Twenty three years of monitoring diffuse CO2 emission from the Tenerife North-West Rift Zone (NWRZ) volcano, Canary Islands

Tenerife (2,034 km²), the largest island of the Canarian archipelago, is characterized by three volcanic rifts oriented NW-SE, NE-SW and N-S with a central volcanic complex, Las Cañadas Caldera, hosting Teide-Pico Viejo volcanoes. The North West volcanic Rift Zone (NWRZ, 72 km²) of Tenerife is one of the youngest and most active volcanic systems of the island, where four historical eruptions have occurred: the volcanic eruption witnessed by Christopher Columbus in 1492, Boca Cangrejo in 16^th Century, Arenas Negras in 1706 and Chinyero in 1909. In order to monitor the volcanic activity of NWRZ, since the year 2000, 56 soil CO₂ efflux surveys have been performed at NWRZ (with more than 300 observation sites each one) to evaluate the temporal an spatial variations of CO₂ efflux and their relationships with the volcanic-seismic activity. Soil CO₂ efflux measurements were performed in accordance with the accumulation chamber method. Spatial distribution maps were constructed following the sequential Gaussian simulation (sGs) procedure. To quantify the total CO₂ emission from the studied area, 100 simulations for each survey have been performed. We report herein the results of the last diffuse CO₂ efflux survey at the NWRZ undertaken in summer 2023 to constrain the total CO₂ output from the studied area. During this survey, soil CO₂ efflux values ranged from non-detectable up to 34 g m^-2 d^-1. The total diffuse CO₂ output released to atmosphere were estimated in 311 ± 11 t d^-1, value higher than the background CO₂ emission estimated on 151 t d^-1. Since the 2000s, total CO₂ output ranged between 52 and 867 t d^-1. Long-term variations in the total CO₂ output suggest the occurrence of subsurface magma degassing and magmatic fluid injection, perhaps due to strain-stress changes beneath the NWR zone (Hernández et al., 2017). Regular surveys of soil CO₂ efflux seem to be an effective geochemical surveillance tool at the NWRZ, able to detect changes in the CO₂ emission rate that might presage future episodes of volcanic unrest.

Hernández et al., (2017). Bull. Volcanol. 79:30.