Journal of Volcanology and Geothermal Research最新文献

Distinguishing volcanic debris avalanche deposits from other epiclastic breccia could be complex. For more than 60 years, the Tinguiririca deposit (sourced from the homonymous volcano) in the Andes of Central Chile has been described by different authors as glacial moraines, a lahar, a volcanic debris avalanche, and even a debris flow deposit. To decipher its obscured origin and emplacement dynamics, we have carried out a detailed investigation of its distribution, contact relationships, sedimentology, and facies. Our findings unravel that the 57 km-long deposit is 5 to 300 m thick, totalling a reconstructed volume of 3.64 ± 0.05 km³. It is composed of unsorted heterometric breccias formed by clasts and blocks arranged in mixed and matrix facies characterised by distinctive lithological domains. In general, three clasts lithologies are dominant, consisting of black and grey andesites and hydrothermally altered clasts with jigsaw cracks and fractures. The deposit overlies terraced colluvium along the valleys and forms hummocks and ridges. Emplacement velocities estimates range from 39.6 m/s to 108.4 m/s. Therefore, the Tinguiririca deposit should represent a massive volcanic debris avalanche that formed after a lateral collapse that affected the ancient Tinguiririca Volcanic Complex, during the Late Pleistocene (between 45 ± 18 and c. 19.2 ± 1.2 ka). The abundance of hydrothermal minerals within the deposit's matrix and clasts (i.e., illite, phengite, epidote, tridymite, chlorite, hematite, jarosite, and alunite) all represent the volcano's hydrothermal system that likely favoured rock weakness and edifice collapse. Finally, the new interpretation is valuable for evaluating volcanic hazards and requires further mapping and research efforts.

The mass eruption rate (MER) of an explosive volcanic eruption is a commonly used quantifier of the magnitude of the eruption, and estimating it is important in managing volcanic hazards. The physical connection between the MER and the rise height of the eruption column results in a scaling relationship between these quantities, allowing one to be inferred from the other. Eruption source parameter datasets have been used to calibrate the relationship, but the uncertainties in the measurements used in the calibration are typically not accounted for in applications. This can lead to substantial over- or under-estimation. Here we apply a simple Bayesian approach to incorporate uncertainty into the calibration of the scaling relationship using Bayesian linear regression to determine probability density functions for model parameters. This allows probabilistic prediction of mass eruption rate given a plume height observation in a way that is consistent with the data used for calibration. By using non-informative priors, the posterior predictive distribution can be determined analytically. The methods and datasets are collected in a python package, called merph. We illustrate their use in sampling plausible MER—plume height pairs, and in identifying usual eruptions. We discuss applications to ensemble-based hazard assessments and potential developments of the approach.

Typical eruptions at Kīlauea volcano involve the evacuation of magma from the summit and/or south caldera reservoirs towards the East or Southwest rift zones. The reservoir drainage provokes the summit deflation, and on extreme occasions, such as in 2018, the summit caldera collapse. Systematically, seismic tremor, often with a particular multichromatic spectral signature characterized by frequency gliding, accompanies summit deflation episodes. In 2018, this type of continuous tremor accompanied the steady subsidence stage, whereas discrete earthquakes dominated the collapse stage. In this work, we aim to understand the source mechanism of the syn-deflation tremor of 2018. To locate the seismic source, we develop a novel machine-learning-based algorithm as an alternative to the amplitude source location technique. We use a large high-resolution catalog to resolve a composite amplitude decay function. Under these conditions, our method outperforms the traditional technique. We locate the tremor source 1 km below the eastern perimeter of the Halema‘uma‘u crater, which coincides with the position of the summit magma reservoir, as determined in many other studies. Furthermore, we model the seismic source as pressure oscillations driven by gas porous flow at the roof of the reservoir. In this model, gas accumulates temporarily in many gas pockets between the magma and the roof. Our modeling shows that the gas flux is responsible for the tremor amplitude modulations, whereas the gas pocket thickness controls the frequency variations. Beyond a critical point of depressurization, the magma cannot contribute further to the tremor oscillations via decompression-driven degassing, nor support the roof above it, resulting in rock failure. This work advances our understanding of magma-degassing dynamics and tremor generation at Kilauea volcano, and provides novel seismological techniques for volcano seismology monitoring and research.

The 1991 eruption of Avacha volcano resulted in a lava plug inside its crater, making high-temperature fumaroles available for sampling. At present, there are two high-temperature fumarolic fields: the Eastern (up to 665 °C) and the Western (up to 840 °C), both associated with a fissure in the lava plug caused by a weak 2001 explosion. The paper presents chemical and isotopic compositions (H-O-C-S) of the directly sampled fumaroles over the period 2013–2023, mainly from the Eastern field. We revealed seasonal variations of water isotopic composition and concentrations of some components of the gas. High-temperature gases from Avacha volcano are characterized by chemical and isotopic compositions typical for volcanoes in subduction zones, but with a slightly increased content of H₂O, a reduced content of HCl. A relatively high concentration of methane is noted in the gases of low-temperature field. Methane in high-temperature gas with δ¹³C(CH₄) = −16.8 ‰ has abiogenic origin. For high-temperature gases, their redox state (H₂/H₂O and CO/CO₂) is controlled mainly by the sulfur gas buffer (H₂S/SO₂); methane is not chemically equilibrated. The molar ratio C/S ∼ 1 is typical for volcanoes in the Kuril-Kamchatka Arc. The measured fumarolic temperatures at the Eastern field are descending over time from 626 °C in 2013 to 410 °C in 2023. The apparent equilibrium temperatures calculated for reactions that include CO, CO₂, H₂, H₂O, H₂S and SO₂ are generally higher than the measured temperatures and do not show the descending trend. However, calculated equilibrium temperatures for the H₂O-CO-CO₂-CH₄ system are very close to the measured temperatures. Two periods of the increased seismic activity which occurred from 2013 to 2023, in November 2014–January 2015 and October–December 2019, correlated with changes in the morphology and gas flow rates at the Western fumarolic field.

In this paper, we present our understanding of the importance of affects in people's sense-making of volcanic risk in everyday life. In doing so, we explore how local knowledge on volcanism is produced and circulated through communities' ongoing affective encounters with volcanoes. Through ethnographic fieldwork and semi-structured interviews, we draw on the heterogeneous experiences and narratives of Malalcahuello residents living next to the Lonquimay volcanic complex in the Southern Andes of Chile. Its last eruption in 1988–1990 formed a new cone on the NE flank, called Navidad (Christmas), which has allowed residents to experience active volcanism in a twofold sense: being affected by its impacts during the eruption, and responding affectively to the volcano in everyday life. The results pave the way for a typology of affect-based ways of knowing volcanism. These are constituted by multiple people's viewpoints: 1) knowing the ground, 2) knowing the territory, 3) knowing the risk, and 4) knowing the behaviour. These ways of knowing vary according to, and are in part determined by, the different rhythms of the volcano itself. Therefore, active volcanism becomes a more-than-human agent of knowledge through its rhythmic presence in people's everyday lives. Over time, the local population has become affectively attuned to both ‘hazardous situations’ related to volcanic eruption and ‘risk and safe situations’ during volcanic quiescence. These attributes of human-volcano encounters turn hazardous spaces into affect-laden spaces at different times, raising the need to rethink spatio-temporal dimensions in knowledge dialogue and disaster risk reduction. Overall, the paper underlines the importance of affect-oriented risk research in Chile and worldwide to account for the pre-existent viewpoints from which a volcano is at the heart of people's concerns.

