Journal of Volcanology and Geothermal Research最新文献

The thermal conductivity of volcanic rock is an essential input parameter in a wide range of models designed to better understand volcanic and geothermal processes. However, although volcanoes and geothermal reservoirs are often characterised by temperatures above ambient, laboratory thermal conductivity measurements are often performed at ambient temperature. In addition, there are currently few data on the temperature dependence of thermal conductivity for andesite, a common volcanic rock. Here, we provide elevated-temperature (up to 120 °C) laboratory measurements of thermal conductivity for variably porous (∼0.05 to ∼0.6) and variably glassy andesites from Mt. Ruapheu (New Zealand) using the transient hot-strip method. Our data show that (1) the thermal conductivity of these andesites has little to no temperature dependence and, therefore, (2) there is also no influence of porosity on the temperature dependence of thermal conductivity. We compare our new data with compiled published data to show that the thermal conductivity of volcanic rocks may decrease, remain constant, or increase as a function of temperature. We show that the thermal conductivity of amorphous glass and crystalline material increase and decrease, respectively, as temperature increases. We therefore interpret the temperature dependence of the thermal conductivity of volcanic rock to be dependent on glass content. The thermal conductivity of the studied andesites, the microstructure of which can be characterised by phenocrysts within a variably glassy groundmass, has little to no temperature dependence because the decrease in the thermal conductivity of the crystalline materials, due to decreases in lattice thermal conductivity, is offset by the increase in the thermal conductivity of the amorphous glass. A simple modelling approach, using the temperature dependence of the thermal conductivity of glass and crystalline material, provides a crystal content of 0.26 for a thermal conductivity independent of temperature, a common crystal content for andesite dome rock. Our findings imply that calculations of heat transfer through partially glassy volcanic rocks need not consider a temperature-dependent thermal conductivity, but that decreases and increases in thermal conductivity with temperature should be expected for fully crystallised or devitrified volcanic rocks and completely glassy volcanic rocks, respectively. We highlight that more experimental studies are now required to assess the evolution of thermal conductivity as a function of temperature in a wide range of volcanic rocks with different crystallinities.

Pululahua is a potentially active andesite and dacite lava dome complex. This paper presents the results of a survey focused on carbon dioxide (CO₂) diffuse degassing at Pululahua, which was conducted during the 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Commission of the Chemistry of Volcanic Gases (CCVG) 13th Gas Workshop. Our objective was to conduct a comprehensive investigation of CO₂ diffuse degassing by employing standard methods for measuring CO₂ flux and temperature, and data processing. These methods were applied to map the spatial distribution of the measured parameters, investigate the origin of CO₂, and quantify the volcanic CO₂ output within the surveyed area of Pululahua. We carried out a total of 350 soil CO₂ flux and 329 soil temperature measurements and collected 12 gas samples for carbon isotopic composition analysis, surrounding the three youngest domes in the complex. In addition, seventeen CO₂ flux measurements over a thermal water pool were performed. Our findings indicate that the diffuse emission at Pululahua's crater floor is fed by both biogenic and volcanic CO₂. Fluxes from each source are similar in magnitude, with approximately 90% of the measurements falling into an intermediate flux range. The occurrence of volcanic CO₂ emissions is supported by the carbon isotopic composition. Diffuse degassing distribution highlights a CO₂ anomaly surrounding the younger domes within the crater. We estimated the CO₂ diffuse emission using both statistical and geostatistical approaches over area of 3.36 km², resulting in values of 154.2 t d⁻¹ and 126.2 t d⁻¹ respectively. Based on the geostatistical quantification of the total CO₂ emission from soil degassing, Pululahua's crater volcanic CO₂ contribution is estimated between 59 and 97 t d⁻¹. Finally, the potential hazards associated with the release of cold CO₂ at Pululahua's crater are also discussed.

Explosive volcanism is one of the most dangerous and far-reaching natural hazards. The largest eruptions are the rarest, so studies of their temporal patterns have to rely on long archives. In this paper, we apply fractal and spectral analyses to the 6.2 Ma-long record of ash-falls at the Detroit Seamount (DS6M), > 600 km east of the Kamchatka Peninsula, NW Pacific, combined with a terrestrial record for the last 30 ka (T30ka). These datasets are the most complete for volcanism in the North Pacific, and DS6M spans all Pleistocene glaciations. In both datasets, events are grouped (Weibull parameter k < 0.84) with no characteristic scale of grouping in the time domain of thousands to millions of years. The fractal dimension of the studied data below the unity may be intrinsic to the volcanism (e.g. as a proxy of fractal composition and topography of a subducting plate) or represent uneven deposition and recovery of tephra. Only for the last 700 ka of DS6M, an increase in the correlation dimension values suggests the applicability of spectral analysis; however, no Milankovitch frequencies have been detected in this dataset. When compared to other North Pacific data for areas repeatedly glaciated in the Middle and Late Pleistocene and to a climate proxy of ¹⁸O isotopic stack LR04, the studied data suggest that variation in timing of ash-falls among the sites predominates over hemispheric-scale climatic forcing. If so, Quaternary glaciations had a limited effect on the timing of large explosive eruptions in North Pacific, still affecting the transit and deposition of erupted material.

