HR: 14:15h
AN: V13C-03 INVITED     [Abstracts]
TI: Geophysical investigations of volcano hydrogeology at Masaya Caldera, Nicaragua
AU: * Connor, C
EM: cconnor@chuma1.cas.usf.edu
AF: Department of Geology University of South Florida, 4202 East Fowler, Tampa, FL 33620 United States
AU: Sanford, W
EM: wsanford@usgs.gov
AF: US Geological Survey, MS 431, Reston, VA 20192 United States
AU: MacNeil, R
EM: rmacneil@mail.cas.edu
AF: Department of Geology University of South Florida, 4202 East Fowler, Tampa, FL 33620 United States
AU: MacNeil, R
EM: rmacneil@mail.cas.edu
AF: US Geological Survey, MS 431, Reston, VA 20192 United States
AU: Sandberg, S
EM: ssandberg@cas.usf.edu
AF: Department of Geology University of South Florida, 4202 East Fowler, Tampa, FL 33620 United States
AU: Sandberg, S
EM: ssandberg@cas.usf.edu
AF: US Geological Survey, MS 431, Reston, VA 20192 United States
AB: The distribution and flow of groundwater is poorly known for the vast majority of active volcanoes, and hydrologic properties of active volcanoes are rarely characterized. This situation persists because such volcanic systems are not typically developed for their groundwater resources. Given that theses systems need to be characterized in the absence of sufficient well data, characterization of the groundwater system on active volcanoes is practical through the application of transient electromagnetic (TEM) soundings and innovative inversion techniques. Here, we employ this approach to constrain depth to the groundwater table at Masaya Caldera, Nicaragua, one of the largest active basaltic calderas on Earth. The active Santiago Crater within the caldera is the site of persistent volcano degassing, and the scene of occasional phreatic explosions, the most recent of which occurred in June, 2004. We present first estimates of depth to the groundwater table within the caldera, based on interpretation of 30 soundings. Uncertainty in depth estimates is constrained by using alternative one-dimensional inversion methods. Our results suggest that Masaya caldera is hydrologically isolated from the surrounding groundwater flow system by its caldera-bounding faults. Thus, these geophysical data potentially will provide a baseline for forecasting the response of this isolated groundwater system to changes in magmatic activity. In addition, characterization of the depth to groundwater provides context for interpretation of VLF anomalies, which indicate that a shallow degassing magma body (400 m diameter; 250 m depth) is located in the shallow subsurface beneath Santiago Crater, and interpretation diffuse degassing from the flanks of Masaya volcano, which produces elevated carbon dioxide flux in thermal areas, and related spontaneous potential anomalies.
DE: 8424 Hydrothermal systems (8135)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly