STRUCTURE AND DEPTH OF THE HYDROTHERMAL SYSTEMS OF MASAYA VOLCANO, NICARAGUA

Masaya volcano, Nicaragua, is a persistently active volcano characterized by continuous degassing for more than 150 years. This study highlights the existence of an extended hydrothermal system throughout the caldera complex, which is spatially controlled by a ring fault structure. The most intense hydrothermal activity is found on the North flank of Masaya cone, while the active Comalito solfatara is of lower intensity in comparison to it. In close vicinity to the active vent of Santiago crater, the Nindiri hydrothermal system is established throughout the center and south part of Nindiri cone.

Water depth was determined by Multi-scale wavelet tomography on Self-potential data using wavelets from the Poisson family. Water depths were found to be always less than 150 m depth and often less than 100 m below the topographic surface. Between 2006 and 2009, this study shows that the hydrothermal systems are stable without significant change, due likely to the constant volcanic activity expressed on the surface by the continuous passive degassing. Multi-scale wavelet tomography on Self-potential data, especially when use in conjunction with soil CO₂ concentrations and ground temperature measurements, has proven to be an efficient way to locate and investigate the vertical distribution of underground water on the active Masaya volcano. The extended hydrothermal system through Masaya and the significant ground CO₂ anomalies show while the majority of magmatic gas escapes from the open vent of Santiago crater, the ring fault structure nevertheless has a significant control on the extent of the hydrothermal system.