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1.
At Vesuvio, a significant fraction of the rising hydrothermal–volcanic fluids is subjected to a condensation and separation process producing a CO 2–rich gas phase, mainly expulsed through soil diffuse degassing from well defined areas called diffuse degassing structures (DDS), and a liquid phase that flows towards the outer part of the volcanic cone. A large amount of thermal energy is associated with the steam condensation process and subsequent cooling of the liquid phase. The total amount of volcanic–hydrothermal CO 2 discharged through diffuse degassing has been computed through a sequential Gaussian simulation (sGs) approach based on several hundred accumulation chamber measurements and, at the time of the survey, amounted to 151 t d –1. The steam associated with the CO 2 output, computed assuming that the original H 2O/CO 2 ratio of hydrothermal fluids is preserved in fumarolic effluents, is 553 t d –1, and the energy produced by the steam condensation and cooling of the liquid phase is 1.47×10 12 J d –1 (17 MW). The location of the CO 2 and temperature anomalies show that most of the gas is discharged from the inner part of the crater and suggests that crater morphology and local stratigraphy exert strong control on CO 2 degassing and subsurface steam condensation. The amounts of gas and energy released by Vesuvio are comparable to those released by other volcanic degassing areas of the world and their estimates, through periodic surveys of soil CO 2 flux, can constitute a useful tool to monitor volcanic activity.Editorial responsibility: H. Shinohara 相似文献
2.
On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity
on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the
model that had been developed previously (2002–2003 eruption) and to improve our understanding of the relationship between
the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic
equilibrium between the volatiles (CO 2 and SO 2) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of
criticality of the volcanic activity. One of the major accomplishments of this study is a 4-year database of summit soil CO 2 flux on the basis of which we define the thresholds (low–medium–high) for this parameter that are empirically based on the
natural volcanological evolution of Stromboli. The SO 2 fluxes of the degassing plume and the CO 2 fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. It is noteworthy that geochemical signals of volcanic
unrest have been clearly identified before, during and after the effusive activity. These signals were found almost simultaneously
in the degassing plume (SO 2 flux) and in soil degassing (CO 2 flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results
will be useful for future volcanic surveillance at Stromboli. 相似文献
3.
Since October 2001, four soil CO 2 flux stations were installed in the island of São Miguel (Azores archipelago), at Fogo and Furnas quiescent central volcanoes. These stations perform measurements by the accumulation chamber method and, as the gas flux may be influenced by external variables, the stations are equipped with several meteorological sensors. Multivariate regression analysis applied to the large datasets obtained allowed observing that the meteorological variables may influence the soil CO 2 flux oscillations from 18% to 50.5% at the different monitoring sites. Additionally, it was observed that meteorological variables (mainly soil water content, barometric pressure, wind speed and rainfall) play a different role in the control of the gas flux, depending on the selected monitoring site and may cause significant short-term (spike-like) fluctuations. These divergences may be potentially explained by the porosity and hydraulic conductivity of the soils, topographic effects, drainage area and different exposure of the monitoring sites to the weather conditions. Seasonal effects are responsible for long-term oscillations on the gas flux. 相似文献
4.
