Temperature Fumaroles Research Articles

Multiparametric Approach in Investigating Volcano-Hydrothermal Systems: the Case Study of Vulcano (Aeolian Islands, Italy)

Seismic activity, ground deformation, and soil and fumarole temperatures acquired during 2004–2007 at Vulcano (Aeolian Islands) are analysed and the time relations among the different time series are discussed. Changes in temperature of fumarolic gases took place during four “anomalous” periods (November 2004–March 2005; October 2005–February 2006; August–October 2006; July–December 2007) at the same time as an increasing number of volcano-seismic events. In particular, the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440°C and from 20 to 90°C, respectively. The maximum daily number of volcano-seismic events was 57, reached during the second anomalous period. This seismicity, characterised by focal depth generally lower than 1 km below sea level (b.s.l.) and composed of different kinds of events associated to both resonance and shear failure processes, is related to the shallow dynamics of the hydrothermal system. During the analysed period, very few volcano-tectonic earthquakes took place and tilt recordings showed no sharp or important changes. In light of such observations, the increases in both temperature and volcano-seismic events number were associated to increases in the release of gas from a deep and stable magma body, without magma intrusions within the shallow hydrothermal system. Indeed, a greater release of gas from depth leads to increased fluid circulation, that can promote increases in volcano-seismic events number by both fracturing processes and resonance and vibration in cracks and conduits. The different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body. Finally, all the observed variations, together with the changing temporal distribution of the different seismic event kinds, suggest that the hydrothermal system at Vulcano can be considered unsteady and dynamic.

Geophysical, geochemical and geodetical signals of reawakening at Turrialba volcano (Costa Rica) after almost 150 years of quiescence

Turrialba is a basaltic–andesitic stratovolcano (3340 masl), in the Cordillera Volcánica Central in Costa Rica. After the last eruption (1864–1866), volcanic manifestations were limited to weak fumarolic discharge (continuous since 1980) from the summit. From 1996 onward, the degassing activity has progressively been increasing, reaching its climax after 2005. New fumaroles have appeared in the Central and West summit craters, the latter now being the most active, and in the fracture system in between, showing sulphur deposits and progressively increasing degassing rate. In 2004, fumaroles and new fissures have appeared on the SW outer and SSW distal flanks, the latter being located along a major NE-oriented tectonic lineament. Fumarolic temperatures at the bottom of the West crater have increased from 88 to 282 °C in early 2008. Changes in chemical and isotopic compositions of discharged fluids have shown a progressive enhancing of the magmatic signature since 2001. Since late 2007, SO 2 flux, measured with mini-DOAS, has increased two orders of magnitude (1 t/day in 2002 to 740 t/day in January 2008). The enhanced gas discharge at Turrialba volcano has caused significant interference on tropospheric O 3 measurements at 2–3 km altitude ~ 50 km W from the volcano. Seismic swarms followed an increasing trend consistent with that of the fumaroles. The maximum seismic activity to date, up to thousands of events/day, was recorded in mid 2007. An inflationary trend was observed in the crater area. In this paper we present for the first time all the available data on the activity of Turrialba volcano. New geophysical, geodetical and geochemical data and published geophysical and geochemical data are presented and discussed as a whole. The multidisciplinary approach indicated that from 1996 to 2009 three stages, deriving by the delicate equilibrium between the hydrothermal and the magmatic reservoirs, were recognized. The magmatic-dominated phase is still prevailing as evidenced by the fact that, while completing the present paper, on the 4th of January 2010 at 16.57 (GMT) a loud explosion occurred at the West crater and was followed by three others spaced out every 10 min. These events were interpreted as associated with phreatic eruptions.

