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 16th 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.