Fumarolic Pathways Were Structurally Controlled by a Strike-Slip Fault System Beneath the Bishop Tuff, Bishop, California

The Volcanic Tableland, a plateau at the northern end of Owens Valley, CA, is capped by the rhyolitic Bishop Tuff. It hosts many tectonic and volcanic landforms, including hundreds of fault scarps, large joint sets, and inactive fumarolic mounds and ridges. The 1986 Chalfant Valley earthquake sequence shed light on a blind strike-slip fault system beneath the Bishop Tuff. The spatial relationships of the volcanic and tectonic structures have previously been well documented, however, the mechanisms of formation of structures and their enhancement as fumarolic pathways remain largely unexplored. We collected fault kinematic indicators, joint orientations, and documented fumarolic alterations of microcrystalline quartz in the Bishop Tuff and combined those field observations with fault response modeling to assess whether strike-slip activity played a key role in the development of fumarolic pathways. We found field evidence of dip-slip and strike-slip faulting that are consistent with the overall transtensional regional tectonics. Our modeling indicates that a blind strike-slip fault system would dilate joints in the overlying Bishop Tuff with preferred orientations that match observed orientations of joints along which fumarolic activity occurred. Our results imply that the localization of fumaroles was tectonically controlled and that fault activity in the valley floor likely initiated prior to tuff emplacement.

Changing hazard awareness over two decades: the case of Furnas, São Miguel (Azores)

Furnas (ca. 1,500 inhabitants) lies within the caldera of Furnas volcano on the island of São Miguel (Azores) and has the potential to expose its inhabitants to multiple hazards (e.g. landslides, earthquakes, volcanic eruptions and degassing). The present population has never experienced a volcanic eruption or a major earthquake, although the catalogue records six eruptions, sub-Plinian in style over the last 2 ka years. Today, the area experiences strong fumarolic activity. In the case of an eruption, early evacuation would be necessary to prevent inhabitants being trapped within the caldera. Awareness of potential threats and knowledge of what to do in the case of an emergency would assist in evacuation. In this paper inhabitants' awareness of volcanic and seismic threats in 2017 is compared with those revealed in a similar study completed more than two decades ago. It is concluded that, whereas awareness of earthquakes and the dangers posed by volcanic gas discharge has increased, knowledge of the threat of volcanic eruptions and the need to prepare for possible evacuation has not. Research suggests that changing awareness is related to effective collaboration that has developed between the regional government, through its civil protection authorities and scientists, and the people of Furnas.

Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography

Atka is a subduction-related volcanic island located in the central part of Aleutian Arc. The northeastern part of this island forms the Atka Volcanic Complex (AVC), which is built as a relict shield volcano of a circular shape overlain by several active and extinct volcanic vents of different ages. During the past few decades, two active volcanoes within AVC—Korovin and Kliuchef—demonstrated mostly phreatic eruptions and intensive fumarolic activity. We have created the first tomographic model of the crust beneath AVC with the use of data of eight permanent stations of the Alaskan Volcanological Observatory operated in the time period from 2004 to 2017 that included arrival times of the P and S waves from local seismicity. Based on a series of checkerboard tests, we have demonstrated fair vertical and horizontal resolution of the model down to ~6 km depth. Beneath the Korovin and Kliuchef volcanoes, we have revealed two isolated anomalies of high Vp/Vs with values exceeding 2, which represent separate magma chambers that are responsible for magmatic eruptions of these two volcanoes. In shallow layers down to 2–3 km deep, we observe an alternation of zones with low and high values of the Vp/Vs ratio, which are likely associated with the circulation of meteoric fluids in the uppermost crust. Moderately high Vp/Vs anomalies indicate zones of meteoric water penetration down to the ground. On the other hand, the very low values of Vp/Vs reaching 1.5 depict the areas where meteoric water reached the hot magma reservoir and transformed into steam. On the surface, these zones coincide with the distributions of fumaroles. The outflow of these steam currents from active vents of Korovin and Kliuchef led to episodic phreatic eruptions, sometimes synchronous.

Geochemistry of fluid manifistations of the Ebeko Volcano, Paramushir Island (Kurile Islands, Russia).

