Bulletin of Volcanology最新文献

Sangay volcano is considered as one of the most active volcanoes worldwide. Nevertheless, due to its remote location and low-impact eruptions, its eruptive history and hazard scenarios are poorly constrained. In this work, we address this issue by combining an analysis of monitoring data and historical chronicles with expert elicitation. During the last 400 years, we recognize periods of quiescence, weak, and enhanced eruptive activity, lasting from several months to several years, punctuated by eruptive pulses, lasting from a few hours to a few days. Sangay volcano has been mainly active since the seventeenth century, with weak eruptive activity as the most common regime, although there have also been several periods of quiescence. During this period, eruptive pulses with VEI 1–3 occurred mainly during enhanced eruptive activity and produced far-reaching impacts due to ash fallout to the west and long-runout lahars to the south-east. Four eruptive pulse scenarios are considered in the expert elicitation: strong ash venting (SAV, VEI 1–2), violent Strombolian (VS, VEI 2–3), sub-Plinian (SPL, VEI 3–4), and Plinian (PL, VEI 4–5). SAV is identified as the most likely scenario, while PL has the smallest probability of occurrence. The elicitation results show high uncertainty about the probability of occurrence of VS and SPL. Large uncertainties are also observed for eruption duration and bulk fallout volume for all eruptive scenarios, while average column height is better characterized, particularly for SAV and VS. We interpret these results as a consequence of the lack of volcano-physical data, which could be reduced with further field studies. This study shows how historical reconstruction and expert elicitation can help to develop hazard scenarios with uncertainty assessment for poorly known volcanoes, representing a first step towards the elaboration of appropriate hazard maps and subsequent planning.

Eruption source parameters (ESPs) are crucial for characterising volcanic eruptions and are essential inputs to numerical models used for hazard assessment. Key ESPs of explosive volcanic eruptions include plume height, mass eruption rate, eruption duration, and grain-size distribution. Some of these ESPs can be directly observed during an eruption, but others are difficult to measure in real-time, or indeed, accurately and precisely quantify afterwards. Estimates of ESPs for eruptions that cannot be observed, for example, due to the remote location of a volcano or poor weather conditions, are often defined using expert judgement and data from past eruptions, both from the volcano of interest and analogue volcanoes farther afield. Analysis of such information is time intensive and difficult, particularly during eruption response. These difficulties have resulted in the production of datasets to aid quick identification of ESPs prior to or during an eruption for use in operational response settings such as those at volcano observatories and Volcanic Ash Advisory Centres. These resources include the Mastin et al. (2009a) ESP dataset and the Catalogue of Icelandic Volcanoes and European Catalogue of Volcanoes aviation tables. Here, we review and compare these resources, which take different approaches to assigning ESPs. We identify future areas for development of these resources, highlighting the need for frequent updates as more knowledge of volcanic activity is gained and as modelling capabilities and requirements change.

The Rocourt Tephra (RT) is a widespread stratigraphic marker distributed in Germany, Belgium, and the Netherlands, where it is used for stratigraphic correlations, dating of host sediments and of Middle Palaeolithic archaeological assemblages, sometimes including Neandertal remains. Its age is estimated between 78 and 80 ka. This tephra has been linked to the West Eifel Volcanic Field in Germany, but its corresponding source volcano is unknown. Such a discovery would make it possible to confirm or challenge the age of the tephra, because this source volcano could be dated by various methods. It would also be possible to know the composition of the magma, which cannot be determined from the altered clasts of the tephra, as well as the original mineralogical composition, thereby strengthening the validity of the marker by providing more distinctive data. Two Eifel monogenic volcanoes have been cited as potential sources, the Dreiser Weiher and the Pulvermaar, due to their large sizes and broadly similar compositions. A study of the tephra layers from these volcanoes was carried out to compare their mineral compositions with that of the Rocourt Tephra. Based on new analytical data on the composition and magmatic trends of pyroxenes, it is concluded that neither of the two volcanoes can be the source of the RT.

We address emplacement mechanisms of pyroclastic density currents (PDCs) through relationships between their runout distance and mass discharge rate of their parent eruptions. Assuming axisymmetric propagation typical of dilute currents that are little controlled by topography, we apply a simple method to estimate the runout distance of concentrated PDCs channelized in valleys. With these data, the runout distance of concentrated currents varies, as for their dilute counterparts, with the discharge rate to the power ~ 0.5, the latter being the consequence of radial propagation of the currents. This simple dependence between runout distance and discharge rate is both surprising and remarkable considering the fundamentally different natures of dilute or concentrated PDCs, which are governed by complex physics involving many parameters. This dependence further suggests that particle settling velocity, which controls the rate of decrease of the flow mass, has a second-order effect on the runout distance. We argue that the hindered settling model established for particle suspensions in a static fluid is relevant for estimating the settling velocity of particles in concentrated PDCs. Settling velocities of ~ 0.1 to 10 cm/s calculated for some natural examples correspond to deposit aggradation rates of the same order. These rates imply timescales of deposit formation significantly shorter than flow durations in some cases, suggesting that onset of deposition occurs at late stages of emplacement.

