Eruptive Vents Research Articles

The petrologic and degassing behavior of sulfur and other magmatic volatiles from the 2018 eruption of Kīlauea, Hawaiʻi: melt concentrations, magma storage depths, and magma recycling

Kīlauea Volcano’s 2018 lower East Rift Zone (LERZ) eruption produced exceptionally high lava effusion rates and record-setting SO2 emissions. The eruption involved a diverse range of magmas, including primitive basalts sourced from Kīlauea’s summit reservoirs. We analyzed LERZ matrix glasses, melt inclusions, and host minerals to identify melt volatile contents and magma storage depths. The LERZ glasses and melt inclusions span nearly the entire compositional range previously recognized at Kīlauea. Melt inclusions in Fo86-89 olivine from the main eruptive vent (fissure 8) underwent 70–170 °C cooling during transport in LERZ carrier melts, causing extensive post-entrapment crystallization and sulfide precipitation. Many of these melt inclusions have low sulfur (400–900 ppm) even after correction for sulfide formation. CO2 and H2O vapor saturation pressures indicate shallow melt inclusion trapping depths (1–5 km), consistent with formation within Kīlauea’s Halemaʻumaʻu and South Caldera reservoirs. Many of these inclusions also have degassed δ34S values (− 1.5 to − 0.5‰). Collectively, these results indicate that some primitive melts experienced near-surface degassing before being trapped into melt inclusions. We propose that decades-to-centuries of repeated lava lake activity and lava drain-back during eruptions (e.g., 1959 Kīlauea Iki) recycled substantial volumes of degassed magma into Kīlauea’s shallow reservoir system. Degassing and magma recycling from the 2008–2018 Halemaʻumaʻu lava lake likely reduced the volatile contents of LERZ fissure 8 magmas, resulting in lower fountain heights compared to many prior Kīlauea eruptions. The eruption’s extreme SO2 emissions were due to high lava effusion rates rather than particularly volatile-rich melts.

Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications

AbstractTaupō volcano, New Zealand, is a large caldera volcano that has been highly active through the Holocene. It most recently erupted ∼1,800 years ago but there have been multiple periods of historic volcanic unrest. We use seismological and geodetic analysis to show that in 2019 Taupō underwent a period of unrest characterized by increased seismic activity through multiple swarms and was accompanied by ground deformation within the caldera. The earthquakes, which include non‐double‐couple events, serve to outline an aseismic zone beneath the most recent eruptive vents. This aseismic zone is coincident with an inflating source, based on forward modeling of ground deformation data. We infer that this aseismic and deforming region delineates the location of the present day magma reservoir that is ≥250 km3 in volume and has a melt fraction of >20%–30%, inhibiting seismic activity. Our analysis shows that the 2019 unrest at Taupō was volcanic in nature and origin, demonstrating that this is an active and potentially hazardous volcano, and that improving our monitoring and understanding of its behavior is important.

Pre-eruptive conditions at satellite vent eruptions at Teide-Pico Viejo complex (Tenerife, Canary Islands)

The Teide-Pico Viejo (T-PV) stratovolcanoes constitute one of the most potentially active volcanic complexes in Europe. T-PV was traditionally considered as a non-explosive system, but recent studies have pointed out the explosive character of their phonolitic magmas, including plinian and subplinian eruptions and the generation of pyroclastic density currents, as is evidenced in the volcanological record of the last 30 kyr. This explosive activity is mostly associated with satellite dome-like vents, which are characterised by presenting progressive transitions between explosive and effusive activity. In order to improve our understanding of these types of eruptions and their controlling mechanisms, we conducted a petrological and mineral characterisation of the products from the different eruptive phases of Pico Cabras dome. This permitted us to constrain the pre-eruptive conditions of the magma and to infer the potential factors that control the changes in the volcanic activity of dome-forming eruptions at T-PV and, in particular, the transition between explosive and effusive phases.Feldspar (anorthoclase and sanidine), clinopyroxene (diopside and augite), biotite, amphibole (kaersutite), magnetite, ilmenite, sodalite, and glass samples were analysed using EPMA and Micro-XRF. Our results suggest the presence of a compositionally, thermally, and volatile stratified magma chamber at 100 ± 50 MPa prior to the Pico Cabras eruption (between 9210 and 5911 years BP), which was characterised by a progressive change in the style of activity, from an efficiently fragmented magma dispersed by a sustained plume, to a poorly-fragmented, low-height, non-convective fountain (forming the fountain-fed lava dome) to a glass-bearing lava flow activity. The transition in the eruptive style was controlled by changes in temperature and amount of volatiles dissolved in the phonolitic melt (i.e., differences in magma rheology). The initial explosive phase was related to the emission of highly evolved phonolitic magma ponding at 725–825 °C while containing 3.5–5 wt% H2O and located in the upper part of the magma reservoir. The magma that fed the phonolitic lava flow formed the main body of the reservoir and was stored below the preceding melt at 880 ± 30 °C and with 2.5–3 wt% H2O dissolved. Feldspar zonation suggests that the eruption was triggered by the intrusion of hotter mafic magma at the base of the phonolitic chamber, which induced the overturn of the interior of the reservoir. However, the interaction between the internal magmas was short enough to prevent the hybridization phenomena among them. The compositions of some feldspars from the most explosive phase are equivalent to those found in the El Abrigo eruption, the last caldera-forming episode (ca. 190 ka), demonstrating that T-PV volcanic system can already produce evolved and highly explosive magmas, a factor that should be considered in future hazard assessment for Tenerife.

Late Holocene Malpaís de Zacapu (Michoacán, Mexico) andesitic lava flows: rheology and eruption properties based on LiDAR image

Few monogenetic eruptions that produced lava flows have occurred in historical times, limiting the observations of their impact on human settlements. However, rheological models based on morphological and petrological datasets can contribute to decipher the eruptive dynamics and durations of ancient eruptions. The Malpaís de Zacapu, a temporal-spatial monogenetic volcano cluster at the western margin of the Zacapu lacustrine basin (Michoacán, Mexico), offers a good opportunity to apply such models because of the availability of a high-resolution LiDAR topography from which detailed morphological data was extracted. The Malpaís de Zacapu comprises late Holocene lava flow fields emplaced in the last 3200 years by four different low magnitude volcanic eruptions: Infiernillo, Malpaís Las Víboras, Capaxtiro, and Malpaís Prieto. Jointly these eruptions produced thick andesitic block lava flows covering an area of 38.3 km2 with a volume of ~ 4.4 km3. The lava viscosities at eruption vents were estimated from petro-textural analyses and range between 103 and 106 Pa s, while the final flow apparent viscosities, obtained from dimensional analyses, vary from 108 to 1010 Pa s. We estimated the mean effusion rate and lava flow emplacement duration for each flow field. Results revealed that the more viscous flows, Malpaís Las Víboras and Malpaís Prieto, could have been emplaced in less than 3 years, while the more fluid Infiernillo probably took less than 1 year. In stark contrast, the morphologically different and more voluminous Capaxtiro flow field could have been emplaced in ~ 27 years. These findings can help to evaluate the impact that these eruptions had on adjacent pre-Hispanic populations, known to have inhabited the region since at least 3000 years ago.

Stress Inversion in a Gelatin Box: Testing Eruptive Vent Location Forecasts With Analog Models

AbstractAssessing volcanic hazard in regions of distributed volcanism is challenging because of the uncertain location of future vents. A statistical‐mechanical strategy to forecast such locations was recently proposed: here, we further develop and test it with analog models. We stress a gelatin block laterally and with surface excavations, and observe air‐filled crack trajectories. We use the observed surface arrivals to sample the distributions of parameters describing the stress state of the gelatin block, combining deterministic crack trajectory simulations with a Monte Carlo approach. While the individual stress parameters remain unconstrained, we effectively retrieve their ratio and successfully forecast the arrival points of subsequent cracks.

Volcanism and rapid sedimentation affect the benthic communities of Deception Island, Antarctica