<p>The Ebeko volcano (50°41′N, 156°01′E) is located at the northern part of Paramushir Island and composed of several Quaternary volcanic cones. The Neogene volcano-clastic basement occurs below ~200 m asl. The post-glacial cone of Ebeko is composed by lava flows and pyroclastics of andesitic composition. The summit is represented by three craters (Northern, Middle and Southern). The modern phreatic and fumarolic activity of Ebeko started after a strong explosive phreatic–magmatic eruption from the Middle crater in 1934–1935 which ejected about 10<sup>6</sup> t of andesitic ash and bombs. Last eruptive activity of Ebeko volcano began in October 2016 and continues to the present. </p><p>Main feature of the hydrothermal activity of Ebeko is the existence of two thermal fields separated in the space. The summit field consists ~ 10 thermal grounds, low-temperature fumaroles (<120 °C) and near-boiling pools with no or weak outflowrates. The second thermal field, Yurievskie springs, is locatedat low elevations, ~550 m asl down to 280 m asl, on the western slope of Ebeko volcano in the canyon of Yurieva River. Gases from different parts of the summit thermal field are all water-rich (97–99 mol%) and show varying contents of HCl and total sulfur and ratios of C/S and H<sub>2</sub>S/SO<sub>2</sub>. All waters from the Yurievskie springs and Ebeko pools are ultra-acidic, with pH < 2. The Yurievskie waters are of the SO<sub>4</sub>–Cl type (SO<sub>4</sub>/Cl ratios are ~1:1molar and 3:1 by weight), whereas the SO<sub>4</sub>/Cl ratio in Ebeko pools show low (<1) and varying SO<sub>4</sub>/Cl ratios. Major and trace element composition of Ebeko-Yurievskie acidic waters is suggesting congruent dissolution of volcanic rocks. Oxygen and hydrogen isotopic composition of water and Cl concentration for Yurieva springs show an excellent positive correlation, indicating a mixing between meteoric water and magmatic vapor. In contrast, volcanic gas condensates of Ebeko fumaroles do not show a simple mixing trend but rather a complicated data suggesting evaporation of the acidic brine. Temperatures calculated from gas compositions and isotope data are similar, ranging from 150 to 250 °C, which is consistent with the presence of a liquid aquifer below the Ebeko fumarolic fields.</p><p>Thermal grounds and pools of the summit field are closely associated with the volcano activity. Each period of volcano excitation causes changes in the locations of major fumarole vents, crater lakes, and affects the chemical composition of water and gas. The Ebeko volcano eruption (from 2016 to the present) also triggered changes in the isotope and chemical composition of the Yuryevskie springs.</p><p>In this paper we report data on water and gas compositions of samples obtained during the 2016-2019 field seasons and compare partially published data from 2005-2014 field campaigns. This work was supported by the RFBR grant #20-05-00517.</p>

Erosional processes in the natural-anthropic geosystem of Vulcano Island (Italy)

<p>Vulcano, the southernmost island of the Aeolian Archipelago, has been characterized by an intense fumarolic activity since its last eruption from La Fossa cone (1888-1890). This island has a strong touristic vocation and frequentation, and here volcano-hydrothermal activity represents, at the same time, a landmark, one of the main causes of hydrogeological instability and a severe risk for human health. The space-time dynamic of this complex system is controlled by the mutual interactions among micro-meteorological, volcanic, tectonic, morphogenetic and anthropic processes.</p><p>La Fossa cone is affected by intense water erosion phenomena, also controlled by fumarolic activity as an obstacle for the growth of vegetation and a weathering factor. Man-made structures, with particular reference to deep modifications in the natural stream network induced by buildings and roads, exert a strong influence on these erosion processes, also fostered by episodic wildfires.</p><p>Another relevant theme is the acceleration of the coastal erosion processes in the Baia di levante area, driven by the circulation of chemically-aggressive hydrothermal fluids, which transforms the pristine volcanic minerals into phases like gypsum, anhydrite and clay minerals, significantly reducing the mechanical resistance of the rocks to the action of wave erosion. A general retreatment of the coastline (several meters in some locations) has been observed in the last twenty years, caused by the combined effect of volcanic activity, anthropic modifications and changes in sea level.</p>

Spatio-Temporal Relationships between Fumarolic Activity, Hydrothermal Fluid Circulation and Geophysical Signals at an Arc Volcano in Degassing Unrest: La Soufrière of Guadeloupe (French West Indies)

： Over the past two decades, La Soufrière volcano in Guadeloupe has displayed a growing degassing unrest whose actual source mechanism still remains unclear. Based on new measurements of the chemistry and mass flux of fumarolic gas emissions from the volcano, here we reveal spatio-temporal variations in the degassing features that closely relate to the 3D underground circulation of fumarolic fluids, as imaged by electrical resistivity tomography, and to geodetic-seismic signals recorded over the past two decades. Discrete monthly surveys of gas plumes from the various vents on La Soufrière lava dome, performed with portable MultiGAS analyzers, reveal important differences in the chemical proportions and fluxes of H2O, CO2, H2S, SO2 and H2, which depend on the vent location with respect to the underground circulation of fluids. In particular, the main central vents, though directly connected to the volcano conduit and preferentially surveyed in past decades, display much higher CO2/SO2 and H2S/SO2 ratios than peripheral gas emissions, reflecting greater SO2 scrubbing in the boiling hydrothermal water at 80–100 m depth. Gas fluxes demonstrate an increased bulk degassing of the volcano over the past 10 years, but also a recent spatial shift in fumarolic degassing intensity from the center of the lava dome towards its SE–NE sector and the Breislack fracture. Such a spatial shift is in agreement with both extensometric and seismic evidence of fault widening in this sector due to slow gravitational sliding of the southern dome sector. Our study thus provides an improved framework to monitor and interpret the evolution of gas emissions from La Soufrière in the future and to better forecast hazards from this dangerous andesitic volcano.

