1,721,055 research outputs found
Water chemistry, fluid-rock interaction processes and new estimates of deep temperatures in the Colli Albani volcano, central Italy
No full textIn the framework of a multidisciplinary project funded by the Italian “Dipartimento della Protezione Civile”, focused on the Alban Hills volcanic district (Central Italy), a detailed geochemical survey in groundwater was carried out in 2006-2007 in the Alban Hills area (central Italy), sampling a total of 183 water sites (springs and wells), Figure 1. Physical-chemical parameters and, on selected samples, main chemistry, minor and trace element contents, as well as dissolved gases were analyzed. The study had the main goals to: i) characterise the chemical background of the discharging fluids, gathered in a period with low seismicity; ii) define the main gas-water-rock interaction processes presently ongoing and iii) give reliable estimates of the deep aquifer temperatures, only partially performed till now.
The bulk of the samples fall in the field of the earth (alkaline)- bicarbonate waters, while some of them show alkaline-bicarbonate and acid-sulphate chemistry. Earth (alkaline)-bicarbonate waters have a relatively fast circulation in the volcanic rocks in a low temperature environment; in some sectors of the volcano they receive a huge gas input from below (mainly CO2). Waters with longer interaction with volcanic rocks and/or clays, in presence of CO2, evolve towards the alkaline-bicarbonate field. Acid-sulphate waters are formed by dissolution of acid and reducing gases (CO2, H2S) into oxygen-rich shallow aquifers. CO2 and N2 are the principal dissolved gases. Nitrogen, in particular, characterises shallow waters (atmospheric component), while carbon dioxide has a prevalent deep origin. H2S, He and H2 show very low contents, while methane was found both in same CO2-rich waters and shallow samples. The main gas-water-rock interaction processes and their extent were assessed by means of activity plots. Waters can be divided into two main groups: i) earth (alkaline)- bicarbonate waters fall prevalently in the field of kaolinite, representing the early stage of the silicate weathering. They show under-saturation with respect to the main rock-forming minerals, and are considered as “immature” ii) alkaline-bicarbonate show a partial equilibrium with the main clay minerals, representing an evolution towards more “mature” terms. Acid-sulphate waters are out of any equilibrium with the host rocks and were not considered. Physical-chemical parameters and observed chemistry fully fit this chemical scenario.
Statistical assessment (Factor Analysis) was used to emphasise the main geochemical processes affecting groundwater, accounting for their observed different chemical evolutions.
Geothermometric estimations allowed to define the geothermal system beneath the volcano as characterised by a medium-low enthalpy, with temperatures comprised in the range 110-140°C.UnpublishedIceland4.5. Degassamento naturaleope
Natural Gas Hazard (CO2 and radon) in the Colli Albani volcano, central
No full textWe present a very detailed study focused on the CO2 and radon content in the groundwater circulating in the Colli Albani volcano and surroundings. A total of 650 water sites (wells and springs) were visited, with a more detailed sampling in the calderic and extra-calderic sectors of the volcano, acquiring new and more complete data with respect to the past. This study was aimed at highlighting the areas characterised by high CO2 and radon contents in groundwater in order to: i) deepen their relationships with the tectonic features of the area; ii) evaluate the present level of Natural Gas Hazard (NGH) and iii) start a continuous radon indoor survey and pursue discrete measurements. In particular, new radon detectors have been built and tested in the frame of an agreement between INGV and DINCE (Department of Nuclear Engineering and Conversions of Energy) of the “La Sapienza” University of Rome.
Large areas with CO2 and radon-rich groundwater were recognised. They correspond to the well known main tectonic and volcanic structures affecting the area (horsts, regional faults, caldera rim). Existing faults and associated fracture networks allow deep gases to upraise and dissolve in shallow aquifers, generally over-saturated in CO2, allowing a free gas phase to reach the surface, thus affecting soils and causing a widespread degassing (Figg. 1, 2, 3). Moreover, CO2 can act as carrier for radon, also produced by quaternary volcanic rocks rich in U and Th-bearing minerals. As a consequence, the detailed mapping of both CO2 and radon contents in groundwater can be a powerful tool in order to assess and evaluate the NGH-prone areas (Figg. 4, 5). Our new data showed the existence of NGH-prone sectors, so far unknown, very close to the city of Rome.
