Anomalous CO2 concentrations of volcanic origing in the ambient air of banana plantations at La Palma, Canary Islands

The recent eruption of Tajogaite volcano occurred between September and December 2021 at La Palma Island is considered the most devastating of Europe since that of Vesuvio in 1944. The post-eruptive period is being characterized by the appearance of high outdoor and indoor CO₂ concentrations at inhabited areas such as La Bombilla and Puerto Naos (Hernández et al., 2022), forcing the eviction of numerous homes. However, anomalous concentrations of CO₂ have not only appeared in inhabited areas, but also in cultivated lands. In fact, the highest CO₂ concentration values measured in the outdoor environment during the entire post-eruption period have been in a banana plantation of approximately 4,200 m² that INVOLCAN has been monitoring since June 2022, named Las Hoyas.

Since June 2022, 26 scientific observation surveys have been carried out at Las Hoyas consisting of the measurement at 39 homogeneously distributed sites of the CO₂ and O₂ concentration at two heights, 40 and 170 cm from the ground, as well as sampling of atmospheric air in 19 sites at 40 cm for carbon isotope ratio of air CO₂. Air CO₂ and O₂ concentrations are measured with a hand portable Dräger X-am® 8000 meter and the carbon isotope ratio of air CO₂ (expressed as δ¹³C-CO₂ ‰ vs. VPDB) is analyzed at ITER/INVOLCAN 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 air CO₂ concentration. Observed air CO₂ concentration values ranged from air value (412ppm) up to 69%, the highest ever measured during the post-eruptive period, with an average value of 7.1%. Air O₂ concentration values ranged between 7.9% to air value (20.9%), with an average value of 19.2%. δ¹³C-CO₂ values ranged between –8.90 to -2.66‰, with an average value of -4.87‰, indicating a clear volcanic-hydrothermal origin for the anomalous CO₂ emitted from Las Hoyas banana plantation and ruling out a single biogenic origin.

In order to investigate the temporal evolution of the observed high CO₂ concentrations in Las Hoyas, a Sinclair statistical graphic analysis was applied to the data from each survey. Time series of background and peak populations does not show a clear trend, with the occurrence of peaks and valleys throughout the entire series, and maintaining values much higher than those of the air. Likewise, the temporal evolution of the δ¹³C-CO₂ values shows a trend towards heavier values, indicating that the volcanic-hydrothermal contribution increases with time. The spatial distribution of the air CO₂ concentration measured at 40 cm shows that in most of the surveys, the anomalous values (>10%) are located mainly along the walls of Las Hoyas and in the NW sector, where in more than a year after the eruption, the banana plants are still withered and dead terrestrial and aerial fauna constantly appear due to poisoning and suffocation from CO₂ inhalation.

 

Hernández et al. EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.