Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America |
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| Authors: | Rodolfo Olmos José Barrancos Claudia Rivera Francisco Barahona Dina L López Benancio Henriquez Agustín Hernández Efrain Benitez Pedro A Hernández Nemesio M Pérez Bo Galle |
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| Institution: | (1) Consejo de Investigaciones Cientìficas, Universidad de El Salvador, El Salvador, Centro America;(2) Enviromental Research Division, ITER, 38611, Granadilla, Tenerife, Canary Island, Spain;(3) Department of Radio and Space Science, Chalmers University of Technology, 41296 Gothenburg, Sweden;(4) Department of Geological Sciences, Ohio University, Athens, Ohio 45701, USA |
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| Abstract: | Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005,
101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet
degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements
of SO2 degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity
prior to the eruption, during, and after the eruption. Vehicle measurements of SO2 flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here
is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive
periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154
ton/day of SO2 flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as
the recorded values just after the October 1st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase
in SO2 flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation
of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point
of explosion. A correlation between SO2 fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations
in the SO2 and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that
convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing
degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks
to give space to a new magma pulse. These results illustrate that the measurements of SO2 flux can provide important warning signals for incoming explosive activity in active volcanoes. |
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| Keywords: | Sulfur dioxide flux RSAM magma degassing volcanic eruption Santa Ana volcano |
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