CO2 hazard monitoring in the inhabited area of La Bombilla (La Palma, Canary Islands) by means of diffuse degassing studies

After the Tajogaite eruption at Cumbre Vieja volcano (La Palma, Canary Islands), volcanic gas hazard continues to affect the inhabited coastal areas of Puerto Naos and La Bombilla, as well as the nearby agricultural fields, which are located about 6 km distance from the eruptive vents. This gas hazard is primarily due to CO₂ (Hernández et al. 2022) and persist during the post-eruptive phase of the eruption. According to long-term geochemical studies conducted by INVOLCAN, the high levels of CO₂ emissions in these coastal areas were first recorded approximately three weeks before the end of the Tajogaite eruption on December 13, 2021.

To monitor this anomalous diffuse CO₂ degassing at La Bombilla, 46 surveys consisting of approximately 84 sampling observation sites have been regularly conducted since December 2021, covering an area of 0.033 square kilometers. In-situ measurements of soil CO₂ efflux and ground temperature as well as collection of samples of the soil gas atmosphere at a depth of 40cm for chemical and isotopic analysis were carried out at each sampling site. Soil CO₂ efflux measurements have been performed following the accumulation chamber method. Soil gas chemical analysis were carried out by means of a microGC and the carbon isotope ratio of soil gas CO₂ (expressed as δ¹³C-CO₂ ‰ vs. VPDB) was analyzed also in our geochem lab by a Thermo Finnigan MAT 253 mass spectrometer. Spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) to evaluate the spatial distribution of the soil CO₂ efflux measurements and quantify the diffuse CO₂ emission from the studied area. Observed soil CO₂ efflux values ranged from <0.5 (detection limit) to 449,500 gm^-2d^-1 with a mean value of 513 gm^-2d^-1. Diffuse CO₂ emission values ranged between 4.0 and 170 td^-1, with an average value of 16 td^-1. δ¹³C-CO₂ values ranged between -8.63 to -4.31 (‰ vs. VPDB) with an average value of -5.68 (‰ vs. VPDB). The temporal evolution of the diffuse CO₂ emission rate at La Bombilla shown a rapid initial decrease from the first survey (170 td^-1) remaining relatively stable between 55 and 4 td^-1. Since November 2022, the time series seems to show a progressive decreasing trend. However, the temporal evolution of the δ¹³CO₂ values shows that volcanic-hydrothermal contribution to these diffuse emanations continues to be important. In order to evaluate other potential geochemical parameters as indicators of a possible mitigation of this problem related to the CO₂ hazard, we are investigating the temporal evolution of the La Bombilla / Cumbre Vieja diffuse CO₂ emission ratio normalized per area unit.

 

Hernández, P. A., Padrón, E., Melián, G. V., Pérez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.