Thermal expansion-contraction and slope instability of a fumarole field inferred from geodetic measurements at Vulcano

Between 1987 and 1993, fumarole temperatures at the Fossa crater of Vulcano (Italy) were characterized by the highest values since the 1920’s, increasing from about 300°C in 1987 to 690°C in May 1993, before decreasing to 400°C by 1996–1997. During 1990, Vulcano’s Electronic Distance Measurement (EDM) network was expanded to provide more detailed coverage of the northern sector of the Fossa crater and, in particular, to monitor the movement of the northern flank the Fossa cone. Measurements, carried out between 1990 and 1994, showed shortening by about 6 to 7 cm along baselines measured to a small section of the northern rim. Over the following four years these baselines showed a slow extension by about 3 cm, to gradually recover part of the previous deformation. We believe that the shortening and lengthening of the EDM baselines was respectively due to the increasing and decreasing temperature of the rock body lying close to the deforming area. This caused thermal expansion, followed by contraction. The positive movement of the rim was not completely matched by a negative recovery, suggesting that a non-recoverable sliding movement was also responsible for some of the shortening of the baselines. We verified our hypothesis by calculating the expected dilatation of a rock body, as a function of the volume of rock heated and its thermal expansion coefficient, and compared the expected deformation to that observed. The geodetic investigation showed that the unstable portion affects a small length of the rim (about 100 m long) and involves a volume of about 0.8 × 106 m3. However, this zone lies directly above a particularly unstable portion of the flank, as well as the main village and port on the island.

Infrared thermography of the fumarole area in the active crater of the Aso volcano, Japan, using a consumer digital camera

Thermal information of volcanoes is crucial for understanding their magmatic activity. In active volcanoes, the fumarole temperature is measured in order to monitor the magmatic activity. In this study, a consumer digital camera has been used as an infrared thermometer in order to obtain the infrared images for a fumarole area in the active crater of the Aso volcano, Japan; the temperature of the fumaroles that are more than a few centimeters in diameter can be estimated from the recorded images. The aperture value and the exposure time of the digital camera can be optimized manually, and clear images can be obtained in a wider temperature range of fumaroles by using the digital camera than by the consumer camcorder used in the previous study. The spatial resolution can also be chosen by changing the lens. The sensor of the digital cameras is sensitive to the near-infrared wavelengths of light, and the temperature estimation by using light of these wavelengths is robust against disturbances such as atmospheric absorption. The temperature, size, and spatial distribution of the fumaroles estimated by using this thermometer are considered to be more reliable than those measured by the dedicated thermometer used in the Aso volcano and the consumer camcorder used in the previous study. The thermometer used in this study is handy and cost-effective. Moreover, it has better temperature and spatial resolutions for monitoring high-temperature volcanic activity.

Seismicity and fluid geochemistry at Lassen Volcanic National Park, California: Evidence for two circulation cells in the hydrothermal system

Seismic analysis and geochemical interpretations provide evidence that two separate hydrothermal cells circulate within the greater Lassen hydrothermal system. One cell originates south to SW of Lassen Peak and within the Brokeoff Volcano depression where it forms a reservoir of hot fluid (235–270 °C) that boils to feed steam to the high-temperature fumarolic areas, and has a plume of degassed reservoir liquid that flows southward to emerge at Growler and Morgan Hot Springs. The second cell originates SSE to SE of Lassen Peak and flows southeastward along inferred faults of the Walker Lane belt (WLB) where it forms a reservoir of hot fluid (220–240 °C) that boils beneath Devils Kitchen and Boiling Springs Lake, and has an outflow plume of degassed liquid that boils again beneath Terminal Geyser. Three distinct seismogenic zones (identified as the West, Middle, and East seismic clusters) occur at shallow depths (< 6 km) in Lassen Volcanic National Park, SW to SSE of Lassen Peak and adjacent to areas of high-temperature (≤ 161 °C) fumarolic activity (Sulphur Works, Pilot Pinnacle, Little Hot Springs Valley, and Bumpass Hell) and an area of cold, weak gas emissions (Cold Boiling Lake). The three zones are located within the inferred Rockland caldera in response to interactions between deeply circulating meteoric water and hot brittle rock that overlies residual magma associated with the Lassen Volcanic Center. Earthquake focal mechanisms and stress inversions indicate primarily N–S oriented normal faulting and E–W extension, with some oblique faulting and right lateral shear in the East cluster. The different focal mechanisms as well as spatial and temporal earthquake patterns for the East cluster indicate a greater influence by regional tectonics and inferred faults within the WLB. A fourth, deeper (5–10 km) seismogenic zone (the Devils Kitchen seismic cluster) occurs SE of the East cluster and trends NNW from Sifford Mountain toward the Devils Kitchen thermal area where fumarolic temperatures are ≤ 123 °C. Lassen fumaroles discharge geothermal gases that indicate mixing between a N 2-rich, arc-type component and gases derived from air-saturated meteoric recharge water. Most gases have relatively weak isotopic indicators of upper mantle or volcanic components, except for gas from Sulphur Works where δ 13C–CO 2, δ 34S–H 2S, and δ 15N–N 2 values indicate a contribution from the mantle and a subducted sediment source in an arc volcanic setting.

