Journal of Environmental Radioactivity, Feb 1, 2011
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, locate... more Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m(-2) d(-1). Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(2) concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m(-3), but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO(2) advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m(-3), remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(2) component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S(1) component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle.
Egu General Assembly Conference Abstracts, May 1, 2010
Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in ... more Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in all the rocks and soils in variable amount. However, a small part only of the radium atoms is able to produce radon atoms in the porous media of the rock allowing this radon to escape the rock media through the pore space. This fraction of radium is referred to as the radon source term in rocks or soils, and is usually called the effective radium concentration (ECRa). This parameter is expressed in Bq kg-1, where CRa is the radium-226 concentration and E the emanation coefficient. Considering a sample, it is not possible to estimate its ECRa value a priori. Therefore, this parameter has to be measured in the laboratory. The method in the laboratory to obtain ECRa values is based on the measurement of the concentration of radon in the inner air of a hermetically sealed container in which one rock or one soil sample was previously placed. In order to measure this radon concentration, Lucas scintillation flasks were used, and their radon content counted by a photomultiplier (Stoulos et al., Journal of Environmental Radioactivity, 2003). This method was compared in detail with another method using SSNTD (Solid-State Nuclear Track Detector). Detailed investigations have been carried out, including systematic effects such as the shape or volume of container, mass and preparation method of the sample, using a large number of rock, soil and building material samples (more than 800) collected in France and Nepal. Preliminary results will be given based on this data set. With such a large sample, some effects of intrinsic and external factors on the measurement technique and on the obtained results could also be accurately studied: the effect of atmospheric pressure, of the ambient temperature, or of the water content of the sample. ECRa measurements appear to be particularly useful for human health hazards study on a considered natural site, as well as for other applications. Indeed, some studies were performed in an overpopulated area, more precisely in the Kathmandu Basin, Nepal, where sediments from several terraces and scarps were sampled and analysed. In addition, ECRa values exhibit characteristic patterns, and therefore can be used for stratigraphy studies. Similarly, this parameter could be relevant in geological mapping, especially where it is not particularly easy to discriminate the diverse encountered layers, as in the Main Central Thrust (MCT) Zone of the Himalayan range. The measurement of effective radium concentration is also important to assess health hazard, and for detailed modelling of radon flux from the soil. Examples of such modelling will be given in the case of the high radon flux observed in geothermal areas of the Nepal Himalayas (Perrier et al., Earth and Planetary Science Letters, 2009; Girault et al., Journal of Environmental Radioactivity, 2009). Thus, these various results illustrate that it is useful to develop the knowledge of effective radium concentration in different natural and artificial media, both for practical and fundamental problems.
Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in ... more Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in all the rocks and soils in variable amount. However, a small part only of the radium atoms is able to produce radon atoms in the porous media of the rock allowing this radon to escape the rock media through the pore space. This fraction of radium is referred to as the radon source term in rocks or soils, and is usually called the effective radium concentration (ECRa). This parameter is expressed in Bq kg-1, where CRa is the radium-226 concentration and E the emanation coefficient. Considering a sample, it is not possible to estimate its ECRa value a priori. Therefore, this parameter has to be measured in the laboratory. The method in the laboratory to obtain ECRa values is based on the measurement of the concentration of radon in the inner air of a hermetically sealed container in which one rock or one soil sample was previously placed. In order to measure this radon concentration, Lucas...
