199 research outputs found
Temperature and pressure gas geoindicators at the Solfatara fumaroles (Campi Flegrei)
Long time series of fluid pressure and temperature within a hydrothermal
system feeding the Solfatara fumaroles are investigated here, on the basis
of the chemical equilibria within the CO2-H2O-H2-CO gas system. The
Pisciarelli fumarole external to Solfatara crater shows an annual cycle of
CO contents that indicates the occurrence of shallow secondary processes
that mask the deep signals. In contrast, the Bocca Grande and Bocca Nova
fumaroles located inside Solfatara crater do not show evidence of
secondary processes, and their compositional variations are linked to the
temperature–pressure changes within the hydrothermal system. The
agreement between geochemical signals and the ground movements of the
area (bradyseismic phenomena) suggests a direct relationship between the
pressurization process and the ground uplift. Since 2007, the gas
geoindicators have indicated pressurization of the system, which is most
probably caused by the arrival of deep gases with high CO2 contents in
the shallow parts of the hydrothermal system. This pressurization process
causes critical conditions in the hydrothermal system, as highlighted by
the increase in the fumarole temperature, the opening of new vents, and
the localized seismic activity. If the pressurization process continues with
time, it is not possible to rule out the occurrence of phreatic explosions
Soil CO2 emissions at Furnas volcano (São Miguel Island, Azores archipelago) - volcano monitoring perspectives, geomorphologic studies and land-use planning application
Carbon dioxide (CO2) diffuse degassing structures (DDS) at Furnas Volcano (São
Miguel Island, Azores) are mostly associated with the main fumarolic fields, evidence
that CO2 soil degassing is the surface expression of rising steam from the hydrothermal
system. Locations with anomalous CO2 flux are mainly controlled by tectonic structures
oriented WNW-ESE and NW-SE and by the geomorphology of the volcano, as
evidenced by several DDS located in depressed areas associated with crater margins.
Hydrothermal soil CO2 emissions in Furnas volcano are estimated to be ~ 968 t d-1.
Discrimination between biogenic and hydrothermal CO2 was determined using a
1
statistical approach and the carbon isotope composition of the CO2 efflux. Different
sampling densities were used to evaluate uncertainty in the estimation of the total CO2
flux, and showed that a low density of points may not be adequate to quantify soil
emanations from a relatively small DDS. Thermal energy release associated to diffuse
degassing at Furnas caldera is about 118 MW (from an area of ~ 4.8 km2) based on the
H2O/CO2 ratio in fumarolic gas. The DDS affect also Furnas and Ribeira Quente
villages, which are located inside the caldera and in the south flank of the volcano,
respectively. At these sites, 58% and 98% of the houses are built over hydrothermal
CO2 emanations, and the populations are at risk due to potential high concentrations of
CO2 accumulating inside the dwellings.
Keywords: Soil diffuse degassing; soil CO2 flux; emission rates; Azores archipelago
Improving monitoring techniques by exploiting TerraSAR-X data: an application to Campi Flegrei (Naples, Italy)
Geodetic monitoring of the Neapolitan Volcanic District, including the Campi Flegrei caldera on the west of the
city of Naples (Italy), is carried out via an integration between ground based networks and space-borne DInSAR
techniques, exploiting the SAR sensors onboard ERS1-2 and ENVISAT satellites. This allowed, for instance, to
follow the time evolution of the small uplift events which took place in 2000 and 2005-2006. Unfortunately, the
use of the ENVISAT C-band could result sometimes in no information when dealing with very low deformation
rates, as in the 2005-2006 case, when only continuous ground stations were able to detect the very beginning of
the uplift event.
To overcome this problem, from December 2009 we decided to use an high resolution SAR sensor operating in
the X band, i.e. TerraSAR-X from DLR.
TerraSAR-X High Resolution Spotlight scenes covering the main part of the Campi Flegrei caldera and centred on
the Solfatara crater were used for a DInSAR analysis, using the GENESIS DLR’s software. The first two scenes
(Dec. 15 and 26) were acquired with a temporal baseline of only one repetition cycle (11 days) and formed an
interferogram with a very small perpendicular baseline (16.5 m).
Apart from some minor atmospheric effects, the interferogram shows a small but clear deformation signal in the
Pisciarelli area, close to the east side of the Solfatara crater. The ellipse shaped uplift area extends approximately
30 meters in E-W and 20 meters in N-S directions and the maximum deformation is up to 10 mm in the centre of
the uplifted area.
