[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.