MultiGAS measurements of fumarole gas emissions from the summit crater of Teide volcano, Tenerife, Canary Islands

Teide volcano (Tenerife, Canary Islands) is an active stratovolcano characterized by persistent low-temperature degassing (81–83 °C) at its summit crater, associated with a hydrothermal system dominated by meteoric steam and deep magmatic inputs. This study presents results from a permanent MultiGAS station operating in continuous mode at the summit crater, designed to monitor the main chemical ratios in the fumarolic gas emissions in situ, to characterize their temporal variability and to look for significant changes that could be related to possible future volcanic unrest periods. The instrument enabled continuous and simultaneous measurements of key gas species, including CO₂, H₂S, SO₂ and water vapour. The data indicate a gas composition dominated by H₂O, followed by CO₂, minor concentrations of H₂S and negligible SO₂ contents, consistent with hydrothermally dominated gas emission. Since the installation of the instrument in the summer of 2025, the H2O/CO2 molar ratio has shown big fluctuations, ranging between 2 and 18, likely affected by meteorological inputs. The CO₂/H₂S molar ratio has shown a more stable value around 1,900. The absence of SO₂ supports the interpretation that the current degassing regime of Teide is decoupled from an open magmatic conduit and is governed by hydrothermal conditions.

The continuous MultiGAS monitoring provides high–temporal resolution data that complement other geochemical surveillance techniques, such as diffuse soil CO₂ emission surveys. This study contributes to a better understanding of the present state of the Teide volcano–hydrothermal system and highlights the value of continuous gas monitoring as a key tool for volcanic activity assessment and for the early detection of potential precursory changes.