Rapid response of a hydrologic system to volcanic activity: Masaya volcano, Nicaragua

Abstract

Hydrologic systems change in response to volcanic activity, and in turn may be sensitive indicators of volcanic activity. Here we investigate the coupled nature of magmatic and hydrologic systems using continuous multichannel time series of soil temperature collected on the fl anks of Masaya volcano, Nicaragua, one of the most active volcanoes in Central America. The soil temperatures were measured in a low-temperature fumarole fi eld located 3.5 km down the fl anks of the volcano. Analysis of these time series reveals that they respond extremely rapidly, on a time scale of minutes, to changes in volcanic activity also manifested at the summit vent. These rapid temperature changes are caused by increased fl ow of water vapor through fl ank fumaroles during volcanism. The soil temperature response, ~5 °C, is repetitive and complex, with as many as 13 pulses during a single volcanic episode. Analysis of the frequency spectrum of these temperature time series shows that these anomalies are characterized by broad frequency content during volcanic activity. They are thus easily distinguished from seasonal trends, diurnal variations, or individual rainfall events, which triggered rapid transient increases in temperature during 5% of events. We suggest that the mechanism responsible for the distinctive temperature signals is rapid change in pore pressure in response to magmatism, a response that can be enhanced by meteoric water infi ltration. Monitoring of distal fumaroles can therefore provide insight into coupled volcanic-hydrologic-meteorologic systems, and has potential as an inexpensive monitoring tool.

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

“…On Masaya volcano, RFD is considered to be the main electrical source generation process in the hydrothermal environment, such as in the Comalito solfatara (Lewicki et al, 2003;Pearson et al, 2008). Otherwise, the electrokinetic process is the main source of electrical generation due to gravitational ground water flow (Lewicki et al, 2003).…”

“…Over a short period of time (1 day or less), the ground temperature at more than 30 cm depth, is relatively well protected from diurnal temperature variation due to the poor thermal conduction of soil. Over longer time periods (weeks, months), atmospheric temperature variation can affect ground temperature to 1 m below the surface (Pearson et al, 2008). On Masaya volcano, diurnal temperature variations are less than 5°C in amplitude, rain events can generate variations of 5°C and volcanic events can cause a temperature variation up to 10°C over a short period of time (less than 1 day) (Pearson et al, 2008).…”

“…Over longer time periods (weeks, months), atmospheric temperature variation can affect ground temperature to 1 m below the surface (Pearson et al, 2008). On Masaya volcano, diurnal temperature variations are less than 5°C in amplitude, rain events can generate variations of 5°C and volcanic events can cause a temperature variation up to 10°C over a short period of time (less than 1 day) (Pearson et al, 2008). When no magmatic heat source is present, the temperature of the ground is commonly below the atmospheric temperature (> 20°C).…”

“…When no magmatic heat source is present, the temperature of the ground is commonly below the atmospheric temperature (> 20°C). When the ground is heated by hot rising gas or hot/boiling hydrothermal fluids, the ground temperature can reach 75°C on Masaya volcano (Lewicki et al, 2003;Pearson et al, 2008;Pearson, 2010). On other volcanoes, ground temperature can reach more than 300°C and is usually linked with CO 2 gas anomalies and thus allows for detection of the main fracture pathways (e.g., Finizola et al, 2004;Chiodini et al, 2005;Bruno et al, 2007 and references there in).…”

“…In the case of an open system such as at Masaya volcano, where the magma is directly in contact with the atmosphere, magmatic gases are easily evacuated through the open conduit and thus only a small percentage of the total gas flux may escape diffusely through the surrounding edifice. At Masaya, numerous studies have investigated the low temperature hydrothermal system of Comalito cone (Lewicki et al, 2003;Shaw et al, 2003;Pearson et al, 2008;Pearson, 2010), which has been described as a diffuse degassing structure (DDS) (Chiodini et al, 2005). However, at the caldera scale only a few published studies have looked at the subsurface water flow or distribution of soil gas emissions (Crenshaw et al, 1982;St-Amand, 1999;MacNeil et al, 2007).…”