Diffuse CO2 degassing surveys for geochemical monitoring of the Tenerife North–South Rift Zone (NSRZ) volcano (Canary Islands) from 2002 – 2024.

Tenerife (2,034 km²), the largest of the Canary Islands, hosts three active volcanic rift zones (RZ), including the North-South (NSRZ; 325 km²). Characterized predominantly by effusive basaltic activity, the NSRZ comprises 139 monogenetic cones, representing the island’s most active volcanic system over the last 1 million years. To monitor potential changes in volcanic activity, 11 diffuse CO₂ emission surveys have been conducted since 2002 until 2024. Each survey involves 600 sampling sites where soil CO₂ efflux is measured following the accumulation chamber method, whereas soil gas samples are collected at 40 cm depth for chemical and isotopic analysis. 

During 2024 survey, soil CO₂ efflux values ranged from undetectable levels (∼0.5 g·m⁻²·d⁻¹) to 23 g·m⁻²·d⁻¹, with an average efflux of 1.3 g·m⁻²·d⁻¹. A Sinclair graphical analysis categorized the data into three geochemical populations: a background population (98% of the data) with a mean efflux of 0.8 g·m⁻²·d⁻¹ and a peak population (0.1% of the data) averaging 19.9 g·m⁻²·d⁻¹. Sequential Gaussian simulation estimated diffuse CO₂ emission rate in 2024 from the studied area in 279 ± 11 t·d⁻¹, value lower than the range 466 - 819 t·d⁻¹ measured from 2002 to 2023, and peaking at 707 t·d⁻¹ in 2015. 

Inspection of diffuse CO₂ emissions rate time series suggests a relationship with seismic activity in and around Tenerife, particularly from late 2016 onward. This observation emphasizes the usefulness of soil CO₂ efflux surveys in areas lacking visible degassing phenomena. The integration of geochemical data with geophysical observations enhances volcanic monitoring assessment, improves risk management, and strengthens early-warning systems. This study underlines the importance of discrete geochemical monitoring for understanding the dynamics of the NSRZ, offering critical insights to mitigate the impacts of potential volcanic threats on Tenerife.