Explosive Activity Research Articles

Long-term volcano evolution controlled by lateral collapse at Antuco volcano, southern Andes, Chile

Beyond the catastrophic environmental effects of large (>1 km3) volcanic landslides, their impact on underlying magmatic systems remains unclear. Chemical variations in post-collapse volcanic products, alongside dramatic eruptive behaviour transitions reported from several volcanoes, imply that surface unloading directly influences subsurface magmatic processes. By combining petrologic data with magma ascent models, we track the post-collapse (<7 ka) magmatic system evolution of Antuco volcano (Chile). During the pre-collapse period, low-explosivity eruptions were sourced from a hotter and deeper storage region. However, the landslide-induced unloading and decompression reactivated a pre-existing, shallower, silicic magma reservoir, favouring more explosive activity. The pre-collapse conditions were restored after edifice regeneration over a few thousand years. Since shallow magma reservoirs are common beneath volcanoes (e.g. in Etna, Villarrica, or Fuji), similar responses could follow future lateral collapses. These findings are relevant when assessing volcanic hazards at gravitationally unstable or collapsed volcanoes on a hundred- to thousand-year timescale.

PETROLOGICAL and GEOCHEMICAL CHARACTERISATION of the KGWEBE VOLCANIC FORMATION in the ghanzi-chobe BELT PORTION of the KALAHARI COPPER BELT, western Botswana.

A combination of petrography and geochemistry was utilised to investigate the magma sources, magma evolution and petrogenesis of the Kgwebe Volcanic Formation (KVF) rock units. Based on their texture, the KVF rock units comprise amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks, porphyritic subvolcanic bodies, quartz-feldspar porphyries and clastic sedimentary rocks, that are intercalated with amygdaloidal rocks. The amygdaloidal rocks are commonly crosscut by calcite veins and characterised by amygdales (filled vesicles) set in the hyalopilitic groundmass. The porphyritic mafic flows are composed of plagioclase laths set in an aphanitic groundmass. The pyroclastic rocks are generally characterised by up to 75% of both mineral and lithic fragments originating from explosive volcanic activities. Porphyritic subvolcanic bodies are characterised by high content of subrounded epidote (after plagioclase) set in a microcrystalline groundmass. The quartz-feldspar porphyries are characterised by quartz and feldspar phenocrysts in variable proportions set in a fine-grained groundmass of variable colour. Rock units of the KVF represent two geochemically contrasting series that are not co-genetic and are derived from different geotectonic settings. The amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies are sub-alkaline and basaltic in composition, whereas the quartz-feldspar porphyries span from the rhyolite/dacite (mostly) to the andesite/andesite basalt (accessorily) field compositions. Likewise, while quartz-feldspar porphyries are consistently high-K calc-alkaline bodies, their spatially associated amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies counterparts are calc-alkaline. Similarly, quartz-feldspar porphyries are within plate bodies, whereas the more mafic KVF units are arc-related. Furthermore, the ferroan quartz-feldspar porphyries generated from the crust and the magnesian amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies are mantle-derived, with however, significant crustal contamination fingerprints. Textural evidence (resorbed, embayed and rounded phenocrysts) and the inferred high-water content (as supported by the abundance of plagioclase phenocrysts) also suggest a rapid magma ascent and magma mingling occurred during the KVF eruption, which was both effusive and explosive. Concomitant volcanism and sedimentary processes likely occurred as supported by the intercalation of clastic sedimentary rocks within volcanics of the KVF.

Analysis of magma rheology from lava spreading and explosive activity during the 2020–21 eruption of La Soufrière, St Vincent, with implications for eruption dynamics

Abstract We apply dynamical models to estimate the rheological properties of magma and lava during the 2021–22 eruption of La Soufrière Volcano, St Vincent. Analysis of the emplacement of a lava coulée gives viscosities in the range 0.94 × 10 10 Pa s to 5.97 × 10 10 Pa s. A static Bingham model gives a yield strength of 4.1 × 10 5 Pa. A dynamical model of conduit flow during the explosive phase of the eruption gives a viscosity range from 1.2 × 10 7 to 2.3 × 10 9 Pa s. A petrological model of magma viscosity in the source region falls in the range 10 2 to 10 3 Pa s. The very high viscosity of the lava is attributed to the presence of a remnant degassed and partially crystallized magma from previous eruptions that occupied the shallow conduit–vent system prior to onset of the 2021 explosive eruptions. Gas-rich magma pushed this degassed remnant magma out over a three-month period at a steady rate of about 1.2 m 3 s −1 and the explosive phase began when volatile-rich and much lower viscosity magma reached the surface.

Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM)

Abstract. There is a temporal correlation between the peak activity of the North Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum (PETM), suggesting that the NAIP may have initiated and/or prolonged this extreme warming event. However, corroborating a causal relationship is hampered by a scarcity of expanded sedimentary records that contain both climatic and volcanic proxies. One locality hosting such a record is the island of Fur in Denmark, where an expanded pre- to post-PETM succession containing hundreds of NAIP ash layers is exceptionally well preserved. We compiled a range of environmental proxies, including mercury (Hg) anomalies, paleotemperature proxies, and lithium (Li) and osmium (Os) isotopes, to trace NAIP activity, hydrological changes, weathering, and seawater connectivity across this interval. Volcanic proxies suggest that NAIP activity was elevated before the PETM and appears to have peaked during the body of the δ13C excursion but decreased considerably during the PETM recovery. This suggests that the acme in NAIP activity, dominated by flood basalt volcanism and thermogenic degassing from contact metamorphism, was likely confined to just ∼ 200 kyr (ca. 56.0–55.8 Ma). The hundreds of thick (&gt; 1 cm) basaltic ashes in the post-PETM strata likely represent a change from effusive to explosive activity, rather than an increase in NAIP activity. Detrital δ7Li values and clay abundances suggest that volcanic ash production increased the basaltic reactive surface area, likely enhancing silicate weathering and atmospheric carbon sequestration in the early Eocene. Signals in lipid biomarkers and Os isotopes, traditionally used to trace paleotemperature and weathering changes, are used here to track seaway connectivity. These proxies indicate that the North Sea was rapidly cut off from the North Atlantic in under 12 kyr during the PETM recovery due to NAIP thermal uplift. Our findings reinforce the hypothesis that the emplacement of the NAIP had a profound and complex impact on Paleocene–Eocene climate, both directly through volcanic and thermogenic degassing and indirectly by driving regional uplift and changing seaway connectivity.

Differential impact of COVID-19 on urological surgeries in public and private institutions between 2019 and 2021 in France.

The COVID-19 pandemic disrupted all routine health care services in 2020. To date, data regarding adjustment and coverage of surgical backlog in the post-COVID era actually remains scarce. The aim of this study was to compare the number of urological procedures coded between 2019 and 2021 in public and private institutions to (i) quantify the variation in surgical activity linked to the shutdown in 2020 and (ii) study the adjustment of procedures over the year 2021. This is a comprehensive retrospective analysis of all urological surgeries coded between January 1, 2019 and December 31, 2021 in France. Data were extracted from the open access dataset of the national Technical Agency for Information on Hospital Care (ATIH) website. In total, 453 urological procedures were retained and allocated in 8 categories. Primary outcome was the impact of COVID-19 analyzed by the 2020/2019 variation. The secondary outcome was the post-COVID catch-up analyzed by the 2021/2019 variation. Surgical activity in public hospitals dropped by 13.2% in 2020 compared to 7.6% in the private sector. The most impacted areas were functional urology, stones and BPH. Incontinence surgery did not recover at all in 2021. BPH and stone surgeries were far less impacted in the private sector, with even explosive activity in 2021, post-COVID period. Onco-urology procedures were roughly maintained with a compensation in 2021 in both sectors. The recovery of surgical backlog was much more efficient in the private sector in 2021. The pressure on the health system associated to the multiple COVID-19 waves may generate a gap between public and private surgical activity in the future.

The 2021 Semeru volcano eruption: An insight from visual, seismic, and deformation monitoring data