Soil CO 2 concentration data were collected periodically from July 2001 to June 2005 from sampling site grids in two areas located
on the lower flanks of Mt. Etna volcano (Paternò and Zafferana Etnea–Santa Venerina). Cluster analysis was performed on the
acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources. In both
areas three clusters were recognised, whose average CO 2 concentration values throughout the whole study period remained significantly different from one another. The clusters with
the lowest CO 2 concentrations showed time-averaged values ranging from 980 to 1,170 ppm vol, whereas those with intermediate CO 2 concentrations showed time-averaged values ranging from 1,400 to 2,320 ppm vol, and those with the highest concentrations
showed time-averaged values between 1,960 and 55,430 ppm vol. We attribute the lowest CO 2 concentrations largely to a biogenic source of CO 2. Conversely, the highest CO 2 concentrations are attributed to a magmatic source, whereas the intermediate values are due to a variable mixing of the two
sources described above. The spatial distribution of the CO 2 values related to the magmatic source define a clear direction of anomalous degassing in the Zafferana Etnea–Santa Venerina
area, which we attribute to the presence of a hidden fault, whereas in the Paternò area no such oriented anomalies were observed,
probably because of the lower permeability of local soil. Time-series analysis shows that most of the variations observed
in the soil CO 2 data from both areas were related to changes in the volcanic activity of Mt. Etna. Seasonal influences were only observed
in the time patterns of the clusters characterised by low CO 2 concentrations, and no significant interdependence was found between soil CO 2 concentrations and meteorological parameters. The largest observed temporal anomalies are interpreted as release of CO 2 from magma batches that migrated from deeper to shallower portions of Etna’s feeder system. The pattern of occurrence of
such episodes of anomalous gas release during the observation period was quite different between the two studied areas. This
pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano’s feeder system after
June 2003, interpreted as magma accumulation into a shallow (<8 km depth) reservoir. 相似文献
5.
Soil temperature and gas (CO 2 concentration and flux) have been investigated at Merapi volcano (Indonesia) during two inter-eruptive periods (2002 and
2007). Precise imaging of the summit crater and the spatial pattern of diffuse degassing along a gas traverse on the southern
slope are interpreted in terms of summit structure and major caldera organization. The summit area is characterized by decreasing
CO 2 concentrations with distance from the 1932 crater rim, down to atmospheric levels at the base of the terminal cone. Similar
patterns are measured on any transect down the slopes of the cone. The spatial distribution of soil gas anomalies suggests
that soil degassing is controlled by structures identified as concentric historical caldera rims (1932, 1872, and 1768), which
have undergone severe hydrothermal self-sealing processes that dramatically lower the permeability and porosity of soils.
Temperature and CO 2 flux measurements in soils near the dome display heterogeneous distributions which are consistent with a fracture network
identified by previous geophysical studies. These data support the idea that the summit is made of isolated and mobile blocks,
whose boundaries are either sealed by depositional processes or used as pathways for significant soil degassing. Within this
context, self-sealing both prevents long-distance soil degassing and controls heat and volatile transfers near the dome. A
rough estimate of the CO 2 output through soils near the dome is 200–230 t day −1, i.e. 50% of the estimated total gas output from the volcano summit during these quiescent periods. On Merapi’s southern
slope, a 2,500 m long CO 2 traverse shows low-amplitude anomalies that fit well with a recently observed electromagnetic anomaly, consistent with a
faulted structure related to an ancient avalanche caldera rim. Sub-surface soil permeability is the key parameter that controls
the transfer of heat and volatiles within the volcano, allowing its major tectonic architecture to be revealed by soil gas
and soil temperature surveys. 相似文献
6.
The northwestern flank of the Colli Albani, a Quaternary volcanic complex near Rome, is characterised by high pCO 2 values and Rn activities in the groundwater and by the presence of zones with strong emission of gas from the soil. The most significant of these zones is Cava dei Selci where many houses are located very near to the gas emission site. The emitted gas consists mainly of CO 2 (up to 98 vol%) with an appreciable content of H 2S (0.8–2%). The He and C isotopic composition indicates, as for all fluids associated with the Quaternary Roman and Tuscany volcanic provinces, the presence of an upper mantle component contaminated by crustal fluids associated with subducted sediments and carbonates. An advective CO 2 flux of 37 tons/day has been estimated from the gas bubbles rising to the surface in a small drainage ditch and through a stagnant water pool, present in the rainy season in a topographically low central part of the area. A CO 2 soil flux survey with an accumulation chamber, carried out in February–March 2000 over a 12 000 m 2 surface with 242 measurement points, gave a total (mostly conductive) flux of 61 tons/day. CO 2 soil flux values vary by four orders of magnitude over a 160-m distance and by one order of magnitude over several metres. A fixed network of 114 points over 6350 m 2 has been installed in order to investigate temporal flux variations. Six surveys carried out from May 2000 to June 2001 have shown large variations of the total CO 2 soil flux (8–25 tons/day). The strong emission of CO 2 and H 2S, which are gases denser than air, produces dangerous accumulations in low areas which have caused a series of lethal accidents to animals and one to a man. The gas hazard near the houses has been assessed by continuously monitoring the CO 2 and H 2S concentration in the air at 75 cm from the ground by means of two automatic stations. Certain environmental parameters (wind direction and speed; atm P, T, humidity and rainfall) were also continuously recorded. At both stations, H 2S and CO 2 exceeded by several times the recommended concentration thresholds. The highest CO 2 and H 2S values were recorded always with wind speeds less than 1.5 m/s, mostly in the night hours. Our results indicate that there is a severe gas hazard for people living near the gas emission site of Cava dei Selci, and appropriate precautionary and prevention measures have been recommended both to residents and local authorities. 相似文献
7.
