Spatial and temporal variations of diffuse CO2 degassing at the Santa Ana–Izalco–Coatepeque volcanic complex, El Salvador, Central America
José M.L. Salazar, Pedro A. Hernández, Nemesio M. Pérez, Rodolfo Olmos, Francisco Barahona, Rafael Cartagena, Tomás Soriano, Dina L. López, Hirochika Sumino, Kenji Notsu, 2004. "Spatial and temporal variations of diffuse CO2 degassing at the Santa Ana–Izalco–Coatepeque volcanic complex, El Salvador, Central America", Natural Hazards in El Salvador, William I. Rose, Julian J. Bommer, Dina L. López, Michael J. Carr, Jon J. Major
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We report the first detailed study of spatial and temporal variations on the diffuse emission of carbon dioxide from the Santa Ana–Izalco–Coatepeque volcanic complex. Soil CO2 efflux measurements were performed at 447 sampling sites and reached values up to 293 g m−2 d−1 for the March 2001 survey. Most of the diffuse CO2 degassing is occurring at the center of this volcanic complex, near the Cerro Pacho dome where the intersection of one of the regional NW-SE fault/fracture systems and the south Coatepeque caldera rim occurs. Soil CO2 efflux measurements were not performed inside Santa Ana's summit crater due to accessibility problems at the time of this survey. The total diffuse CO2 emission for this volcanic complex was estimated at ∼600 t/d. Low CO2 efflux values were identified on the flanks and summit regions of the Izalco and Santa Ana volcanoes. Isotopic data of gases collected from low-temperature fumaroles in the study area showed 3He/4He ratios close to the atmospheric composition, except for the fumarolic discharges inside Santa Ana summit crater (7.54). Carbon isotopic signature of these gases suggested that 74% of CO2 is limestone-derived from thermodecarbonation processes, while the fumarole sample from Santa Ana crater showed ∼48% of limestone-derived CO2. Temporal variations of the diffuse CO2 degassing observed at the Cerro Pacho dome ranged from 4.3 to 327 g m−2 d−1, with a median value of 98 g m−2 d−1. Time domain analysis of the soil CO2 efflux showed a strong autoregressive behavior, whose covariance slowly dies through time. Spectral analysis showed the existence of soil CO2 efflux variations at diurnal and semidiurnal frequencies. This finding suggests that soil CO2 efflux variations are coupled with those of meteorological variables (i.e., barometric pressure, wind speed, etc.), accounting for much of the behavior of the soil CO2 efflux time series at the short-term scale.