Semeru is the highest volcano on the island of Java and one of Indonesia’s volcanoes that has a potential threat of pyroclastic flows. The eruption of Semeru often shows a transition pattern between explosive and effusive styles. An increased eruptive activity occurred in 2021 with series of explosions dominated the first two thirds of the year and then transition to series of pyroclastic flows in December 2021. On 4 December 2021, a dome collapse triggered significant pyroclastic flows that reached a maximum distance of 16 km from the crater and resulted in 51 casualties. In this paper, we aimed to study the dynamics of magma movement from depth to the surface and assessing the style transition of the eruptions between explosive and effusive activity from visual, seismic and deformation monitoring data. We analyzed Semeru volcano monitoring data throughout the year 2021. The volcanic activity monitoring system of Semeru volcano consists of 4 seismic stations, 5 deformation stations (2 tiltmeters and 3 GPS stations), and 2 Web Camera/CCTV. Our analysis on seismic data indicates that the series of large pyroclastic flows were triggered by excess pressure at shallow depths a few hours before the events. Deep volcanic earthquakes are relatively increased after the collapse of the lava dome or pyroclastic flows, possibly caused by the sudden decrease in hydrostatic pressure of the rock mass around the magma pocket, thus triggering gas expansion. Deformation monitoring using a tiltmeter at Argosuko and Jawar stations indicates inflation of a deep source since 15 August 2021. Since 7 November 2021, tiltmeter measurement has shown deep source deflation patterns which indicate magma movement from the deep reservoir to a shallower reservoir. After 21 November, inflation of the deep source was observed again, indicating an increase in magma supply from the deep pocket. The results of the pressure source modeling from GPS vector data in the period before the eruption, 1 November – 4 December 2021, showed an anomaly in the form of an increased volume at a depth of > 1.7 km of about 0.84 million/m3. Between 5 December and 31 December 2021, after the 4 December pyroclastic flow, the deformation modeling indicates the transition of the pressure source from a depth of 1.7 km to 8 km. In addition, we also observed a decrease in volume of 5.6 million/m3. The deformation pattern at shallow depths showed a deflationary pattern indicating a decrease in magma overpressure.

Formation stages of the Kholodninskoye pyrite-polymetallic deposit ore zone

The Kholodninskoe pyrite-polymetallic deposit (Baikal-Patom plateau, Russia) was discovered in 1968, but the questions of its genesis still remain controversial. It is assumed that the explosive activity of volcanic apparatuses of the southern part of the Baikal-Muya zone as well as underwater exhalations of the scattered spreading zone of the back-arc basin could have most likely influenced the geochemical features of amagmatic deposits of the Bodaibo and Patom zones. To investigate the influence of underwater hydrothermal activity on the geochemical features of Neoproterozoic carbonbearing sediments of the Baikal Mountain region, the Olokit zone, which is a fragment of the spreading zone of the backarc basin, was chosen. According to the geochemical parameters, the sediments of the Itykit and Ondokskaya formations hosting the Kholodninskoye deposit fall into the sedimentation area of DalnyaTaiga period paleobasins. Having compared the development of sulfide mineralization of ore objects of the Bodaibo and Olokit structural-formation zones, the authors suggest the unity of deposit formation processes within the Baikal Mountain area. The presence of framboidal pyrite indicates that the early stages of ore formation of the Kholodninskoe hydrothermal-stratiform polymetallic deposit were synchronous with sedimentation. The source of deposit ore zone enrichment with zinc lead, silver and other elements typical for low- and medium-temperature associations was a hydrothermal solution of the scattered spreading zone of back-arc basins. It is likely that the explosive and exhalation activities of the southern Baikal-Muya zone within the studied region also spread further northward, thus influencing the formation of siderochalcophilic geochemical specialization of amagmatic black shale strata of the Bodaibo and Patom zones.

Unsuspected explosive activity of Montagne Pelée (Lesser Antilles) during the 25–10 ka period

The recent eruptive history of Montagne Pelée volcano was dominated by a period of vigorous basaltic andesitic magma production (36−25 ka) followed by a long period of lower activity (i.e., with less frequent and less voluminous eruptions) and a renewal of felsic magma production in the last 10 ka. The temporal succession of volcanic events that occurred during the 25−10 ka period and the timing of felsic magma production are currently poorly constrained. This study focuses on the stratigraphy and eruptive dynamics of the pyroclastic deposits emplaced immediately after 25 ka. New on-land stratigraphic correlations and radiocarbon dating measurements allow us identifying six major explosive eruptions. We use field data on tephra dispersal, thickness and grain-size distribution together with physical models of explosive volcanic plumes to estimate the eruption source parameters. Our results show that these events are VEI 4 eruptions with intermediate magnitudes (from M = 4.2 to M = 5.1) and intensities (from I = 10.6 to I = 11.6). These eruptions share several characteristics with the most recent Plinian eruptions of Montagne Pelée volcano (i.e., mass eruption rate, maximum column height, runout of pyroclastic density currents, glass composition). The tephra succession documents two phases of magma production rates. The first phase from 25 to 14 ka corresponds to a period of low activity with a magma production rate of 0.04 km3 kyr−1. The second phase from 14 to 10 ka is characterized by a significant increase of the volcanic activity with a magma production rate of 0.4 km3 kyr−1, consistent with previous estimates.

