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

Abstract

<p>Tenerife (2,034 km<sup>2</sup>) is the largest of the Canary Islands. Its structure is controlled by a volcano-tectonic rift-system with NW, NE and NS directions, with the volcanic system Teide-Pico Viejo 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. Persistent degassing activity, both visible and diffuse, takes place at the summit cone of the volcano, being the diffuse degassing the principle mechanism.</p><p>During the period 1999-2020, more than 200 diffuse CO<sub>2</sub> efflux surveys have been performed in the summit crater of Teide Volcano. For each survey, 38 sampling sites homogeneously distributed inside the crater covering an area of 6,972 m<sup>2</sup> were selected. Diffuse CO<sub>2</sub> emission was estimated in each point by means of a portable non dispersive infrared (NDIR) CO<sub>2</sub> fluxmeter using the accumulation chamber method. Additionally, soil gas samples were taken at 40 cm depth and analyzed later in the lab for the He and H<sub>2</sub> content by means of quadrupole mass spectrometry and micro-gas chromatography, respectively. To estimate the He and H<sub>2</sub> 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 determine CO<sub>2</sub>, He and H<sub>2</sub> emission rates.</p><p>During the study period, CO<sub>2</sub> emissions ranged from 2.2 to 176.1 t/d, He emissions between 0.013 and 4.1 kg/d and H<sub>2</sub> between 1.3 and 35.6 kg/d. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island (D’Auria et al., 2019). Since then, relatively high values have been obtained in the diffuse CO<sub>2</sub>, He and H<sub>2</sub> emission rate the crater of Teide. This increase reflects a process of pressurization of the volcanic-hydrothermal system.</p><p>The variations in CO<sub>2</sub>, He and H<sub>2</sub> 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 at Teide volcano has demonstrated to be an essential tool for predicting future seismic–volcanic unrest, and has become important to reduce volcanic risk in Tenerife (Melián et al., 2012; Pérez et al., 2013).</p><p>D'Auria .L, Barrancos J., Padilla G.D., Pérez N.M., Hernández P.A., Melián G., Padron E., Asensio-Ramos M., García‐Hernández R. (2019). J. Geophys. Res. 124, 8739-8752</p><p>Pérez N. M., Hernández P. A., Padrón E., Melián G., Nolasco D., Barrancos J., Padilla G., Calvo D., Rodríguez F., Dionis S. and Chiodini G. (2013). J. Geol. Soc., 170(4), 585-592.</p><p>Melián G., Tassi F., Pérez N. M., Hernández P., Sortino F., Vaselli O., Padrón E., Nolasco D., Barrancos J., Padilla G., Rodriguez F., Dionis S., Calvo D., Notsu K., Sumino H. (2012).  Bull. Volcanol, 74(6), 1465-1483.</p><p> </p>