As a consequence, the detailed mapping of both CO2 and radon contents in groundwater can be a powerful tool in order to assess and evaluate the NGH-prone areas (Figg. 4, 5). Our new data showed the existence of NGH-prone sectors, so far unknown, very close to the city of Rome.UnpublishedIceland4.5. Degassamento naturaleope
Geochemistry of gas and water at the CA1 borehole (Alban Hills volcano, central Italy): new insights on deep fluids circulation and origin
No full textIn the framework of a multidisciplinary project funded by the Italian “Dipartimento della Protezione Civile”, focused on the Alban Hills volcanic district (Central Italy), a 350 m deep borehole (named CA1) was drilled for geophysical and petrographic explorations (Mariucci et al., 2008). The borehole is located near Santa Maria delle Mole village (onwards SMM), adjacent to the western rim of the Tuscolano-Artemisio caldera, where several phenomena of unrest recently occurred (i.e. seismicity, episodes of gas exhalation from soil and/or gas burst, Figure 1). Gas exhalation can occurs due to i) human activity (removal of the shallow impermeable fine-grained sediments that discontinuously cover the area) and drillings (mainly for water supply) intercepting pressurised gas pockets that form at depth (the last episode occurred few kilometres from the CA1 well in June 2008) and ii) natural causes (i.e. opening of new cracks and variation of the fracture networks in the pervious shallow sediments, mainly clays) due to changes in the local/regional stress field and/or local seismic activity. All these phenomena caused in the past illness and casualties among local inhabitants and animals, marking the considered area as exposed to a high Natural Gas Hazard. During the phase of hydraulic fracturing tests at the CA1 borehole, in a sandy unit at a depth between 345 and 350m, a blow-out occurred (Figure 2), causing the collapse of its deepest part.
In order to emphasise the origin of the fluids emitted from the CA1 borehole (gas mainly, with minor water) and to highlight the main gas-water-rock interaction processes that account for the observed chemistry, gas and water were collected and analysed for their chemical and isotopic characterisation. Moreover, for a general discussion on the fluid geochemistry of the Alban Hills and on the ongoing degassing processes, water and gas compositions are discussed and compared together with other new data (samples collected in 2006-2007). New geochemical data provided additional information about both the deep volcanic circulation of fluids and their possible connection to a deep-seated magma chamber. Furthermore, CA1 borehole provided very important information for identifying the depth, the thickness and the spatial location of both the fine-grained sediments and the impervious layers in order to mitigate and, possibly, prevent further harmful gas escapes. All these geological and stratigraphical data were still unknown for the SMM sector; the CA1 borehole provided very useful information and filled this gap of knowledge.UnpublishedIceland4.5. Degassamento naturaleope
Geochemistry of gas and water at the CA1 borehole (Alban Hills volcano, central Italy): new insights on deep fluids circulation and origin
No full textIn the framework of a multidisciplinary project funded by the Italian “Dipartimento della Protezione Civile”, focused on the Alban Hills volcanic district (Central Italy), a 350 m deep borehole (named CA1) was drilled for geophysical and petrographic explorations (Mariucci et al., 2008). The borehole is located near Santa Maria delle Mole village (onwards SMM), adjacent to the western rim of the Tuscolano-Artemisio caldera, where several phenomena of unrest recently occurred (i.e. seismicity, episodes of gas exhalation from soil and/or gas burst, Figure 1). Gas exhalation can occurs due to i) human activity (removal of the shallow impermeable fine-grained sediments that discontinuously cover the area) and drillings (mainly for water supply) intercepting pressurised gas pockets that form at depth (the last episode occurred few kilometres from the CA1 well in June 2008) and ii) natural causes (i.e. opening of new cracks and variation of the fracture networks in the pervious shallow sediments, mainly clays) due to changes in the local/regional stress field and/or local seismic activity. All these phenomena caused in the past illness and casualties among local inhabitants and animals, marking the considered area as exposed to a high Natural Gas Hazard. During the phase of hydraulic fracturing tests at the CA1 borehole, in a sandy unit at a depth between 345 and 350m, a blow-out occurred (Figure 2), causing the collapse of its deepest part.