Analysis of magma flux and eruption intensity during the 2021 explosive activity at La Soufrière, St Vincent, West Indies

Abstract Real-time Seismic Amplitude Measurement signals and eruption cloud height measurements were used to estimate peak intensities of 40 explosive events during the 8–22 April 2021 activity of La Soufrière volcano. We estimated magma supply rates and erupted volumes in each explosion, characterized uncertainty by stochastic modelling and identified four eruptive stages. Stage 1 included an intense period of 9.5 hours with 11 explosive events with peak eruption intensity between 2000 and 4000 m 3 s −1 and magma supply rate reaching 828 m 3 s −1 . Twelve high-intensity explosions ( c. 4000 m 3 s −1 ) occurred in Stage 2 with average magma supply rate of 251 m 3 s −1 . Stage 3 involved both declining intensity and magma supply rate and lengthening repose periods between explosions. Stage 4 involved three much weaker explosions. The total erupted volume of magma is estimated at 38.5 × 10 6 m 3 (90% credible interval: [22.0 .. 61.9] × 10 6 m 3 ) consistent with independent estimates from analysis of tephra deposits and volcano subsidence sourced at c. 6 km depth. The 150-fold increase in magma supply rate, from the preceding effusive phase to Stage 1 of the explosive phase, is attributed to replacement of very high-viscosity degassed magma occupying the shallow conduit system with new, lower-viscosity, volatile-rich magma from the magma chamber.

Ebeko Volcano Activity in 2022: Mechanism and Products of Eruption

The paper provides information about the eruptive activity of the Ebeko volcano in 2022. From January 22 to June 13, phreatic explosions occurred in the crater lake caused by water seeping through the plug formed in the upper part of the magma channel and its boiling. On June 14, Vulcanian explosions began, destroying the lake. The granulometric composition of the ashes has changed in the direction of reducing the particle size. Petrographic and mineralogical-geochemical studies of tephra allow us to define this period as a phreatomagmatic eruption by the presence of fresh juvenile material. It is established that the interaction of magma with the waters of the hydrothermal system of the Ebeko volcano leads to its depletion with alkali metals and enrichment with silica. It is suggested that the formation of amorphous water-containing silica in the form of numerous separations and its subsequent dehydration may contribute to the explosive activity of the volcano.

Volcanic evolution through geomorphological mapping: A case study of Cerro Bravo volcano (Colombia)

Geomorphological mapping is essential for identifying landforms, determining erosion, and reconstructing the morphological evolution over time. The relative chronology between features can be established, supporting the study of the potential hazard and associated risks in volcanic terrains. Geomorphological analysis, performed on a 12.5 m ALOS PALSAR DEM, along with field-work and new K–Ar geochronological data, help to clarify the overall evolution of the Cerro Bravo volcano. The observed north-south arrangement of the craters, the stratigraphic relationships, and the new K–Ar ages reveal that the volcanic activity migrated towards the north, with the younger activity concentrated north of the volcanic area. This evolution, which occurred from the Middle Pleistocene to the Holocene, is evidenced by four consecutive semicircular crater-like structures associated with four building stages. Effusive and explosive activity was observed in all recorded volcanic activity stages, indicating a consistent volcanological behavior of this volcano over time, characterized by a bimodal effusive-explosive eruption style. The effusive activity involved lava domes and lava flows, while the explosive activity included dome collapses and Plinian eruptions. This morphological study can help assess the geological risk and potential hazards of inaccessible areas.

La Soufrière volcano, St Vincent, eruption 2020–21: assessing unrest and eruptive states from limited volcano-seismic data

Abstract Following a month of unrest in June–July 2019 and 3 months of effusive activity from late December 2020 to March 2021, La Soufrière volcano, St Vincent, transitioned to a 2-week period of explosions on 9 April 2021. During initial unrest, there was one working seismograph station on the volcano, providing the only information for tracking fluctuations in seismicity. Subsequently, full capability for locating volcanic earthquakes was achieved on 27 January 2021. Because events prior to this did not have reliable locations, unconventional data tracking approaches were adopted for assessing unrest evolution. Holistic inferences, suggested by combining these novel analyses with decades of knowledge of Lesser Antilles volcanoes, provided punctual evidential support for assessing the possibility that unrest could culminate in explosive activity. However, this case history is not offered as a paradigm for minimalist seismic monitoring at active volcanoes, notwithstanding that information gains were possible. This said, evaluations of seismic moment release, using event duration magnitudes as proxies for moment magnitudes, allowed the magma volume intruded or activated in the volcano to be estimated: 68 ± 14 × 10 6 m 3 dense rock equivalent (DRE) magma; this is a value remarkably similar to a geological estimate of total erupted volume (71 ± 14 × 10 6 m 3 DRE), with matching uncertainties.

