Continuous monitoring of diffuse degassing at the summit cone of Teide volcano, Tenerife, Canary Islands

The chemical composition of volcanic gases provides essential insights into the activity and dynamics of volcanic systems, as well as the magmatic and hydrothermal processes occurring at depth. These gases, including CO₂, H₂, CH₄, and H₂S, are key indicators of physical and chemical processes such as redox reactions and magmatic degassing. Furthermore, the relative concentrations and ratios of specific gas species offer valuable information for interpreting subsurface dynamics and detecting changes in volcanic activity.

In recent decades, researchers have made significant efforts to measure gas concentrations and fluxes in volcanic fluids. However, continuous monitoring of gas emissions and their ratios in active volcanoes remains limited. Here, we present results from a continuous monitoring station (CMS) installed in November 2017 on the southeastern flank of Teide volcano. This station monitors the ground gas atmosphere using a device that collects samples at a depth of 10 cm, measuring CO₂, H₂, He, H₂S, CH₄, and other gases to analyze their temporal evolution and interrelationships. The data collected spans from its installation to the present day, providing a comprehensive record of gas behaviour over time.

The CMS is equipped with an Agilent 490 micro-GC with two channels, capable of analyzing He, Ne, H₂, O₂, N₂, CH₄, CO₂ and H₂S. The system includes an embedded computer with internet connectivity (via WiFi or UMTS router), enabling full remote control of the instrument, automatic data transmission, and automated gas sampling.

High concentrations of CO₂ (with a moving average exceeding 60% for most of the measurement period), H₂ (above 1,200 ppm), He (above 10 ppm), and H₂S (above 1,000 ppm) highlight significant temporal trends linked to variations in volcanic and hydrothermal activity. The analysis of gas ratios, such as He/CO2, H₂/CO₂, and H₂S/CO₂, shows fluctuations consistent with changes in volcanic activity. Decreases in atmospheric gases like N₂ and O₂ often coincide with increases in magmatic components, reinforcing the utility of gas ratios in understanding subsurface processes.

This CMS constitutes a robust system for volcanic monitoring, capable of detecting low concentrations of key gases and providing critical insights through the analysis of both gas concentrations and their ratios. Such tools are invaluable for advancing volcanic surveillance and risk assessment.