The relationships between soil gas emissions and both tectonic and volcano-tectonic structures on Mt. Etna have been studied.
The investigation consisted of soil CO 2 flux measurements along traverses orthogonal to the main faults and eruptive fissures of the volcano. Anomalous levels of
soil degassing were found mainly in coincidence with faults, whereas only 49% of the eruptive fissures were found to produce
elevated CO 2 soil fluxes. This result suggests that only zones of strain are able to channel deep gases to the surface. According to this
hypothesis, several previously unknown structures are suggested. Based on our geochemical data, new structural maps of different
areas of Etna are proposed. The soil CO 2 fluxes observed in this study are higher than those measured in a 1987 study, and they are consistent with the higher level
of volcanic unrest during the current study.
Received: 20 March 1998 / Accepted: 17 June 1998 相似文献
8.
The Phlegraean Fields caldera is an active volcanic system where episodes of ground deformation are accompanied by significant changes in geochemical and geophysical parameters monitored at the surface. These changes derive from a complex interaction between magmatic system and hydrothermal fluid circulation. We calculate the gravity changes associated with the variable density of hydrothermal fluids. We simulate the multi-phase and multi-component fluid circulation triggered by a pulsating magma degassing, periodically increasing the discharge of CO 2-enriched fluids into the shallow hydrothermal system. The simulated evolution of the hydrothermal system successfully reproduces the observed composition of gas discharged at the surface. At the same time, results indicate that changes in average fluid density generate a detectable gravity signal that is of the same order of magnitude of the observed changes. This contribution to gravity changes can explain the peculiar behavior of gravity data collected at Solfatara, where surface hydrothermal phenomena are present. Simultaneous fitting of two independent sets of monitoring data (gas composition and gravity changes) confirms the conceptual model proposed for the hydrothermal system at Solfatara, and it provides new insights for the interpretation of gravity data. 相似文献
9.
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO 2 fluxes and quantify CO 2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO 2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m −2 day −1. Comparative maps of soil CO 2 flux were simulated and CO 2 emission rates estimated from three accumulation chamber (AC) CO 2 flux surveys. Least-squares inversion of measured eddy covariance CO 2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO 2 emission rates estimated based on simulated AC soil CO 2 fluxes. Spatial distributions of modeled surface CO 2 fluxes based on EC and AC observations showed moderate to good correspondence ( R
2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO 2 emissions over relatively large areas. 相似文献
10.
Two soil CO 2 efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO 2 degassing and estimate the total CO 2 output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO 2 efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO 2 efflux data showed a wide range of values up to 552 g m -2 d -1. Carbon isotope signatures of the soil CO 2 ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO 2 efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m -2 d -1, respectively). The spatial distribution of CO 2 efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the
extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan.
The total diffuse CO 2 output of Showa-Shinzan was estimated to be about 14.0–15.6 t d -1 of CO 2 for an area of 0.53 km 2. 相似文献
11.