Koryakite, NaKMg2Al2(SO4)6, a new NASICON-related anhydrous sulfate mineral from Tolbachik volcano, Kamchatka, Russia

Exhalative mineral assemblages from fumaroles of Tolbachik volcano are very rich in anhydrous sulfate minerals of alkali and transition metals. Koryakite, ideally NaKMg2Al2(SO4)6, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Koryakite occurs as a product of fumarolic activity and closely associates with euchlorine and langbeinite. Koryakite is trigonal, R$\bar{3}$, a = 8.1124(11), c = 22.704(7) Å and V = 1294.0(5) Å3. The chemical composition determined by electron-microprobe analysis is (wt.%): Na2O 4.27, K2O 5.85, ZnO 0.31, СaO 0.31, CuO 0.76, MgO 10.15, Al2O3 11.47, Fe2O3 2.73, SO3 64.33 and SiO2 0.13, total 100.31. The empirical formula calculated on the basis of 24 O apfu is Na1.03K0.93(Mg1.89Cu0.07Ca0.04Zn0.03)Σ2.03(Al1.68Fe3+0.26)Σ1.94(S6.02Si0.02)Σ6.04O24. No natural or synthetic chemical analogues of koryakite are known to date. The topology of the [M2+2M3+2(SO4)6]2– heteropolyhedral framework in koryakite is very similar to the one in millosevichite, Al2(SO4)3 and mikasaite, Fe3+2(SO4)3. Replacement of part of the trivalent cations in the [M3+2(SO4)3]0 framework by divalent cations gives the framework a negative charge for koryakite and allows the incorporation of the alkali species in the channels. This structural mechanism is reminiscent of the concept of stuffed derivative structures. Koryakite is also structurally related to synthetic NaMgFe3+(SO4)3 and to the broader family of NASICON-related phases.

Bacterial Communities from Extreme Environments: Vulcano Island

Although volcanoes represent extreme environments for life, they harbour bacterial communities. Vulcano Island (Aeolian Islands, Sicily) presents an intense fumarolic activity and widespread soil degassing, fed by variable amounts of magmatic gases (dominant at La Fossa Crater) and hydrothermal fluids (dominant at Levante Bay). The aim of this study is to analyse the microbial communities from the different environments of Vulcano Island and to evaluate their possible correlation with the composition of the gas emissions. Microbial analyses were carried out on soils and pioneer plants from both La Fossa Crater and Levante Bay. Total DNA has been extracted from all the samples and sequenced through Illumina MiSeq platform. The analysis of microbiome composition and the gases sampled in the same sites could suggest a possible correlation between the two parameters. We can suggest that the ability of different bacterial genera/species to survive in the same area might be due to the selection of particular genetic traits allowing the survival of these microorganisms. On the other side, the finding that microbial communities inhabiting different sites exhibiting different emission profiles are similar might be explained on the basis of a possible sharing of metabolic abilities related to the gas composition.

The Contribution of Multi-Sensor Infrared Satellite Observations to Monitor Mt. Etna (Italy) Activity during May to August 2016

In May 2016, three powerful paroxysmal events, mild Strombolian activity, and lava emissions took place at the summit crater area of Mt. Etna (Sicily, Italy). During, and immediately after the eruption, part of the North-East crater (NEC) collapsed, while extensive subsidence affected the Voragine crater (VOR). Since the end of the May eruptions, a diffuse fumarolic activity occurred from a fracture system that cuts the entire summit area. Starting from 7 August, a small vent (of ~20–30 m in diameter) opened up within the VOR crater, emitting high-temperature gases and producing volcanic glow which was visible at night. We investigated those volcanic phenomena from space, exploiting the information provided by the satellite-based system developed at the Institute of Methodologies for Environmental Analysis (IMAA), which monitors Italian volcanoes in near-real time by means of the RSTVOLC (Robust Satellite Techniques–volcanoes) algorithm. Results, achieved integrating Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) observations, showed that, despite some issues (e.g., in some cases, clouds masking the underlying hot surfaces), RSTVOLC provided additional information regarding Mt. Etna activity. In particular, results indicated that the Strombolian eruption of 21 May lasted longer than reported by field observations or that a short-lived event occurred in the late afternoon of the same day. Moreover, the outcomes of this study showed that the intensity of fumarolic emissions changed before 7 August, as a possible preparatory phase of the hot degassing activity occurring at VOR. In particular, the radiant flux retrieved from MODIS data decreased from 30 MW on 4 July to an average value of about 7.5 MW in the following weeks, increasing up to 18 MW a few days before the opening of a new degassing vent. These outcomes, in accordance with information provided by Sentinel-2 MSI (Multispectral Instrument) and Landsat 8-OLI (Operational Land Imager) data, confirm that satellite observations may also contribute greatly to the monitoring of active volcanoes in areas where efficient traditional surveillance systems exist.