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Investigation of the groundwater system at Masaya Caldera, Nicaragua, using transient electromagnetics and numerical simulation

Journal of Volcanology and Geothermal Research

By:
, , , , and
DOI: 10.1016/j.jvolgeores.2007.07.016

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Abstract

The distribution of groundwater beneath Masaya Volcano, in Nicaragua, and its surrounding caldera was characterized using the transient electromagnetic method (TEM). Multiple soundings were conducted at 30 sites. Models of the TEM data consistently indicate a resistive layer that is underlain by one or more conductive layers. These two layers represent the unsaturated and saturated zones, respectively, with the boundary between them indicating the water-table elevation. A map of the TEM data shows that the water table in the caldera is a subdued replica of the topography, with higher elevations beneath the edifice in the south-central caldera and lower elevations in the eastern caldera, coinciding with the elevation of Laguna de Masaya. These TEM data, combined with regional hydrologic data, indicate that the caldera in hydrologically isolated from the surrounding region, with as much as 60??m of difference in elevation of the groundwater table across caldera-bounding faults. The water-table information and estimates of fluxes of water through the system were used to constrain a numerical simulation of groundwater flow. The simulation results indicate that basalt flows in the outer parts of the caldera have a relatively high transmissivity, whereas the central edifice has a substantially lower transmissivity. A layer of relatively high transmissivity must be present at depth within the edifice in order to deliver the observed flux of water and steam to the active vent. This hydrologic information about the caldera provides a baseline for assessing the response of this isolated groundwater system to future changes in magmatic activity. ?? 2007.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Investigation of the groundwater system at Masaya Caldera, Nicaragua, using transient electromagnetics and numerical simulation
Series title:
Journal of Volcanology and Geothermal Research
DOI:
10.1016/j.jvolgeores.2007.07.016
Volume
166
Issue:
3-4
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Volcanology and Geothermal Research
First page:
217
Last page:
232