Color change of lake water at the active crater lake of Aso volcano, Yudamari, Japan: is it in response to change in water quality induced by volcanic activity?

One feature of volcanic lakes influenced by subaqueous fumaroles existing at lake bottoms (called active crater lakes) is the remarkable color of their waters: turquoise or emerald green. The active crater lake named Yudamari at Mt. Nakadake of Aso volcano, Japan, takes on a milky pale blue-green. The particular blue component of the lake water color results from Rayleigh scattering of sunlight by very fine aqueous colloidal sulfur particles; the green component is attributable to absorption of sunlight by dissolved ferrous ions. An objective color observation conducted during 2000–2007 revealed that the lake water color changed from blue-green to solid green. The disappearance of the blue ingredient of the water color will result in diminution of aqueous colloidal sulfur from chemical analyses of lake waters sampled simultaneously. The aqueous sulfur is produced by the reaction of sulfur dioxide and hydrogen sulfide supplied from subaqueous fumaroles. However, its production efficiency decreases by domination of sulfur dioxide in the subaqueous fumarolic sulfur gas species with increasing subaqueous fumarolic temperature. The disappearance of blue ingredients from the blue-green color of the lake water may be attributed to activation of subaqueous fumarole activity.

Inter-eruptive volcanism at Usu volcano: Micro-earthquakes and dome subsidence

Post-eruptive crustal activity after the 2000 eruption of Usu volcano was investigated by seismic and geodetic field observations. Remarkable features of the magmatic eruptions that occur almost every 30 years include lava dome formation and strong precursory earthquakes. On the other hand, rapid dome subsidence was observed by electronic distance meter (EDM) measurement after the 1977–1982 summit eruption. Since the 2000 eruption, seismic activity at a shallow part under the summit crater has remained at a high level relative to that after the 1977–1982 eruption, although eruption occurred at the western foot of the volcano during the 2000 eruption. To reveal the shallow crustal activity in the inter-eruptive period around the summit area, seismicity and crustal deformation have been investigated since 2006. Dense temporary seismic observations and hypocenter relocation analysis using a three-dimensional velocity structure model revealed that the focal area is localized along the U-shaped fault that developed in the dome-forming stage of the 1977–1982 eruption. Three major focal clusters are distributed on the southwestern side of Usu-Shinzan cryptodome, which was built up during the 1977–1982 eruption. For the seven major events with magnitudes larger than 1, the focal mechanism was a large dip-slip component, which suggests the subsidence of Usu-Shinzan cryptodome. Interferomatetric satellite aperture radar (InSAR) image analysis and repeated GPS measurements revealed subsidence of the summit dome, which is almost centered at the Usu-Shinzan cryptodome. The area of rapid deformation is restricted to a small area around the summit crater. The estimated rate of dome subsidence relative to the crater floor is about 3 cm/year. These results strongly suggest that subsidence of Usu-Shinzan is associated with the small earthquakes along the U-shaped fault that surrounds the cryptodome. According to prior seismic and geodetic studies, it is thought that most of the magma rising under the summit crater during the 2000 eruption stopped around a depth of 2 km below sea level, which is sufficiently deep relative to the focal area of the present seismicity. A part of the magma intruded under the western foot and contributed to the 2000 eruption. We conclude that the 2000 eruption scarcely affected the shallow crustal activity under the summit crater, and that Usu-Shinzan cryptodome is continuing to subside just as it was before the 2000 eruption. The shallow volcanic earthquakes that began increasing from 1995 are closely related to the successive subsidence of the summit domes. Temporal change in fumarole temperature suggests a relationship between the shallow earthquakes and cooling of the magma that intruded under Usu-Shinzan during the 1977–1982 eruption.

Temporal change of characteristics of shallow volcano-tectonic earthquakes associated with increase in volcanic activity at Kuchinoerabujima volcano, Japan

Shallow volcano-tectonic (VT) earthquakes recorded at the Kuchinoerabujima island volcano in southwest Japan are analyzed in order to clarify the role of hydrothermal activity in the development of volcanic seismicity. From analysis of shallow VT earthquakes in 2006, two specific episodes of elevated seismicity are observed in April and November 2006. The VT earthquakes have hypocenters at depths of 0–0.4 km beneath the summit crater, and normal fault focal mechanisms with WNW–ESE extension consistent with the tensional stress field indicated by the alignment of craters and fissures. Although the hypocenters and focal mechanisms are found to be largely invariant during these episodes, the corner frequencies of the VT earthquakes underwent a pronounced increase and decrease accompanying the changes in seismicity rates. The corner frequencies increased to 20–25 Hz approximately one month prior to the onset of elevated seismicity, and then decreased to 10–15 Hz in the period of peak seismicity. The rupture length also decreased at the onset of seismicity, thereafter increasing as the seismicity continued. The peak seismicity in terms of the daily number of VT events was accompanied by inflation around the crater, suggestive of a pressure increase in the volcanic system. It is inferred that the increase in shallow VT seismicity and rupture length is related to the development of a fractured zone. The pressure increase in the volcanic system is attributed to the intrusion of hydrothermal fluids, which is supported by an observed increase in fumarolic temperature and activity. The preceding monochromatic events are thus considered to be generated by the effect of fluid-filled cracks. The shortening of rupture length is then inferred to be related to the closing of non-fluid-filled cracks in the fracture zone under the increasing pressure field, leading to a transition from monochromatic events to low-frequency and shallow VT seismicity.

Ground deformation patterns at White Island volcano (New Zealand) between 1967 and 2008 deduced from levelling data

Since 1967, levelling measurements have been conducted in the main crater of White Island volcano. Interpretation of these data using numerical modelling reveals that shallow pressure sources (200–600 m deep) extending up to the subsurface dominated the long-term deformation pattern consisting of inflation/deflation cycles. The time sequence of height changes, magnetic changes, and fumarole temperature and chemistry reveal that surface changes were caused by increasing temperature below the main crater, reflecting the presence of magma at shallow depth. The uplift and subsidence are interpreted in terms of increase or decrease in fluid pore pressure in response to changes of the heat and gas flux. The subsidence during and following eruptions could be also linked with removal of material at depth to feed the eruptions.