Deception Island is amongst the most active volcanoes in the Southern Ocean, with over 20 explosive eruptions in the last ca. 200 years. The eruption that formed the caldera at Deception Island occurred 3980 ± 125 calendar years Before Present, and it is the largest eruptive event documented in Antarctica during Holocene. Since then, post-caldera volcanic activity has comprised many scattered eruptive vents across the island. Mortality of benthic organisms has been reported during the most recent eruptions occurred on the island, in 1967, 1969, and 1970 Common Era (CE), with very low abundances of organisms during the 1967–1973 CE period. Within the sea-flooded part of the caldera depression, named Port Foster, a submarine volcanic axis with several volcanic cones is observed. An interdisciplinary team sampled the best morphologically preserved volcanic edifice within Port Foster, the so-called Stanley Patch. Geophysical data traced the volcano and characterized its morphology and inner structure. Underwater scuba sampling allowed to acquire sediment and rock samples, photographs and video images of the benthic organisms and seascape. Morphology of Stanley Patch cone and textural characteristics of the collected pyroclastic rocks indicate that the volcanic edifice was originated during an explosive eruption. Furthermore, the lack of palagonitization, quenched pyroclast margins, and hyaloclastite deposits indicate that this cone has formed on-land, before the caldera floor became inundated by the seawater, highlighting the complex intra-caldera evolution of Deception Island. A sediment core from the crater was collected for sedimentological, and geochemical analysis. Antarctic climate and seasonal sea ice, together with organic degradation due to high sedimentation rates, explain the low total organic carbon data measured. The volcanic history of the island has probably avoided the development of a stable benthic community over time, similar to other Antarctic shallow communities. Moreover, the current geomorphological conditions still shape different benthic communities than in the surrounding coastal ecosystems. Stanley Patch, and the whole Port Foster, provide a natural laboratory for benchmarking the reestablishment of benthic communities on a volcanic-influenced shallow marine environment, offering relevant data for future studies evaluating global climate change effects on the Antarctic seabed.

Variable Magnitude and Intensity of Strombolian Explosions: Focus on the Eruptive Processes for a First Classification Scheme for Stromboli Volcano (Italy)

Strombolian activity varies in magnitude and intensity and may evolve into a threat for the local populations living on volcanoes with persistent or semi-persistent activity. A key example comes from the activity of Stromboli volcano (Italy). The “ordinary” Strombolian activity, consisting in intermittent ejection of bombs and lapilli around the eruptive vents, is sometimes interrupted by high-energy explosive events (locally called major or paroxysmal explosions), which can affect very large areas. Recently, the 3 July 2019 explosive paroxysm at Stromboli volcano caused serious concerns in the local population and media, having killed one tourist while hiking on the volcano. Major explosions, albeit not endangering inhabited areas, often produce a fallout of bombs and lapilli in zones frequented by tourists. Despite this, the classification of Strombolian explosions on the basis of their intensity derives from measurements that are not always replicable (i.e., field surveys). Hence the need for a fast, objective and quantitative classification of explosive activity. Here, we use images of the monitoring camera network, seismicity and ground deformation data, to characterize and distinguish paroxysms, impacting the whole island, from major explosions, that affect the summit of the volcano above 500 m elevation, and from the persistent, mild explosive activity that normally has no impact on the local population. This analysis comprises 12 explosive events occurring at Stromboli after 25 June 2019 and is updated to 6 December 2020.

Post-collisional shift from polygenetic to monogenetic volcanism revealed by new 40Ar/39Ar ages in the southern Lesser Caucasus (Armenia)

The post-collisional Syunik and Vardenis volcanic highlands, located in the southern Lesser Caucasus mountains (part of the Arabia-Eurasia collision zone) are host to over 200 monogenetic volcanoes, as well as 2 large Quaternary polygenetic volcanoes in the Syunik highland. The latter are overlain by lavas from the monogenetic volcanoes, suggesting there was a transition in the style of volcanic activity from large-volume central vent eruptions to dispersed small-volume eruptions. 12 new high quality 40Ar/39Ar ages are presented here, with 11 ages calculated by step-heating experiments on groundmass separates, and the final age obtained from total fusions of a population of sanidines. All the ages were younger than 1.5 Ma, except for one ignimbrite deposit whose sanidines gave an age of 6 Ma. While the bulk of the exposed products of post-collisional volcanism relate to Pleistocene activity, it is clear there has been active volcanism in the region since at least the late Miocene. All ages for monogenetic volcanoes in the Syunik highland are younger than 1 Ma, but to the north in Vardenis there is geochronological evidence of monogenetic volcanism at 1.4 and 1.3 Ma. An age of 1.3 Ma is determined for a lava flow from one of the polygenetic volcanoes- Tskhouk, and when combined with other ages helps constrain the timing of the polygenetic to monogenetic transition to around 1 Ma. The new ages illustrate a degree of spatio-temporal coupling in the formation of new vents, which could be related to pull-apart basins focussing ascending magmas. This coupling means that future eruptions are particularly likely to occur close to the sites of the most recent Holocene activity. The polygenetic to monogenetic transition is argued to be the result of a decreasing magma supply based on: (i) volume estimates for Holocene eruptions and for all monogenetic volcanoes and their lava flows in Syunik; and (ii) the volcanic stratigraphy of the Lesser Caucasus region which shows late Pliocene- early Pleistocene continental flood basalts being succeeded by a few large andesite-dacite volcanoes and then the most recent deposits consisting of small-volume scoria cones. The Syunik highland has the highest density of monogenetic centres in the Lesser Caucasus, which is taken to indicate this region has the highest magma flux, and was therefore the last location to transition to monogenetic volcanism, which is why the transition is most clearly seen there. There is no evidence from Sr-Nd-B isotope measurements for the exhaustion of fusible slab components in the mantle source, showing that an inherited slab signature can survive for millions of years after the end of subduction. Although volcanism in the Lesser Caucasus is currently waning, a future pulse of activity is possible.

