Publication Date:
2023-11-20
Description:
Active subaerial volcanoes often discharge large amounts of CO2 and H2S 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 CO2 and H2S emitted to the
atmosphere by subaerial volcanism, but additional volcanic degassing studies will help to
improve the current estimates of bothCO2 andH2S 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 CO2 and H2S, both from plume and diffuse emissions. Surface CO2 and H2S effluxes were
measured by means of the accumulation chamber method at 4075 sites, covering an area of about 972.5 km2. Concurrently, plume SO2 emission at Mt. Etna was remotely measured by
a car-borne Differential Optical Absorption Spectrometry (DOAS) instrument. Crater
emissions of H2O, CO2 and H2S were estimated by multiplying the plume SO2 emission
times the H2O/SO2, CO2/SO2 and H2S/SO2 gas plume mass ratios measured in situ using a
portable multisensor. The total output of diffuse CO2 emission from Mt. Etna was estimated
to be 20,000 ± 400 t day-1 with 4520 t day-1 of deep-seated CO2. Diffuse H2S output was
estimated to be 400 ± 20 kg day-1, covering an area of 9.1 km2 around the summit craters
of the volcano. Diffuse H2S 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 SO2 emission rate was *2100 t day-1. Based on measured SO2 emission
rates, the estimated H2O, CO2 and H2S 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 CO2 emission mass ratio at Mt. Etna was *0.57, that is typical of erupting
volcanoes (mass ratio\1). The average CO2/SO2 molar ratio measured in the plume was
11.5, which is typical of magmatic degassing at great depth beneath the volcano, and the
CO2/H2S 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.
Description:
project CGL2005-07509/CLI, Ministry of Education and Science of Spain
Description:
Published
Description:
327-349
Description:
4V. Vulcani e ambiente
Description:
JCR Journal
Description:
restricted
Keywords:
Mt. Etna
;
Carbon dioxide
;
Hydrogen sulfide
;
Gas budget
;
Diffuse degassing
;
Crater degassing
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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