The availability of a new scene (06/01/2010) allowed three possible combinations.
The deformation event highlighted by this analysis is consistent with geochemical observations carried out in
Pisciarelli by INGV-OV.
Pisciarelli area is seat of a fumarolic field systematically monitored in the frame of the volcanic surveillance of
the Campi Flegrei caldera. Two field surveys highlighted that, during the period of SAR images acquisition, a
new and strong fumarolic vent appeared in the centre of the uplifted area. In fact the vent, firstly observed on
Dec. 21, was absent on Dec. 16. The two independent observations, field surveys and SAR data, suggest that the
opening of the fumarolic vent was preceded by the pressurization of a small part of the fumarolic field highlighted
by the documented uplift. The correlation between the dynamics of the fumarolic field and the deformation
signal is confirmed by the fact that in the 26/12/2009-06/01/2010 interferogram the deformation signal is no more
detectable.
Finally, this case proves the high potentiality of TerraSAR-X High Resolution Spotlight data in monitoring
volcanic activity with a resolution suitable for detecting also minor, but possibly dangerous, changes of the
systems, as it could be in the early recognition of the signals generated by impending phreatic eruptions.
TerraSAR-X High Resolution Spotlight acquisitions will continue every cycle and PS-InSAR and SBAS algorithms
will be applied to carefully monitor any further changes in the activity of the Campi Flegrei volcanic system
Long time-series of chemical and isotopic compositions of Vesuvius fumaroles: evidence for deep and shallow processes
Long time-series of chemical and isotopic compositions of Vesuvius
fumaroles were acquired in the framework of the volcanic surveillance in
the 1998-2010 period. These allow the identification of processes that
occur at shallow levels in the hydrothermal system, and variations that are
induced by deep changes in volcanic activity. Partial condensation
processes of fumarolic water under near-discharge conditions can explain
the annual 18O and deuterium variabilities that are observed at Vesuvius
fumaroles. Significant variations in the chemical compositions of
fumaroles occurred over the 1999-2002 period, which accompanied the
seismic crisis of autumn 1999, when Vesuvius was affected by the most
energetic earthquakes of its last quiescence period. A continuous increase
in the relative concentrations of CO2 and He and a general decrease in the
CH4 concentrations are interpreted as the consequence of an increment in
the relative amount of magmatic fluids in the hydrothermal system. Gas
equilibria support this hypothesis, showing a PCO2 peak that culminated in
2002, increasing from values of ~40 bar in 1998 to ~55-60 bar in 2001-
2002. We propose that the seismic crisis of 1999 marked the arrival of the
magmatic fluids into the hydrothermal system, which caused the observed
geochemical variations that started in 1999 and culminated in 2002
Thermal monitoring of hydrothermal activity by permanent infrared automatic stations: Results obtained at Solfatara di Pozzuoli, Campi Flegrei (Italy)
A permanent automatic infrared (IR) station was installed at Solfatara crater, the most active zone of Campi Flegrei caldera. After a positive in situ calibration of the IR camera, we analyze 2175 thermal IR images of the same scene from 2004 to 2007. The scene includes a portion of the steam heated hot soils of Solfatara. The experiment was initiated to detect and quantify temperature changes of the shallow thermal structure of a quiescent volcano such as Solfatara over long periods. Ambient temperature results as the main parameter affecting IR temperatures while air humidity and rain control image quality. A geometric correction of the images was necessary to remove the effects of slow movement of the camera. After a suitable correction the images give a reliable and detailed picture of the temperature changes, over the period October 2004 – January 2007, which suggests origin of the changes were linked to anthropogenic activity, vegetation growth and to the increase of the flux of hydrothermal fluids in the area of the hottest fumaroles. Two positive temperature anomalies were registered after the occurrence of two seismic swarms which affected the hydrothermal system of Solfatara in October 2005 and October 2006. It is worth noting that these signs were detected in a system characterized by a low level of activity with respect to systems affected by real volcanic crisis where more spectacular results will be expected. Results of the experiment show that this kind of monitoring system can be a suitable tool for volcanic surveillance
New insights into Mt. Vesuvius hydrothermal system and its dynamic based on a critical review of seismic tomography and geochemical features
The seismic velocity and attenuation tomography images, calculated inverting
respectively P-wave travel times and amplitude spectra of local
VT quakes at Mt. Vesuvius have been reviewed and graphically represented
using a new software recently developed using Mathematica8TM.