Tracking volcanic explosions using Shannon entropy at Volcán de Colima

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

The Explosive Activity of the 2021 Tajogaite Eruption (La Palma, Canary Islands, Spain)

AbstractThe explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well‐defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash‐poor jets and ash‐rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high‐speed camera and three high‐definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub‐second mass flux of lapilli to bomb‐sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well‐defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined.

Growth and evolution of the lava dome and coulée during the 2020–21 eruption of La Soufrière, St Vincent

Abstract The 2020–21 eruption of La Soufrière, St Vincent consisted of two distinct phases. The initial, effusive phase was characterized by the extrusion of a small lava dome inside the 1.5 km wide Summit Crater, and was followed by a violent explosive phase. Growth and evolution of the lava dome was monitored by visual observations and photogrammetry using imagery acquired from fixed-wing aircraft, helicopters and consumer-grade unmanned aerial vehicles. Additional monitoring was provided by satellite multispectral and radar imagery. Following the emergence of lava at the surface on 27 December 2020, volume and growth rate calculations showed the extrusion occurred at a steady rate of c . 1.8 m 3 s −1 and c . 16–19 × 10 6 m 3 of lava was extruded. The initial near-perfect hemispherical dome transitioned into a dome with a more elliptical footprint, eventually, evolving into a coulée-like feature with two lobes. The dome was destroyed by the onset of explosive activity on 9 April 2021.

Historical explosive activity of Mount Melbourne Volcanic Field (Antarctica) revealed by englacial tephra deposits

Five tephra layers named BRH1 to 5 were sampled in an ice cliff located on the north-eastern flank of Mount Melbourne (northern Victoria Land, Antarctica). The texture, componentry, mineralogy, and major and trace element compositions of glass shards have been used to characterize these layers. These properties suggest that they are primary fall deposits produced from discrete eruptions that experienced varying degrees of magma/water interaction. The major and trace element glass shard analyses on single glass shards indicate that Mount Melbourne Volcanic Field is the source of these tephra layers and the geochemical diversity highlights that the eruptions were fed by compositionally diverse melts that are interpreted to be from a complex magma system with a mafic melt remobilizing more evolved trachy-andesitic to trachytic magma pockets. Geochemical compositions, along with textural and mineralogical data, have allowed correlations between two of the englacial tephra and distal cryptotephra from Mount Melbourne, recovered within a marine sediment core in the Edisto Inlet (~ 280 km northeast of Mount Melbourne), and constrain the age of these englacial tephra layers to between the third and the fourth century CE. This work provides new evidence of the intense historical explosive activity of the Mount Melbourne Volcanic Field and better constrains the rates of volcanism in northern Victoria Land. These data grant new clues on the eruptive dynamics and tephra dispersal, and considerably expand the geochemical (major and trace elements) dataset available for the Mount Melbourne Volcanic Field. In the future, this will facilitate the precise identification of tephra layers from this volcanic source and will help define the temporal and spatial correlation between Antarctic records using tephra layers. Finally, this work also yields new valuable time-stratigraphic marker horizons for future dating, synchronization, and correlations of different palaeoenvironmental and palaeoclimatic records across large regions of Antarctica.

Explosive sequence of La Soufrière, St Vincent, April 2021: insights into drivers and consequences via eruptive products

Abstract This paper forensically reconstructs the timings, impacts and processes that drove the sequence of explosive eruptions of La Soufrière, St Vincent in April 2021 using a combination of field-based stratigraphy and textural dissection of the deposit character together with contemporary visual observations. Explosive activity on 9 April and early on 10 April involved destruction of almost all of the 2020/2021 lava dome, c. 60% of the 1979 dome and formation of a 600 m diameter crater by 2pm UTC on 10 April. Following the initial explosion, plumes rose to altitudes of c. 15 km and pyroclastic density currents (PDCs), formed by column collapse, first occurred on 10 April, only after &gt;24 h of explosive activity. Dense PDCs reached the sea only in the Larikai and Roseau valleys, and dilute PDCs were restricted to within 2.5 km of the Summit Crater rim. The tephra fallout deposits are stratified, composed of numerous layers of both lapilli-rich and ash-rich layers, which we have grouped into at least 7 units, based on their common characteristics (Units 1 to 7). Volume estimates, using a range of techniques to constrain uncertainties, indicate that the bulk volume of tephra (fallout and PDC) is 1.19 × 10 8 m 3 ± 20% making this a VEI 4 eruption.

