Spatio-temporal evolution of the fumarolic field of La Fossa cone (Vulcano Island, Italy) in 2021–2024

A high-temperature (up to 940°C) fumarolic activity at Kudriavy volcano had been studied during 1990–1999. The maximum gas temperatures of the fumaroles were measured in 1992 as 940°C, then gradually decreased with time and reached to 907°C in 1999. Gas composition of the high-temperature fumarole became enriched in H2O and depleted in other gas components, in particular in CO2. Hydrogen isotopic compositions of the high-temperature fumarolic gases were gradually depleted in deuterium. The gradual and continuous decrease in temperature and changes in gas composition observed during the last 10-year suggest that a magmatic melt have been degassing in a relatively steady-state manner from a single magma chamber. The detail investigations in 1998 and 1999 revealed short-term changes in gas composition characterized by sporadic increases in H2, CO2, and Stotal after intense precipitations. Small-scale eruptions occurred on October 7, 1999 at the summit. The ratios of major gas components (C/S, C/Cl, S/Cl, C/F, S/F, and Cl/F) significantly increased just prior to the eruption. The eruption at the Kudriavy volcano in 1999 was likely a phreatic eruption as a result of the intense precipitations after unusually long dry period. Meteoric water penetrated into the hot zone of volcano edifice and rapidly boiled causing the eruption.

The island of Vulcano, part of the Aeolian Archipelago, is a significant volcanic edifice in Italy. Its active geothermal system and frequent volcanic unrest, particularly the ongoing phase, since September 2021, marked by high fumarole temperatures, changes in gas composition, ground deformation, and micro-seismicity, underscore the importance of understanding the subsurface processes driving volcanic and geothermal phenomena.The present study, using TOUGH2 code (Pruess et al., 1999), aims to enhance our understanding of the active geothermal system of Vulcano. A highly constrained petrophysical model of the island, derived from a 3D resistivity structure obtained from a magnetotelluric (MT) survey (Di Giuseppe et al., 2023), was used to simulate heat flow and fluid flow (H2O and CO2) for the time required to reach the natural thermodynamic state of the system. The numerical modelling results were analyzed by examining the fluid distributions in terms of pressure, temperature and CO2 partial pressure. Pressure increases linearly with depth, as expected in a hydrostatic system, while temperature and CO2 partial pressure show more complex distributions. These observations are consistent with a developed heterogeneous model that incorporates structural and petrophysical data from the MT model, providing a more realistic thermodynamic representation of the Vulcano geothermal system. In particular, the simulated temperature and CO2 partial pressure distributions show a clear differentiation between the central-northern and southern parts of the island, in agreement with literature and empirical data.These results offer new insights into the system’s behavior, significantly enhancing our understanding of its current dynamics and providing a robust foundation for predicting its future evolution. This could potentially lead to more accurate predictive models and hazard scenarios.   

Emissions and efficiency of a domestic gas stove burning natural gases with various compositions

The performance of a newly‐developed portable gas analyzer, capable of real‐time measurement of CO2, SO2 and H2S concentrations in volcanic gases, was tested at La Fossa Crater, Vulcano Island. The gas analyzer was used to acquire about 3000 determinations over the fumarolic field, allowing the definition of its chemical structure and heterogeneity. Our high‐resolution analysis reveals that, in December 2004, the La Fossa fumarolic field was characterized by an oxidized inner core (SO2/H2S ratios of ∼3), and by more reducing conditions on its northern edge (SO2/H2S ratios of ∼1; range: 0.2–3.3). CO2/(SO2+H2S) molar ratios averaged 35 ± 21, with overlapping compositions for rim and inner crater fumaroles. S‐poor compositions (CO2/(SO2+H2S) ≥ 50) characterized the field margins, probably due to deposition of native sulfur. Based on the above data and an SO2 flux of 18 ± 3 t·d−1, we estimate CO2 and H2S output rates from the volcano of 420 ± 250 and 4 ± 2 t·d−1, respectively.