Experiences from near‐real‐time satellite‐based volcano monitoring in Central America: case studies at Fuego, Guatemala

Over the past decade, remote sensing has been used increasingly in the study of active volcanoes and their associated hazards. Ground‐based remote sensing techniques, such as those aimed at the analysis of volcanic gases or fumarole temperatures, are now part of routine monitoring operations with additional satellite‐based remote sensing methods. It is likely that the use of satellite‐based systems will be most beneficial for volcano monitoring in developing country regions and remote areas. In such situations, an operational real‐time satellite remote sensing system could provide rapid assessment of volcanic activity levels and potentially be used to derive crucial information for disaster prevention. This would allow key at‐risk areas to be rapidly and appropriately targeted. An operational test of such a system has been carried out in the past 3 years in Central America, based on local reception and analysis of Advanced Very High Resolution Radiometer (AVHRR) imagery. Here we analyse the performance and data quality for recent activity of Fuego volcano (Guatemala). We assess the ability of the system to detect, quantify and monitor periods of heightened activity and consider the benefits of such information being available in near‐real time to local geoscientists and for hazard mitigation. We show that the system is able to detect significant changes in volcanic activity (November and December 2004, February and December 2005). There are good comparisons for these events with large‐scale monitoring systems using additional remote sensing data. This paper provides one of the few evaluations of the direct application of operational AVHRR data to volcanic hazard monitoring and disaster management in developing countries.

Chemical and isotopic compositions of thermal springs, fumaroles and bubbling gases at Tacaná Volcano (Mexico–Guatemala): implications for volcanic surveillance

This study presents baseline data for future geochemical monitoring of the active Tacana volcano–hydrothermal system (Mexico–Guatemala). Seven groups of thermal springs, related to a NW/SE-oriented fault scarp cutting the summit area (4,100m a.s.l.), discharge at the northwest foot of the volcano (1,500–2,000m a.s.l.); another one on the southern ends of Tacana (La Calera). The near-neutral (pH from 5.8 to 6.9) thermal (T from 25.7°C to 63.0°C) HCO3–SO4 waters are thought to have formed by the absorption of a H2S/SO2–CO2-enriched steam into a Cl-rich geothermal aquifer, afterwards mixed by Na/HCO3-enriched meteoric waters originating from the higher elevations of the volcano as stated by the isotopic composition (δD and δ18O) of meteoric and spring waters. Boiling temperature fumaroles (89°C at ~3,600m a.s.l. NW of the summit), formed after the May 1986 phreatic explosion, emit isotopically light vapour (δD and δ18O as low as −128 and −19.9‰, respectively) resulting from steam separation from the summit aquifer. Fumarolic as well as bubbling gases at five springs are CO2-dominated. The δ13CCO2 for all gases show typical magmatic values of −3.6 ± 1.3‰ vs V-PDB. The large range in 3He/4He ratios for bubbling, dissolved and fumarolic gases [from 1.3 to 6.9 atmospheric 3He/4He ratio (R A)] is ascribed to a different degree of near-surface boiling processes inside a heterogeneous aquifer at the contact between the volcanic edifice and the crystalline basement (4He source). Tacana volcano offers a unique opportunity to give insight into shallow hydrothermal and deep magmatic processes affecting the CO2/3He ratio of gases: bubbling springs with lower gas/water ratios show higher 3He/4He ratios and consequently lower CO2/3He ratios (e.g. Zarco spring). Typical Central American CO2/3He and 3He/4He ratios are found for the fumarolic Agua Caliente and Zarco gases (3.1 ± 1.6 × 1010 and 6.0 ± 0.9 R A, respectively). The L/S (5.9 ± 0.5) and (L + S)/M ratios (9.2 ± 0.7) for the same gases are almost identical to the ones calculated for gases in El Salvador, suggesting an enhanced slab contribution as far as the northern extreme of the Central American Volcanic Arc, Tacana.

