Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland

• Published in: Bulletin of volcanology Vol. 74; no. 10; pp. 2435 - 2448
• Main Authors: Hernández, Pedro A., Pérez, Nemesio M., Fridriksson, Thráinn, Egbert, Jolie, Ilyinskaya, Evgenia, Thárhallsson, Andri, Ívarsson, Gretar, Gíslason, Gestur, Gunnarsson, Ingvi, Jónsson, Birgir, Padrón, Eleazar, Melián, Gladys, Mori, Toshiya, Notsu, Kenji
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.12.2012; Springer; Springer Nature B.V
• Subjects: Carbon dioxide; Crystalline rocks; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geology; Geophysics/Geodesy; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Mineralogy; Natural hazards: prediction, damages, etc; Research Article; Sedimentology; Thermodynamics; Variance analysis; Volcanoes; Volcanology; Europe; Iceland; Western Europe; ANE, Atlantic, Iceland; emission; Diffuse H; Diffuse CO; S emission; Hengill volcano; Heat flux; fissures; degassing; mixing; hydrogen; fumaroles; condensation; discharge; temperature; spatial variations; heat flow; heat flux; soils; flow; energy; sulfides; carbon dioxide; sampling; structural controls; volcanoes; power plants; soil gases; chemical composition
• ISSN: 0258-8900; 1432-0819
• DOI: 10.1007/s00445-012-0673-2

We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S) from Hengill volcanic system, Iceland. Soil CO 2 and H 2 S 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–NNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H 2 S 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 2 O/CO 2 mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4–240.2) as a representative value of the H 2 O/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 .