Journal of Geophysical Research: Solid Earth, 2014
ABSTRACT The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust (MCT) zo... more ABSTRACT The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust (MCT) zone in Central Nepal, is characterized by hot (30–62 °C) water springs and cold (<35 °C) carbon dioxide (CO2) degassing areas. From 2007 to 2011, five gas zones (GZ1-5) were studied, with more than 1600 CO2 and 850 radon flux measurements, with complementary self-potential data, thermal infrared imaging and effective radium concentration (ECRa) measurements of soil samples. Measurement techniques and their uncertainties were evaluated in the field. CO2 and radon flux values vary over 5 to 6 orders of magnitude, reaching exceptional maximum values of 236 ± 50 kg m-2 d-1 and 38.5 ± 8.0 Bq m-2 s-1, with estimated integrated discharges over the whole SBHS area of 5.9 ± 1.6 t d-1 and 140 ± 30 MBq d-1, respectively. In gas zones GZ1-2, radon concentrations are 40 × 103 Bq m-3, and higher in gas zones GZ3-4, ca. 70 × 103 Bq m-3. Strong relationships between CO2 and radon fluxes in all gas zones (correlation coefficient R = 0.86 ± 0.02) indicate related gas transport mechanisms, and support the concept that radon can be considered as a relevant proxy for CO2. CO2 carbon isotopic ratios (δ13C from –1.7 ± 0.1 to –0.5 ± 0.1 ‰), with absence of mantle signature (helium isotopic ratios R/RA < 0.05), suggest metamorphic decarbonation at depth. Thus, the SBHS emerges as a unique geosystem of medium spatial scale with significant deep-origin CO2 discharge located in a seismically active region, where we can test methodological issues and our understanding of transport properties and fluid circulations in both the shallow and deep subsurface.
ABSTRACT Gaseous carbon dioxide (CO2) and radon-222 release from the ground was investigated alon... more ABSTRACT Gaseous carbon dioxide (CO2) and radon-222 release from the ground was investigated along the Main Central Thrust zone in the Nepal Himalayas. From 2200 CO2 and 900 radon-222 flux measurements near 13 hot springs from western to central Nepal, we obtained total CO2 and radon discharges varying from 10-3 to 1.6 mol s-1, and 20 to 1600 Bq s-1, respectively. We observed a coherent organization at spatial scales of ≈10 km in a given region: low CO2 and radon discharges around Pokhara (midwestern Nepal) and in the Bhote Kosi Valley (east Nepal); low CO2 but large radon discharges in Lower Dolpo (west Nepal); large CO2 and radon discharges in the upper Trisuli Valley (central Nepal). A 110-km-long CO2-producing segment, with high carbon isotopic ratios, suggesting metamorphic decarbonation, is thus evidenced from 84.5°E to 85.5°E. This spatial organization could be controlled by geological heterogeneity or large Himalayan earthquakes.
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, locate... more Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m(-2) d(-1). Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(2) concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m(-3), but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO(2) advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m(-3), remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(2) component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S(1) component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle.
... Information , E-mail The Corresponding Author , Patrick Richon b , c , Svetlana Byrdina a , C... more ... Information , E-mail The Corresponding Author , Patrick Richon b , c , Svetlana Byrdina a , Christian France-Lanord d , Sudhir Rajaure e , Bharat Prasad Koirala e , Prithvi Lal Shrestha e , Umesh Prasad Gautam e , Dilli Ram Tiwari e , André Revil f , g , Laurent Bollinger b ...
