Diffuse CO (sub 2) and (super 222) Rn degassing from San Salvador Volcano, El Salvador, Central America
Perez Nemesio, M.; Salazar Jose, M.L.; Hernandez Pedro, A.; Soriano Tomas; Lopez Dina, L.; Notsu Kenji
Special Paper - Geological Society of America 375: 227-236
2004
ISSN/ISBN: 0072-1077 Document Number: 260603
A diffuse CO (sub 2) and (super 222) Rn degassing survey was carried out at San Salvador volcano in February 1999. The goal of this study was to evaluate the spatial distribution of diffuse degassing rates of both gas species and its utility for San Salvador volcano hazard forecasting. Three hundred eighty-eight measurements of CO (sub 2) efflux and 380 of soil gas (super 222) Rn were performed covering most of San Salvador volcano, but taking into consideration geological and structural characteristics of the study area. CO (sub 2) efflux and soil gas (super 222) Rn data showed a wide range of values up to 760 g m (super -2) d (super -1) and 284 pCi L (super -1) , respectively. Most of the study area showed CO (sub 2) efflux background values (B = 12.6 g m (super -2) d (super -1) ). Anomalously high CO (sub 2) efflux data (>9XB) were mainly detected outside El Boqueron crater, suggesting a close spatial correlation with major faults and complex fracture/fault systems. Relatively high (super 222) Rn emissions (>140 pCi L (super -1) ) were also detected outside El Boqueron crater and located parallel to the NW fissure related to the 1917 eruption. The total diffuse CO (sub 2) output of the volcano was estimated at approximately 4000 t d (super -1) for an area of 266 km (super 2) . Carbon isotope signatures of the soil CO (sub 2) ranged from -6.9 per mil to -35.4 per mil, suggesting a mixing between different carbon reservoirs. Spatial distribution of the carbon isotope ratios showed that most of the isotopically positive carbon emission is actually occurring at El Boqueron crater. These results suggest that monitoring spatial and temporal variations of diffuse degassing will be a potential geochemical tool for the San Salvador volcanic surveillance program.