Spatial and temporal variations of soil CO2 flux and pressure gradient measurements at Cumbre Vieja volcano, La Palma, Canary Islands

La Palma (730 km²) is one of the youngest and the most active volcanic island of the Canarian archipelago. Volcanic activity has been concentrated on the southern part of the island, Cumbre Vieja volcano (220 km²), which had been constructed during the last 1 Ma. Three major volcanic rift-zones trending N-S, NW-SE and NE-SW constitute Cumbre Vieja's major structural features. During the last 60 years, two eruptions had occurred at Cumbre Vieja along the N-S rift-zone, and the most recent one took place at the southern part of the volcanic edifice in 1971. Since fumarolic activity is absent at Cumbre Vieja, diffuse CO₂ degassing survey is a major geochemical tool for monitoring changes of volcanic activity at Cumbre Vieja. Since 1997 diffuse CO₂ degassing monitoring is applied for the volcanic surveillance program of Cumbre Vieja. Surface pressure gradient studies are also applied since 2002 to evaluate surface degassing mechanisms. Surface pressure gradient measurements were performed by means of a Setra 239 pressure transducer using a metallic probe inserted 40 cm deep. Soil CO₂ efflux measurements were performed by means of a portable NDIR sensor according to the accumulation chamber method. Most of the study area showed CO₂ efflux values lower than 6 gm^-2d^-1, with background values about 2 gm^-2d^-1. Peak CO₂ efflux values are higher than 500 gm^-2d^-1, and they were mainly observed in the extreme south of the N-S rift-zone near by the most recent eruption. The highest surface pressure gradient measurements (>=30 Pa m^-1) were also detected in and around Teneguia volcano suggesting an advective component for the diffuse CO₂ degassing for this area. The total diffuse CO₂ output released to atmosphere has been estimated for each survey showing a range of 1,250-2,500 t d^-1 for the 1997-2003. Monitoring these geochemical parameters will improve the volcanic surveillance program of Cumbre Vieja.