Dynamics of diffuse carbon dioxide emissions from Cumbre Vieja volcano, La Palma, Canary Islands

We report herein the results of 13 soil CO2 efflux surveys at Cumbre Vieja volcano, La Palma Island, the most active basaltic volcano in the Canary Islands. The CO2 efflux measurements were undertaken using the accumulation chamber method between 2001 and 2013 to constrain the total CO2 output from the studied area and to evaluate occasional CO2 efflux surveys as a volcanic surveillance tool for Cumbre Vieja. Soil CO2 efflux values ranged from non-detectable up to 2442 gm(-2) days(-1), with the highest values observed in the south, where the last volcanic eruption took place (Teneguia, 1971). Isotopic analyses of soil gas carbon dioxide suggest an organic origin as the main contribution to the CO2 efflux, with a very small magmatic gas component observed at the southern part of the volcano. Total biogenic and magmatic combined CO2 emission rates showed a high temporal variability, ranging between 320 and 1544 t days(-1) and averaging 1147 t days(-1) over the 220-km(2) region. Two significant increases in the CO2 emission observed in 2011 and 2013 were likely caused by an enhanced magmatic endogenous contribution revealed by significant changes in the He-3/He-4 ratio in a CO2-rich cold spring. The relatively stable emission rate presented in this work defines the background CO2 emission range for Cumbre Vieja during a volcanic quiescence period.