<p>Vulcano is an active volcanic island located in the south-central sector of the Aeolian Archipelago (Tyrrhenian Sea, Italy). The most recent active edifice is the La Fossa crater located in the center of the island, neighboring the main settlement Vulcano Porto. Its eruptive history is characterized by frequent transitions from phreatomagmatic to minor magmatic activity. The last eruption occurred in 1888–90 with strong phreatic (“Vulcanian”) eruption pulses. During the last decades, it has undergone several periods of volcanic unrest, accompanied by increasing degassing, rising fumarole temperatures, changing gas compositions, or increasing groundwater- and soil temperatures. Major unrest periods were reported in the 1920s, 1940s, and 1990s. Here we report on the ongoing crisis that initiated in September 2021. Rapidly increasing degassing levels and fumarole temperatures, accompanied by seismic activity and surface deformation were detected and monitored by the monitoring network (INGV bulletin reports). The fast evolution and dynamics of the crisis caused authorities to raise the alert level to orange and led to temporary evacuations in Vulcano Porto. We monitored this crisis from the beginning by monthly drone-based optical and thermal infrared overflights. The drone data was processed by using the Structure-from-Motion approach, allowing to generate spatially dense optical and thermal infrared maps. This way we captured the response of the hydrothermal system at the surface in great detail, were able to monitor the spatio-temporal evolution of the high-temperature fumarole field but also associated mean and low-temperature anomalies of diffuse degassing areas. We compared observations to a previous study considering in detail the structure and thermal expression of the La Fossa fumarole field, and the hydrothermal alteration associated (Müller et al., 2021, JVGR). Major aspects of changes observed at the surface during the crisis that could be constrained are (i) an increase of fumarole temperatures, (ii) the development of new fumarole vents, (iii) the evolution of a thermal aureole surrounding the major fumarole field at a distance, and (iv) the formation of a net-shaped thermal anomaly network. Changes are presented on a spatial and temporal scale and highlight the dynamics of degassing systems at the surface with implications for volcanic monitoring and hydrothermal alteration research and suggest that unrest is detectable at fumaroles but also at diffuse degassing zones elsewhere affecting a larger region of the La Fossa cone. </p>

Experimental study on the desorption behavior of high-volatile bituminous coals following CO2 and CH4 injection at various compositional ratios

Surveying fumarole sites and hydrothermal alteration by unoccupied aircraft systems (UAS) at the La Fossa cone, Vulcano Island (Italy)

The geochemical analysis of fumarolic gases collected at quiescent and active volcanic systems over time is one of the main tools to understand changes in the state of activity for surveillance and risk assessment. The continuous output of chemical species through fumarolic activity, which characterizes the inter-eruptive intervals, has also a major and general influence on the environment. The mobilization of chemical species due to weathering of volcanic rocks, or the input of gaseous components from fumarolic activity, results in some kind of modification of the environment affecting, in particular, water, soils, and the consequent growth of the plants present in these areas. In this paper, an investigation on the chemical composition of fumarolic gases collected at Vulcano island (Sicily, southern Italy) is performed, with the aim to discover how data changes during the monitored period of time, and to design a strategy for the environmental surveillance of volcanic systems taking into account the nature of the analyzed data. In order to summarize the contribution of all the components that can affect the chemical composition of volcanic gases, a multivariate statistical approach appears to be suitable. Since many of those methods assume independent observations, the possible presence of time-dependent structures should be carefully verified. In this framework, given the compositional nature of geochemical data, we have applied recent theoretical and practical developments in the field of compositional data analysis to work in the correct sample space and to isolate groups of parts responsible for significant changes in the gas chemistry. The proposed approach can be generalized to the investigation of complex environmental systems.

The measured space point resolution of a D0 Muon Chamber is /+-/0.31 mm perpendicular to the anode wire and 2.7 mm parallel to the wire. A voltage change of 1 kV, which changes the gas gain by a factor of 50, only causes a change of drift velocity of 12%. Tracks inclined of 45/degree/ have a resolution worse than those of 0/degree/ by a factor 3 /+-/ 2. A change in gas composition from CO/sub 2/(10%) to CO/sub 2/(11%) decreases the gas gain by 17 /+-/ 5%, and decreases drift velocity by 0.2 /+-/ 0.2%. The effect of an oxygen contamination of 3200 ppM is to change the mean pulse height by 45% over the 5 cm width of the cell. 4 refs., 15 figs.

Fumarole fields and hydrothermal alteration are prominent signs of volcanic degassing at many volcanoes, and their monitoring is an essential part of the assessment of volcanic unrest. Yet, our knowledge about the detailed structure of fumarole fields and the spatiotemporal processes in their complexity is still poor, owing to limited accessibility. By using modern drone and sensor technologies we now are able to provide high-resolution data that allows us to analyze fumarole fields at cm-scales. From 2018 to 2022, we conducted repeated drone surveys at the fumaroles of La Fossa volcano on Vulcano Island (Italy). Drones equipped with a 20 MP camera and a radiometric thermal infrared sensor allowed the close-range acquisition of optical and thermal infrared images. By means of Structure from Motion (SfM) processing, the generation of high-resolution ortho- and infrared mosaic data was achieved. Applying Principal Component Analysis and image classification to the orthomosaic data, we detected and classified areas affected by degassing and hydrothermal alteration covering more than 60.000 sqm. By analyzing their spectral characteristics, we defined 4 surface types, of which type 1 and 2 are largely coincident with the thermally active surface. Type 3 is an altered low-temperature surface and type 4 is an unaltered surface. To evaluate these surface types, samples were analyzed in the lab for their mineralogical and geochemical composition by X-ray diffraction and fluorescence analysis, showing significant variability in composition. Further, we analyzed the spatial variability of the surface degassing activity using a portable multi-gas device. The combination of these methods allows us to constrain factors that are controlling the observed surface pattern of the degassing system, and to better understand the structural setup of the fumarole field and broader field of activity. We find that the actual high-temperature fumarole sites only account for <10% of the active surface. Besides, large thermally active areas, thermal aureoles for instance, display a rather diffuse activity. During the 2021 volcanic crisis, next to the high-temperature fumaroles, especially those diffuse features showed a response to the increased gas flux, emphasizing their structural importance. We summarize spatiotemporal variations during the crisis, and indicate possible widespread effects of the long-term gas-rock interaction like surface sealing, and forced lateral gas migration, affecting large parts of the fumarole field. The results suggest that detailed structural studies of fumarole fields by means of drone-based remote sensing in combination with in-situ measurements can contribute to a better understanding of degassing and alteration effects, with relevance for degassing sites elsewhere and during volcanic crises. 