Monogenetic volcanoes with initial phreatomagmatic phases in the Ceboruco graben, western Mexico: The cases of Potrerillo I, Potrerillo II, and San Juanito

Potrerillo I, Potrerillo II, and San Juanito volcanoes are part of the 28 Late Quaternary monogenetic eruptive vents concentrated along a ~2-km-wide and ~30-km-long stripe in the vicinity of Ceboruco stratovolcano (western Mexican Volcanic Belt). The studied volcanoes are closely spaced and located within a ~12 km2 sub-drainage basin, northwest of Ceboruco's edifice. Eruptive dynamics were inferred from sedimentary, stratigraphic, and pyroclast characteristics. Unlike Potrerillo I, which was formed by an entirely dry explosive magmatic eruption, evidence for the prevalence of initial short-lived phreatomagmatic phases was found for the Potrerillo II and the San Juanito eruptions that ended effusively.In this study we examine the nature and proportion of different types of pyroclasts within the exposed deposits of these three volcanoes, as well as their sedimentary features to better understand the initiation and progression of their eruptions. Our results indicate that both Potrerillo II and San Juanito tephra ring deposits show dominantly atypical, crudely bedded, coarse-grained deposits where the evidence for energetic, diluted pyroclastic density currents is scarce or subordinated. Instead, low energy, shallow seated, phreatomagmatic explosions generated medium-to-coarse grain-sized pyroclasts that were transported within dense tephra jets that were ballistically ejected, which on deposition formed non-turbulent currents with non-extensive lateral movement. The nature of such eruptive style was controlled by the substrate hydrogeology conditions that prevailed at the time of the eruption. So, magmas of different composition (dacitic for Potrerillo II, and basaltic andesite for San Juanito) followed similar dynamics when interacting with water. We propose that fractured aquifers with shallow water tables (or even surface water) existed at the time of both eruptions and interacted explosively with the magmas.In contrast, the construction of Potrerillo I scoria cone, which is related exclusively to explosive magmatic activity, does not show evidence of phreatomagmatic activity. This eruption may have occurred when the water table was deep, or surface water was unavailable. The variations in the depth of phreatomagmatic explosions, the availability of the water involved in the phreatomagmatic phases, and the absence or presence of these phases in the studied volcanoes were probably strongly influenced by the water-bearing conditions of the aquifers at the time of the eruption, which in turn, depended on the amount and distribution of annual rainfall.This study improves our understanding of phreatomagmatic eruptions of diverse magmatic compositions in similar settings. The recognition of associated hazards will allow to further define eruptive scenarios of monogenetic eruptions and help update the volcanic hazard map of the Ceboruco volcano area in the future.

Multisensor Characterization of the Incandescent Jet Region of Lava Fountain-Fed Tephra Plumes