Fumarole monitoring with a handheld infrared camera: Volcán de Colima, Mexico, 2006–2007

This paper describes a methodology for the monitoring of fumarole temperatures at medium ranges (~ 6 km) using a handheld infrared camera (wavelength range: 8–13.5 µm). As a relationship between fumarole temperatures, gas flux and volcanic activity has been demonstrated by a number of studies, fumarole temperature data has a potential use as a monitoring tool. Volcán de Colima is an andesitic stratovolcano with a 300 m diameter summit crater formed by the destruction of the 2004 lava dome by a series of explosions in 2005. Between January 2006 and August 2007, sequences of thermal images were recorded from a viewpoint 6 km to the north during regular 24–48 hour monitoring excursions. The temperatures of fumaroles on the crater rim and the ground surface on the volcano's flanks were measured. A methodology was developed to remove data affected by clouds or volcanic water vapour based on rates of temperature change and scatter within the data. For the remaining data, it is demonstrated mathematically that at this range, typical variations in atmospheric transmissivity will affect the apparent temperatures by +/− 2 °C, while a 25% change in fumarole heat flux would change it by 5–10 °C. The mean night-time apparent temperature of the fumaroles was calculated for each excursion and showed an irregular decline over the 19 month period. Subtracting the radiant heat flux of flank rocks from those of the fumaroles removes seasonal variations and gives the clearest view of trends in the fumarole heat flux. A sharp drop in fumarole temperature during February 2007 coincided with the emergence of a lava dome in the crater. The declining fumarole temperature is interpreted to reflect decreasing gas flux from the crater in line with a change in eruptive regime from frequent, small, ash-rich explosions to slow effusion of lava.

Chemical evolution of thermal waters and changes in the hydrothermal system of Papandayan volcano (West Java, Indonesia) after the November 2002 eruption

Papandayan is a stratovolcano situated in West Java, Indonesia. Since the last magmatic eruption in 1772, only few hydrothermal explosions have occurred. An explosive eruption occurred in November 2002 and ejected ash and altered rocks. The altered rocks show that an advanced argillic alteration took place in the hydrothermal system by interaction between acid fluids and rocks. Four zones of alteration have been defined and are limited in extension and shape along faults or across permeable structures at different levels beneath the active crater of the volcano. At the present time, the activity is centered in the northeast crater with discharge of low temperature fumaroles and acid hot springs. Two types of acid fluids are emitted in the crater of Papandayan volcano: (1) acid sulfate-chloride waters with pH between 1.6 and 4.6 and (2) acid sulfate waters with pH between 1.2 and 2.5. The water samples collected after the eruption on January 2003 reveal an increase in the SO 4/Cl and Mg/Cl ratios. This evolution is likely explained by an increase in the neutralization of acid fluids and tends to show that water–rock interactions were more significant after the eruption. The evolution in the chemistry observed since 2003 is the consequence of the opening of new fractures at depth where unaltered (or less altered) volcanic rocks were in contact with the ascending acid waters. The high δ 34S values (9–17‰) observed in acid sulfate-chloride waters before the November 2002 eruption suggest that a significant fraction of dissolved sulfates was formed by the disproportionation of magmatic SO 2. On the other hand, the low δ 34S (− 0.3–7‰) observed in hot spring waters sampled after the eruption suggest that the hydrothermal contribution (i.e. the surficial oxidation of hydrogen sulfide) has increased.

Temporal variations of gas compositions of fumaroles in the Tatun Volcano Group, northern Taiwan

Hydrothermal activity is common in the Tatun Volcano Group of northern Taiwan. Helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60% in the previous study. Along with recent seismic results, a magma reservoir is inferred to have existed beneath the area of Da-you-keng, where fumarolic venting is the most active in Tatun Volcano Group. Progressive increases of HCl concentrations and SO 2/H 2S ratio in fumaroles from Da-you-keng have been observed since August 2004. The HCl concentration changed from almost the detection limit to thousands of ppm, even up to 30,000 ppm. SO 2/H 2S ratios varied from almost 0 to 3; hence SO 2 became the dominated S species in this area. These variations were accompanied by rising temperature of fumaroles in the Tatun Volcano Group, especially in the area of Da-you-keng (from boiling point to 131 °C). Meanwhile, 3He/ 4He ratios showed a decreasing trend but returned to normal values shortly thereafter. We propose two possible processes, 1) new magma supply and 2) recent opening of fractures in local area, to explain these observations. Based on the change of 3He/ 4He ratio and lack of ground deformation, we consider the latter might be more plausible.

The magmatic- and hydrothermal-dominated fumarolic system at the Active Crater of Lascar volcano, northern Chile

Low-to-high temperature fumaroles discharging from the Active Crater of Lascar volcano (northern Chile) have been collected in November 2002, May 2005 and October 2006 for chemical and isotopic analysis to provide the first geochemical survey on the magmatic-hydrothermal system of this active volcano. Chemical and isotopic gas composition shows direct addition of high-temperature fluids from magmatic degassing, mainly testified by the very high contents of SO2, HCl and HF (up to 87,800, 29,500 and 2,900 μmol/mol) and the high R/Ra values (up to 7.29). Contributions from a hydrothermal source, mainly in gas discharges of the Active Crater rim, has also been detected. Significant variations in fluid chemistry, mainly consisting of a general decrease of magmatic-related compounds, i.e. SO2, have affected the fumarolic system during the period of observation, indicating an increase of the influence of the hydrothermal system surrounding the ascending deep fluids. The chemical composition of Active Crater fumaroles has been used to build up a geochemical model describing the main processes that regulate the fluid circulation system of Lascar volcano to be utilized in volcanic surveillance.

Mercury and halogen emissions from Masaya and Telica volcanoes, Nicaragua

We report measurements of Hg, SO2, and halogens (HCl, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gaseous SO2 and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO2 and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m−3. Hg/SO2 mass ratios measured with the real‐time instruments ranged from 1.1 × 10−7 to 3.5 × 10−5 (mean 2 × 10−5). Total gaseous mercury (TGM) concentrations measured by gold trap ranged from 100 to 225 ng m−3. Reactive gaseous mercury accounted for 1% of TGM, while particulate mercury was 5% of the TGM. Field measurements of Masaya's SO2 flux, combined with the Hg/SO2 ratio, indicate a Hg flux from Masaya of 7.2 Mg a−1. At Masaya's low temperature fumaroles, Hg/CO2 mass ratios were consistently around 2 × 10−8, lower than observed in the main vent (Hg/CO2 ∼ 10−7). Low‐temperature fumarole Hg fluxes from Masaya are insignificant (∼150 g a−1). Ratios of S, C and halogen species were also measured at Masaya and Telica volcanoes. CO2/SO2 ratios at Masaya ranged from 2.8 to 3.9, comparable to previously published values. At Masaya molar Br/SO2 was 3 × 10−4 and I/SO2 was 2 × 10−5, suggesting fluxes of 0.2–0.5 Mg HBr d−1 and 0.02–0.05 Mg HI d−1. At Telica the Br/SO2 ratio was also 3 × 10−4 and the I/SO2 ratio was 5.8 × 10−5, with corresponding fluxes of 0.2 Mg HBr d−1 and 0.06 Mg HI d−1. Gases at both volcanoes are enriched in I relative to Br and Cl, compared to gases from volcanoes elsewhere.

Mantle source for Oldoinyo Lengai carbonatites: Evidence from helium isotopes in fumarole gases

Oldoinyo Lengai is the world's only active carbonatite volcano and considerable debate still surrounds the genesis of its magmas. Gases were collected from two fumaroles discharging close to the then active vent in October 2003. Measured fumarole temperatures were ≤ 195°C, despite the nearby, vigorous eruptive activity. Gases were sampled and analysed for noble gas isotopes. Freshly erupted natrocarbonatite lavas, a 1917 nephelinite and a sub-recent wollastonite bearing rock were also collected and analysed for noble gas isotopes using vacuum crushing techniques. In all the lava samples the neon, argon, krypton and xenon isotope ratio data are indistinguishable from air implying atmospheric contamination of the hygroscopic rocks. In the fumaroles, measured 3He/ 4He ratios are between 4 and 7 R/R a . This range is similar to published values for silicate xenoliths of the East African Rift implying a local lithospheric mantle source for the volatile component of the Lengai magmas. It is still unclear if the natrocarbonatites themselves come from this region, or if fractionation and/or liquid immiscibility generate the carbonate magmas from a silicate melt within the crust itself.

