Volcanic System Research Articles

Distributed dynamic strain sensing of very long period and long period events on telecom fiber-optic cables at Vulcano, Italy

Volcano-seismic signals can help for volcanic hazard estimation and eruption forecasting. However, the underlying mechanism for their low frequency components is still a matter of debate. Here, we show signatures of dynamic strain records from Distributed Acoustic Sensing in the low frequencies of volcanic signals at Vulcano Island, Italy. Signs of unrest have been observed since September 2021, with CO2 degassing and occurrence of long period and very long period events. We interrogated a fiber-optic telecommunication cable on-shore and off-shore linking Vulcano Island to Sicily. We explore various approaches to automatically detect seismo-volcanic events both adapting conventional algorithms and using machine learning techniques. During one month of acquisition, we found 1488 events with a great variety of waveforms composed of two main frequency bands (from 0.1 to 0.2 Hz and from 3 to 5 Hz) with various relative amplitudes. On the basis of spectral signature and family classification, we propose a model in which gas accumulates in the hydrothermal system and is released through a series of resonating fractures until the surface. Our findings demonstrate that fiber optic telecom cables in association with cutting-edge machine learning algorithms contribute to a better understanding and monitoring of volcanic hydrothermal systems.

Tracking caldera cycles in the Aso magmatic system – Applications of magnetite composition as a proxy for differentiation

Caldera-forming eruptions are among the most hazardous natural events on Earth and pose a significant risk for global consequences in the future. Recent petrological re-evaluations of pre-, syn-, and post-caldera deposits in several volcanic systems worldwide suggest a cyclic behavior in the evolution of the subvolcanic reservoirs feeding these eruptions. Such caldera cycles are usually subdivided into maturation, fermentation and recovery phases, each characterized by distinct petrological features (e.g. variations in mineral and glass compositions). Combined with trends in intensive parameters and geophysical information about the eruptive behavior of the system, these characteristics can be used to determine the current state of a reservoir within the caldera cycle framework. Here, we test the application of this caldera cycle model on the Aso volcanic complex in Central Kyushu (Japan) by analyzing pre-, syn-, and post-caldera activity between the Aso-4 and Aso-3 events and evaluate the recent activity of Aso based on mineral and glass geochemistry. Widely overlapping compositions in most minerals (here plagioclase and orthopyroxene) and melt, as well as similar ranges in intensive parameters (e.g. magmatic H2O content), make it difficult to pinpoint chemical differences between pre- or post-caldera eruptions. Tracing the MnO/Al2O3 ratio in titanomagnetite, on the other hand, appears as a useful proxy to trace the level of differentiation within the reservoir prior to eruption. Titanomagnetite is an abundant mineral phase known to chemically re-equilibrate fast with melt and hence records “average” conditions prevailing just prior to eruption, with MnO showing a typical incompatible behavior during magma evolution, while Al2O3 is typically compatible. The assessment of different case studies revealed clear evolutionary patterns common in all these caldera cycles with low Mn (associated with low levels of differentiation) during recovery, progressively increasing during maturation, and culminating at highest levels (and associated levels of differentiation) during the fermentation phase, right before the next caldera-forming event. The MnO/Al2O3 ratio in titanomagnetite is analytically easy and quick to determine by electron microprobe, and gives valuable information about the current position of a system within the caldera cycle framework. Based on the evaluation of recent eruptive products in context with the current volcanic activity, we conclude that Aso is presently still in recovery after the massive Aso-4 eruption. Depending on magma supply from depth, the system can either enter renewed maturation or activity could decline leading to the cessation of the system.

