[1] Total CO 2 output from fumaroles, soil gas, bubbling gas discharges and water dissolved gases discharged from the island, was estimated for Vulcano island, Italy. The CO 2 emission from fumaroles from the La Fossa summit crater was estimated from the SO 2 crater output, while CO 2 discharged through diffuse soil emission was quantified on the basis of 730 measurements of CO 2 fluxes from the soil of the island, performed by using the accumulation chamber method. The results indicate an overall output of ≅500 t day À1 of CO 2 from the island. The main contribution to the total CO 2 output comes from the summit area of the La Fossa cone (453 t day À1 ), with 362 t day À1 from crater fumaroles and 91 t day À1 from crater soil degassing. The release of CO 2 from peripheral areas is ≅20 t day À1 by soil degassing (Palizzi and Istmo areas mainly), an amount comparable to both the contribution of water dissolved CO 2 (6 t day À1 ), as well as to seawater bubbling CO 2 (4 t day À1 measured in the Istmo area). Presented data (September 2007) refer to a period of moderate solphataric activity, when the fumaroles temperature were 450°C and gas/water molar ratio of fumaroles was up to 0.16. The calculated total CO 2 emission allows the estimation of the mass release and related thermal energy from the volcanic-hydrothermal system.

, CO 2 flux surveys were performed on Lake Rotomahana, New Zealand. The area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of Mt Tarawera in 1886. The total CO 2 emission from the lake calculated by sequential Gaussian simulation is 549 6 72 t d 21 . Two different mechanisms of degassing, diffusion through the water-air interface and bubbling, are distinguished using a graphical statistical approach. The carbon dioxide budget calculated for the lake confirms that the main source of CO 2 to the atmosphere is by diffusion covering 94.5% of the lake area (mean CO 2 flux 25 g m 22 d 21 ) and to a lesser extent, bubbling (mean CO 2 flux 1297 g m 22 d 21 ). Mapping of the CO 2 flux over the entire lake, including over lake floor vents detected during the survey, correlates with eruption craters formed during the 1886 eruption. These surveys also follow regional tectonic patterns present in the southeastern sector of Lake Rotomahana suggesting a deep magmatic source ( 10 km) for CO 2 and different pathways for the gas to escape to the surface. The values of d 13 C CO2 (22.88 and 22.39&) confirm the magmatic origin of CO 2 .

In November 2007, the extrusion of a new lava dome evaporated Kelud volcanic lake in Java, Indonesia. Four months before a detailed echo sounding survey of the volcanic lake coupled to floating accumulation chamber measurements detected abnormally high carbon dioxide emissions. It constituted the earliest sign of the volcanic unrest; well before any other monitored parameter. CO2 flux is quantified using an empirical equation based on the volume of bubbles backscattered in the water column. Its comparison with the fluxes retrieved from the floating chamber method better constrain carbon dioxide dynamics in the volcanic lake. It reveals that 70% of the carbon dioxide enters the lake in a dissolved form, while the remaining 30% is supplied to the lake on a gaseous state. Almost three‐quarter of the ascending bubbles dissolve in the water column leaving the majority of the 330 Tons day−1 of carbon dioxide diffusing at the air‐water interface.

During 2007-2008, three CO 2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO 2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m −2 day −1 (April 2008) with total emission rates of 164±9.5 (March 2007), 59±2.5 (December 2007) and 109± 6.6 t day −1 (April 2008). The mean CO 2 flux estimated from the entire crater floor area was 1,102 g m −2 day −1 for April 2008 with a total emission rate of 144±5.9 t day −1 . Significant change in CO 2 flux was not detected during the period of survey, and the mapping of the CO 2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3 He/ 4 He ratio (as high as 8.1 R A ) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO 2 / 3 He ratios for the high 3 He/ 4 He gases tend to have the MORB-like values (1.41×10 9 ), and the CO 2 / 3 He ratios for the lower 3 He/ 4 He gases fall within the range for the arc-type gases. The high 3 He/ 4 He ratios, the MORB-like CO 2 / 3 He ratios for the high 3 He/ 4 He gases and high proportion of MORB-CO 2 (M=25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.

