Monitoring Diffuse Carbon Dioxide Degassing and Surface Pressure Gradient at Cerro Negro Volcano, Nicaragua

Diffuse CO₂ emission studies are becoming a useful geochemical tool for volcano monitoring. Significant temporal variations of diffuse CO₂ degassing rate seem to be directy related to changes of activity volcanic. Since 1999 a research collaboration program between INETER and ITER has been established for monitoring diffuse CO₂ emission from Cerro Negro, the most active volcano from the western hemisphere.

Surface pressure gradient and diffuse CO₂ degassing surveys were carried out on March 2002 and 2003 at Cerro Negro. An additional survey of CO₂ efflux was performed on December 1999. Sampling site distributions were similar for the 1999, 2002 and 2003 surveys covering an area of 0.6 km². Pressure gradient measurements were performed by means of a Setra 239 pressure transducer, and soil CO₂ efflux measurements were performed by means of a portable NDIR sensor according to the accumulation chamber method. Surface pressure gradient values ranged from -11.7 to 232.8 Pam^-1 and -24.2 to 102.0 Pam^-1 for 2002 and 2003 surveys, respectively. Soil CO₂ efflux ranged from 0.5 to 35,000 gm^-2d^-1 for 1999, 0.3 to 26,500 gm^-2d^-1 for 2002, and 0.3 to 3,002 gm^-2d^-1 for 2003 surveys. The total diffuse CO₂ output for the 2003 survey was estimated about 34 td^-1, which is one and two orders of magnitude lower than the estimated for the 1999 survey, 2,800 td^-1, (Salazar et al., 2001) and the 2002 survey, 280 td^-1, (Galindo et al., 2002). These surveys took place 3 (1999), 17 (2002) and 29 (2003) months after the most recent eruption of Cerro Negro, August 1999. The observed decreasing trend on the diffuse CO₂ emission is temporarily correlated with a reducing tendency on the surface pressure gradient suggesting a lower advective component for the diffuse degassing mechanism on the surface environment at Cerro Negro. These results show a clear relationship between diffuse CO₂ emission and the eruptive cycle of Cerro Negro; therefore, the potential of this geochemical tool for its volcanic surveillance.