A 3D geological model of El Hierro volcanic island reflecting intraplate volcanism cycles

Fully 3D and multidimensional geological models are key for energy, mining and water resources assessment and management, which has a great economic impact. 3D geological models provide critical information regarding geometric properties of the geological bodies of interest, such as ore deposits or reservoirs, allowing inference of volumes and availability to be exploited. However, defining a useful methodology to create a fully digital 3D geological model of volcanic islands is still very challenging due to the intrinsic complexity observed in the structure of volcanic systems. Two-dimensional geological maps, associated vertical geological cross-sectional diagrams and borehole and water-mining tunnels (galleries) logs were examined on El Hierro Island. A geological modelling procedure using the software GeoModeller obtained the first 3D geological model of El Hierro volcanic island, as a basis for volcanic formation definitions and geometric analysis. Surface, volume and center of mass estimations of the differentiated sub-units allowed a better understanding of the spatial distribution and evolution of the volcanic cycles of El Hierro Island over time. The 3D model provided geometry information correlatable with volcanic activity cycles and lava/pyroclast deposition mechanisms that ultimately defines the geometry of the volcanic units. This information provides new variables valuable for the investigation of the existing relationships between rift zones and giant lateral collapses. In addition, the obtained 3D geological model of a volcanic island will support the building of the first hydrogeological and geothermal model of El Hierro Island, allowing advancement of sustainability of isolated systems.

Deep magma degassing and volatile fluxes through volcanic hydrothermal systems: Insights from the Askja and Kverkfjöll volcanoes, Iceland

Mantle volatiles are transported to Earth's crust and surface by basaltic volcanism. During subaerial eruptions, vast amounts of carbon, sulfur and halogens can be released to the atmosphere during a short time-interval, with impacts ranging in scale from the local environment to the global climate. By contrast, passive volatile release at the surface originating from magmatic intrusions is characterized by much lower flux, yet may outsize eruptive volatile quantities over long timescales. Volcanic hydrothermal systems (VHSs) act as conduits for such volatile release from degassing intrusions and can be used to gauge the contribution of intrusive magmatism to global volatile cycles. Here, we present new compositional and isotopic (δD and δ18O-H2O, 3He/4He, δ13C-CO2, Δ33S-δ34S-H2S and SO4) data for thermal waters and fumarole gases from the Askja and Kverkfjöll volcanoes in central Iceland. We use the data together with magma degassing modelling and mass balance calculations to constrain the sources of volatiles in VHSs and to assess the role of intrusive magmatism to the volcanic volatile emission budgets in Iceland.The CO2/ΣS (10−30), 3He/4He (8.3–10.5 RA; 3He/4He relative to air), δ13C-CO2 (−4.1 to −0.2 ‰) and Δ33S-δ34S-H2S (−0.031 to 0.003 ‰ and −1.5 to +3.6‰) values in high-gas flux fumaroles (CO2 > 10 mmol/mol) are consistent with an intrusive magmatic origin for CO2 and S at Askja and Kverkfjöll. We demonstrate that deep (0.5–5 kbar, equivalent to ∼2–18 km crustal depth) decompression degassing of basaltic intrusions in Iceland results in CO2 and S fluxes of 330–5060 and 6–210 kt/yr, respectively, which is sufficient to account for the estimated CO2 flux of Icelandic VHSs (3365–6730 kt/yr), but not the VHS S flux (220–440 kt/yr). Secondary, crystallization-driven degassing from maturing intrusions and leaching of crustal rocks are suggested as additional sources of S. Only a minor proportion of the mantle flux of Cl is channeled via VHSs whereas the H2O flux remains poorly constrained, because magmatic signals in Icelandic VHSs are masked by a dominant shallow groundwater component of meteoric water origin. These results suggest that the bulk of the mantle CO2 and S flux to the atmosphere in Iceland is supplied by intrusive, not eruptive magmatism, and is largely vented via hydrothermal fields.

Analysis of Fluid Flow Pathways in the Mount Meager Volcanic Complex, Southwestern Canada, Utilizing AMT and Petrophysical Data