In order to emphasise the origin of the fluids emitted from the CA1 borehole (gas mainly, with minor water) and to highlight the main gas-water-rock interaction processes that account for the observed chemistry, gas and water were collected and analysed for their chemical and isotopic characterisation. Moreover, for a general discussion on the fluid geochemistry of the Alban Hills and on the ongoing degassing processes, water and gas compositions are discussed and compared together with other new data (samples collected in 2006-2007). New geochemical data provided additional information about both the deep volcanic circulation of fluids and their possible connection to a deep-seated magma chamber. Furthermore, CA1 borehole provided very important information for identifying the depth, the thickness and the spatial location of both the fine-grained sediments and the impervious layers in order to mitigate and, possibly, prevent further harmful gas escapes. All these geological and stratigraphical data were still unknown for the SMM sector; the CA1 borehole provided very useful information and filled this gap of knowledge.UnpublishedIceland4.5. Degassamento naturaleope
Natural Gas Hazard (CO2 and radon) in the Colli Albani volcano, central
No full textWe present a very detailed study focused on the CO2 and radon content in the groundwater circulating in the Colli Albani volcano and surroundings. A total of 650 water sites (wells and springs) were visited, with a more detailed sampling in the calderic and extra-calderic sectors of the volcano, acquiring new and more complete data with respect to the past. This study was aimed at highlighting the areas characterised by high CO2 and radon contents in groundwater in order to: i) deepen their relationships with the tectonic features of the area; ii) evaluate the present level of Natural Gas Hazard (NGH) and iii) start a continuous radon indoor survey and pursue discrete measurements. In particular, new radon detectors have been built and tested in the frame of an agreement between INGV and DINCE (Department of Nuclear Engineering and Conversions of Energy) of the “La Sapienza” University of Rome.
Large areas with CO2 and radon-rich groundwater were recognised. They correspond to the well known main tectonic and volcanic structures affecting the area (horsts, regional faults, caldera rim). Existing faults and associated fracture networks allow deep gases to upraise and dissolve in shallow aquifers, generally over-saturated in CO2, allowing a free gas phase to reach the surface, thus affecting soils and causing a widespread degassing (Figg. 1, 2, 3). Moreover, CO2 can act as carrier for radon, also produced by quaternary volcanic rocks rich in U and Th-bearing minerals. As a consequence, the detailed mapping of both CO2 and radon contents in groundwater can be a powerful tool in order to assess and evaluate the NGH-prone areas (Figg. 4, 5). Our new data showed the existence of NGH-prone sectors, so far unknown, very close to the city of Rome.
As a consequence, the detailed mapping of both CO2 and radon contents in groundwater can be a powerful tool in order to assess and evaluate the NGH-prone areas (Figg. 4, 5). Our new data showed the existence of NGH-prone sectors, so far unknown, very close to the city of Rome.UnpublishedIceland4.5. Degassamento naturaleope
Origin of waters and hydrological paths in the Colli Albani volcano, central Italy: new hints from stable and radioactive isotopes
No full textIn the framework of a multidisciplinary project funded by the Italian Department of Civil Protection, very detailed analyses of stable (O, 2H, Sr,) and radioactive (3H) isotopes were performed for the first time in the waters circulating in the Colli Albani volcano area (central Italy) in order to: i) define their origin; ii) reconstruct their different hydrological paths; iii) deepen the knowledge of the gas-water-rock interaction processes.
Waters are meteoric in origin (Fig. 1), excluding any other source (magmatic, seawater, juvenile). Almost all samples lie on the Global Meteoric Water Line (GMWL), while others draw a line with different slope due to local evaporation processes, affecting waters discharging both in the Albano and Nemi lakes. Some samples show a shift in their 18O content with respect to the GMLW, probably due to: i) exchange with gas phases and CO2-exsolution phenomena (negative shift, such as in the sample CA1 well); and ii) interaction with rocks at relatively high temperature (positive shift). It is worthy of note that waters showing positive 18O circulate in the same areas (Ciampino, Tivoli, Pomezia, Ardea) where anomalies in other geochemical parameters such as temperature, chemical composition and gas content, were found (see posters P05, P06 and P08, this session). Finally, one sample (the acidic pool of the Zolf. Pomezia) shows a 2H shift towards positive values, mainly due both to dissolution of deep H2S in a high gas/water ratio system and/or exsolution of H2S from water as free gas phase.UnpublishedIceland4.5. Degassamento naturaleope
Origin of waters and hydrological paths in the Colli Albani volcano, central Italy: new hints from stable and radioactive isotopes
No full textIn the framework of a multidisciplinary project funded by the Italian Department of Civil Protection, very detailed analyses of stable (O, 2H, Sr,) and radioactive (3H) isotopes were performed for the first time in the waters circulating in the Colli Albani volcano area (central Italy) in order to: i) define their origin; ii) reconstruct their different hydrological paths; iii) deepen the knowledge of the gas-water-rock interaction processes.