Explosive basaltic eruptions eject a great amount of pyroclastic material into the atmosphere, forming columns rising to several kilometers above the eruptive vent and causing significant disruption to both proximal and distal communities. Here, we analyze data, collected by an X-band polarimetric weather radar and an L-band Doppler fixed-pointing radar, as well as by a thermal infrared (TIR) camera, in relation to lava fountain-fed tephra plumes at the Etna volcano in Italy. We clearly identify a jet, mainly composed of lapilli and bombs mixed with hot gas in the first portion of these volcanic plumes and here called the incandescent jet region (IJR). At Etna and due to the TIR camera configuration, the IJR typically corresponds to the region that saturates thermal images. We find that the IJR is correlated to a unique signature in polarimetric radar data as it represents a zone with a relatively high reflectivity and a low copolar correlation coefficient. Analyzing five recent Etna eruptions occurring in 2013 and 2015, we propose a jet region radar retrieval algorithm (JR3A), based on a decision-tree combining polarimetric X-band observables with L-band radar constraints, aiming at the IJR height detection during the explosive eruptions. The height of the IJR does not exactly correspond to the height of the lava fountain due to a different altitude, potentially reached by lapilli and blocks detected by the X-band weather radar. Nonetheless, it can be used as a proxy of the lava fountain height in order to obtain a first approximation of the exit velocity of the mixture and, therefore, of the mass eruption rate. The comparisons between the JR3A estimates of IJR heights with the corresponding values recovered from TIR imagery, show a fairly good agreement with differences of less than 20% in clear air conditions, whereas the difference between JR3A estimates of IJR height values and those derived from L-band radar data only are greater than 40%. The advantage of using an X-band polarimetric weather radar in an early warning system is that it provides information in all weather conditions. As a matter of fact, we show that JR3A retrievals can also be obtained in cloudy conditions when the TIR camera data cannot be processed.

Influence of Weather Conditions on Particulate Matter Suspension following the 2010 Eyjafjallajökull Volcanic Eruption

AbstractThe 2010 eruption of Eyjafjallajökull produced volcanic ash that was mostly deposited to the south and east of the volcano, with the thickest deposits closest to the eruption vents. For months following the eruption there were numerous reports of resuspended volcanic ash made by weather observers on the ground. A saltation sensor (SENSIT) and an optical particle counter (OPC) located on the southern side of Eyjafjallajökull measured posteruptive particulate matter (PM) saltation and suspension events, some of which were also observable by satellite imagery. During the autumn/winter following the eruption, visible satellite images and the SENSIT show that PM measured by the OPC was only detected when winds had a northerly component, making the source on the slopes of Eyjafjallajökull. During the largest observed events, particles >10μm were suspended but measured in extremely low concentrations (<1 particle per centimeter cubed). The saltation measurements, however, show high concentrations of particles >100μm in size during these events. During the largest events, winds were at least 5 m s−1with a relative humidity < 70%. Ground conditions in Iceland change quickly from unfavorable to favorable for the suspension of particles. It is hypothesized that this is due to the porosity of the surface material allowing water to filter through quickly as well as the fast drying time of surface material. The high moisture content of the atmosphere and the ground do not appear to be a deterrent for large PM events to occur in Iceland.

Rhyolitic volcano dynamics in the Southern Andes: Contributions from 17 years of InSAR observations at Cordón Caulle volcano from 2003 to 2020

In this article I present a review of InSAR observations of ground deformation at Cordón Caulle volcano, whose 2011–2012 VEI 4-5 eruption is the best scientifically observed and instrumentally recorded rhyolitic eruption to date. I document a complete cycle of pre-eruptive uplift, co-eruptive subsidence and post-eruptive uplift with InSAR data between March 2003 and May 2020, and produced by a complex interplay of magmatic processes. Pre-eruptive data show ~0.5 m of ground uplift in three distinct episodes between 2003 and 2011, with uplift rates between ~3 and ~30 cm/yr. The uplift was likely caused by magma injection resulting in pressurization of the magmatic system at depths of 4–9 km. Data spanning the first 3 days of the eruption show ~1.5 m of deflation produced by two distinct sources at 4–6 km depth located 18 km from each other and up to 10 km from the eruptive vent -- suggesting hydraulic connectivity of a large magma mush zone. A third source of deformation was recorded during the rest of the eruption at a depth of ~5 km, resulting in a total subsidence of ~4.2 m during the whole eruption. On a much smaller spatial scale (~25 km2), InSAR-derived digital elevation models recorded ~250 m of uplift in the area of the eruptive vent interpreted as the intrusion of a shallow laccolith during the first 2.5 months of the eruption and time averaged lava discharge rates up to ~150 m3/s. The co-eruptive time series of reservoir pressure drop and extruded volume follow exponential trends that can be explained by a model of magma reservoir depressurization and conduit flow. Since the end of the eruption, the surface of the volcano was uplifted ~1 m in a sequence of three transient episodes of unrest during 2012 and 2019, with uplift rates between 6 and 45 cm/yr and lasting between 0.5 and 3.2 years. These pulses can be modeled by the same source, a sub-horizontal sill at a depth of ~6 km. Viscoelastic relaxation is not significant on these time scales, hence I interpret these uplift signals as being produced by episodic pulses of magma injection in the crystal mush that likely underlies the volcano. The episodic and abrupt changes of the ground deformation suggest a restless trans-lateral magmatic system at depths of 4–9 km, and active across multiple spatial and temporal scales. Finally, I also discuss challenges of the InSAR technology that should be addressed to detect ground deformation on short time scales, particularly under the low coherence conditions of Cordón Caulle.

