A Sulfur Trigger for the 2017 Phreatomagmatic Eruption of Poás Volcano, Costa Rica? Insights from MultiGAS and Drone-based Gas Monitoring
Abstract
In April 2017 Poás volcano entered its first magmatic eruption period of the 21st century. The initial explosive blasts produced eruption columns up to 4 km in height, destroyed the pre-existing dome that was emplaced during the last magmatic eruption in the 1950s, and showered the tourist observation deck with bombs. Over the following months, the hyperacid crater lake dried out and a transition from phreatomagmatic to strombolian activity was observed. Two vents now dominate the activity. The main vent (old dome site) produces gas, ash, and scoria. A second vent is located in the dried-out lake bed and produces a peculiar canary-yellow gas plume. A fixed MultiGAS instrument installed in the crater bottom recorded large changes in gas composition prior to the explosive eruptions. The station recorded a dramatic increase in SO2/CO2 from an average of 0.04 for March 2017 to an average of 7.4 the day before the first explosive eruption that occurred at 18:30 on 12 April. A simultaneous rapid decrease in H2S/SO2 from 2.7 to <0.01 was observed prior to the eruptions. The MultiGAS station stopped transmitting data after 2 days of explosive eruptions. We since developed new methods for measuring gas compositions and SO2 fluxes using drones, allowing continued gas monitoring despite dangerous conditions. Extremely high SO2/CO2 of 33 was measured with drone-based miniaturized MultiGAS ("miniGAS") in May 2017, and the ratio has since dropped to 3, which are more typical values of high temperature magmatic gases at Poás. The SO2 flux from Poás was at record low levels (< 5 T/d) in late 2016 and early 2017. Drone-based SO2 DOAS ("DROAS") measurements indicate high SO2 fluxes from Poas of >2000 T/d since the explosive eruptions, indicating a strong magmatic source and open conduits. We attribute the unusually S-rich gas compositions observed at Poás prior to and during the initial eruptions to combustion of previously deposited hydrothermal sulfur. The very low gas flux from the system prior to the explosive eruptions suggests that this sulfur may have played a role in hydrothermal sealing, leading to pressurization of the magmatic-hydrothermal system and ultimately triggering phreatomagmatic eruptions and "top down" remobilization of previously emplaced magma.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.V23F..04D
- Keywords:
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- 3640 Igneous petrology;
- MINERALOGY AND PETROLOGY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 5225 Early environment of Earth;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 8439 Physics and chemistry of magma bodies;
- VOLCANOLOGY