Publikationsdatum:
2023-06-07
Beschreibung:
Volcanic degassing provides important information for the assessment of volcanic
hazards. Santa Ana and San Miguel are open vent volcanoes along the Central
American Volcanic Arc–CAVA, where the magmatism, basaltic to dacitic, is related
to the near-orthogonal convergence of the Caribbean Plate and the subducting
Cocos Plate. Both volcanoes are the most active ones in El Salvador with recent
eruptive events in October 2005 (Santa Ana) and December 2013 (San Miguel), but
still not much data on gas composition and emission are available today. At each
volcano, SO2 emissions are regularly monitored using ground-based scanning
Differential Optical Absorption Spectrometer (Scan-DOAS) instruments that are
part of the global “Network for Observation of Volcanic and Atmospheric Change”
(NOVAC). We used the data series from these NOVAC stations in order to retrieve
SO2 and minimum bromine emissions, which can be retrieved from the same
spectral data for the period 2006–2020 at Santa Ana and 2008–2019 at San
Miguel. However, BrO was not detected above the detection limit. SO2 emission
ranged from 10 to 7,760 t/d, and from 10 to 5,870 t/d for Santa Ana and San Miguel,
respectively. In addition, the SO2 emissions are complemented with in situ plume
data collected during regular monitoring surveys (2018–2020) and two field
campaigns in El Salvador (2019 and 2020). MultiGAS instruments recorded
CO2, SO2, H2S and H2 concentrations. We determined an average CO2/SO2
ratio of 2.9 ± 0.6 when peak SO2 concentration exceeded 15 ppmv at Santa
Ana, while at San Miguel the CO2/SO2 ratio was 7.4 ± 1.8, but SO2 levels reached
only up to 6.1 ppmv. Taking into account these ratios and the SO2 emissions
determined in this study, the resulting CO2 emissions are about one order of
magnitude higher than those determined so far for the two volcanoes. During the
two field campaigns Raschig tubes (active alkaline trap) were used to collect plume
samples which were analyzed with IC and ICP-MS to identify and quantify CO2,
SO2, HCl, HF, and HBr. Additionally, also 1,3,5-trimethoxybenzene (TMB)-coated
denuders were applied and subsequently analyzed by GC-MS to determine the
sum of the reactive halogen species (RHS: including Cl2, Br2
, interhalogens, hypohalous acids). The RHS to sulfur ratios at Santa Ana and San Miguel lie in the
range of 10−5. Although no new insights could be gained regarding changes with
volcanic activity, we present the most comprehensive gas geochemical data set of
Santa Ana and San Miguel volcanoes, leading to a solid data baseline for future
monitoring purposes at both volcanoes and their improved estimate of CO2, SO2
and halogens emissions. Determining the reactive fraction of halogens is a first step
towards a better understanding of their effects on the atmosphere.
Beschreibung:
Published
Beschreibung:
1049670
Beschreibung:
3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
Beschreibung:
JCR Journal
Repository-Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Materialart:
article
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