Invited perspectives: The volcanoes of Naples: how can the highest volcanic risk in the world be effectively mitigated?

Abstract. The Naples (southern Italy) area has the highest volcanic risk in the world due to the coexistence of three highly explosive volcanoes (Vesuvius, Campi Flegrei and Ischia) with extremely dense urbanisation. More than 3 million people live to within 20 kilometres from a possible eruptive vent. Mitigating such an extreme risk is made difficult because volcanic eruption forecasting is currently an empirical procedure with a very uncertain outcome. This paper starts by recalling the state of the art of eruption forecasting, and then describes the main hazards in the Neapolitan area, shortly presenting the activity and present state of its volcanoes. Then, it proceeds to suggest the most effective procedures to mitigate the extreme volcanic and associated risks. The problem is addressed in a highly multidisciplinary way, taking into account the main economic, sociological and urban issues. The proposed mitigation actions are then compared with the existing emergency plans, developed by Italian Civil Protection, by highlighting their numerous, very evident faults. Our study, besides regarding the most complex and extreme situation of volcanic risk in the world, gives guidelines for assessing and managing volcanic risk in any densely urbanised area.

Geomorphology of the post-caldera monogenetic volcanoes at Deception Island, Antarctica — Implications for landform recognition and volcanic hazard assessment

Deception Island 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 have shown that volcanic activity on Deception Island can become a concern for tourists, scientists, and military personnel working on or near the island.The objective of this work is to identify eruptive processes and the geomorphic evolution of post-caldera monogenetic volcanic edifices at Deception Island by morphometric analyses, supported by field observations. Morphometric analysis has been used since the 1970s to analyse scoria cones, but it has rarely been applied to other monogenetic volcanoes, such as tuff cones and tuff rings. Tuff cones and tuff rings represent the most common landforms during Deception Island's recent geological past, with over 70 scattered eruptive vents inside and along the caldera rim. These volcanic landforms have been studied based on field observations and later, Digital Elevation Model analyses. Their geometry ranges from 10 to 100 m in height, and diameters vary between 300 and 2500 m. The morphometric data suggest that tuff cones have a more circular crater than tuff rings, with a significant separation between the two landforms using the height (Hco) and basal width (Wco) parameters. Tuff cones have Hco/Wco ratios with values between 0.04 and 0.16 and outer slopes between 7° and 34°. Tuff rings have lower Hco/Wco ratios that are between 0.01 and 0.04 and lower outer slopes between 3° and 21°.This study shows that basic shape parameters in combination with slope angle analysis can be used to discriminate among different types of monogenetic volcanoes. The initial eruptive-related morphometric diversity, however prevents correlation of eruption ages with morphometric parameters, or constructing a relative chronology of the monogenetic eruptions. This work provides a better comprehension of the potential evolution of a future eruption and a broader understanding of volcanic hazards on Deception Island.

Muographic monitoring of the volcano-tectonic evolution of Mount Etna

At Mount Etna volcano, the focus point of persistent tectonic extension is represented by the Summit Craters. A muographic telescope has been installed at the base of the North-East Crater from August 2017 to October 2019, with the specific aim to find time related variations in the density of volcanic edifice. The results are significant, since the elaborated images show the opening and evolution of different tectonic elements; in 2017, a cavity was detected months before the collapse of the crater floor and in 2018 a set of underground fractures was identified, at the tip of which, in June 2019, a new eruptive vent started its explosive activity, still going on (February, 2020). Although this is the pilot experiment of the project, the results confirm that muography could be a turning point in the comprehension of the plumbing system of the volcano and a fundamental step forward to do mid-term (weeks/months) predictions of eruptions. We are confident that an increment in the number of telescopes could lead to the realization of a monitoring system, which would keep under control the evolution of the internal dynamic of the uppermost section of the feeding system of an active volcano such as Mount Etna.