The 3-D plots of the interpolated velocity and attenuation fields obtained
through this software evidence low-velocity volumes associated with high
attenuation anomalies in the depth range from about 1 km to 3 km below
the sea level. The heterogeneity in the distribution of the velocity and attenuation
values increases in the volume centred around the crater axis
and laterally extended about 4 km, where the geochemical interpretation
of the data from fumarole emissions reveals the presence of a hydrothermal
system with temperatures as high as 400-450°C roughly in the same
depth range (1.5 km to 4 km). The zone where the hydrothermal system
is space-confined possibly hosted the residual magma erupted by Mt. Vesuvius
during the recent eruptions, and is the site where most of the seismic
energy release has occurred since the last 1944 eruption
Long Time Series Of Fumarolic Compositions At Volcanoes: The Key To Understand The Activity Of Quiescent Volcanoes
Long time series of fumarolic chemical and isotopic
compositions at Campi Flegrei, Vulcano, Panarea,
Nisyros and Mammoth volcanoes highlight the occurrence
of mixing processes among magmatic and hydrothermal
fluids. At Campi Flegrei temperatures of
about 360°C of the hydrothermal system are inferred by
chemical and isotopic geoindicators. These high temperatures
are representative of a deep zone where magmatic
gases mix with hydrothermal liquids forming the gas plume feeding the fumaroles. Similar mixing processes
between magmatic fluids and a hydrothermal
component of marine origin have been recognized at
Vulcano high temperature fumaroles. In both the system
a typical ‘andesitic’ water type composition and high
CO2 contents characterizes the magmatic component.
Our hypothesis is that pulsing injections of these CO2-
rich magmatic fluids at the bottom of the hydrothermal
systems trigger the bradyseismic crises, periodically
affecting Campi Flegrei, and the periodical volcanic
unrest periods of Vulcano. At Campi Flegrei a strong
increase of the fraction of the magmatic component
marked the bradyseismic crisis (seismicity and ground
uplift) of 1982-84 and four minor episodes occurred in
1989, 1994 and 2000 and 2006. Increases of the magmatic
component in the fumaroles of Vulcano were recorded
in 1979-1981, 1985, 1988, 1996, 2004 and 2005
concurrently with anomalous seismic activity. Physicalnumerical
simulations of the injection of hot, CO2 rich
fluids at the base of a hydrothermal system, asses the
physical feasibility the process. Ground deformations,
gravitational anomalies and seismic crisis can be well
explained by the complex fluid dynamic processes
caused by magma degassing episodes. Sporadic data
on the fumaroles of other volcanoes, for example Panarea,
Nisyros (Greece), Mammoth (California), suggest
that magma degassing episodes frequently occur in
dormant volcanoes causing volcanic unrest processes
not necessarily linked to magma movement but rather
to pulsating degassing processes from deep pressurized,
possibly stationary, magma bodies
Geochemical and biochemical evidence of lake overturn and fish-kill at Lake Averno, Italy.
Lake Averno is situated in the homonymous crater in the northwestern sector of the Campi Flegrei active
volcanic system in Campania region, Italy. In February 2005 a fish kill event was observed in the lake,
prompting a geochemical survey to ascertain the possible cause. In February 2005 a geochemical survey
revealed that the lake water was unstratified chemically and isotopically, presumable, as a result of lake
overturn. This fish-kill phenomenon was recorded at least two other times in the past. In contrast to the
February 2005 results, data collected in October 2005, shows the Lake Averno to be stratified, with an oxic
epilimnion (surface to 6 m) and an anoxic hypolimnion (6 m to lake bottom at about 33 m).
Chemical and isotopic composition of Lake Averno waters suggests an origin by mixing of shallow waters
with a Na-Cl hydrothermal component coupled with an active evaporation process. The isotopic composition
of Dissolved Inorganic Carbon, as well as the composition of the non-reactive dissolved gas species again
supports the occurrence of this mixing process.
Decreasing levels of SO4 and increasing levels of H2S and CH4 contents in lake water with depth, strongly
suggests anaerobic bacterial processes are occurring through decomposition of organic matter under anoxic
conditions in the sediment and in the water column. Sulfate reduction and methanogenesis processes coexist
and play a pivotal role in the anaerobic environment of the Lake Averno. The sulfate reducing bacterial
activity has been estimated in the range of 14-22 μmol.m-2.day-1.