Waters are meteoric in origin (Fig. 1), excluding any other source (magmatic, seawater, juvenile). Almost all samples lie on the Global Meteoric Water Line (GMWL), while others draw a line with different slope due to local evaporation processes, affecting waters discharging both in the Albano and Nemi lakes. Some samples show a shift in their 18O content with respect to the GMLW, probably due to: i) exchange with gas phases and CO2-exsolution phenomena (negative shift, such as in the sample CA1 well); and ii) interaction with rocks at relatively high temperature (positive shift). It is worthy of note that waters showing positive 18O circulate in the same areas (Ciampino, Tivoli, Pomezia, Ardea) where anomalies in other geochemical parameters such as temperature, chemical composition and gas content, were found (see posters P05, P06 and P08, this session). Finally, one sample (the acidic pool of the Zolf. Pomezia) shows a 2H shift towards positive values, mainly due both to dissolution of deep H2S in a high gas/water ratio system and/or exsolution of H2S from water as free gas phase.UnpublishedIceland4.5. Degassamento naturaleope
Rischio da emissioni gassose naturali
No full textSi tratta della seconda Geopagina della collana del TTC "Formazione e Informazione"Nelle aree vulcaniche e spesso anche nelle aree sismicamente attive, si possono osservare rilasci improvvisi di gas dal suolo o dagli acquiferi in presenza di determinate strutture geologiche, come faglie e/o sistemi di fratture, in concomitanza di terremoti o in occasione di scavi come quelli effettuati per la realizzazione di pozzi.Published5.8. TTC - Formazione e informazioneope
Water chemistry, fluid-rock interaction processes and new estimates of deep temperatures in the Colli Albani volcano, central Italy
No full textIn the framework of a multidisciplinary project funded by the Italian “Dipartimento della Protezione Civile”, focused on the Alban Hills volcanic district (Central Italy), a detailed geochemical survey in groundwater was carried out in 2006-2007 in the Alban Hills area (central Italy), sampling a total of 183 water sites (springs and wells), Figure 1. Physical-chemical parameters and, on selected samples, main chemistry, minor and trace element contents, as well as dissolved gases were analyzed. The study had the main goals to: i) characterise the chemical background of the discharging fluids, gathered in a period with low seismicity; ii) define the main gas-water-rock interaction processes presently ongoing and iii) give reliable estimates of the deep aquifer temperatures, only partially performed till now.
The bulk of the samples fall in the field of the earth (alkaline)- bicarbonate waters, while some of them show alkaline-bicarbonate and acid-sulphate chemistry. Earth (alkaline)-bicarbonate waters have a relatively fast circulation in the volcanic rocks in a low temperature environment; in some sectors of the volcano they receive a huge gas input from below (mainly CO2). Waters with longer interaction with volcanic rocks and/or clays, in presence of CO2, evolve towards the alkaline-bicarbonate field. Acid-sulphate waters are formed by dissolution of acid and reducing gases (CO2, H2S) into oxygen-rich shallow aquifers. CO2 and N2 are the principal dissolved gases. Nitrogen, in particular, characterises shallow waters (atmospheric component), while carbon dioxide has a prevalent deep origin. H2S, He and H2 show very low contents, while methane was found both in same CO2-rich waters and shallow samples. The main gas-water-rock interaction processes and their extent were assessed by means of activity plots. Waters can be divided into two main groups: i) earth (alkaline)- bicarbonate waters fall prevalently in the field of kaolinite, representing the early stage of the silicate weathering. They show under-saturation with respect to the main rock-forming minerals, and are considered as “immature” ii) alkaline-bicarbonate show a partial equilibrium with the main clay minerals, representing an evolution towards more “mature” terms. Acid-sulphate waters are out of any equilibrium with the host rocks and were not considered. Physical-chemical parameters and observed chemistry fully fit this chemical scenario.
Statistical assessment (Factor Analysis) was used to emphasise the main geochemical processes affecting groundwater, accounting for their observed different chemical evolutions.
Geothermometric estimations allowed to define the geothermal system beneath the volcano as characterised by a medium-low enthalpy, with temperatures comprised in the range 110-140°C.UnpublishedIceland4.5. Degassamento naturaleope
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