Using Crater Lake chemistry to predict volcanic activity at Poás Volcano,Costa Rica |
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| Authors: | Gary L Rowe Jr Shinji Ohsawa Bokuichiro Takano Susan L Brantley Jose F Fernandez Jorge Barquero |
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| Institution: | (1) Department of Geosciences, The Pennsylvania State University, 236 Deike Bldg, 16802 University Park, PA, USA;(2) Department of Chemistry, College of Arts and Sciences, University of Tokyo, Komaba Meguro-ku, 153 Tokyo, Japan;(3) Department Estudios Basicos, Seccion Laboratorio Quimico, Instituto Costariccense de Electricidad, San Jose, Costa Rica;(4) Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional, Heredia, Costa Rica;(5) Present address: Water Resources Division, US Geological Survey, 975 West Third Avenue, 43212 Columbus, OH, USA |
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| Abstract: | Monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of Poás Volcano revealed that large variations in SO4/Cl, F/Cl, and Mg/Cl ratios were caused by the enhanced release of HCl vapor from the lake surface due to increasing lake temperature and solution acidity. Variation in the concentration of polythionic acids (H2SxO6, x=4–6) was the most reliable predictor of renewed phreatic eruptive activity at the volcano, exhibiting sharp decreases three months prior to the initiation of phreatic eruptions in June 1987. Polythionic acids may offer a direct indicator of changing subsurface magmatic activity whereas chloride-based element ratios may be influenced by surface volatilization of HCl and subsequent recycling of acidic fluids in crater lake volcanoes. |
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