Total gas pressure of dissolved gases ranges between 800 and 1400 mbar, well below the hydrostatic
pressure throughout the water column, excluding the possibility, at least at the survey time, of a limnic
eruption.
Vertical changes in the density of lake waters indicate that overturn may be triggered by cooling of
epilimnetic waters below 7°C. This is a possible phenomenon in winter periods if atmospheric temperatures
remain frosty for enough time, as occurred in February 2005.
The bulk of these results strongly support the hypothesis that fish kill was caused by a series of events that
began with the cooling of the epilimnetic waters with breaking of the thermal stratification, followed by lake
overturn and the rise of toxic levels of H2S from the reduced waters near the lake bottom
Carbon dixide emission in Italy: Shallow crustal sources or subduction related fluid recycling?
Anomalous non-volcanic CO2 release in central and
southern Italy has been highlighted by ten years of detailed
investigations on Earth degassing processes. Two regional
degassing structures are located in the Tyrrhenian sector
where more then 200 emissions of CO2 are located and has
been recently included in the first web based catalogue of
degassing sites (http://googas.ov.ingv.it). The total amount of
CO2 released by the two structures were evaluated to be >
2×1011 mol a-1 ( >10% of the estimated global volcanic CO2
emission). The anomalous flux of CO2 suddenly disappears in
the Apennine in correspondence of a narrow band where most
of the Italian seismicity concentrates. Here, at depth, the gas
accumulates in crustal traps generating CO2 overpressurised
reservoirs. These overpressured structures are, in our opinion,
one of the main cause of Apennine earthquake activation
processes. The results of these investigations suggested that
Earth degassing in Italy may have an active primary role in the
geodynamics of the region. What is the origin of gas? The
large extension of the degassing structures and petrologic data
suggested that the main source of gas is a mantle
metasomatised by the fluids produced in the subdacted slabs.
However, has been also hypothesised the presence of localised
crustal source of the gas. This matter will be discussed on the
base of unpublished isotopic data of the main gas emissions
One year of geochemical monitoring of groundwater in the Abruzzi region after the 2009 earthquakes.
The presence of a deep and inorganic source of CO2 has been recently recognized in Italy on the basis of the
deeply derived carbon dissolved in the groundwater. In particular, the regional map of CO2 Earth degassing
shows that two large degassing structures (Tuscan Roman degassing structure, TRDS, and Campanian degassing
structure, CDS) affect the Tyrrhenian side of the Italian peninsula. The comparison between the map of CO2
Earth degassing and of the location of the Italian earthquakes highlights that the anomalous CO2 flux suddenly
disappears in the Apennine in correspondence of a narrow band where most of the seismicity concentrates. A
previous conceptual model proposed that in this area, at the eastern borders of TRDS and CDS, the CO2 from the
mantle wedge intrudes the crust and accumulate in structural traps generating over-pressurized reservoirs. These
CO2 over-pressurized levels can play a major role in triggering the Apennine earthquakes.
The 2009 Abruzzo earthquakes, like previous seismic crises in the Northern Apennine, occurred at the border of
the TRDS, suggesting also in this case a possible role played by deeply derived fluids in the earthquake generation.
Detailed hydro-geochemical campaigns, with a monthly frequency, started immediately after the main shock of
the 6th of April 2009. The new campaigns include the main springs of the area which were previously studied in
detail, during a campaign performed ten years ago, constituting a pre-crisis reference case. Almost one year of
geochemical data of the main dissolved ions, of dissolved gases (CO2, CH4, N2, Ar, He) and of the stable isotopes
of the water (H, O), CO2 (13C) and He (3He/4He), highlight both that the epicentral area of L’Aquila earthquakes
is affected by an important process of CO2 Earth degassing and that that the gases dissolved in the groundwater
reflects the input in to the aquifers of a deep gas phase, CO2- rich, with an high He content and with low 3He/4He
ratios, similar to the gases emitted by natural manifestations located in the northern Apennines which are fed by
deep pressurized reservoirs. Furthermore a systematic increase in the content of the deeply derived CO2 dissolved
in the aquifers occurred respect to the July 1997 samples. This increase, followed by a gentle decline of the
anomaly, can be compatible with the occurrence of an episode of deep CO2 degassing concurrently with the earthquakes.
The origin of this regional variation is under investigation and, at the present moment, an unambiguous
interpretation of the data is not possible because the lack of a systematic monitoring of the springs before the
seismic events and because eventual seasonal effects on observed variation in CO2 flux are still under investigatio
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