Large CO2 flux has been found in the Trisuli Valley, North of Kathmandu, Central Nepal, in 2005. ... more Large CO2 flux has been found in the Trisuli Valley, North of Kathmandu, Central Nepal, in 2005. This leakage zone is located in the vicinity of the Syabru-Bensi hot springs, and is characterized by an average flux of CO2 of 6500±1100 g m-2 day-1 over an area of 15 m × 15 m (Perrier et al., Earth and Planetary Science Letters, 2009). The site is also located close to the Main Central Thrust Zone (MCT Zone), one of the large Himalayan thrust, connected at depth to the Main Himalayan Thrust, the main thrust currently accommodating the India-Tibet collision (Bollinger et al., Journal of Geophysical Research, 2004). Isotopic carbon ratios (δ13C) indicate that this CO2 may come from metamorphic reactions at about 15 km of depth (Becker et al., Earth and Planetary Science Letters, 2008; Evans et al., Geochemistry Geophysics Geosystems, 2008). Actually, this zone was originally found because of the large δ13C found in the water of the hot springs suggesting degassing (Evans et al., Geochemistry Geophysics Geosystems, 2008). In 2007, another zone of CO2 discharge was discovered 250 m away from the main Syabru-Bensi hot springs. This new zone, located next to the road and easy to access all over the year, was intensely studied, from the end of 2007 to the beginning of 2009. In this zone, an average value of CO2 flux of 1700±300 g m-2 d-1 was obtained over an area of about 40 m × 10 m. Using CO2 flux data from repeated measurements, similar flux values were observed during the dry winter season and the wet summer period (monsoon) (Girault et al., Journal of Environmental Radioactivity, 2009). Thus, in addition to fundamental issues related to global CO2 balance in orogenic belts and tectonically active zones, these small scale (100-meter) CO2 discharge sites emerge as a potentially useful laboratory for detailed methodological studies of diffusive and advective gas transport. Recently, the search for further gas discharge zones has been carried out using various clues: the presence of a hot spring with high δ13C, of H2S smell, of hot spots in thermal images, of a geological contact, of self-potential anomalies (Byrdina et al., Journal of Geophysical Research, 2009) or of large radon-222 flux. Preliminary results about the failures or successes of the various methods will be given in the Trisuli and Langtang valleys (Central Nepal), in the Kali Gandaki valley (Western Nepal) and in the Thuli Bheri valley (Lower Dolpo, Far Western Nepal). These various sites also offer an opportunity to test the optimal estimation of total CO2 flux, using the least amount of experimental measurements. Preliminary results complemented by simulations will also be given on the total CO2 flux. In parallel, monitoring methods are being studied in the Syabru-Bensi pilot site. First, CO2 flux has been studied as a function of time using repeated measurements. Furthermore, the high radon content of the geological CO2 allows cost-effective monitoring using BARASOL probes. More than two years of data are already available and give hints on the use of radon to follow CO2 discharge as a function of time. These first results show how experimental studies carried out in natural discharge zones provide a rich laboratory to test the methodological approaches useful for CO2 leakage and monitoring.
Journal of Environmental Radioactivity, Feb 1, 2011
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, locate... more Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m(-2) d(-1). Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(2) concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m(-3), but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO(2) advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m(-3), remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(2) component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S(1) component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle.
Egu General Assembly Conference Abstracts, May 1, 2010
Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in ... more Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in all the rocks and soils in variable amount. However, a small part only of the radium atoms is able to produce radon atoms in the porous media of the rock allowing this radon to escape the rock media through the pore space. This fraction of radium is referred to as the radon source term in rocks or soils, and is usually called the effective radium concentration (ECRa). This parameter is expressed in Bq kg-1, where CRa is the radium-226 concentration and E the emanation coefficient. Considering a sample, it is not possible to estimate its ECRa value a priori. Therefore, this parameter has to be measured in the laboratory. The method in the laboratory to obtain ECRa values is based on the measurement of the concentration of radon in the inner air of a hermetically sealed container in which one rock or one soil sample was previously placed. In order to measure this radon concentration, Lucas scintillation flasks were used, and their radon content counted by a photomultiplier (Stoulos et al., Journal of Environmental Radioactivity, 2003). This method was compared in detail with another method using SSNTD (Solid-State Nuclear Track Detector). Detailed investigations have been carried out, including systematic effects such as the shape or volume of container, mass and preparation method of the sample, using a large number of rock, soil and building material samples (more than 800) collected in France and Nepal. Preliminary results will be given based on this data set. With such a large sample, some effects of intrinsic and external factors on the measurement technique and on the obtained results could also be accurately studied: the effect of atmospheric pressure, of the ambient temperature, or of the water content of the sample. ECRa measurements appear to be particularly useful for human health hazards study on a considered natural site, as well as for other applications. Indeed, some studies were performed in an overpopulated area, more precisely in the Kathmandu Basin, Nepal, where sediments from several terraces and scarps were sampled and analysed. In addition, ECRa values exhibit characteristic patterns, and therefore can be used for stratigraphy studies. Similarly, this parameter could be relevant in geological mapping, especially where it is not particularly easy to discriminate the diverse encountered layers, as in the Main Central Thrust (MCT) Zone of the Himalayan range. The measurement of effective radium concentration is also important to assess health hazard, and for detailed modelling of radon flux from the soil. Examples of such modelling will be given in the case of the high radon flux observed in geothermal areas of the Nepal Himalayas (Perrier et al., Earth and Planetary Science Letters, 2009; Girault et al., Journal of Environmental Radioactivity, 2009). Thus, these various results illustrate that it is useful to develop the knowledge of effective radium concentration in different natural and artificial media, both for practical and fundamental problems.
Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in ... more Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present in all the rocks and soils in variable amount. However, a small part only of the radium atoms is able to produce radon atoms in the porous media of the rock allowing this radon to escape the rock media through the pore space. This fraction of radium is referred to as the radon source term in rocks or soils, and is usually called the effective radium concentration (ECRa). This parameter is expressed in Bq kg-1, where CRa is the radium-226 concentration and E the emanation coefficient. Considering a sample, it is not possible to estimate its ECRa value a priori. Therefore, this parameter has to be measured in the laboratory. The method in the laboratory to obtain ECRa values is based on the measurement of the concentration of radon in the inner air of a hermetically sealed container in which one rock or one soil sample was previously placed. In order to measure this radon concentration, Lucas...
Journal of Geophysical Research: Solid Earth, 2014
ABSTRACT The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust (MCT) zo... more ABSTRACT The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust (MCT) zone in Central Nepal, is characterized by hot (30–62 °C) water springs and cold (<35 °C) carbon dioxide (CO2) degassing areas. From 2007 to 2011, five gas zones (GZ1-5) were studied, with more than 1600 CO2 and 850 radon flux measurements, with complementary self-potential data, thermal infrared imaging and effective radium concentration (ECRa) measurements of soil samples. Measurement techniques and their uncertainties were evaluated in the field. CO2 and radon flux values vary over 5 to 6 orders of magnitude, reaching exceptional maximum values of 236 ± 50 kg m-2 d-1 and 38.5 ± 8.0 Bq m-2 s-1, with estimated integrated discharges over the whole SBHS area of 5.9 ± 1.6 t d-1 and 140 ± 30 MBq d-1, respectively. In gas zones GZ1-2, radon concentrations are 40 × 103 Bq m-3, and higher in gas zones GZ3-4, ca. 70 × 103 Bq m-3. Strong relationships between CO2 and radon fluxes in all gas zones (correlation coefficient R = 0.86 ± 0.02) indicate related gas transport mechanisms, and support the concept that radon can be considered as a relevant proxy for CO2. CO2 carbon isotopic ratios (δ13C from –1.7 ± 0.1 to –0.5 ± 0.1 ‰), with absence of mantle signature (helium isotopic ratios R/RA < 0.05), suggest metamorphic decarbonation at depth. Thus, the SBHS emerges as a unique geosystem of medium spatial scale with significant deep-origin CO2 discharge located in a seismically active region, where we can test methodological issues and our understanding of transport properties and fluid circulations in both the shallow and deep subsurface.
ABSTRACT Gaseous carbon dioxide (CO2) and radon-222 release from the ground was investigated alon... more ABSTRACT Gaseous carbon dioxide (CO2) and radon-222 release from the ground was investigated along the Main Central Thrust zone in the Nepal Himalayas. From 2200 CO2 and 900 radon-222 flux measurements near 13 hot springs from western to central Nepal, we obtained total CO2 and radon discharges varying from 10-3 to 1.6 mol s-1, and 20 to 1600 Bq s-1, respectively. We observed a coherent organization at spatial scales of ≈10 km in a given region: low CO2 and radon discharges around Pokhara (midwestern Nepal) and in the Bhote Kosi Valley (east Nepal); low CO2 but large radon discharges in Lower Dolpo (west Nepal); large CO2 and radon discharges in the upper Trisuli Valley (central Nepal). A 110-km-long CO2-producing segment, with high carbon isotopic ratios, suggesting metamorphic decarbonation, is thus evidenced from 84.5°E to 85.5°E. This spatial organization could be controlled by geological heterogeneity or large Himalayan earthquakes.