Volcán de Colima, one of the Earth's most active and hazardous andesitic stratovolcanoes, experienced its last major explosive eruption on July 2015 with two distinct events. The July-10 event comprised the collapse of a large summit dome, forming block-and-ash flow deposits of dense dome lava clasts. The July-11 event produced pyroclastic density currents (PDCs) that flowed to maximum 10.5 km-distance from the crater, burned the vegetation, and formed valley and overbank deposits of up to 30 vol% vesicular scoria clasts. Whereas the July-10 event fits well within the last 20 years' typical activity of Volcán de Colima, the July-11 PDCs were unprecedented. We present a close examination of the July-11 deposits via combined field, microtextural, and chemical analyses, including electron microscopy and X-ray microtomography. Results show that andesite magma (58–59 wt% SiO₂) at 1021 °C and having 2 wt% H₂O degassed and crystallized (10²–10⁵ mm⁻³ vesicles and 10²–10³ mm⁻³ microlite number densities) while ascending to the surface from ∼2 km-depth reservoirs, driven by decompression rates of 0.4–1.7 MPa s⁻¹. These variable rates reflected heterogenous andesite magma rheology produced by different stages of melt genesis, mobility, stalling, crystallization and vesiculation. Prior to experiencing fragmentation, the andesite magma mingled with rhyolite melts produced from partial melting of silicic mush stored at depths from ∼2 to 5 km. Magmas fragmented at maximum strain rates of 10⁻³ s⁻¹, powering the July-11 energetic (10⁶–10⁷ kg s⁻¹) and pulsating PDCs that released 10²–10³ m³ s⁻¹ on surface. The rapid <20 h transition from the July-10 to the July-11 events suggests only hours timescales from dome collapse to magma decompression and explosive eruption.

We investigated the accurate locations of 443 explosion earthquakes that happened at Sinabung Volcano, North Sumatra, between October 2014 and June 2017. The explosion earthquakes were concentrated at shallow depths of approximately 1–5 km from the active crater. We used seismic tomography imaging to track the magma migration. Low Vp anomalies with low seismicity at shallow depths indicate that molten material originated from the shallow magma chamber. The presence of a shallow magma chamber of the Sinabung volcano was also revealed. The magma chamber with a volume of 2 km³ is located at a depth of 1.5–3.5 km below the summit. The magma plumbing system at shallow depths of approximately 1–5 km beneath the active crater was successfully imaged in detail.

It is intuitive to think that an earthquake near a volcano could disrupt its equilibrium and potentially trigger an eruption. But this cause-and-effect link is far from obvious for active volcanoes with an unknown internal stress state and the complexity of its magma-hydrothermal processes. This phenomenon is clearer in continental-oceanic subduction zones where volcanoes generally have closed-vent systems, differentiated high-viscosity magma, and active hydrothermal systems. This phenomenon is less well known in oceanic-oceanic subduction zones, where volcanoes often have open-vent systems, low-viscosity mafic magma, and hypothetic hydrothermal systems. The Vanuatu oceanic-oceanic subduction is an ideal zone to perform such study due to a high-seismic rate and volcanoes with different characteristics. The Vanuatu volcanoes display both open- and closed-vent systems, low and relatively high viscosity magma that enhance different types of volcanic activities (such as lava lakes, strombolian eruptions, high-eruptive columns, phreatic activity), and potential active hydrothermal systems. We compiled and identified sixty-nine cases of earthquakes potentially triggering volcanic activities on Vanuatu volcanoes from 1913 to 2018. Our findings indicate that the triggered volcanic responses occur co-seismically or shortly (at most 2–3 months later) after the earthquake, that the activated volcanoes are mainly located at near-field distances of the potentially triggering earthquake, implying a strong influence of static stress changes. Using the value of the seismic density energy, we suggest that the mechanism of the Vanuatu volcanic responses is due to changes of the permeability within active hydrothermal systems at Lopevi and Ambrym volcanoes in addition to the well-established ones, at Ambae, Garet, and Yasur volcanoes.

Magma migrations frequently trigger seismic swarms, resulting in seismic events that overlap in time and hinder real-time phase picking commonly used for hypocenter location. Addressing this challenge, seismic amplitude ratio analysis (SARA) allows identification of seismic migrations in real-time by simply tracking the relative seismic amplitude between a pair of seismic stations.

This paper aims to identify key statistical features of the seismic network array locations that improve their ability to detect seismic migrations using SARA. We evaluated the capability to detect the most frequently oriented magma migrations in over 100 volcanoes, using a criterion previously proposed to study vertical magma migrations in Piton de la Fournaise. Additionally, we investigate the influence of vent-station proximity on magma conduit coverage and identify the distance ratio that yields improved detection.

Furthermore, we estimate the seismic network efficiency by calculating the detection capability volume per station. We then use the random forest regression algorithm to identify which statistical features of the seismic network location contribute more to the efficiency disparity among different volcanoes. Notably, our findings reveal that optimizing seismic network coverage entails maximizing the standard deviation of relative pair station distances, while maintaining a prescribed minimum separation distance between station pairs. Our results reveal important criteria that can be used to optimize seismic network location design.

This research presents an extensive inventory of 103 small-volume monogenetic phreatomagmatic volcanoes (PVs) along the Trans-Mexican Volcanic Belt (TMVB), aiming to evaluate the influence of the external environmental parameters in phreatomagmatic volcanism. The formation of PVs (maar-diatremes, tuff rings, and tuff cones) is facilitated by the interaction of small volumes of magma and available water, conditions supported by frequent small-volume distributed volcanism and inter-montane lacustrine basins in the TMVB, a Plio-Quaternary continental volcanic arc with over 3000 monogenetic volcanic structures, of which only about 3% are PVs. The inventory was analyzed, dividing the structures into two groups based on their surface morphology: maar-diatremes and tuff rings (MD-TR, 81%), and tuff cones (TC, 19%). Morphometric correlations allow differentiation between these groups, although there is an overlap that could be caused by the presence of magmatic eruptive phases in some PVs. The type of aquifer host is the only environmental parameter with some discernible influence on the size of PVs.

Most of the PVs are clustered in three specific areas: Valle de Santiago, Serdán-Oriental, and Los Tuxtlas. The PV clusters highlight the combinations of environmental parameters under which phreatomagmatism is most successful in terms of frequency and size. Less frequent sets of parameters are reflected in the scattered PVs. The magmatic flux, presumably low, is considered the first-degree influence on the conditions for a phreatomagmatic eruption, provided that there is water availability. This availability is determined by the local climate as second-degree influence and by the local hydrogeological configuration as third-degree. The hydrogeological configuration parameters involve the aquifer host, permeability, spatial distribution and hydraulic gradient. If these conditions, enhanced by a humid climate, facilitate the development of an extensive aquifer in an area of small-volume volcanism, it is more likely that a PV cluster will form. This inventory serves as a foundation for future research on phreatomagmatic volcanism in the TMVB, emphasizing the need for multidisciplinary studies to fill the existing gaps in knowledge regarding internal parameters and the interaction between magmatic and environmental factors.

Understanding the detailed eruptive history and conditions during the buildup to catastrophic caldera-forming eruptions is essential for understanding the evolution of caldera volcanoes and predicting eruptive hazards. Towada Volcano is an active caldera volcano in the northern part of the Northeast Japan Arc. At least two catastrophic caldera-forming eruptions (eruptive episodes N and L) occurred during its caldera-forming stage (61–15.7 ka). A detailed geological survey identified three small vulcanian tephra layers that were erupted during the caldera-forming stage. The tephra layers are blue–gray ash fall deposits that consist mainly of fresh blocky dacite–rhyolite fragments. In ascending order, these deposits are assigned to eruptive episodes O′, N′, and M′. Each eruption had a volume of <0.11 km³, which is much smaller than that of other eruptions during the caldera-forming stage. The eruptive ages of episodes O′, N′, and M′ are estimated to be ca. 40, 23.1, and 17.2 ka, respectively, based on new ¹⁴C ages and paleosol thicknesses data. At least three cycles of a medium- to large-scale (3–20 km³) explosive eruption, preceded by a small vulcanian eruption (<0.11 km³), occurred during the latter half of the caldera-forming stage. The small vulcanian eruptions (episodes O′, N′, and M′) occurred after relatively long periods of quiescence (4000–14,000 years) and were followed by medium- to large-scale explosive eruptions (episodes N, M, and L) 1500–4000 years later. This cyclic activity probably reflects changes in overpressure in the magma reservoir. As the overpressure increased, episodes O′, N′, and M′ probably occurred when the overpressure had not increased sufficiently to trigger a medium- to large-scale explosive eruption, and episodes N, M, and L occurred at higher overpressures. These cycles characterize the fermentation phase of Towada Volcano, and terminated with the formation of the Towada Caldera during episode L at 15.7 ka. The magma composition and eruption frequency changed abruptly after episode L, and a small stratovolcano was formed through intermittent eruptions of mafic magma. This change suggests that the caldera collapse during episode L changed the entire shallow magmatic system that existed during the fermentation phase, and the system shifted to a recovery (post-caldera) phase. Based on eruptive volumes and frequencies, the present Towada Volcano has not yet reached the conditions that existed during the late caldera-forming stage and is therefore unlikely to produce a catastrophic caldera-forming eruption in the near future.