Toward a Real-Time Analysis of Column Height by Visible Cameras: An Example from Mt. Etna, in Italy

Volcanic plume height is one the most important features of explosive activity; thus, it is a parameter of interest for volcanic monitoring that can be retrieved using different remote sensing techniques. Among them, calibrated visible cameras have demonstrated to be a promising alternative during daylight hours, mainly due to their low cost and low uncertainty in the results. However, currently these measurements are generally not fully automatic. In this paper, we present a new, interactive, open-source MATLAB tool, named ‘Plume Height Analyzer’ (PHA), which is able to analyze images and videos of explosive eruptions derived from visible cameras, with the objective of automatically identifying the temporal evolution of eruption columns. PHA is a self-customizing tool, i.e., before operational use, the user must perform an iterative calibration procedure based on the analysis of images of previous eruptions of the volcanic system of interest, under different eruptive, atmospheric and illumination conditions. The images used for the calibration step allow the computation of ad hoc expressions to set the model parameters used to recognize the volcanic plume in new images, which are controlled by their individual characteristics. Thereby, the number of frames used in the calibration procedure will control the goodness of the model to analyze new videos/images and the range of eruption, atmospheric, and illumination conditions for which the program will return reliable results. This also allows improvement of the performance of the program as new data become available for the calibration, for which PHA includes ad hoc routines. PHA has been tested on a wide set of videos from recent explosive activity at Mt. Etna, in Italy, and may represent a first approximation toward a real-time analysis of column height using visible cameras on erupting volcanoes.

Explosive eruptions at Stromboli volcano (Italy): a comprehensive geochemical view on magma sources and intensity range

A comprehensive understanding of the processes that occur during magmatic storage and pre-eruptive ascent—and of their associated timescales—is critical to identifying potential precursory signals, and to developing robust volcano early-warning systems. Stromboli’s persistent activity comprises continuous degassing and explosive activity that ranges from hourly, low-intensity “normal” activity to occasional, more violent, paroxysmal activity. While the magma source processes that drive normal and paroxysmal activity are reasonably constrained, eruptive activity intermediate in magnitude and intensity (i.e., major explosions) remains elusive in terms of classification, source region, and pre-eruptive timescales. Here, we investigate the 19 July 2020 major explosion that geophysical parameters place at the upper limit of the major explosions field, close to small-scale paroxysms such as the 2003 and 2007 events. The geochemical signatures of matrix glass, olivine, melt inclusions, and embayments—integrated with gas measurements—highlight important differences in eruption source, ascent behaviour, and pre-eruptive timescales of the studied event when compared to paroxysms. Melt inclusion volatile contents identify that magma rise begins from a slightly shallower source (~9.5 km below sea level, b.s.l.) than for paroxysms (11.4 km b.s.l.), with the activation of a shallower ponding zone at 5–6 km b.s.l.. This, in combination with intermediate matrix glass compositions, suggests complex ascent behaviour, characterised by CO2 buffering in the deep ponding region and magma self-mixing in the shallower zone. Fe–Mg-diffusion modelling in olivine indicates a system perturbation starting ~20–25 days before eruption onset, in agreement with the timescale of volcanic gas CO2/SO2 ratio changes observed in the plume, and significantly shorter than that observed prior to paroxysms (~4 months). The geochemical dataset provides insights into the processes controlling the steady-state conditions and the broad spectra in eruption magnitude and intensity at Stromboli and bears important implications for eruption forecasting.

Eruptive history of the Fort Selkirk area, Central Yukon

Lying at the large-scale tectonic boundary between the Yukon Tanana and northern extremity of the Stikinia and Quesnellia terranes, mafic eruptions have occurred over the past 4 million years in the Fort Selkirk area. Eruptions have included effusive (lava), explosive activity, and subglacial and subaqueous eruptions that produced hyaloclastite complexes. Eruptions have dammed or disrupted Yukon River at least five times. These volcanic rocks and interstratified sediments are collectively referred to as the Fort Selkirk Volcanic Group. Eruptions occurred from seven centers with activity progressively moving north. An explanation for the northern migration of volcanism is elusive at present.