Eruptive history and volcano-tectonic evolution of Paka volcanic complex in the northern Kenya rift: Insights into the geothermal heat source

In this paper, we provide insights into the eruptive history and volcano-tectonic evolution of the Paka volcanic complex in a revised stratigraphic framework. We integrate all available 40Ar/39Ar radiometric dates along with field observations, remote sensing data, and the analysis of surface and cutting samples from a 2552 m deep borehole (PK-01). Chemical analyses distinguish basalt, hawaiite, mugearite, benmorite, and trachyte rock type in Paka. It also indicates that the eruptive products are genetically related by fractional crystallization. Major element mass balance and Rhyolite-MELTS models are consistent with the trachyte being generated by 74–83% fractional crystallization of Paka basalt. Before the growth of the volcano, volcanic activity was characterised by plateau fissure eruptions at 582–405 ka. Eruptions directly related to the Paka edifice are divided into four different volcanic sequences. Sequences 1–4 span the periods 390–278 ka, 247–205 ka, 160–36 ka, and 36–8 ka. The Pre-Paka plateau eruption products outcrop at the base of the volcano flanks and are overlain by edifice-forming trachyte. Initial caldera-related subsidence is expressed by arcuate structures to the west and southeast parts of the volcano. These initial collapses are associated with tuff and pyroclastic eruptions estimated to have occurred at ~38 ka. Following these explosive eruptions, a ~1.5 by ~1.6 km main caldera developed. The lithological information from the drilled geothermal exploration borehole PK-01 indicates a minimum thickness of ~2200 m for the extrusive lava sequences, with the uppermost 1050 m of the strata being directly related to eruptions from the Paka volcano (Phases 1–4). We estimate a minimum total bulk volume of ~50 km3 for the volcanic material erupted from Paka during the last ~390 ka. This translates to an average eruption rate of ~1.2 × 10−4 km3/yr. The associated advected magmatic heat supported an ‘excess’ heat flux ranging between 110 and 138 mW/m2 or about twice present day average continental flux (57 mW/m2) and about 1.3 times the background values in geothermal areas (90 mW/m2). The apparent high heat flux implies a magma-driven geothermal system, where convection of the hydrothermal fluid is occurring above the heat source. Structural mapping revealed normal faults, strike-slip faults, lineaments, and an array of eruptive vents and domes as the main volcano-tectonic structures. We infer at least four faulting and fault reactivation events that have occurred during Paka geological history. The structural orientations in the area are dominated by NNE and NW with subordinate N-S and NNW striking structures. Evidence suggests that the intersection of NNE and NW trending structures may have had a major influence on the volcanism in the area.

Spatiotemporal Seismic Structure Variations Associated With the 2018 Kīlauea Eruption Based on Temporary Dense Geophone Arrays

AbstractDuring the 2018 Kīlauea volcanic eruption, lava erupted from a series of new fissures in the lower East Rift Zone more than 30 km away from the summit through a dike intrusion. Between late May and early August, variations in the effusion rate at the persistent eruptive vent (Fissure 8) were observed following near‐daily summit caldera collapse events. Targeting the ongoing eruptive activity and the subsurface magma movement, we deployed a temporary dense seismic array. The observed time‐lapse changes in seismic velocity associated with the response of the summit collapse in three areas are presented in this study. The results show (1) clear spatially dependent co‐collapse velocity reductions across the newly‐intruded dike structure, (2) a gradual post‐collapse velocity increase near Fissure 8 correlated with the surge of magma supply, and (3) a gradual post‐collapse velocity increase on the summit likely associated with reservoir pressurization and crustal welding.

Machine Learning Reveals the Seismic Signature of Eruptive Behavior at Piton de la Fournaise Volcano.

Volcanic tremor is key to our understanding of active magmatic systems, but due to its complexity, there is still a debate concerning its origins and how it can be used to characterize eruptive dynamics. In this study we leverage machine learning techniques using 6 years of continuous seismic data from the Piton de la Fournaise volcano (La Réunion island) to describe specific patterns of seismic signals recorded during eruptions. These results unveil what we interpret as signals associated with various eruptive dynamics of the volcano, including the effusion of a large volume of lava during the August–October 2015 eruption as well as the closing of the eruptive vent during the September–November 2018 eruption. The machine learning workflow we describe can easily be applied to other active volcanoes, potentially leading to an enhanced understanding of the temporal and spatial evolution of volcanic eruptions.