The CO 2 and H 2S concentration in the Solfatara atmosphere has been measured. The concentrations of both gases are higher neraby the more active areas and decrease away from them. A sharp horizontal and vertical gradient of the CO 2 content has been recognized.Such gradient is assumed to result from a diffusion of gas from the ground to the atmosphere.The total output of CO 2 has been computed based on a turbulent diffusion model. The obtained value is in good agreement with previously abserved values ( Italiano
et al., 1984).The feasibility of monitoring the atmosphere of Solfatara for either gas hazard and surveillance of volcanic activity has also been evaluated. 相似文献
12.
Field observations coupled with experimental results show that CO 2 can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that
degassed from the mantle or produced by thermometamorphism. The evidence that a large amount of carbon dioxide associated
with radiogenic-type helium (R/Ra as low as 0.01–0.08) is released through continental areas, denotes the absence of a contribution
from the mantle or from mantle-derived fluids. Data collected during the seismic crisis which struck the Central Apennines
in 1997–98 have shown an enhanced CO 2 flux not associated with the presence of mantle or thermometamorphic-derived fluids. On the other hand, new experimental
results highlight the possibility of producing CO 2 by mechanical energy that acts on the calcite crystalline lattice. While the CO 2 released over the geothermal areas (e.g., Larderello Geothermal Field) is obviously derived by mantle-derived activities,
this is not the case of the huge amount of CO 2 released over the seismically active areas where the presence mantle-derived products is ruled out. We propose that mechanical
energy, e.g., released during seismic events, microseismicity or creeping processes is a possible additional energy source
able to produce CO 2 and thus could explain the presence of CO 2 degassing over tectonic areas where the influence of the mantle is low. 相似文献
13.
Soil CO 2 flux measurements were carried out along traverses across mapped faults and eruptive fissures on the summit and the lower
East Rift Zone of Kilauea volcano. Anomalous levels of soil degassing were found for 44 of the tectonic structures and 47
of the eruptive fissures intercepted by the surveyed profiles. This result contrasts with what was recently observed on Mt.
Etna, where most of the surveyed faults were associated with anomalous soil degassing. The difference is probably related
to the differences in the state of activity at the time when soil gas measurements were made: Kilauea was erupting, whereas
Mt. Etna was quiescent although in a pre-eruptive stage. Unlike Mt. Etna, flank degassing on Kilauea is restricted to the
tectonic and volcanic structures directly connected to the magma reservoir feeding the ongoing East Rift eruption or in areas
of the Lower East Rift where other shallow, likely independent reservoirs are postulated. Anomalous soil degassing was also
found in areas without surface evidence of faults, thus suggesting the possibility of previously unknown structures.
Received: November 2003, revised: January 2005, accepted: January 2005 相似文献
14.
Continuous monitoring of soil CO 2 dynamic concentration (which is proportional to the CO 2 flux through the soil) was carried out at a peripheral site of Mt. Etna during the period November 1997–September 2000 using an automated station. The acquired data were compared with SO 2 flux from the summit craters measured two to three times a week during the same period. The high frequency of data acquisition with both methods allowed us to analyze in detail the time variations of both parameters. Anomalous high values of soil CO 2 dynamic concentration always preceded periods of increased flux of plume SO 2, and these in turn were followed by periods of summit eruptions. The variations were modeled in terms of gas efflux increase due to magma ascent to shallow depth and its consequent depressurization and degassing. This model is supported by data from other geophysical and volcanological parameters. The rates of increase both of soil CO 2 dynamic concentration and of plume SO 2 flux are interpreted to be positively correlated both to the velocity of magma ascent within the volcano and to lava effusion rate once magma is erupted at the surface. Low rates of the increase were recorded before the nine-month-long 1999 subterminal eruption. Higher rates of increase were observed before the violent summit eruption of September-November 1999, and the highest rates were observed during shorter and very frequent spike-like anomalies that preceded the sequence of short-lived but very violent summit eruptions that started in late January 2000 and continued until late June of the same year. Furthermore, the time interval between the peaks of CO 2 and SO 2 in a single sequence of gas anomalies is likely to be controlled by magma ascent velocity.Editorial responsibility: H. Shinohara 相似文献
15.
