation chamber. At each sampling site pH, temperature and conductivity were measured at 15 cm depth from the water surface. To study the possible water stratification and CO2 accumulation in the lake, a dissolved gases were analysed at several depths in a vertical profile was performed reaching 80 m depth. The CO2 efflux values ranged between 4 and 70 g•m−2•d−1 with an average value of 19 g•m−2•d−1. In order to compute the diffuse CO2 emission at the studied area, the CO2 emission spatial distribution map was constructed averaging results of the 100 simulations following the sequential Gaussian simulation algorithm. The highest values of diffuse CO2 efflux and water temperature were observed close to one of the domes located inside the crater lake. The diffuse CO2 output was computed as 76 ± 3 t•d-1, being released through an area of 4.7 km2. Temporal evolution diffuse CO2 output presents a range from 76 to 652 t•d-1, being the 2018 survey the lower value. During March 2012, more than a hundred of earthquakes (M<3) were recorded in the southwestern zone of the Cuicocha volcanic lake, coinciding with the maximum value of diffuse CO2 emission of 652 t•d-1. Periodic diffuse CO2 emission surveys will be tremendously useful to improve the early warning system of future magmatic reactivations. [ABSTRACT FROM AUTHOR]

Taal volcano is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Located on the southwestern part of Luzon Island, Taal consists of a 15-22-km prehistoric caldera, occupied by the Taal Lake, the active vent complex of Volcano Island and the Crater Lake (TCL), 1.9 km in diameter. Six of 24 known eruptions at Taal since 1572 have caused many fatalities, and several million people live within a 20-km radius of Taal's caldera rim, making the volcano the largest threat to the Philippine population. An alarming increase in seismicity, gas emission, deformation and temperature of the TCL from March 2011, was interpreted as the result of a new magma intrusion (Arpa et al., 2013; Hernández et al., 2017). Between 2008 and 2014, ITER/INVOLCAN has collaborated with PHIVOLCS and from 2015 to the present with the University of the Philippines, also counting with the support of the Spanish Agency for International Development Cooperation (AECID), to perform diffuse CO2 efflux surveys at the surface of the TCL. In total, 18 surveys have been undertaken since 2008. Last survey was performed in November 2018, with 75 sites distributed homogenously along the surface of TCL. Together with diffuse CO2 efflux measurements, at each sampling site, water temperature and pH were measured. The CO2 measurements were carried out following the accumulation chamber method by means of a portable LICOR soil CO2 efflux instrument. To estimate the diffuse CO2 output, sequential Gaussian simulations (sGs) were used. The CO2 efflux values ranged from 231 to 20,920 gm-2•d-1. Main CO2 contributions were always observed at those areas where bubbling activity occurs. The estimated diffuse CO2 emission released from the Taal crater lake during 2018 survey was 3,050 ± 107 t•d-1. Observing the time series, the results reveal significant variations from 2008 to 2018 and do not seem to be masked by external variations, showing a temporal correlation with the onsets of high frequency seismic events recorded by PHIVOLCS at Taal. The above observations suggest subsurface magma movement as the cause for the observed changes in the total output of diffuse CO2 emission at the Taal crater lake, and CO2 efflux surveys become an effective volcanic surveillance tool for Taal volcano.Arpa et al., 2013. 2013. BullVolcanol. 75, 1–13.Hernández et al., 2017. J Geol. Soc. Lon. doi.org/10.1144/SP437.1. [ABSTRACT FROM AUTHOR]

Teide volcano (3,718 m.a.s.l.) is located in Tenerife, the largest island of the canarian archipelago. The most recent volcanic activity of Tenerife is represented, on the one hand, by many, mostly basaltic, volcanoes scattered throughout the island and, on the other hand, by the central Teide-Pico Viejo edifice, with basaltic and salic emissions (Ancochea at. al.,1990). The existence of a volcanic–hydrothermal system beneath Teide volcano is suggested by the occurrence of a weak 83ºC fumarolic system. As part of the volcanic monitoring program of INVOLCAN in Tenerife, 14 surveys were performed weekly during summer 2018 in order to evaluate the short term variations in the heat flux released from the summit crater of Teide. The heat flux was calculated using data from 38 sampling sites distributed inside the crater and covering and area of 6,972 m2, following the method described by Dawson (1964). Zones with highest heat flux values were characterized by a relatively high soil temperature (>60 ºC) and intense hydrothermal alteration. Sequential Gaussian simulation was used to construct spatial distribution maps to estimate the heat flux emission of the study area. During the study period heat flux values ranged from 0.505 MW to 0.755 MW, with an average value of 0.635 MW. In spite of the small changes observed during the study period, the range of values should be considered normal for a period of volcanic quiescence. The measurement of the total heat flux through the ground surface can provide valuable information about the changes in the energy balance of the volcanic system and also improve early warning system of the volcano.Ancochea E. et. Al., (1990). J. Vol. Geo.Res., 44, 231-249Dawson G. B. (1964). N.Z. J. Geol. Geophys., 7:1, 155-171 [ABSTRACT FROM AUTHOR]

Deception Island (DI) is one of the most active volcanoes in Antarctica, with more than 20 monogenetic eruptions during the Holocene. The latest episodes of 1967, 1969 and 1970 destroyed, or severely damaged, the scientific bases that operated on the island and have shown that volcanic activity on DI can become a concern for tourists, scientists and military personnel working on or near the island. Indeed, it is not possible to rule out the possibility of a future eruption in the future. One of the main problems at DI is related to the lack of data about the ages of most of the edifices, in order to evaluate the eruptive recurrence.The objective of this study is to carry out the morphometric analysis of the post-caldera volcanic structures (volcanic edifices and craters) recognizable on the island. This methodology has been used since the 70′s to analyse mafic monogenetic volcanoes but it has not been fully developed until recently. Several works were carried out in Campo de Calatrava-Ciudad Real, Tenerife, Gran Canaria and Lanzarote (Spain), Mauna Kea (USA) and Highlands of Bakony-Batalon (Hungary).This approach has been used at DI with the aim to establish a correlation between morphometry and the age of the post-caldera monogenetic landforms. The morphometric parameters include Crater maximum (Crmax) and minor (Crmin) diameter, Cone height (Hcomax and Hcomin), Crater depth (Cdep), Cone major (Comax) and minor (Comin) diameter, Cone slope (Scomax and Scomin) and Crater slope (Scrmax and Scrmin). One of the main peculiarity of DI is that these structures were probably affected by post-eruptive volcanic or erosive processes and that most of the volcanic edifices are tuff cone, as results of magma-water interaction. The results obtained will allow improving the estimation of the eruptive recurrence of the island and, in turn, fundamental point for the advising of the volcanic hazard.This research was supported by the MICINN grant CTM2011- 13578-E and was partially funded by the POSVOLDEC project (CTM2016-79617-P) (AEI/FEDER-UE). A.G. is grateful for her Ramón y Cajal contract (RYC-2012-11024). D.P. is grateful for his Beatriu de Pinós contract (2016 BP 00086). [ABSTRACT FROM AUTHOR]