Three‐Dimensional Mapping of Mt. Ruapehu Volcano, New Zealand, From Aeromagnetic Data Inversion and Hyperspectral Imaging

AbstractCombining 3‐D inversion of high‐resolution aeromagnetic data with airborne hyperspectral imaging creates a new method to map buried structure and hydrothermal alteration, applied to Mt. Ruapehu volcano, New Zealand. Hyperspectral imaging is sensitive to surface mineralogy including alteration minerals, while magnetic vector inversion reveals the volumetric distribution of magnetic susceptibility from which we interpret buried geology. Probability assessment from multiple model regularizations provides an important model uncertainty estimate. At Ruapehu, hyperspectral imaging highlights two main regions of surface alteration: the Pinnacle Ridge and the southeast flanks. The magnetic model of Pinnacle Ridge shows that alteration seen at surface continues to depth, but strongly magnetic, unaltered dikes form the core of the ridge. On the southeast flanks, the magnetic model also shows alteration imaged on the surface continues to depth; however, a previously unknown, magnetized sill intrudes part of the flank. Several smaller demagnetized regions are modeled, unlike at neighboring Mt. Tongariro where the hydrothermal system created a large demagnetized core. We propose that these differences relate to spatially focused (Ruapehu) vs distributed (Tongariro) eruption vents, the degree of faulting of the edifice and its glaciation history. Lava‐ice interaction produces fine‐grained lavas with measured magnetic susceptibilities similar to some moderately altered lavas, illustrating that care must be taken in the interpretation of magnetic data in the absence of geological information. The combination of hyperspectral imaging and aeromagnetic data inversion distinguishes shallow surface weathering from deeper‐seated hydrothermally altered rock masses, with implications for the magnitude and probability of collapse events.

Initiation of dilute and concentrated pyroclastic currents from collapsing mixtures and origin of their proximal deposits

Numerical solution of the time-dependent conservation equations for mass, momentum, specific internal energy, and granular temperature in flows involving gas-particle mixtures is used to explore the initiation of pyroclastic currents from collapsing mixtures such as during fountaining eruptions. One objective is to determine when a depth-averaged granular flow model or a box model for dilute currents is most applicable for hazards modeling of pyroclastic currents produced by column collapse; a second objective is to gain insight into the formation of proximal breccia facies of ignimbrites. Collapsing gas-particle mixtures impacting a flat surface are modeled with mixtures of coarse particles that are poorly coupled with the gas phase and well-coupled fine particles. Resulting lateral flows are sensitive to the impact speed, overall particle concentration, and proportions of fine and coarse particles. For total particle concentrations of around 1 vol.%, an impacting mixture consisting of at least ~ 50% coarse particles, relative to fines, will tend to form a concentrated lateral underflow, which can be approximated by a depth-averaged granular flow model for hazard assessment purposes starting from the impact zone. Low total particle concentrations (e.g., total concentrations of ~ 0.1 vol.%) tend to produce dilute lateral flows that could be simplified to box model approaches for dilute pyroclastic currents. Larger total particle concentrations in impacting mixtures (~ 10 vol.%) produce granular underflows if they have any coarse particles, but these can be complicated by Mach number effects. For intermediate concentrations of the impacting mixture, a rough threshold for development of a concentrated underflow versus a dilute-only current is based upon the flux per unit area of coarse particles to the impact and their Stokes numbers. In general, some knowledge of the eruption column (fountain) conditions is required in order to make an informed decision as to which hazards modeling approach is most applicable for a given scenario. Modeling indicates that proximal breccias are related to influxes of coarse wall-rock material into an eruptive mixture, which increase both the total particle concentration and the proportion of coarse, dense clasts in the mixture that subsequently collapses and impacts the ground. The breccias record concentration of dominantly coarse clasts immediately upon impact and formation of concentrated flows that propagate laterally while expelled fines and gas flow rapidly overhead as dilute currents. Lateral and vertical heterogeneity in proximal deposits likely record rapid time and space variations in avalanches of material into eruptive vents, and the occurrence of breccia hummocks might record the temporary positions of impact zones.