The nonlinearity of the relationship between CO2 flux and other micrometeorological variables flux parameters limits the applicability of carbon flux models to accurately estimate the flux dynamics. However, the need for carbon dioxide (CO2) estimations covering larger areas and the limitations of the point eddy covariance technique to address this requirement necessitates the modeling of CO2 flux from other micrometeorological variables. Artificial neural networks (ANN) are used because of their power to fit highly nonlinear relations between input and output variables without explaining the nature of the phenomena. This paper applied a multilayer perception ANN technique with error back propagation algorithm to simulate CO2 flux on three different ecosystems (forest, grassland and cropland) in ChinaFLUX. Energy flux (net radiation, latent heat, sensible heat and soil heat flux) and temperature (air and soil) and soil moisture were used to train the ANN and predict the CO2 flux. Diurnal half-hourly fluxes data of observations from June to August in 2003 were divided into training, validating and testing. Results of the CO2 flux simulation show that the technique can successfully predict the observed values with R
2 value between 0.75 and 0.866. It is also found that the soil moisture could not improve the simulative accuracy without water stress. The analysis of the contribution of input variables in ANN shows that the ANN is not a black box model, it can tell us about the controlling parameters of NEE in different ecosystems and micrometeorological environment. The results indicate the ANN is not only a reliable, efficient technique to estimate regional or global CO2 flux from point measurements and understand the spatiotemporal budget of the CO2 fluxes, but also can identify the relations between the CO2 flux and micrometeorological variables. 相似文献
16.
We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO 2) and hydrogen sulfide (H 2S) from Hengill volcanic system, Iceland. Soil CO 2 and H 2S efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722?g?m ?2?day ?1, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO 2 degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW?CNNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H 2S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO 2 efflux and soil temperatures were also measured. The total diffuse CO 2 emission estimated for this volcanic system was about 1,526?±?160?t?day ?1 of which 453?t?day ?1 (29.7?%) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO 2 output, we used the average H 2O/CO 2 mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4?C240.2) as a representative value of the H 2O/CO 2 mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154?t?day ?1. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07?×?10 14?J?day ?1 or to a total heat flow of 1,237?MW t. 相似文献
17.
The rates of passive degassing from volcanoes are investigated by modelling the convective overturn of dense degassed and
less dense gas-rich magmas in a vertical conduit linking a shallow degassing zone with a deep magma chamber. Laboratory experiments
are used to constrain our theoretical model of the overturn rate and to elaborate on the model of this process presented by
Kazahaya et al. (1994). We also introduce the effects of a CO 2–saturated deep chamber and adiabatic cooling of ascending magma. We find that overturn occurs by concentric flow of the magmas
along the conduit, although the details of the flow depend on the magmas' viscosity ratio. Where convective overturn limits
the supply of gas-rich magma, then the gas emission rate is proportional to the flow rate of the overturning magmas (proportional
to the density difference driving convection, the conduit radius to the fourth power, and inversely proportional to the degassed
magma viscosity) and the mass fraction of water that is degassed. Efficient degassing enhances the density difference but
increases the magma viscosity, and this dampens convection. Two degassing volcanoes were modelled. At Stromboli, assuming
a 2 km deep, 30% crystalline basaltic chamber, containing 0.5 wt.% dissolved water, the ∼700 kg s –1 magmatic water flux can be modelled with a 4–10 m radius conduit, degassing 20–100% of the available water and all of the
1 to 4 vol.% CO 2 chamber gas. At Mount St. Helens in June 1980, assuming a 7 km deep, 39% crystalline dacitic chamber, containing 4.6 wt.%
dissolved water, the ∼500 kg s –1 magmatic water flux can be modelled with a 22–60 m radius conduit, degassing ∼2–90% of the available water and all of the
0.1 to 3 vol.% CO 2 chamber gas. The range of these results is consistent with previous models and observations. Convection driven by degassing
provides a plausible mechanism for transferring volatiles from deep magma chambers to the atmosphere, and it can explain the
gas fluxes measured at many persistently active volcanoes.