Fluxes of volatiles (H2O, CO2, N2, Cl, F) from arc volcanoes

This review gives an overview of the estimates of volatile emissions from arc and mid-ocean ridge volcanoes to the atmosphere and hydrosphere with particular focus on H2O, CO2, N2, Cl and F. The gas compositions of high temperature (>500°C) fumaroles are compiled and used to derive magmatic H2O/SO2, CO2/SO2, HCl/SO2 and HF/SO2 ratios on an arc-by-arc basis to obtain new estimates of major volatile fluxes from arcs globally. The estimate of F flux from arcs is two orders of magnitude smaller than the amount of F released from mid ocean ridges whereas the arc Cl flux exceeds the ridge flux. An important observation is that globally the water budget of subduction zones seems to be balanced and the amount of water degassed through arc volcanism is within the estimates of the amount of water released from the slab below the volcanic front. Recent work that focused on the Central American arc shows that detailed knowledge of the subduction input compositions, coupled with gas emission studies is critical to further constrain the fate of volatiles during the subduction processes.

Accidental gas emission from shallow pressurized aquifers at Alban Hills volcano (Rome, Italy): Geochemical evidence of magmatic degassing?

Recent studies suggested that Alban Hills (Rome) is a quiescent and not an extinct volcano, as it produced Holocene eruptions and several lahars until Roman times by water overflow from the Albano crater lake. Alban Hills are presently characterized by high P CO2 in groundwaters and by several cold gas emissions usually in sites where excavations removed the superficial impervious cover. Gas consists mostly of CO 2 with minor H 2S and the diffuse CO 2 soil flux is locally very high. Accidental gas blowouts, occurred during shallow well drillings (tens to hundreds m depth) in zones with no surface gas manifestations, indicate the presence of gas pressurized aquifers confined underneath impermeable layers, within both the volcanic rock pile and the underlying Pleistocene loose sediments. Degassing mostly occurs in correspondence of bordering faults of buried horsts cut in the Mesozoic carbonate basement, hosting the main aquifer. Carbon isotopic composition ( δ 13C CO2) suggests that CO 2 is at least partly originated by thermal decarbonation of these limestones. 3He/ 4He isotopic ratio of the gas (up to 1.9 Ra) is the same or even slightly higher than that of olivine and clinopyroxene fluid inclusions of the Alban Hills volcanic products, indicating a possible magmatic source for the gas. Low R/Ra values, compared to MORB and island arc magmas, are characteristic of the potassic Roman Comagmatic Province and reflect a deep involvement of crustal material in the magma genesis. The lack of high temperature fumaroles can be explained by an efficient meteoric cold water penetration and circulation in the volcano permeable terrains.

Volcanic activity influenced by tectonic earthquakes: Static and dynamic stress triggering at Mt. Merapi

Mt. Merapi is one of the most dangerous volcanoes in Indonesia, located within the tectonically active region of south‐central Java. This study investigates how Mt. Merapi affected ‐ and was affected by ‐ nearby tectonic earthquakes. In 2001, a Mw6.3 earthquake occurred in conjunction with an increase in fumarole temperature at Mt. Merapi. In 2006, another Mw6.3 earthquake took place, concomitant with an increase of magma extrusion and pyroclastic flows. Here, we develop theoretical models to study the amount of stress transfer between the earthquakes and the volcano, showing that dynamic, rather than static, stress changes are likely responsible for the temporal and spatial proximity of these events. Our examination of the 2001 and 2006 events implies that volcanic activity at Mt. Merapi is influenced by stress changes related to remote tectonic earthquakes, a finding that is important for volcano hazard assessment in this densely inhabited area.