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Elsevier, Journal of Volcanology and Geothermal Research, (227-228), p. 15-31

DOI: 10.1016/j.jvolgeores.2012.02.003

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A geochemical and geophysical investigation of the hydrothermal complex of Masaya volcano, Nicaragua

Journal article published in 2012 by Guillaume Mauri, Glyn Williams-Jones ORCID, Ginette Saracco, Jeffrey M. Zurek
This paper is available in a repository.
This paper is available in a repository.

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Abstract

Masaya volcano, Nicaragua, is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of Santiago crater. This study applies self-potential, soil CO 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degas-sing structures throughout the volcano. The diffuse degassing areas are organized in a semi-circular pattern and coincide with several visible and inferred surface volcanic structures (cones, fissure vents) and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow. Water depths have been estimated by multi-scale wavelet tomography of the self-potential data using wavelets from the Poisson kernel family. Compared to previous water flow models, our water depth estimates are shallower and mimic the topography, typically less than 150 m below the surface. Between 2006 and 2010, the depths of rising fluids along the survey profiles remained sta-ble suggesting that hydrothermal activity is in a steady state. This stable activity correlates well with the con-sistency of the volcanic activity expressed at the surface by the continuously passive degassing. When compared to previous structural models of the caldera floor, it appears that the diffuse degassing struc-tures have an important effect on the path that shallow groundwater follows to reach the Laguna de Masaya in the eastern part of the caldera. The hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the Laguna de Masaya. Furthermore, these diffuse degassing structures show clear ev-idence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the cal-dera. As such, the heat budget for Masaya must be significantly larger than previously estimated. © 2012 Published by Elsevier B.V.