AbstractDefining the spatial distribution of geological structures and rock properties is important for understanding how fluid flow is controlled in a geothermal reservoir. Here, we present a procedure to examine the potential fluid pathways. By combining 3‐D resistivity models derived from audio‐magnetotelluric (AMT) data with available rock properties (porosity and permeability) and fluid sample data (fluid resistivity, salinity, and temperature), we investigated the relationship between electrical resistivity and fluid flow in an active volcanic system. Different petrophysical models and empirical relations are evaluated to determine the relationship between the fluid flow system at Mount Meager, British Columbia, and the resistivity model. In addition, we utilized porosity and permeability measured in the laboratory to define the porosity‐permeability relationship. The porosity of the volcanic core samples showed a range of 2.6%–23.2% and the permeability was in a range of 0.001–5,186.57 mD. The results showed the potential of 3‐D inversion of AMT data to map the fluid pathways at Mount Meager. These pathways are correlated with loss circulation zones in boreholes and can account for porosity up to 8.5%, which using the porosity‐permeability relationship translates to permeability of the order 0.249 mD. Not only are the fault and fracture zones important for reservoir exploitation, but they also provide permeability for the circulation of meteoric water. Our studies suggest that a set of fractures with 0.1 m spacing and 20 mm aperture can keep 40% fluid in pores and transmit fluid with possible permeability of 666 mD.

Evolution of Stresses Over Conjugate Faults in Hjalli‐Ölfus, South Iceland

AbstractHjalli‐Ölfus is the westernmost segment of the east‐west transform South Iceland Seismic Zone (SISZ), which is the eastward extension of the ∼ENE‐trending transtensional Reykjanes Peninsula (RP). Historically, the area has shown an interactive behavior with the Hengill volcanic system to the north and the central SISZ to the east. We analyzed the state of stress and faulting mechanisms in Hjalli‐Ölfus between July 1991 and December 1999, in connection with the Hengill inflation episode (Feigl et al., 2000, https://doi.org/10.1029/2000JB900209) and the 13th November 1998 Mw 5.1 Hjalli‐Ölfus earthquake. We find that this region predominantly hosted oblique‐normal and left‐lateral strike‐slip events (4–10 km‐depth), with most nodal planes oriented along ∼ENE or ∼WSW directions (75° ± 15° or 255° ± 15°). We identify 5 stages of stress evolution from January 1991 to December 1999 over which Hjalli‐Ölfus experiences both spatial and temporal shifts in stress‐states. The Hengill inflation likely loaded both the fissure zone and western Ölfus, culminating in the Mw 5.4 (Hengill) and Mw 5.1 (Hjalli‐Ölfus) earthquakes. Following these events, the maximum compressive stress (SHmax) orientation near the location of the Mw 5.1 earthquake showed a ∼5°–7° counterclockwise swing, compared to SHmax before June 1998. The average SHmax (∼40° ± 1°) and minimum principal stress ( ∼ 130° ± 1°) are comparable to geological trends in the RP. We conclude that Hjalli‐Ölfus shows clockwise SHmax rotation upon loading, while a stress‐drop reverses the rotation. We also posit that the region, especially the western end, behaves like the RP during interseismic periods.

Detection of Geothermal Anomalies in Hydrothermal Systems Using ASTER Data: The Caldeiras da Ribeira Grande Case Study (Azores, Portugal).

Current-day volcanic activity in the Azores archipelago is characterized by seismic events and secondary manifestations of volcanism. Remote sensing techniques have been widely employed to monitor deformation in volcanic systems, map lava flows, or detect high-temperature gas emissions. However, using satellite imagery, it is still challenging to identify low-magnitude thermal changes in a volcanic system. In 2010, after drilling a well for geothermal exploration on the northern flank of Fogo Volcano on São Miguel Island, a new degassing and thermal area emerged with maximum temperatures of 100 °C. In the present paper, using the ASTER sensor, we observed changes in the near-infrared signals (15 m spatial resolution) six months after the anomaly emerged. In contrast, the thermal signal (90 m spatial resolution) only changed its threshold value one and a half years after the anomaly was recognized. The results show that wavelength and spatial resolution can influence the response time in detecting changes in a system. This paper reiterates the importance of using thermal imaging and high spatial resolution images to monitor and map thermal anomalies in hydrothermal systems such as those found in the Azores.

