Evidences of volcanic unrest on high-temperature fumaroles by satellite thermal monitoring: The case of Santa Ana volcano, El Salvador

Abstract

Soil CO2 flux and 222Rn activity measurements may positively contribute to the geochemical monitoring of active volcanoes. The influence of several environmental parameters on the gas signals has been substantially demonstrated. Therefore, the implementation of tools capable of removing (or minimizing) the contribution of the atmospheric effects from the acquired timeseries is a challenge in volcano surveillance. Here, we present four years-long continuous monitoring (from April 2007 to September 2011) of radon activity and soil CO2 flux collected on the NE flank of Stromboli volcano. Both gases record higher emissions during fall-winter (up to 2700 Bq*m-3 for radon and 750 g m-2 day-1 for CO2) than during spring-summer seasons. Short-time variations on 222Rn activity are modulated by changes in soil humidity (rainfall), and changes in soil CO2 flux that may be ascribed to variations in wind speed and direction. The spectral analyses reveal diurnal and semidiurnal cycles on both gases, outlining that atmospheric variations are capable to modify the gas release rate from the soil. The long-term soil CO2 flux shows a slow decreasing trend, not visible in 222Rn activity, suggesting a possible difference in the source depth of the of the gases, CO2 being deeper and likely related to degassing at depth of the magma batch involved in the February-April 2007 effusive eruption. To minimize the effect of the environmental parameters on the 222Rn concentrations and soil CO2 fluxes, two different statistical treatments were applied: the Multiple Linear Regression (MLR) and the Principal Component Regression (PCR). These approaches allow to quantify the weight of each environmental factor on the two gas species and show a strong influence of some parameters on the gas transfer processes through soils. The residual values of radon and CO2 flux, i.e. the values obtained after correction for the environmental influence, were then compared with the eruptive episodes that occurred at Stromboli during the analysed time span (2007)(2008)(2009)(2010)(2011) but no clear correlations emerge between soil gas release and volcanic activity. This is probably due to i) the distal location of the monitoring stations with respect to the active craters and to ii) the fact that during the investigated period no major eruptive phenomena (paroxysmal explosion, flank eruption) occurred. Comparison of MLR and PCR methods in time-series analysis indicates that MLR can be more easily applied to real time data processing in monitoring of open conduit active volcanoes (like Stromboli) where the transition to an eruptive phase may occur in relatively short times.

Spatio-temporal evolution of temperature and fluid flow through a new “thermo-lithological” boundary; the case of a pit crater of Karthala volcano (Comoros archipelago) refilled on January 13th 2007 by a lava flow

“…On active volcanoes, temperature appears as one of the most intuitive parameter to look for precursors of major or paroxysmal eruptive activity. This parameter can be measured directly by temperature sensors inserted into the soil (Friedel et al, 2004;Ricci et al, 2015;Gaudin et al, 2017) or by remote sensors (Wright et al, 2004;Coppola et al, 2015a;Laiolo et al, 2017). Thermal anomalies recorded on active volcanoes can be subdivided into two groups depending on how the heat transfer is directed toward the surface:…”

Surface Temperature Multiscale Monitoring by Thermal Infrared Satellite and Ground Images at Campi Flegrei Volcanic Area (Italy)

“…Moreover, the use of Thermal InfraRed (TIR) satellite sensors is also a consolidated technique [10][11][12][13][14][15][16] for monitoring the volcanic activity at different spatial resolutions: low (e.g., Meteosat Second Generation, MSG, or the Geostationary Environmental Satellite, GOES), moderate (e.g., MODIS, AVHRR, Sentinel 3) and high (e.g., Advanced Spaceborne Thermal Emission and Reflection Radiometer, ASTER, and Landsat 8) [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The development of remote sensing techniques aimed at the estimation of surface temperatures of lava flows, lava lakes, and domes, as well as fumaroles of active volcanic areas, has allowed significant improvements in volcano monitoring activity [6,[31][32][33][34]. Indeed, recent studies have shown thermal anomalies as an indicator of change in volcanic systems [4,35].…”

Water and dissolved gas geochemistry at Coatepeque, Ilopango and Chanmico volcanic lakes (El Salvador, Central America)

“…1a) is a land of volcanoes, being located within the volcanic belt known as Central American Volcanic Front (CAVF) that extends from Guatemala to Costa Rica and is related to the subduction of the Cocos Plate beneath the Caribbean Plate (Corti et al, 2005;Agostini et al, 2006 and references therein). In El Salvador, many lakes are associated with volcanic systems, considered as quiescent or showing moderate hydrothermal activity (Alegria, Apastepeque, Aramuaca, Cuscachapa, Coatepeque, Ilopango, Verde lakes; Rouwet, 2013), or characterized by strong fumarolic emissions (Lake Santa Ana; Bernard et al, 2004;Hernández et al, 2007;Scolamacchia et al, 2010;Colvin et al, 2013;Laiolo et al, 2017). This work focuses on Lake Coatepeque (close to Santa Ana Volcano) and Lake Ilopango (inside the Ilopango Caldera) ( Fig.…”