Bulletin of Volcanology

, 81:66 | Cite as

The crater lake of Ilamatepec (Santa Ana) volcano, El Salvador: insights into lake gas composition and implications for monitoring

  • Nathalie Hasselle
  • Francisco Montalvo
  • Dmitri Rouwet
  • Angelo Battaglia
  • Marcello Bitetto
  • Demetrio Escobar
  • Eduardo Gutiérrez
  • Jacqueline Rivera
  • Ana Mirian Villalobos
  • Raffaello Cioni
  • J. Maarten de Moor
  • Tobias P. Fischer
  • Alessandro AiuppaEmail author
Research Article


We here present the first chemical characterization of the volcanic gas plume issuing from the Santa Ana crater lake, a hyper-acidic crater lake (pH of − 0.2 to 2.5) in north-western El Salvador. Our results, obtained during regular surveys in 2017 and 2018 using a Multi-GAS instrument, demonstrate a hydrous gas composition (H2O/SO2 ratios from 32 to 205) and SO2 as the main sulfur species (H2S/SO2 = 0.03–0.1). We also find that gas composition evolved during our investigated period, with the CO2/SO2 ratio decreasing by one order of magnitude from March 2017 (37.2 ± 9.7) to November 2018 (< 3). This compositional evolution toward more magmatic (SO2-rich) compositions is interpreted in the context of the long-term evolution of the volcano following its 2005 and 2007 eruptions. We find that, in spite of reduced (background-level) seismicity, the magmatic gas supply into the lake was one order of magnitude higher in March 2017 (total volatile flux: 20,200–30,200 t/day) than in the following periods (total volatile flux: 900–10,167 t/day). We propose that the elevated magmatic/hydrothermal transport in March 2017, combined with a 15% reduction in precipitation, caused the volume of the lake to decrease, ultimately reducing its sulfur absorbing and scrubbing capacity, and hence causing the gas plume CO2/SO2 ratio to decrease. The recently observed increases in temperature, acidity, and salinity of the lake are consistent with this hypothesis. We conclude that the installation of a continuous, fully-automated Multi-GAS is highly desirable to monitor any future change in lake plume chemistry, and hence the level of degassing activity.


Santa Ana volcano Crater lakes Volcanic gas plumes Multi-GAS Gas scrubbing CO2/SO2 ratio Wet volcano 



This research was funded by the Agenzia italiana per la cooperazione allo sviluppo (AICS) via the project RIESCA. A.A. acknowledges funding from the Deep Carbon Observatory and from Miur (Grant n. 2017LMNLAW). The manuscript benefited from comments from A. Terada and one anonymous reviewer. Associate Editor P. Allard and Editor-in-Chief A. Harris fine-tuned the final manuscript.

Supplementary material

445_2019_1331_MOESM1_ESM.xls (66 kb)
Table S1 Summary of all derived (molar) gas ratios in the Santa Ana crater lake plume. For each ratio, the correlation coefficient of the best-fit regression line is indicated (R2). SO2 MAX is the peak SO2 concentration measured in each measurement inteval where a ratio was calculated. (XLS 65 kb)


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Copyright information

© International Association of Volcanology & Chemistry of the Earth's Interior 2019

Authors and Affiliations

  • Nathalie Hasselle
    • 1
  • Francisco Montalvo
    • 2
  • Dmitri Rouwet
    • 3
  • Angelo Battaglia
    • 1
  • Marcello Bitetto
    • 1
  • Demetrio Escobar
    • 2
  • Eduardo Gutiérrez
    • 2
  • Jacqueline Rivera
    • 2
  • Ana Mirian Villalobos
    • 2
  • Raffaello Cioni
    • 4
  • J. Maarten de Moor
    • 5
  • Tobias P. Fischer
    • 6
  • Alessandro Aiuppa
    • 1
    Email author
  1. 1.Dipartimento DiSTeMUniversità di PalermoPalermoItaly
  2. 2.Dirección del Observatorio AmbientalMARNSan SalvadorEl Salvador
  3. 3.Istituto Nazionale di Geofisica e Vulcanologia, Sezione di BolognaBolognaItaly
  4. 4.Dipartimento di Scienze della TerraUniversità di FirenzeFlorenceItaly
  5. 5.UNA-OVSICORIHerediaCosta Rica
  6. 6.University of New MexicoAlbuquerqueUSA

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