We use new geochemical, petrological, and rheological data to constrain the formation and emplacement of the highly compositionally unusual(andesitic basalt) Kīlauea 2018 Fissure 17 (F17) eruptive products. Despite the restricted spatial and temporal distribution, F17 samples are texturally and geochemically diverse. The western samples are enriched in SiO₂ by up to 10 wt%, relative to their eastern equivalents; additionally, the western samples contain microcrystalline enclaves, absent from the homogenous eastern samples. The compositions erupted along F17 suggest interaction between the basaltic 2018 juvenile magma and a crystal mush at depth, likely a left-over from the nearby 1955 eruption. Magma mingling caused heating and local melting of remnant mush, leading to melt hybridization and volatile exsolution. Rapid water exsolution likely caused overpressurization of the reservoir underneath the western side of F17, leading to Strombolian explosions of viscous magma, in contrast to sustained Hawaiian fountaining on the eastern side. Remelting of remnant crystal mush and melt hybridization in open-conduit systems may hence be an effective mechanism in inducing volatile saturation.

Volcanic regions are prime areas for harnessing geothermal energy. However, the geological complexity of these regimes can hinder the efficient exploitation of this renewable resource. As useful as geophysical surveys are in understanding the subsurface, models can be unconstrained due to the lack of realisitic data. Here, we present the results of a new laboratory study measuring permeability and P-wave velocity on altered lavas, volcaniclastic sediments and limestones samples obtained from three cores retrieved from the MON-3 well, drilled in the Montserrat geothermal field. By measuring these parameters at increasing effective pressure varying from 10 to 70 MPa, we found permeability stress senstivity factors varying from 0.006 to 0.122 MPa⁻¹ and increases in P- wave velocity between 2 and 20 %. The highest permeability stress senstivity factor and largest increase in P-wave velocity found in altered lavas were interpreted to be as a result of the easy closure and deformation of slit shaped microfractures and smectite clays characteristic of low bulk modulus. Conversely, lowest permeability stress senstivity factors and smallest increases in P-wave velocity found in volcaniclastic sediments, were coincident with intergranular pore geometries and higher bulk modulus minerals such as quartz and illite-smectite that may enhance the rigidity of the rock. Additionally, by measuring permeability and P-wave velocity on samples cored perpendicular (vertical) and parallel (horizontal) to the axis of the core, we found higher permeability senstivity factors (0.001–0.05 MPa⁻¹ higher) and P-wave velocity increases (1–4 % higher) on horizontal samples, which is consistent with the preferential closure of horizontally oriented pore spaces. From this experimental study, we provide implications for enhancing geothermal energy recovery in Montserrat. Overall, our findings can be utilized to help improve on geophysical and numerical models of volcanic geothermal regimes.

A long-lived eruption of Popocatépetl volcano in central México has produced almost continuous ash fall on the populated areas for 30 years. The eruptive phase that began in 1994, has been characterized since 1996 by the growth of about 90 subsequent crater domes and their destruction that has produced most of the ongoing ash emissions. Since the beginning of the ash emission in 1994, we designed, established, and maintained an ash-sampling network of more than 200 sites around the volcano. This sampling network has been improved over the years and there are currently also 19 automated samplers, that we describe in this manuscript. This ash sampling network is part of the Popocatépetl monitoring system run by Universidad Nacional Autónoma de México (UNAM). The sampling sites that are distributed over an area of ∼8000 km² where ash fall occurs, involve collection of ash over 0.4 cm² and 1 m² areas during ash emission events associated with plumes over 1 km high. Community participation has greatly enhanced both, ash sample collection efficiency and public awareness.

Growth and destruction of lava domes are variable over time, with growth times that could last up to weeks and residence times ranging from days to months, producing frequent ash emissions. There have been about 1225 ash emissions >1 km high, of these, 110 have been identified with ash columns from 3 to 13 km high above the crater (8.5–18.5 km asl), some of which has produced abundant ash fall in nearby populations. Ashfall has been distributed in all directions around the volcano up to 2 50 km from the crater but dominantly in the east and northeast direction. The total minimum volume of non-compacted ash emitted over these three decades is >149 × 10⁶ m³ while the estimated total volume of lava emitted in the form of domes is >70 × 10⁶ m³.