The eruption of Hunga volcano on 15 January 2022 produced a higher plume and faster-growing umbrella cloud than has ever been previously recorded. The plume height exceeded 58 km, and the umbrella grew to 450 km in diameter within 50 min. Assuming an umbrella thickness of 10 km, this growth rate implied an average volume injection rate into the umbrella of 330–500 km³ s⁻¹. Conventional relationships between plume height, umbrella-growth rate, and mass eruption rate suggest that this period of activity should have injected a few to several cubic kilometers of rock particles (tephra) into the plume. Yet tephra fall deposits on neighboring islands are only a few centimeters thick and can be reproduced using ash transport simulations with only 0.1–0.2 km³ erupted volume (dense-rock equivalent). How could such a powerful eruption contain so little tephra? Here, we propose that seawater mixing at the vent boosted the plume height and umbrella growth rate. Using the one-dimensional (1-D) steady plume model Plumeria, we find that a plume fed by ~90% water vapor at a temperature of 100 °C (referred to here as steam) could have exceeded 50 km height while keeping the injection rate of solids low enough to be consistent with Hunga’s modest tephra-fall deposit volume. Steam is envisaged to rise from intense phreatomagmatic jets or pyroclastic density currents entering the ocean. Overall, the height and expansion rate of Hunga’s giant plume is consistent with the total mass of fall deposits plus underwater density current deposits, even though most of the erupted mass decoupled from the high plume. This example represents a class of high (> 10 km), ash-poor, steam-driven plumes, that also includes Kīlauea (2020) and Fukutoku-oka-no-ba (2021). Their height is driven by heat flux following well-established relations; however, most of the heat is contained in steam rather than particles. As a result, the heights of these water-rich plumes do not follow well-known relations with the mass eruption rate of tephra.

On 15 January 2022, Hunga volcano erupted, creating an extensive and high-reaching umbrella cloud over the open ocean, hindering traditional isopach mapping and fallout volume estimation. In MODIS satellite imagery, ocean surface water was discolored around Hunga following the eruption, which we attribute to ash fallout from the umbrella cloud. By relating intensity of ocean discoloration to fall deposit thicknesses in the Kingdom of Tonga, we develop a methodology for estimating airfall volume over the open ocean. Ash thickness measurements from 41 locations are used to fit a linear relationship between ash thickness and ocean reflectance. This produces a minimum airfall volume estimate of ({1.8}_{-0.4}^{+0.3}) km³. The whole eruption produced > 6.3 km³ of uncompacted pyroclastic material on the seafloor and a caldera volume change of 6 km³ DRE. Our fall estimates are consistent with the interpretation that most of the seafloor deposits were emplaced by gravity currents rather than fall deposits. Our proposed method does not account for the largest grain sizes, so is thus a minimum estimate. However, this new ocean-discoloration method provides an airfall volume estimate consistent with other independent measures of the plume and is thus effective for rapidly estimating fallout volumes in future volcanic eruptions over oceans.

We report CO₂ emission rates and plume δ¹³C during the July 2023 eruption at Litli Hrútur in the Fagradalsfjall region of the Reykjanes Peninsula. The CO₂ emission rates were measured by UAV utilizing a new method of data extrapolation that enables obtaining rapid flux results of dynamic eruption plumes. The δ¹³C values are consistent with degassing-induced isotopic fractionation of the magma during and after the eruption. Our results show that rapid, real-time CO₂ flux measurements coupled with isotopic values of samples collected at the same time provide key insights into the dynamics of volcanic eruptions and have the potential of forecasting the termination of activity.

Magma mingling and mixing are common processes at basaltic volcanoes and play a fundamental role in magma petrogenesis and eruption dynamics. Mingling occurs most commonly when hot primitive magma is introduced into cooler magma. Here, we investigate a scenario whereby cool, partially degassed lava is drained back into a conduit, where it mingles with hotter, less degassed magma. The 1959 eruption of Kīlauea Iki, Hawaiʻi involved 16 high fountaining episodes. During each episode, fountains fed a lava lake in a pit crater, which then partially drained back into the conduit during and after each episode. We infer highly crystalline tachylite inclusions and streaks in the erupted crystal-poor scoria to be the result of the recycling of this drain-back lava. The crystal phases present are dendrites of plagioclase, augite and magnetite/ilmenite, at sizes of up to 10 µm. Host sideromelane glass contains 7–8 wt% MgO and the tachylite glass (up to 0.5% by area) contains 2.5–6 wt% MgO. The vesicle population in the tachylite is depleted in the smallest size classes (< 0.5 mm) and has overall lower vesicle number densities and a higher degree of vesicle coalescence than the sideromelane component. The tachylite exhibits increasingly complex ‘stretching and folding’ mingling textures through the episodes, with discrete blocky tachylite inclusions in episodes 1 and 3 giving way to complex, folded, thin filaments of tachylite in pyroclasts erupted in episodes 15 and 16. We calculate that a lava lake crust 8–35 cm thick may have formed in the repose times between episodes, and then foundered and been entrained into the conduit during drain-back. The recycled fragments of crust would have been reheated in the conduit, inducing glass devitrification and crystallisation of pyroxene, magnetite and plagioclase dendrites and eventually undergoing ductile flow as the temperature of the fragments approached the host magma temperature. We use simple models of magma mingling to establish that stretching and folding of recycled, ductile lava could involve thinning of the clasts by up to a factor of 10 during the timescale of the eruption, consistent with observations of streaks and filaments of tachylite erupted during episodes 15 and 16, which may have undergone multiple cycles of eruption, drain-back and reheating.

Crystal-rich silicic lavas commonly erupt from hazardous lava dome-forming volcanoes, characterized by both effusive and explosive eruptions. Magma explosivity is inherently dependent on its ability to store pressurized gas, which can be released through permeable pathways like fractures or connected bubbles, yet the role crystals play in regulating gas escape is poorly constrained in crystal-rich systems. We explored the gas storage capacity and outgassing efficiency of crystal-rich magmas through experimental vesiculation of hydrous dacite samples containing crystal volume fractions (({phi }_{x})) between 0.5 and 0.8. The maximum unconnected gas volume (isolated porosity) decreases exponentially with increasing crystallinity. We quantify the relative outgassing efficiency as a function of ({phi }_{x}) using changes in isolated melt porosity during open-system degassing (outgassing). Mean isolated porosity, for ({phi }_{x}) = 0.5, increases from ~ 0.33 at the start of outgassing to ~ 0.67 by the end, doubling its trapped bubbles. For ({phi }_{x}) = 0.7, isolated porosity increases from ~ 0.1 to ~ 0.2, implying gas retention and outgassing efficiency are strongly dependent on crystallinity. Outgassing occurs rapidly via fracturing at porosities < 0.1 when ({phi }_{x}) ≥ 0.7. Fracturing and bubble coalescence are both inefficient outgassing mechanisms at ({phi }_{x}) = 0.5 due to viscoelastoplastic deformation, which leads to an increase of isolated porosity. Between ({phi }_{x}) of 0.5 and 0.7, samples sustained a three-fold difference in isolated porosity, implying that gas retention and eruptive behavior of crystal-rich magmas may be controlled by the onset and efficacy of crack-dominated outgassing and can be modulated by relatively small changes in crystallinity.

The 15 January 2022 eruption of Hunga volcano, Tonga, significantly impacted the Kingdom of Tonga as well as the wider Pacific region. The eruption column attained a maximum height of 58 km whilst the umbrella cloud reached a diameter approaching 600 km within about 3 h. The frequency of volcanic lightning generated during the eruption was also unprecedented, with the Vaisala Global Lightning Database (GLD360) recording over 3 × 10⁵ strikes over a 2-h period. We have combined Himawari-8 satellite imagery with the spatiotemporal distribution of lightning strikes to constrain the dynamics of umbrella spreading and infer a timeline of events for the climactic phase of the eruption. Lightning was initially concentrated directly above Hunga, with an areal extent that grew with the observed eruption cloud. However, about 20 min after the eruption onset, radial structure appeared in the lightning spatial distribution, with strikes clustered both directly above Hunga and in an annulus of radius ~ 50 km. Comparison with satellite imagery shows that this annulus coincided with the umbrella cloud front. The lightning annulus and umbrella front grew synchronously to a radius of ~ 150 km before the umbrella cloud growth rate decreased whilst the annulus itself contracted to a smaller radius of about 50 km again. We interpret that the lightning annulus resulted from an enhanced rate of particle collisions and subsequent triboelectrification due to enhanced vorticity in the umbrella cloud head. Our results demonstrate that volcanic lightning observations can provide insights into the internal dynamics of umbrella clouds and should motivate more quantitative models of umbrella spreading.