Giggenbach bottle technique is used to systematically analyze fumarolic gas composition of the Tatun Volcano Group, northern Taiwan. The area is quite active hydrothermally and is also considered volcanically active. The gas composition of fumarolic samples is predominantly steam water with CO2 as the dominant component after de-watering. Minor components include sulfur species (mainly H2S and SO2), N2 and CH4. Interestingly, in the study area, H2S concentration is always much higher than SO2 for all measured fumarolic gases. This result resembles the typical composition of low temperature fumaroles, when comparisons are made on a worldwide basis. Hsiao-you-keng and Liou-huang-ku were selected as testing sites to discuss factors pertaining to weather and sampling time as these may affect fumarolic gas composition. Test results show that the length of sampling time in this area mainly depends on the saturation of alkali solution. Furthermore, based on continuous data, gas composition of fumaroles seems not to be affected by weather factors. This implies that the de-gassing system in the Tatun volcanic area is quite steady and generated no significant variation in gas composition during the study period. These results indicate that current sampling and analytical procedures are suitable for volcanic gas study and further surveillance in the Tatun volcanic area.

Monitoring fluid and gas compositions at active and dormant volcanoes is becoming increasingly important, both as a tool for recognizing precursory geochemical changes associated with impending activity, as well as for increasing our understanding of magmatic and hydrothermal systems and how they interact. This chapter discusses geochemical changes in both thermal waters and soil gases at a number of volcanic localities. At the present time the modelling of active volcanoes using geochemical methods is in its infancy, and to date there have been few opportunities to monitor the geochemical changes of fluids and gases through a volcanic crisis which has culminated in eruption. Volcanic fluids and gases can be analyzed using a number of very different methods, although some attempt has been made in recent years to standardize analytical techniques. The chapter looks at geochemical variations in fumaroles in more detail, with particular reference to recent studies at Campi Flegrei and Vulcano island.

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

The detection of volcanic unrest is a critical component of volcanic monitoring and risk mitigation, especially for volcanoes with persistent hydrothermal activity and no recent eruptions. Identifying early signs of reactivation in such systems is particularly challenging due to the complex interplay between magmatic and hydrothermal processes.Vulcano, one of the seven volcanic islands in the Aeolian archipelago (Southern Italy), is characterized by fumarolic activity and well-documented historical eruptions. The last eruptive event, occurring in 1888–1890 AD, featured episodic explosive activity of varying intensity, with the most violent explosions ejecting bombs and blocks over 1 km from the crater. Due to its small size and the proximity of active volcanic features to densely populated and tourist areas, Vulcano represents a critical site for volcanic risk management. In mid-September 2021, the island experienced significant degassing episodes at La Fossa cone, marking a period of unrest without eruptive activity. This unique scenario makes Vulcano an ideal natural laboratory for studying volcanic unrest in the absence of eruptions, providing valuable insights into the underlying magmatic-hydrothermal system.Using continuous seismic records from Vulcano, we analyze relative seismic velocity changes (dv/v) through the cross-correlation of ambient noise, employing the MSNoise package \citep{lecocq2014msnoise}. Our analysis covers the pre-unrest, unrest, and post-unrest periods from 2016 to 2024, offering a long-term perspective on the temporal evolution of the system. Preliminary results show significant changes in dv/v that appear to be related to the 2021 episode of unrest, which corresponds to increased seismic activity, variations in gas emissions, and ground deformation. Long-term monitoring of Vulcano is crucial for identifying early signs of reactivation, which can significantly improve eruption forecasting and risk mitigation strategies. These findings highlight the potential of seismic noise analysis for real-time monitoring and to advance our understanding of the dynamics of volcanic unrest.ReferencesLecocq, T., Caudron, C., & Brenguier, F. (2014). Msnoise, a python package for monitoring seismic velocity changes using ambient seismic noise. Seismological Research Letters, 85 (3), 715–726.

Conspicuous changes in gas composition were observed at a fumarole and a mineral spring just before the occurrence of an inland earthquake (magnitude, 6.8) in central Japan in September 1984; the fumarole and spring were 9 and 50 kilometers, respectively, from the earthquake's epicenter. Deep-seated fluids emitted as a result of the compressional stress of the earth tide had been observed previously at this mineral spring and at a lava lake in Hawaii. By analogy, the gas anomaly observed before the earthquake in Japan probably resulted from deepseated fluids being squeezed to the surface by the tectonic stress that caused the earthquake.