In:
Frontiers in Earth Science, Frontiers Media SA, Vol. 11 ( 2023-6-1)
Abstract:
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, SO 2 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 SO 2 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. SO 2 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 SO 2 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 CO 2 , SO 2 , H 2 S and H 2 concentrations. We determined an average CO 2 /SO 2 ratio of 2.9 ± 0.6 when peak SO 2 concentration exceeded 15 ppmv at Santa Ana, while at San Miguel the CO 2 /SO 2 ratio was 7.4 ± 1.8, but SO 2 levels reached only up to 6.1 ppmv. Taking into account these ratios and the SO 2 emissions determined in this study, the resulting CO 2 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 CO 2 , SO 2 , 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 Cl 2 , Br 2 , 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 CO 2 , SO 2 and halogens emissions. Determining the reactive fraction of halogens is a first step towards a better understanding of their effects on the atmosphere.
Type of Medium:
Online Resource
ISSN:
2296-6463
DOI:
10.3389/feart.2023.1049670
DOI:
10.3389/feart.2023.1049670.s001
Language:
Unknown
Publisher:
Frontiers Media SA
Publication Date:
2023
detail.hit.zdb_id:
2741235-0
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