HR: 10:50h
AN: V42A-03    [Abstracts]
TI: Geochemical and Geophysical Signatures of Poas Volcano, Costa Rica
AU: * Martinez, M
EM: mmartine@una.ac.cr
AF: Volcanological and Seismological Observatory of Costa Rica, OVSICORI, Universidad Nacional, Heredia, Costa Rica
AU: * Martinez, M
EM: mmartine@una.ac.cr
AF: Dept Earth Sciences - Petrology, Faculty Geosciences, Utrecht University, Utrecht, Netherlands
AU: van Bergen, M
EM: vbergen@geo.uu.nl
AF: Dept Earth Sciences - Petrology, Faculty Geosciences, Utrecht University, Utrecht, Netherlands
AU: Fernandez, E
EM: efernan@una.ac.cr
AF: Volcanological and Seismological Observatory of Costa Rica, OVSICORI, Universidad Nacional, Heredia, Costa Rica
AU: Takano, B
EM: b-takano@nyc.odn.ne.jp
AF: Graduate School of Arts and Sciences, Department of Chemistry, Tokyo University, Tokyo, Japan
AU: Barboza, V
EM: vbarboza@una.ac.cr
AF: Volcanological and Seismological Observatory of Costa Rica, OVSICORI, Universidad Nacional, Heredia, Costa Rica
AU: Saenz, W
EM: wsaenz@una.ac.cr
AF: Volcanological and Seismological Observatory of Costa Rica, OVSICORI, Universidad Nacional, Heredia, Costa Rica
AB: Among many research fields in volcanology, prediction of eruptions is the most important from the hazard- mitigation point of view. Most geophysicists have sought for the best physical parameters for this objective: various kinds of wave signals and geodesic data are two of such parameters. Being able to be remotely monitored gives them advantage over many other practical methods for volcano monitoring. On the other hand, increasing volcanic activity is always accompanied by mass transfer. The most swiftly-moving materials are volcanic gases which are the target geochemists have intensively studied although monitoring gases is rather tedious and limited for active volcanoes hosting crater lakes. A Japanese group lead by Bokuichiro Takano has recently developed an indirect method for monitoring gas injection into volcanic crater lakes. Polythionates are formed when SO2 and H2S are injected into the lake from subaqueous fumaroles. Such polythionates consist of chains of 4 to 6 sulphur atoms, the terminal ones of which are bonded with three oxygen atoms. The general formula for these anions is SxO62- (x= 4 to 6). Important to note is that SO2 input into the lake also depends upon the plumbing system of the volcanoes: conduits, cracks and hydrothermal reservoirs beneath the lake that usually differ from volcano to volcano. Despite such site-specific characters some general statements can be made on the behaviour of these chemical species. For example, at low volcanic activity S6O62- predominates while S4O62- and S5O62- become predominant with increasing SO2 that increases with volcanic activity. At higher SO2 input and high temperature polythionates disappear in the lake through interaction with aqueous SO2 (sulfitolysis). Thus, the ratios of the three polythionates or their absence serve as an indicator for various stages of volcanic activity. Monitoring polythionates is an independent method that can be compared with results from geophysical methods. However, it still remains open to a question if they will play a helpful role as a geophysical monitoring tool in determining the commencement of volcanic events. A range of Poas volcano geochemical and geophysical parameters have been combined to envisage relationships between them and to gain a better insight in the understanding of the Poas volcanic system.
DE: 1299 General or miscellaneous (1709)
DE: 8419 Volcano monitoring (7280)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8430 Volcanic gases
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly