Geochemical monitoring of Cumbre Vieja volcano (La Palma, Canary Islands) by soil CO2 degassing surveys from 2001 to 2023 

Abstract

La Palma Island is located in the northwest of the Canary Islands. Volcanic activity at La Palma in the last 123 ka has taken place exclusively at Cumbre Vieja volcano located at the southern part, which is characterized by a main north–south rift zone 20 km long and up to 1950 m in elevation. Cumbre Vieja covers an area of 220 km2 with vents located also at the northwest and northeast. On 19 September 2021, a new eruption began at the west flank of Cumbre Vieja volcano: the 2021 Tajogaite eruption. It resulted in a fissure and powerful strombolian eruption with a magnitude VEI = 3 (Bonadonna et al., 2022), the longest volcanic event on the island during the last 600 years and the most important eruption of Europe during the last 75 years in terms of the significant amount of SO2 released (Burton et al., 2023). Since no visible degassing (fumaroles, etc.) at Cumbre Vieja occurred before the eruption, the geochemical program for the volcanic surveillance has been mainly focused on diffuse degassing monitoring. Diffuse CO2 emission surveys have been yearly performed in summer to minimize the influence of meteorological variations with continuous surveillance diffuse CO2 surveys during periods with anomalous seismic activity and during the eruptive and post-eruptive periods. Diffuse CO2 emission is measured following the accumulation chamber method in about 600 sites and later spatial distribution maps are constructed following the sequential Gaussian simulation (sGs). Important increases in the diffuse CO2 emission rate were observed after the occurrence of several seismic swarms registered in 2017 and 2020, caused by an upward magma migration from an ephemeral magmatic reservoir. During the eruptive period (18 September – 13 December 2021), the diffuse CO2 emission rate showed a sustained increase up to the maximum value of the series: 4,573 ± 284 t/d in 15 December 2021. After the eruption, the time series showed a rapid decline until background values were recovered in March 2022. Diffuse CO2 emission surveys has demonstrated to be an important monitoring tool that contributes to detect early warning signals in the volcanic activity of Cumbre Vieja and to track the depressurization of magma batches beneath the volcanic system during seismo-volcanic unrest and eruptive episodes.Bonadonna et al. (2022). J.  Geophys. Res: Solid Earth, 127, e2022JB025302.Burton et al. (2023). Communications Earth & Environment, 4:467.