Persistence of radon-222 flux during monsoon at a geothermal zone in Nepal

Girault, Frédéric; Koirala, Bharat Prasad; Perrier, Frédéric; Richon, Patrick; Rajaure, Sudhir

doi:10.1016/j.jenvrad.2009.07.004

Cited by 18 publications

(37 citation statements)

References 30 publications

(49 reference statements)

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“…The observed CO 2 fluxes are associated with exceptional radon fluxes, larger than 2 Bq m À2 s À1 , comparable with values measured on uranium waste piles (Ferry et al, 2001). High carbon dioxide and radon fluxes were also identified in other locations away from the hot springs, and these gas discharges, were found, in a first approximation, to persist during the monsoon season (Girault et al, 2009). Gas discharges in the Syabru-Bensi geothermal system, thus, offer potentially interesting candidates to study the spatial and temporal properties of radon transport at a key location of a geodynamically active context.…”

Section: Introductionsupporting

confidence: 75%

“…1b). In this zone, CO 2 flux was found to be larger than 1 kg m À2 d À1 over a 25 m long section of a reference transect along the road (Girault et al, 2009), associated with radon fluxes larger than 300 Â 10 À3 Bq m À2 s À1 . Gas fluxes also reached spectacular values in this zone, with a peak CO 2 flux of 8.7 AE 1.5 kg m À2 d À1 and a peak radon flux of 3.4 AE 0.1 Bq m À2 s À1 .…”

Section: The Syabru-bensi Geothermal Systemmentioning

confidence: 88%

“…An extended gas discharge zone (GZ3) was indeed identified in 2007 (Girault et al, 2009), 450 m south-west of the main hot springs, near the road leading to Syabru-Bensi village, in terrace and slope debris at the contact between Kuncha schists and graphitic schists/marbles of the LHS (Fig. 1b).…”

Section: The Syabru-bensi Geothermal Systemmentioning

confidence: 96%

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Temporal signatures of advective versus diffusive radon transport at a geothermal zone in Central Nepal

Richon¹,

Perrier²,

Koirala³

et al. 2011

Journal of Environmental Radioactivity

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Section: Introductionsupporting

confidence: 75%

Section: The Syabru-bensi Geothermal Systemmentioning

confidence: 88%

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Temporal signatures of advective versus diffusive radon transport at a geothermal zone in Central Nepal

Richon¹,

Perrier²,

Koirala³

et al. 2011

Journal of Environmental Radioactivity

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“…Samples S1 to S4 were characterized by a mixture of sulphur deposits and organic matter in GZ1 with more sandy soils in GZ2. In GZ3 (S5 to S8 samples), soils were characterized by a mixture between sulphur deposits, micaceous fallen debris, sand and organic matter (Girault et al, 2009). S1 to S8 soil samples were taken in various conditions of degassing: high degassing (HD, CO 2 flux >1000 g m ST2, Fig.…”

Section: Rock and Soil Samplesmentioning

confidence: 99%

“…In volcanic or geothermal areas, EC Ra of rock or soil samples may be affected by the distribution of hot geological fluids. This question, for example, arises when trying to model the spatial and temporal variations of large radon discharge associated with carbon dioxide degassing near the Syabru-Bensi hot springs in Central Nepal Girault et al, 2009;Richon et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Heterogeneous temperature sensitivity of effective radium concentration from various rock and soil samples

Girault

Perrier

2011

Nat. Hazards Earth Syst. Sci.

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Abstract. Temporal variations of radon concentration, or spatial variations around geothermal systems, are partly driven by the effect of temperature on the radon source term, the effective radium concentration (EC Ra ). EC Ra from 12 crushed rock and 12 soil samples from Nepal was measured in the laboratory using the radon accumulation method and Lucas scintillation flasks at three temperatures: 7, 22 and 37 • C. For each sample and at each temperature, 5 or 6 measurements were carried out, representing a total of 360 measurements, with an EC Ra average varying from 1.1 to 75 Bq kg −1 . While the effect is small, EC Ra was observed to increase with temperature in a significant and sufficiently reproducible manner. The increase was approximately linear with a slope (temperature sensitivity, TS) expressed in % • C −1 . We observed a large heterogeneity of TS with average values (range min-max) of 0.79 ± 0.05 (0.16-2.0) % • C −1 and 0.61 ± 0.05 (0.10-2.0) % • C −1 , for rock and soil samples, respectively. While this range overlaps with the results of previous studies, our values of TS tend to be smaller. The observed heterogeneity implies that the TS, rather poorly understood, needs to be assessed by dedicated experiments in every case where it is of consequence for the interpretation.

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The Syabru‐Bensi hydrothermal system in central Nepal: 1. Characterization of carbon dioxide and radon fluxes

et al. 2014

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The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust zone in central Nepal, is characterized by hot (30-62°C) water springs and cold (<35°C) carbon dioxide (CO 2 ) degassing areas. From 2007 to 2011, five gas zones (GZ1-GZ5) were studied, with more than 1600 CO 2 and 850 radon flux measurements, with complementary self-potential data, thermal infrared imaging, and effective radium concentration of soils. Measurement uncertainties were evaluated in the field. CO 2 and radon fluxes vary over 5 to 6 orders of magnitude, reaching exceptional maximum values of 236 ± 50 kg m À2 d À1 and 38.5 ± 8.0 Bq m À2 s À1 , with estimated integrated discharges over all gas zones of 5.9 ± 1.6 t d À1 and 140 ± 30 MBq d À1 , respectively. Soil-gas radon concentration is 40 × 10 3 Bq m À3 in GZ1-GZ2 and 70 × 10 3 Bq m À3 in GZ3-GZ4. Strong relationships between CO 2 and radon fluxes in all gas zones (correlation coefficient R = 0.86 ± 0.02) indicate related gas transport mechanisms and demonstrate that radon can be considered as a relevant proxy for CO 2 . CO 2 carbon isotopic ratios (δ 13 C from À1.7 ± 0.1 to À0.5 ± 0.1‰), with the absence of mantle signature (helium isotopic ratios R/R A < 0.05), suggest metamorphic decarbonation at depth. Thus, the SBHS emerges as a unique geosystem with significant deep origin CO 2 discharge located in a seismically active region, where we can test methodological issues and our understanding of transport properties and fluid circulations in the subsurface.

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Persistence of radon-222 flux during monsoon at a geothermal zone in Nepal

Cited by 18 publications

References 30 publications

Temporal signatures of advective versus diffusive radon transport at a geothermal zone in Central Nepal

Temporal signatures of advective versus diffusive radon transport at a geothermal zone in Central Nepal

Heterogeneous temperature sensitivity of effective radium concentration from various rock and soil samples

The Syabru‐Bensi hydrothermal system in central Nepal: 1. Characterization of carbon dioxide and radon fluxes

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