Early fumarolic minerals from the Tajogaite volcanic eruption (La Palma, 2021)

This work constitutes the first geochemical, mineralogical and textural analysis of the early fumarolic deposits that appeared in the Tajogaite Volcano (La Palma island, Spain) one month after the official end of the eruptive process. Fourteen fumaroles grouped into 5 study areas have been characterized following a novel methodology that includes on-site microscopic observations and weak samples preservation for their laboratory characterization. Three main mineralogical zones were identified in the fumaroles: 1) sulphur-sulphate; 2) halides; and 3) salammoniac zone. Zones 1 and 2 are included in the S-gas domain and the predominance of sulphur-sulphate minerals or halides in the mineral deposits is dependent on the gas temperature (halides appear in the high temperature fumaroles). Zone 3 overlaps the (HCl-CO) and (HCl) -gas domains. The thermal analysis of the fumaroles provides the sequence of mineral suites according to the vent temperature. Sylvite-halite-tenorite are revealed as typical minerals of high-temperature fumaroles (>530 °C), whilst Ca, Mg and Na sulphates appear in low-temperature fumaroles (<200 °C). Salammoniac-Mascagnite forms in intermediate ranges (170–350 °C). Finally, three different fumarole types are recognized (punctual, diffuse and associated to fissures), establishing different environmental conditions for mineral precipitation. Differences are based on the gas flux mechanism, the gas-rock interaction intensity, temperature and gas concentrations. All these data will serve as a referenced starting point for later studies focused on fumarole evolution and the degassing process of volcanic systems in oceanic volcanic islands framework.

Contribution to the characterization of the Nevado del Ruiz geothermal conceptual model based on rock properties dataset

The assessment of the geothermal resources available in a specific area requires a detailed knowledge of the thermal and hydraulic properties of host rock formations. These properties were quantified with rock samples mainly collected at the intersection between Nereidas, Cueva-Pirineos, and La Tosca-El Descanso faults, to the West of the Nevado del Ruiz volcano (Colombia), to improve the characterization of this volcanic geothermal system. The geological formations analyzed in this study are the Cajamarca Complex, PRE-Ruiz lava flows, Andesites unit, and volcanic member of the Quebradagrande Complex. A 3D geological conceptual model for the study area and a geological cross-section are presented. 113 laboratory measurements allowed to quantify thermal conductivity (TC) and diffusivity (TD), heat capacity (HC), porosity, and permeability of the rock samples collected. The Cajamarca Complex is the lithology with the highest TC (2.9 W m−1 K−1), but with the lowest primary permeability (0.038mD) and porosity (3.4%). Regarding extrusive igneous rocks, the Andesites unit present significative porosity (10.7%), and the PRE-Ruiz lava flows show a low TC (1.5 W m−1 K−1). The results of 6 petrographic analyses of thin sections of the PRE-Ruiz lava flows and Cajamarca Complex helped to justify the values of their thermal properties. Quartz-filled veinlets and garnet are identified in the volcanic member of the Quebradagrande Complex. Both minerals indicate that fluids might have circulated at high temperature. It is the first time that garnet is identified in rock samples of this region; since it can be the result of high temperature hydrothermal alteration mineral, its origin must be confirmed, and its identification provides new insights about the geothermal resources in the area. The conceptual model, the thin section results, and the quantification of rock properties are relevant public data for future geothermal development. All data reported in this manuscript are disclosed as supplementary material, providing a significant scientific contribution in the form of an open dataset that can be used as a basis for future hydrothermal modelling of the Nevado del Ruiz geothermal system, where is the most advanced geothermal development project in Colombia, and other similar geothermal systems.

Structural and diagenetic signatures of a very shallow sub-volcanic intrusion into a carbonate platform (Albian, Basque-Cantabrian Basin, Northern Spain)

