Long-term monitoring of anomalous diffuse CO2 and H2S emissions at Teide Crater, Tenerife, Canary Islands

Tenerife (2,034 km²), the largest of the Canary Islands, is characterized by a complex volcanic structure controlled by a volcano-tectonic rift system with dominant NW, NE and NS trends. The intersection of these rifts hosts the Teide-Pico Viejo volcanic complex, which culminates at 3,718 m a.s.l. The Teide volcano last erupted in 1798 through an adventive vent of the Teide-Pico Viejo system. The summit area of Teide volcano is affected by persistent visible and diffuse activity, with diffuse degassing representing the main pathway for gas release to the atmosphere.

Since the late 1990s and until 2025, a long-term monitoring programme has been carried out at the summit crater of Teide volcano, based on repeated diffuse gas emission surveys (more than 250). These surveys were designed to characterise the spatial and temporal variability of diffuse degassing within the summit crater area, providing a robust and consistent dataset for the assessment of changes in the volcanic-hydrothermal system over time.

Diffuse CO₂ and H₂S emission rates were directly estimated from field measurements obtained using the accumulation chamber method. Spatial distribution maps were generated by averaging the results of 100 sequential Gaussian simulations, allowing the estimation of total emission rates and their spatial variability.

During the study period, diffuse CO₂ emissions ranged between 2 and 1257 t·d^-1, while H₂S emissions ranged between 0 and 31 kg·d^-1. From 2007 until around 2016, diffuse CO₂ emissions remained low and relatively stable, with an average of approximately 20 t·d^-1. From late 2016 onwards, emissions show a sustained increase, a trend that continues to the present. Since 2021, low emission values are no longer observed, and in September 2023 the maximum value of the series was recorded (1257 t·d^-1). H₂S shows a nearly synchronous behaviour with CO₂. Along with the observed increase in gas emissions, an increase in seismicity has also been recorded, particularly since 2016, suggesting a relationship between seismic activity and the release of diffuse volcanic gases.

Temporal variations in diffuse CO₂ and H₂S emissions provide valuable insights into changes in the activity of the Teide volcanic system and represent an effective tool for tracking unrest processes. Continuous monitoring of diffuse degassing at Teide volcano has proven essential for improving the understanding of volcanic behaviour and contributes significantly to volcanic risk assessment and mitigation on Tenerife.