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

Abstract

a b s t r a c t KeywordsMasaya Hydrothermal Self-potential Wavelet Groundwater Volcano 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 degassing 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 stable suggesting that hydrothermal activity is in a steady state. This stable activity correlates well with the consistency 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 structures 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 evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera. As such, the heat budget for Masaya must be significantly larger than previously estimated.

Integrated geophysical and hydrothermal models of flank degassing and fluid flow at Masaya volcano, Nicaragua

“…Our various geophysical data and models provide constraints on the shallow hydrothermal system that can be used in a numerical model. Transient electromagnetic soundings throughout the caldera indicate that the groundwater table is approximately 250 m beneath the surface in the study area [ MacNeil et al , 2007], although there is also some evidence of shallower groundwater [ Mauri et al , 2012]. Magnetic data and models are consistent with a faulted terrain, dominated in this area by steeply dipping (60°) normal faults.…”

“…On the northeast flank of the volcano, outside of the pit crater network, there is a fault and fracture zone extending some kilometers where water vapor and CO 2 are emitted at moderate temperatures (40–80°C) [ Lewicki et al , 2003; Pearson et al , 2008; Mauri et al , 2012]. This radial fracture zone extends from Masaya cone past Comalito cinder cone (Figure 1b), where CO 2 fluxes of up to 5.8 × 10 −4 kg/m 2 s have been measured [ Lewicki et al , 2003].…”

Curvelet-based seismoelectric data processing

“…2007; Mauri et al. 2010; Ma & Plonka 2010; Mauri et al. 2012) and are now extensively used in seismic data processing (Roueff et al.…”

Determination of the Direction of Hot Fluid Flow in Cangar Area, Arjuno-Welirang Volcano Complex, East Java Using Self Potential Method

“…The self potential method is a passive geophysical method that measures the Earth's natural static potential [7,8,9]. Potential measurements are made between two points above the earth's surface.…”

“…This geothermal reservoir can be a geothermal fluid flow beneath the surface that forms a hydrothermal system in geothermal potential areas. Several studies have been conducted to detect the direction of the subsurface heat fluid flow, where the flow of sub-surface fluids causes self potential anomalies [8,12].…”