In several tectonic contexts and especially in hyper-extensive basins, magmatic rise may crosscut shallow marine carbonate series, forming either volcanic systems or only igneous intrusions at various depths. Impacts of these magmatic events on the surrounding carbonate sediments can be significant and are relatively well documented from a geometrical, sedimentological and hydrochemical point of view. Their diagenetic signature (e.g., early diagenetic phases in cases where magma reaches or approaches the surface) still remains poorly investigated. In this paper the authors use a multi-proxy approach combining morpho-structural, diagenetic (cement stratigraphy), geochemical (carbon and oxygen isotope, U–Pb dating) and sedimentological study to investigate the Larrano igneous body contemporaneous with the Urgonian limestones (Early Albian) of the Duranguesado platform, in the well-preserved and hyper-extended Basque-Cantabrian Basin. This investigative work produced several results: the first result, combining morpho-structural and sedimentological data, is the model of a basaltic magma rising along normal faults but stopping about 50 m below the paleo-seafloor; another is the detailed description the “Larrano eogenetic anomaly” that includes cataclastic fractures, dissolution, Fe oxy-hydroxides, ferroan saddle dolomite and magnesian calcite. Such phases form an early diagenetic overprint around the igneous body and testify to the thermal shock and warm seawater circulation occurring at the time of and just after the intrusion. Pre-intrusive and post-intrusive hydrothermally-influenced cements and facies are also recorded and are perfectly calibrated by a detailed cement stratigraphy associated with a layering model of the sedimentary units. The role of magmatic CO2 contribution is not quantified in the present study. Furthermore, the δ13C signature of various cements, micrites and bioclasts suggests no thermogenic methane contribution, unlike other Albian magmatic intrusions hosted by different lithologies and recorded at various depths below the paleo-seafloor.

Monitoring groundwater storage in a fractured volcanic aquifer system.

The use of groundwater resources is under increasing pressure to meet the demands of the society. Despite this, the understanding of its availability is still limited when compared to other water reserves. The aquifer studied was the volcanic Serra Geral Aquifer System (SASG) located in a humid subtropical region. This research aims to explore in a pioneering way the large-scale hydrogeological processes taking place at the SASG using a unique and complementary tool of intensive field monitoring, remote sensing data, and hydrological modeling. Results showed a fast response of groundwater levels to rainfall, with an average of 29days of lag times. We also identified areas in the southern region of the basin with higher depletion rates, with GRACE results indicating a negative trend (- 57mmyear-1) associated with a major recharge event that occurred in the region before the period monitored. Also, the interflow calculated using the MGB hydrological model showed that the flow within the limits between the soil and the volcanic rocks (different in hydraulic conductivity) varies spatially, influencing the baseflow of rivers as for slopes and soil capacity to store water.

A pseudo-karst approach to groundwater modeling in volcanic basalt aquifer systems: application of a discrete-continuum model to simulate Lyman spring, Hawaii Island

A pseudo-karst approach to groundwater modeling in volcanic basalt aquifer systems: application of a discrete-continuum model to simulate Lyman spring, Hawaii Island

Pre-eruptive dynamics at the Campi Flegrei Caldera: from evidence of magma mixing to timescales estimates

We review pre-eruptive dynamics and evidence of open-system behavior in the volcanic plumbing system beneath Campi Flegrei Caldera, together with estimates of magma residence time, magma ascent, and mixing-to-eruption timescales. In detail, we compile pre- and syn-eruptive dynamics reported in the literature for (a) the Campanian Ignimbrite ~ 40 ka, (b) the Neapolitan Yellow Tuff (~ 15 ka), and (c) the recent activity within the Phlegrean area. We first summarize geochemical and textural evidence (e.g., magma mixing, crystal disequilibria, vertical zonings, and isotopic records) of open-system behavior for the pyroclasts erupted in the last 40 ky at Campi Flegrei Caldera. We show that the fingerprint of open-system dynamics is ubiquitous in the deposits associated with the volcanic activity at the Campi Flegrei Caldera in the last 40 ky. Then, we describe the results of geophysical and petrological investigations that allow us to hypothesize the structure of the magma feeding system. We point to a trans-crustal magmatic feeding system characterized by a main storage reservoir hosted at ~ 9 km that feeds and interacts with shallow reservoirs, mainly placed at 2–4 km. Finally, we define a scenario depicting pre-eruptive dynamics of a possible future eruption and provide new constraints on timescales of magma ascent with a physical model based on magma-driven ascending dyke theory. Results show that considerably fast ascent velocities (i.e., of the order of m/s) can be easily achieved for eruptions fed by both shallow (i.e., 3–4 km) and deep (i.e., ~ 9 km) reservoirs. Comparing the results from experimental and numerical methods, it emerges that mixing-to-eruption timescales occurring at shallow reservoirs could be on the order of minutes to hours. Finally, we highlight the volcanological implications of our timescale estimates for magma ascent and mixing to eruption. In particular, explosive eruptions could begin with little physical ‘warning’, of the order of days to months. In this case, the onset of volatile saturation might provide pre-eruptive indicators.Graphical

Quaternary Intrusions from the Zhongjiannan Basin, South China Sea: Their Relationship with the Hainan Mantle Plume and Influence on Hydrocarbon Reservoirs

AbstractThe transportation of magma in sedimentary basins often occurs through extensive dyke‐sill networks. The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate. Based on 2D seismic reflection, we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin (ZJNB). The results show that sixty‐nine sills and fourteen forced folds have been identified. The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface. The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca. 0.2 Ma. The spatial and temporal occurrences of intrusions imply that the strong post‐rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core‐mantle boundary. Furthermore, these forced folds could produce several types of hydrocarbon traps, due to accommodation through bending and uplift of the overlying rock and free surface, but it is critical to evaluate the effect of such emplacement when setting exploration targets.

Imaging deep-mantle plumbing beneath La Réunion and Comores hot spots: Vertical plume conduits and horizontal ponding zones.

Whether the two large low-shear velocity provinces (LLSVPs) at the base of Earth's mantle are wide compact structures extending thousands of kilometers upward or bundles of distinct mantle plumes is the subject of debate. Full waveform shear wave tomography of the deep mantle beneath the Indian Ocean highlights the presence of several separate broad low-velocity conduits anchored at the core-mantle boundary in the eastern part of the African LLSVP, most clearly beneath La Réunion and Comores hot spots. The deep plumbing system beneath these hot spots may also include alternating vertical conduits and horizontal ponding zones, from 1000-km depth to the top of the asthenosphere, reminiscent of dyke and sills in crustal volcanic systems, albeit at a whole-mantle scale.

National-scale distribution of strontium isotope ratios in environmental samples from South Korea and its implications for provenance studies

Successful application and accurate interpretation of strontium (Sr) isotope ratios (87Sr/86Sr) requires underlying information about the large-scale variabilities in their signatures from a variety of environmental samples, which can be correlated with the Sr isotopic signatures of underlying local geology. In this national-scale study, we analyzed 87Sr/86Sr in soil, plants, stream water, and Chinese mystery snail (Cipangopaludina chinensis) shells collected from South Korea to evaluate large-scale spatial variabilities, interpret relationships among isotopic signatures of various sample types, and generate spatial distribution isoscapes reflecting the heterogeneity of isotopic signatures across South Korea. Non-parametric comparisons among environmental samples showed non-significant differences in their isotopic ratios. The 87Sr/86Sr of plant and soil samples were strongly correlated (R2adj = 0.93), suggesting that both reflect national-scale lithological properties. Similarly, the 87Sr/86Sr of shells showed strong correlations with the 87Sr/86Sr of both plant and soil samples (R2adj = 0.90). The 87Sr/86Sr signatures of environmental samples in this study aligned with expected Sr isotopic values and generally reflected local geology. Spatial distribution maps of samples showed similar 87Sr/86Sr spatial patterns, with high radiogenic values from granitic and granitic gneiss rocks systems and low radiogenic values from volcanic and sedimentary rock systems. Stream water samples showed significant correlations with soil and plant isotopic ratios, but with a low coefficient of determination (R2adj = 0.68). The deviations were much larger for samples with 87Sr/86Sr > 0.720. Further study is needed to improve the accuracy of baseline determination and interpretation of stream water isotopic variations.

Imaging and seismic modelling inside volcanoes using machine learning

Despite advances in seismology and computing, the ability to image subsurface volcanic environments is poor, limiting our understanding of the overall workings of volcanic systems. This is related to substantive structural heterogeneities which strongly scatters seismic waves obscuring the ballistic arrivals normally used in seismology for wave velocity determination. Here we address this constraint by, using a deep learning approach, a Fourier neural operator (FNO), to model and invert seismic signals in volcanic settings. The FNO is trained using 40,000+ simulations of elastic wave propagation through complex volcano models, and includes the full scattered wavefield. Once trained, the forward network is used to predict elastic wave propagation and is shown to accurately reproduce the seismic wavefield. The FNO is also trained to predict heterogeneous velocity models given a limited set of input seismograms. It is shown to capture details of the complex velocity structure that lie far outside the ability of current methods available in volcano imagery.

