Contribution of CO2 and H2S emitted to the atmosphere by plume and diffuse degassing from volcanoes: the Etna volcano case study

• Published in: Surveys in geophysics Vol. 36; no. 3; pp. 327 - 349
• Main Authors: Hernández, Pedro A., Melián, Gladys, Giammanco, Salvatore, Sortino, Francesco, Barrancos, José, Pérez, Nemesio M., Padrón, Eleazar, López, Manuela, Donovan, Amy, Mori, Toshiya, Notsu, Kenji
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.05.2015; Springer Nature B.V
• Subjects: Astronomy; Carbon dioxide; Earth and Environmental Science; Earth Sciences; Emissions; Geophysics; Geophysics/Geodesy; Hydrogen sulfide; Observations and Techniques; Volcanoes; Mount Etna; Hydrogen sulfide; Diffuse degassing; Gas budget; Mt. Etna; Crater degassing; Carbon dioxide
• ISSN: 0169-3298; 1573-0956
• DOI: 10.1007/s10712-015-9321-7

Active subaerial volcanoes often discharge large amounts of CO 2 and H 2 S to the atmosphere, not only during eruptions but also during periods of quiescence. These gases are discharged through focused (plumes, fumaroles, etc.) and diffuse emissions. Several studies have been carried out to estimate the global contribution of CO 2 and H 2 S emitted to the atmosphere by subaerial volcanism, but additional volcanic degassing studies will help to improve the current estimates of both CO 2 and H 2 S discharges. In October 2008, a wide-scale survey was carried out at Mt. Etna volcano, one the world’s most actively degassing volcanoes on Earth, for the assessment of the total budget of volcanic/hydrothermal discharges of CO 2 and H 2 S, both from plume and diffuse emissions. Surface CO 2 and H 2 S effluxes were measured by means of the accumulation chamber method at 4075 sites, covering an area of about 972.5 km 2 . Concurrently, plume SO 2 emission at Mt. Etna was remotely measured by a car-borne Differential Optical Absorption Spectrometry (DOAS) instrument. Crater emissions of H 2 O, CO 2 and H 2 S were estimated by multiplying the plume SO 2 emission times the H 2 O/SO 2 , CO 2 /SO 2 and H 2 S/SO 2 gas plume mass ratios measured in situ using a portable multisensor. The total output of diffuse CO 2 emission from Mt. Etna was estimated to be 20,000 ± 400 t day −1 with 4520 t day −1 of deep-seated CO 2 . Diffuse H 2 S output was estimated to be 400 ± 20 kg day −1 , covering an area of 9.1 km 2 around the summit craters of the volcano. Diffuse H 2 S emission on the volcano flanks was either negligible or null, probably due to scrubbing of this gas before reaching the surface. During this study, the average crater SO 2 emission rate was ~2100 t day −1 . Based on measured SO 2 emission rates, the estimated H 2 O, CO 2 and H 2 S emission rates from Etna’s crater degassing were 220,000 ± 100,000, 35,000 ± 16,000 and 510 ± 240 t day −1 , respectively. These high values are explained in terms of intense volcanic activity at the time of this survey. The diffuse/plume CO 2 emission mass ratio at Mt. Etna was ~0.57, that is typical of erupting volcanoes (mass ratio <1). The average CO 2 /SO 2 molar ratio measured in the plume was 11.5, which is typical of magmatic degassing at great depth beneath the volcano, and the CO 2 /H 2 S mass ratio in total diffuse gas emissions was much higher (~11,000) than in plume gas emissions (~68). These results will provide important implications for estimates of volcanic total carbon and sulfur budget from subaerial volcanoes.