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, locate... more Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m(-2) d(-1). Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(2) concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m(-3), but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO(2) advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m(-3), remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(2) component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S(1) component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle.
... Information , E-mail The Corresponding Author , Patrick Richon b , c , Svetlana Byrdina a , C... more ... Information , E-mail The Corresponding Author , Patrick Richon b , c , Svetlana Byrdina a , Christian France-Lanord d , Sudhir Rajaure e , Bharat Prasad Koirala e , Prithvi Lal Shrestha e , Umesh Prasad Gautam e , Dilli Ram Tiwari e , André Revil f , g , Laurent Bollinger b ...
Large CO2 flux has been found in the Trisuli Valley, North of Kathmandu, Central Nepal, in 2005. ... more Large CO2 flux has been found in the Trisuli Valley, North of Kathmandu, Central Nepal, in 2005. This leakage zone is located in the vicinity of the Syabru-Bensi hot springs, and is characterized by an average flux of CO2 of 6500±1100 g m-2 day-1 over an area of 15 m × 15 m (Perrier et al., Earth and Planetary Science Letters, 2009). The site is also located close to the Main Central Thrust Zone (MCT Zone), one of the large Himalayan thrust, connected at depth to the Main Himalayan Thrust, the main thrust currently accommodating the India-Tibet collision (Bollinger et al., Journal of Geophysical Research, 2004). Isotopic carbon ratios (δ13C) indicate that this CO2 may come from metamorphic reactions at about 15 km of depth (Becker et al., Earth and Planetary Science Letters, 2008; Evans et al., Geochemistry Geophysics Geosystems, 2008). Actually, this zone was originally found because of the large δ13C found in the water of the hot springs suggesting degassing (Evans et al., Geochemistry Geophysics Geosystems, 2008). In 2007, another zone of CO2 discharge was discovered 250 m away from the main Syabru-Bensi hot springs. This new zone, located next to the road and easy to access all over the year, was intensely studied, from the end of 2007 to the beginning of 2009. In this zone, an average value of CO2 flux of 1700±300 g m-2 d-1 was obtained over an area of about 40 m × 10 m. Using CO2 flux data from repeated measurements, similar flux values were observed during the dry winter season and the wet summer period (monsoon) (Girault et al., Journal of Environmental Radioactivity, 2009). Thus, in addition to fundamental issues related to global CO2 balance in orogenic belts and tectonically active zones, these small scale (100-meter) CO2 discharge sites emerge as a potentially useful laboratory for detailed methodological studies of diffusive and advective gas transport. Recently, the search for further gas discharge zones has been carried out using various clues: the presence of a hot spring with high δ13C, of H2S smell, of hot spots in thermal images, of a geological contact, of self-potential anomalies (Byrdina et al., Journal of Geophysical Research, 2009) or of large radon-222 flux. Preliminary results about the failures or successes of the various methods will be given in the Trisuli and Langtang valleys (Central Nepal), in the Kali Gandaki valley (Western Nepal) and in the Thuli Bheri valley (Lower Dolpo, Far Western Nepal). These various sites also offer an opportunity to test the optimal estimation of total CO2 flux, using the least amount of experimental measurements. Preliminary results complemented by simulations will also be given on the total CO2 flux. In parallel, monitoring methods are being studied in the Syabru-Bensi pilot site. First, CO2 flux has been studied as a function of time using repeated measurements. Furthermore, the high radon content of the geological CO2 allows cost-effective monitoring using BARASOL probes. More than two years of data are already available and give hints on the use of radon to follow CO2 discharge as a function of time. These first results show how experimental studies carried out in natural discharge zones provide a rich laboratory to test the methodological approaches useful for CO2 leakage and monitoring.
Uploads
Papers by bharat koirala