Interconnection of magma sources beneath the Katmai volcanic system inferred from seismic tomography and petrology

The Katmai volcanic cluster in Alaska hosts eight volcanoes, most of which are presently active, including Novarupta, whose eruption in 1912 is considered as the largest in the World during the 20th and 21st centuries. We present a new seismic tomographic model for the upper crust beneath the Katmai Group calculated with the use of ∼173,000 arrival times of the P and S waves from ∼11,000 local earthquakes. The resulting distribution of the Vp/Vs ratio reveals a common deep magma source for the entire system below the depth of 5 km centered in the area of Katmai Pass. The tomographic model also demonstrates interconnections of this source with most of the active volcanoes of the group. Based on this model, we propose a possible mechanism for the Novarupta eruption in 1912. The high-Vp/Vs anomaly beneath Novarupta at depths below 5 km may represent a trace of intrusion of low-density volatile-rich rhyolite magma that was made additionally buoyant by vesiculation. This hypothesis is supported by our petrological analysis showing that amphibole is a stable phase in 1912 rhyolite, which require a deeper source than previously suggested. This ascent was accompanied by draining of denser andesite and dacite magmas from under Mount Katmai, which caused the Katmai edifice to collapse. A shallow anomaly of low Vp/Vs ratio right below Novarupta may trace the conduit filled with pumice-type highly porous rocks remained after the eruption.

Разнообразие рельефа подводных вулканических гор Северо-Восточной Атлантики

The structure of the volcanic seamounts of the Atlantis-Great Meteor group, as well as areas of the archipelagos of the Cape Verde Islands, the Canary Islands and the Azores was analyzed. Their simplest type is a cone-like structure with one peak (Mt. Maio). A more complex type is represented by two closely spaced volcanic edifices (Mt. Nola). Seamounts were also formed as a result of the activity of a central-type volcano and a fissure system (Mt. Te-Paps). A more complex morphology is represented by mountains that were formed as a result of the activity of an underwater volcano of the central type, which was combined with the activity of 3–4 radial fissure volcanic systems (Mt.Tropic). Seamounts were also formed only during fissure eruptions (Mts. Kondor, Kadamosto). They are ridges, tens of kilometers long without a clearly defined peak. All of the above types of mountains, with their rise above sea level, subsequent abrasion and subsidence, lead to the creation of flat-topped structures (guyots) (Mt. Sengor).

Dynamics of Magma Chamber Replenishment Under Buoyancy and Pressure Forces

AbstractActive magma chambers are periodically replenished upon a combination of buoyancy and pressure forces driving upward motion of initially deep magma. Such periodic replenishments concur to determine the chemical evolution of shallow magmas, they are often associated to volcanic unrests, and they are nearly ubiquitously found to shortly precede a volcanic eruption. Here, we numerically simulate the dynamics of shallow magma chamber replenishment by systematically investigating the roles of buoyancy and pressure forces, from pure buoyancy to pure pressure conditions and across combinations of them. Our numerical results refer to volcanic systems that are not frequently erupting, for which magma at shallow level is isolated from the surface (“closed conduit” volcanoes). The results depict a variety of dynamic evolutions, with the pure buoyant end‐member associated with effective convection and mixing and generation of no or negative overpressure in the shallow chamber, and the pure pressure end‐member translating into effective shallow pressure increase without any dynamics of magma convection associated. Mixed conditions with variable extents of buoyancy and pressure forces illustrate dynamics initially dominated by overpressure, then, over the longer term, by buoyancy forces. Results globally suggest that many shallow magmatic systems may evolve during their lifetime under the control of buoyancy forces, likely triggered by shallow magma degassing. That naturally leads to long‐term stable dynamic conditions characterized by periodic replenishments of shallow partially degassed, heavier magma by volatile‐rich fresh deep magma, similar to those reconstructed from petrology of many shallow‐emplaced magmatic bodies.