The average ash mass load is 32 g/m² and the ash is commonly deposited <30 km from the crater and up to 250 g/m² have been deposited in periods of intense activity. Ash grainsizes range from coarse to extremely fine (MdPhi 1–6) with up to 37% of particles smaller than 10 μm and up to 10% smaller than 2.5 μm. Medium lapilli (MdPhi −3) was ejected during a sub Plinian event in 2001.

Ash emission is common in both dome growth and destruction phases, as well as in the clearing of the conduits during explosive phases in the absence of domes. Vitreous lithic fragments are produced by fragmentation of the degassed lava domes in the vent. Higher amounts of vesicular clasts, individual glass particles and crystals, on the other hand, are associated with magma ascent into a more open vent. The higher percentage of accidental lithic particles is linked to clearing of the vent.

Seismicity at Mt. Vesuvius has been relatively weak in the last decades. While the occurrence of shallow volcano-tectonic (VT) events at Mt. Vesuvius is well known, the occurrence of deeper low frequency events (LF) was only recently recognized. Previous source studies only targeted VT events, which were found to have quite heterogeneous focal mechanisms. In this paper, we perform for the first time the source inversion of LF seismicity at Mt. Vesuvius, analysing 27 LF events recorded from 2012 to 2021 with the aim to investigate their source processes. Given the challenges of analysing weak LF earthquakes, we implement a specific moment tensor (MT) inversion approach that combines the fit of displacement seismograms in the time domain and amplitude spectra in the frequency domain. The inversion is simultaneously performed for the source depth and moment tensor components in the 2–7 and 2–5 Hz frequency band, assuming either a full or deviatoric MT representation. Source parameter uncertainties are estimated by using a Bayesian bootstrapping scheme. Our results confirm a larger depth of LF events compared to VTs and show a strong heterogeneity of the LF seismic sources, which present various rupture types, different orientations and heterogeneous, whilst poorly resolved, non-double-couple components. The MT variability is qualitatively confirmed by significant differences among the recorded waveforms. The heterogeneity of both VT and LF source processes is attributed to complex source processes in a highly fractured seismogenic volume submitted to a heterogeneous stress field.

Efficient outgassing of shallow magma bodies reduces the risk of explosive eruption. Silica-rich magmas are too viscous for exsolved gas bubbles to escape the system through buoyant forces alone, and so volatile overpressure is often released through deformation-related processes. Here we present a case study on magma emplacement-related deformation in a shallow (∼500 m depth) rhyolite intrusion (the Sandfell laccolith, Eastern Iceland) to investigate the establishment of degassing (volatile exsolution) and outgassing (gas escape) networks in silicic sub-volcanic intrusions. We observe viscous and brittle deformation features: from vesiculated flow bands that organized into ‘pore channels’ in the ductile regime, to uniform bands of tensile fractures (‘fracture bands’) that grade into breccia and gouge in the brittle regime. Through field mapping, structural analysis, and anisotropy of magnetic susceptibility (AMS) measurements, we show that areas with higher degrees of brittle deformation are proximal to abruptly changing AMS fabrics, and flow band orientations and point to laccolith-wide strain partitioning in the magma. We associate the changes in flow fabrics and the intensity of brittle deformation to the transition from dominantly horizontally flowing magma during initial sill-stacking to up to the NE magma flow linked to the propagation of a trap-door fault from the N to the SE. The establishment of intrusion-scale brittle permeable networks linked to changes in strain partitioning that facilitated magma flow during different stages of laccolith growth would have profoundly assisted the outgassing of the entire laccolith. Magmatic fracturing captures viscous and brittle processes working in tandem as an efficient outgassing mechanism, and should be considered in sub-volcanic intrusions elsewhere.