Long-term variations of diffuse CO2, He and H2 at the summit crater of Teide volcano, Tenerife, Canary Islands during 1999-2021

Tenerife Island (2,034 km2) is the largest island of the Canarian archipelago. Its structure is controlled by a volcano-tectonic rift-system with NW, NE and NS directions, with the Teide-Pico Viejo volcanic system located in the intersection. Teide is 3,718 m.a.s.l. high and its last eruption occurred in 1798 through an adventive cone of Teide-Pico Viejo volcanic complex. Although Teide volcano shows a weak fumarolic system, volcanic gas emissions observed in the summit cone consist mostly of diffuse CO2 degassing. In this study we investigate the Teide-Pico Viejo volcanic system evolution using a comprehensive diffuse degassing geochemical dataset 216 geochemical surveys have been performed during the period 1999-2021 at the summit crater of Teide Volcano covering an area of 6,972 m2. Diffuse CO2 emission was estimated in 38 sampling sites, homogeneously distributed inside the crater, by means of a portable non dispersive infrared (NDIR) CO2 fluxmeter using the accumulation chamber method. Additionally, soil gases were sampled at 40 cm depth using a metallic probe with a 60 cc hypodermic syringe and stored in 10 cc glass vials and send to the laboratory to analyse the He and H2 content by means of quadrupole mass spectrometry and micro-gas chromatography, respectively. To estimate the He and H2 emission rates at each sampling point, the diffusive component was estimated following the Fick’s law and the convective emission component model was estimated following the Darcy’s law. In all cases, spatial distribution maps were constructed averaging the results of 100 simulations following the sequential Gaussian simulation (sGs) algorithm, in order to estimate CO2, He and H2 emission rates. During 22 years of the studied period, CO2 emissions ranged from 2.0 to 345.9 t/d, He emissions between 0.013 and 4.5 kg/d and H2 between 1.3 and 64.4 kg/d. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by an increase of the seismic activity in and around the island (D’Auria et al., 2019; Padrón et al., 2021). Several geochemical parameters showed significant changes during ∼June–August of 2016 and 1–2 months before the occurrence of the October 2, 2016, long-period seismic swarm (Padrón et al., 2021). Diffuse degassing studies as useful to conclude that the origin of the 2 October 2016 seismic swarm an input of magmatic fluids triggered by an injection of fresh magma and convective mixing. Thenceforth, relatively high values have been obtained in the three soil gases species studied at the crater of Teide, with the maximum emission rates values registered during 2021. This increase reflects a process of pressurization of the volcanic-hydrothermal system. This increment in CO2, He and H2 emissions indicate changes in the activity of the system and can be useful to understand the behaviour of the volcanic system and to forecast future volcanic activity. Monitoring the diffuse degassing rates has demonstrated to be an essential tool for the prediction of future seismic–volcanic unrest, and has become important to reduce volcanic risk in Tenerife.D'Auria, L., et al. (2019). J. Geophys. Res.124,8739-8752Padrón, E., et al., (2021). J. Geophys. Res.126,e2020JB020318