Received: 26 September 1997 / Accepted: 11 July 1998 相似文献
18.
At present, using Eddy Covariance (EC) method to estimate the “true value” of carbon sequestration in terrestrial ecosystem arrests more attention. However, one issue is how to solve the uncertainty of observations (especially the nighttime CO 2 flux data) appearing in post-processing CO 2 flux data. The ratio of effective and reliable nighttime EC CO 2 flux data to all nighttime data is relatively low (commonly, less than 50%) for all the long-term and continuous observation stations in the world. Thus, the processing method of nighttime CO 2 flux data and its effect analysis on estimating CO 2 flux annual sums are very important. In this paper, the authors analyze and discuss the reasons for underestimating nighttime CO 2 flux using EC method, and introduce the general theory and method for processing nighttime CO 2 flux data. By analyzing the relationship between nighttime CO 2 flux and air fraction velocity u*, we present an alternate method, Average Values Test (AVT), to determine the thresholds of fraction velocity ( u* c) for screening the effective nighttime CO 2 flux data. Meanwhile, taking the data observed in Yucheng and Changbai Mountains stations for an example, we analyze and discuss the effects of different methods or parameters on nighttime CO 2 flux estimations. Finally, based on the data of part ChinaFLUX stations and related literatures, empirical models of nighttime respiration at different sites in ChinaFLUX are summarized. 相似文献
19.
At present, using Eddy Covariance (EC) method to estimate the “true value” of carbon sequestration in terrestrial ecosystem arrests more attention. However, one issue is how to solve the uncertainty of observations (especially the nighttime CO2 flux data) appearing in post-processing CO2 flux data. The ratio of effective and reliable nighttime EC CO2 flux data to all nighttime data is relatively low (commonly, less than 50%) for all the long-term and continuous observation stations in the world. Thus, the processing method of nighttime CO2 flux data and its effect analysis on estimating CO2 flux annual sums are very important. In this paper, the authors analyze and discuss the reasons for underestimating nighttime CO2 flux using EC method, and introduce the general theory and method for processing nighttime CO2 flux data. By analyzing the relationship between nighttime CO2 flux and air fraction velocity u*, we present an alternate method, Average Values Test (AVT), to determine the thresholds of fraction velocity (u*c) for screening the effective nighttime CO2 flux data. Meanwhile, taking the data observed in Yucheng and Changbai Mountains stations for an example, we analyze and discuss the effects of different methods or parameters on nighttime CO2 flux estimations. Finally, based on the data of part ChinaFLUX stations and related literatures, empirical models of nighttime respiration at different sites in ChinaFLUX are summarized. 相似文献
20.
Wide variations were measured in the diffuse CO 2 flux through the soils in three selected areas of Mt Etna between August 1989 and March 1993. Degassing of CO 2 from the area of Zafferana Etnea-S. Venerina, on the eastern slope of the volcano, has been determined to be more strongly influenced by meteorological parameters than the other areas. The seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between CO 2 flux values and those of air temperature. The filtered data appear to have variations temporally coincident with those from the other areas, thus suggesting a common and probably deep source of gas. The highest fluxes measured in the two most peripheral areas may correlate well with other geophysical and volcanological anomalous signals that preceded the strong eruption of 1991–1993 and that were interpreted as deep pressure increases. Anomalous decreases in CO 2 fluxes accompanied the onset and the evolution of that eruption and have been interpreted as a sign of upward migration of the gas source. The variations of CO 2 flux at the 1989 SE fracture have also given interesting information on the timing of the magmatic intrusion that has then fed the 1991–1993 eruption. 相似文献
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