Continuous Monitoring of Diffuse CO2 Degassing From Cumbre Vieja Volcano, La Palma, Canary Islands, Spain

La Palma (730 Km²) is the northwesternmost island of the Canarian archipelago. Cumbre Vieja (<1 Ma) is situated in the southern part of La Palma, and is the most active basaltic volcano in The Canaries (7 eruptions in 500 yrs). The main geostructural features of Cumbre Vieja volcano are three volcanic rift-zones of N-S, NE, and NW orientation. The most recent eruption in the archipelago occurred in the southern part of the N-S rift-zone, Teneguía volcano, in 1971. To date fumarolic activity is absent and relative low diffuse CO₂ efflux values (<65 gm^-2d^-1) are found around this volcano. Diffuse degassing of CO₂ is continuously measured according to the accumulation chamber method at Pico Birigoyo (1,900 m elevation), a cincer cone located at the intersection of the three volcanic-rift zones. Meteorological and soil physical variables are also measured in an hourly basis and GSM-transmitted to ITER facilities about 150 Km far away. Medium-term diffuse CO₂ efflux values ranged from non-detectable levels to 7.9 gm^-2d^-1, with a median value of 3.4 gm^-2d^-1. The sample efflux distribution could be described as a normal distribution N (3.40, 1.22). Secular variations of diffuse CO₂ efflux show a strong linear dependence with the regression coeficient (R²=+0.79) due to the IR sensor's capability to discriminate these low CO₂ emission rates. Wind speed ranged from 0 to 28.8 Km/h, with an upper quartile of 12.9 Km/h. Wind speed (R²=+0.01) and wind direction (R²=+0.03) do not show a correlation with the observed diffuse CO₂ efflux. On the contrary, barometric pressure fluctuations (range 9.43 HPa) at diurnal and semi-diurnal frequencies are inversely correlated with diffuse CO₂ efflux (R²=-0.22). CO₂ efflux lags the barometric pressure variations by 4-6 hours. These results suggest a combination of viscous flow (driven by pressure gradients) and diffusion (driven by concentration gradients) as the main transport components to explain the observed diffuse CO₂ efflux temporal variations at Cumbre Vieja volcano.