CO2 hazard monitoring in the inhabited area of La Bombilla (La Palma, Canary Islands) by means of diffuse degassing studies
Authors: Hernández Pedro A. , Melián Gladys V. , Rodríguez Fátima , Álvarez Díaz Antonio J. , Padilla Germán D. , Asensio-ramos María , Barrancos José , Calvo David , Padrón Eleazar , González Pérez Alexis M. , Pérez Nemesio M. 
Published: February 2023

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 (Hern&#225;ndez 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 &#948;13C-CO2 &#8240; 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. &#948;13C-CO2 values ranged between -8.63 to -4.31 (&#8240; vs. VPDB) with an average value of -5.68 (&#8240; 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 &#948;13CO2 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.&#160;Hern&#225;ndez, P. A., Padr&#243;n, E., Meli&#225;n, G. V., P&#233;rez, 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&#8211;27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.