A model of diffuse degassing at three subduction-related volcanoes |
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| Authors: | Glyn Williams-Jones John Stix Martin Heiligmann Anne Charland Barbara Sherwood Lollar N Arner Gustavo V Garzón Jorge Barquero Erik Fernandez |
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| Institution: | (1) Département de Géologie, Université de Montréal, Montréal, Québec, H3C 3J7, Canada e-mail: g.williams-jones@open.ac.uk Tel.: +44-1908-659023 Fax: +44-1908-655151, CA;(2) Department of Earth and Planetary Sciences, McGill University, Montréal, Québec, H3A 2A7, Canada, CA;(3) Falconbridge Ltd., 3296 Francis-Hugues Avenue, Laval, Québec, H7L 5A7, Canada, CA;(4) Department of Geology, University of Toronto, Toronto, Ontario, M5S 3B1, Canada, CA;(5) INGEOMINAS, Observatorio Volcanológico y Sismológico, Pasto, A.A. 1795, Pasto, Colombia, CO;(6) Observatorio Volcanológico y Sismológico de Costa Rica, Universidad Nacional, Apartado 86-3000, Heredia, Costa Rica, CR |
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| Abstract: | 2 and δ13C in soil gas were measured at three active subduction-related stratovolcanoes (Arenal and Poás, Costa Rica; Galeras, Colombia).
In general, Rn, CO2 and δ13C values are higher on the lower flanks of the volcanoes, except near fumaroles in the active craters. The upper flanks of
these volcanoes have low Rn concentrations and light δ13C values. These observations suggest that diffuse degassing of magmatic gas on the upper flanks of these volcanoes is negligible
and that more magmatic degassing occurs on the lower flanks where major faults and greater fracturing in the older lavas can
channel magmatic gases to the surface. These results are in contrast to findings for Mount Etna where a broad halo of magmatic
CO2 has been postulated to exist over much of the edifice. Differences in radon levels among the three volcanoes studied here
may result from differences in age, the degree of fracturing and faulting, regional structures or the level of hydrothermal
activity. Volcanoes, such as those studied here, act as plugs in the continental crust, focusing magmatic degassing towards
crater fumaroles, faults and the fractured lower flanks.
Received: 16 December 1997 / Accepted: 27 January 2000 |
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| Keywords: | Diffuse degassing Radon Carbon dioxide Poás Arenal Galeras |
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