The Whakaari/White Island volcano, located ~ 50 km off the east coast of the North Island in New Zealand, has experienced sequences of quiescence, unrest, magmatic and phreatic eruptions over the last decades. For the last 15 years, seismic data have been continuously archived providing potential insight into this frequently active volcano. Here we take advantage of this unusually long time series to retrospectively process the seismic data using ambient noise and tremor-based methodologies. We investigate the time (RSAM) and frequency (Power Spectral Density) evolution of the volcanic tremor, then estimate the changes in the shallow subsurface using the Displacement Seismic Amplitude Ratio (DSAR), relative seismic velocity (dv/v) and decorrelation, and the Luni-Seismic Correlation (LSC). By combining our new set of observations with the long-term evolution of earthquakes, deformation, visual observations and geochemistry, we review the activity of Whakaari/White Island between 2007 and the end of 2018. Our analysis reveals the existence of distinct patterns related to the volcano activity with periods of calm followed by cycles of pressurization and eruptions. We finally put these results in the wider context of forecasting phreatic eruptions using continuous seismic records.

The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high-resolution measurement of carbon dioxide flux (uCO 2 ) and heat flow at the surface to characterize the mass (CO 2 and steam) and heat released to the atmosphere from two magma-hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taup o Volcanic Zone, New Zealand, include over 3000 direct measurements of uCO 2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO 2 emission rates (RCO 2 ) of 441 6 84 Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO 2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal-sourced CO 2 emission (constrained using stable isotopes) with reservoir H 2 O:CO 2 mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MW t ) is 10 times greater than the White Island crater floor (22.5 MW t ).

Here, we report the first continuous data of geochemical parameters acquired directly from the active summit crater of Vulcano. This approach provides a means to better investigate deep geochemical processes associated\ud with the degassing system of Vulcano Island. In particular, we report on soil CO2 fluxes from the upper part of Vulcano,a closed-conduit volcano, from September 2007 to October2010. Large variations in the soil CO2 and plume SO2 fluxes(order of magnitude), coinciding with other discontinuous geochemical parameters (CO2 concentrations in fumarole gas) and physical parameters (increase of shallow seismic activity and fumarole temperatures) have been recorded.\ud The results from this work suggest new prospects for strengthening geochemical monitoring of volcanic activity and for improving the constraints in the construction of a“geochemical model”, this being a necessary condition to\ud better understand the functioning of volcanic systems

On Vulcano Island (Italy), many geochemical crises have occurred during the last 130 years of solfataric activity. The main crises occurred in 1978–1980, 1988–1991, 1996, 2004–2007, 2009–2010 and the ongoing 2021 anomalous degassing activity. These crises have been characterized by early signals of resuming degassing activity, measurable by the increase of volatiles and energy output emitted from the summit areas of the active cone, and particularly by increases of gas/water ratios in the fumarolic area at the summit. In any case, a direct rather than linear correspondence has been observed among the observed increase in the fluid output, seismic release and ground deformation, and is still a subject of study. We present here the results obtained by the long-term monitoring (over 13 years of observations) of three extensive parameters: the SO2 flux monitored in the volcanic plume, the soil CO2 flux and the local heat flux, monitored in the mild thermal anomaly located to the east of the high-temperature fumarole. The time variations of these parameters showed cyclicity in the volcanic degassing and a general increase in the trend in the last period. In particular, we focused on the changes in the mass and energy output registered in the period of June–December 2021, to offer in near-real-time the first evaluation of the level and duration of the actual exhalative crisis affecting Vulcano Island. In this last event, a clear change in degassing style was recorded for the volatiles emitted by the magma. For example, the flux of diffused CO2 from the soils reached the maximum never-before-recorded value of 34,000 g m−2 d−1 and the flux of SO2 of the plume emitted by the fumarolic field on the summit crater area reached values higher than 200 t d−1. The interpretation of the behavior of this volcanic system, resulting from the detailed analyses of these continuous monitoring data, will complete the framework of observations and help in defining and possibly forecasting the next evolution of the actual exhaling crisis.